1600 John F. Kennedy Blvd. Ste 1800 Philadelphia, PA 19103-2899 MUSCULOSKELETAL DISORDERS IN THE WORKPLACE: ISBN-13: 978-0-323-02622-2 PRINCIPLES AND PRACTICE ISBN-10: 0-323-02622-2 Copyright © 2007, 1997 by Mosby Inc., an affiliate of Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permissions may be sought directly from Elsevier’s Health Sciences Rights Department in Philadelphia, PA, USA: phone: (+1) 215 239 3804, fax: (+1) 215 239 3805, e-mail:
[email protected]. You may also complete your request on-line via the Elsevier homepage (http://www.elsevier.com), by selecting ‘Customer Support’ and then ‘Obtaining Permissions’. Notice Knowledge and best practice in this field are constantly changing. As new research and experience broaden our knowledge, changes in practice, treatment, and drug therapy may become necessary or appropriate. Readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose of formula, the method and duration of administration, and contraindications. It is the responsibility of the practitioner, relying on their own experience and knowledge of the patient, and to make diagnoses, to determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions. To the fullest extent of the law, neither the Publisher nor the Editors assume any liability for any injury and/or damage to persons or property arising out of or related to any use of the material contained in this book. The Publisher
Library of Congress Cataloging-in-Publication Data Musculoskeletal disorders in the workplace: Principles and practice / [edited by] Margareta Nordin, Gunnar B.J. Andersson, Malcolm H. Pope. —2nd ed. p. ; cm. Includes bibliographical references and index. ISBN 0-323-02622-2 1. Musculoskeletal system—Diseases. 2. Occupational diseases. I. Nordin, Margareta. II. Pope, M. H. (Malcolm Henry), 1941- III. Andersson, Gunnar, 1942[DNLM: 1. Musculoskeletal Diseases—therapy. 2. Biomechanics. 3. Human Engineering. 4. Musculoskeletal Diseases—prevention & control. 5. Occupational Diseases—etiology, WE 140 M9854 2006] RC925.5M8783 2006 616.7—dc22 2006043830
Acquisitions Editor: Rolla Couchman Project Manager: Bryan Hayward
Printed in United States of America Last digit is the print number: 9 8 7 6 5 4 3 2 1
Foreword Workers’ health priorities are now driven by demographics. All of the First World Nations are facing a future with a rapidly diminishing work force, an aging population, and a growing number of pensioners. The prevention and efficient management of work place injuries and disabilities has become a priority. Medical professionals work in an increasingly specialized world brought on by an explosion of knowledge, the demand from society for "the very best" in services, and the need for expertise to keep pace with technological change and innovation. Modern medical history, in particular, is replete with examples of sudden bursts of information that challenged the growth of new domains and abilities. The period of World War II saw an explosion of medical knowledge, rapidly dividing General Surgery into numerous subspecialties. Similarly, the 1970s was a critical period in orthopaedic surgical practice as many subspecialties developed that allowed greater expert use of modern technology. Occupational orthopaedics is a relatively young specialty that is still evolving rapidly. As in sports medicine, we have learned that it is not sufficient to examine and treat injuries alone. After recovery, an injured football player is expected to return to the game and perform at his previous level of athletic ability. The injured industrial worker is also expected to return
to his or her previous level of performance, accomplishing a particular task within a reasonable time frame. Although the average orthopaedic surgeon may be well-versed with the conditions of the gridiron, he or she may not be familiar with the requirements and limitations of the industrial playing field. In industrial medicine, it is not only necessary to "fix" the worker; one must have an idea about how to fix the workplace to prevent further injury. Like sports medicine, the management and prevention of industrial injury demands a dedicated and knowledgeable cadre of physicians, surgeons, and therapists who are able to apply modern knowledge and expertise to a successful medical program. This volume brings together chapters authored by the most knowledgeable group of surgeons, physicians, scientists, ergonomists, and therapists currently addressing the prevention and management of workplace injury. The editors have assembled a most versatile and practical tool for the many allied-health professionals involved with work-related injuries. This updated text will have a strong impact within industry and on the management of patients well into the 21st century. Victor H. Frankel KNO, MD, PhD Professor of Orthopaedic Surgery, NYU President Emeritus, Hospital for Joint Diseases
v
Contributors K. N. An, Ph.D. John and Posy Krehbiel Professor of Orthopaedics Maylo Clinic College of Medicine Orthopaedics Biomechanics Lab Rochester, MN 55905
Amit Bhattacharya, Ph.D., C.P.E. Professor Biomechanics-Ergonomics Research Laboratories Department of Environmental Health University of Cincinnati Medical College Cincinnati, OH 45267-0056
Gunnar B. J. Andersson, M.D., Ph.D. Professor and Chairman Department of Orthopaedic Surgery Rush-PresbyterianSt. Luke’s Medical Center Chicago, IL 60612
Anthony M. Buoncristiani, M.D., L.T. Orthopaedics Department Naval Medical Center San Diego, CA 92134
Thomas J. Armstrong, Ph.D. Professor Industrial and Operations Engineering Director Center for Ergonomics University of Michigan Ann Arbor, MI 48109-2117 Federico Balagué Médecin Chef Adjoint Division of Rheumatology, Physical Medicine and Rehabilitation Hôpital Cantonal 1708 Fribourg Switzerland and Adjunct Associate Professor Department of Orthopaedic Surgery New York University School of Medicine New York, NY 10014 Michele Crites Battié, Ph.D. Professor Department of Physical Therapy University of Alberta Edmonton, Alberta T6G 2G4 Canada Jane Bear-Lehman, Ph.D., OTR, FAOTA Associate Professor New York University Steinhardt School of Education Occupational Therapy Department New York, NY 10012 David P. Beason, M.S. Research Engineer Laboratory Manager McKay Orthopaedic Research Laboratory University of Pennsylvania Philadelphia, PA 19104
Linda Carroll, M.D. Associate Professor Department of Public Health Sciences University of Alberta Edmonton, Alberta T6G 2E1 Canada J. David Cassidy, M.D. Department of Public Health Sciences University of Alberta Edmonton, Alberta T6G 2E1 Canada Christine Cedraschi Division of General Medical Rehabilitation & Multidisciplinary Pain Center Division of Clinical Pharmacology and Toxicology Geneva University Hospitals 1211 Geneva 14 Switzerland Mark S. Cohen, M.D. Department of Orthopaedic Surgery Rush-PresbyterianSt. Luke’s Medical Center Chicago, IL 60612 Pierre Côté, D.C., Ph.D. Scientist Institute for Work and Health Toronto, Ontario M5G 2E9 Canada
Craig J. Della Valle, M.D. Assistant Professor of Orthopaedic Surgery Rush-Presbyterian-St. Luke's Medical Center Chicago, IL 60612 James A. Dewees, M.S., C.P.E., C.E.E.S. ERGO Accommodations Inc P O Box 499 Union, KY 41091-0499 Jiri Dvorak, M.D., Ph.D. Department of Neurology Schulthess Hospital 8008 Zurich Switzerland Ulf Eklund M.D. Orthopedic Surgeon Department of Orthopedics Molndal Hospital Molndal, Sweden Freddie H. Fu, M.D. Department of Orthopaedic Surgery University of Pittsburgh Pittsburgh, PA 15203 Douglass Gross, Ph.D. Assistant Professor Department of Physical Therapy University of Alberta Edmonton, Alberta T6G 2G4 Canada Robert Gunzburg, M.D., Ph.D. Senior Consultant Department of Orthopaedics Centenary Clinic 2018 Antwerp Belgium
Benjamin Crane, M.D. Resident Department of Orthopaedic Surgery Rush University Medical Center Chicago, IL 60612
Daniel J. Habes, M.S.E., C.P.E. Industrial Engineer Industrial Hygiene Section Hazard Evaluations and Technical Assistance Branch Division of Surveillance, Hazard Evaluations, and Field Studies National Institute for Occupational Safety and Health Cincinnati, OH
James N. DeBritz, M.D. Assistant Instructor Department of Orthopaedics Georgetown University Hospital Washington, DC 20007
Robert H. Haralson, III, M.D., M.B.A. Executive Director of Medical Affairs American Association of Orthopaedic Surgeons Rosemont, IL 60018
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Contributors
Rudi Hiebert, B.S. Interim Director Musculoskeletal Epidemiology Unit Occupational & Industrial Orthopaedic Center NYU Hospital for Joint Diseases New York, NY 10014 Beat Hintermann, M.D. Chief Orthopaedic Clinic University of Basel Kantonsspital CH-4410 Liestal Switzerland David M. Kalainov, M.D. Clinical Assistant Professor Department of Orthopaedic Surgery Northwestern University Chicago, IL 60611 Dennis D.J. Kim, M.D. Associate Professor Department of Physical Medicine and Rehabilitation Montefiore Medical Center Bronx, NY 10467 Stephan Konz, Ph.D., P.E. Professor Department of Industrial Engineering Kansas State University Manhattan, KS 66506 Vicki Kristman, B.Sc., M.Sc. Ph.D. Candidate, Epidemiology Department of Public Health Sciences University of Toronto Research Associate Institute for Work & Health Toronto, Ontario M5F 2E9 Canada Shrawan Kumar, Ph.D., D.Sc., F.Erg.S., F.R.S.C. Professor Department of Physical Therapy Faculty of Rehabilitation Medicine University of Alberta Edmonton, Alberta T6G 2G4 Canada Marianne Magnusson, R.P.T., Dr.Med.Sci. Senior Lecturer Liberty Safe Work Research Centre Department of Economy and Technology Halmstad University SE-301 18 Halmstad Sweden Paul H. Marks, M.D. Associate Professor Department of Surgery University of Toronto Toronto, ON M4Y 1H1 Canada Ronald Moskovich, M.D. Assistant Professor Department of Orthopaedic Surgery NYU Hospital for Joint Diseases New York, NY 10003
Margareta Nordin, Dr.Sci. Professor Departments of Orthopaedics and Environmental Medicine School of Medicine New York University Program Director Program of Ergonomics and Biomechanics Graduate School of Arts and Science New York University Director Occupational and Industrial Orthopaedic Center (OIOC) NYU Hospital for Joint Diseases New York University Medical Center New York, NY 10014 Mooyeon Oh-Park, M.D. Clinical Associate Professor Department of Rehabilitation Medicine Montefiore Medical Center Bronx, NY 10467 Rita M. Patterson, Ph.D. Associate Professor and Deputy Director Orthopaedics Biomechanics Laboratory Division of Research Department of Orthopaedic Surgery and Rehabilitation University of Texas Medical Branch Galveston, TX 77555 David I. Pedowitz, M.S., M.D. Chief Resident Department of Orthopaedic Surgery University of Pennsylvania Philadelphia, PA 19004 Anthony Petrizzo, M.D c/o Ronald Moskovich, M.D. 301 East 17th Street New York, New York 10003 Derek Plausinis, M.D. Shoulder & Elbow Surgery Fellow Department of Orthopaedic Surgery NYU Hospital for Joint Diseases New York, NY 10003 Malcolm H. Pope, Dr.Med.Sci., Ph.D. Professor Liberty Safework Research Centre Department of Environmental & Occupational Health Foresterhill Aberdeen, Scotland AB 25 2ZD United Kingdom Laura Punnett, Sc.D. Professor Department of Work Environment University of Massachusetts Lowell Lowell, MA 01854 Robert G. Radwin, Ph.D. Professor and Chair Department of Biomedical Engineering University of Wisconsin Madison, WI 53706
David Rempel, M.D., M.P.H. Professor School of Medicine –Ergonomics Program Division of Occupational and Environmental Medicine University of California, San Francisco Richmond, CA 94804 Michiel Reneman, Ph.D, P.T. Center for Rehabilitation University Medical Center Groningen University of Groningen P.O. Box 30002, 9750 RA Haren The Netherlands Per A.F.H. Renström, M.D., Ph.D. Professor Department of Molecular Medicine and Surgery Section of Orthopaedics and Sports Medicine Karolinska Hospital SE-171 76 Stockholm Sweden Mana Rezai, H.B.Sc., D.C., M.H.Sc. Candidate Research Associate Institute for Work & Health University of Toronto Toronto, Ontario M5G 2E9 Canada Tonu Saartok, M.D., Ph.D. Department of Surgical Sciences Section of Sports Medicine Karolinska Institute SE-171 76 Stockholm, Sweden G. James Sammarco, M.D. The Center for Orthopaedic Care, Inc. Cincinnati, OH 45219-2906 Peter Sheehan, M.D. Director Diabetes Center of Greater New York Cabrini Medical Center New York, NY 10003 Ali Sheikhzadeh, Ph.D., C.I.E. Research Assistant Professor Departments of Orthopaedic Surgery and Environmental Medicine New York University School of Medicine Associate Director of Research Occupational and Industrial Orthopaedic Center NYU Hospital for Joint Diseases New York, NY 10014 Mary-Louise Skovron, Dr. PH. Group Director, Pharmaco-epidemiology Global Epidemiology Bristol–Myers Squibb 311 Pennington-Rocky Hill Road Pennington, NJ 09534
Contributors
Louis J. Soslowsky, Ph.D. Professor of Orthopaedic Surgery and Bioengineering Vice Chair for Research Director, McKay Orthopaedic Research Laboratory University of Pennsylvania Philadelphia, PA 19104 Dan M. Spengler, M.D. Professor and Chair Department of Orthopaedics and Rehabilitation Vanderbilt Orthopaedics Institute Nashville, TN 37232 Marek Szpalski, M.D. Associate Professor and Chair Department of Orthopaedics IRIS South Teaching Hospitals Free University of Brussels 1190 Brussels Belgium James B. Talmage M.D. Occupational Health Center Cookeville, TN 38501
Ross Taylor, M.D. Coastal Orthopaedic Associates Conway, SC 29526 Victor Valderrabano, M.D., Ph.D. Human Performance Laboratory and Orthopaedic Department University of Calgary Calgary, Alberta T2N1N4 Canada also Orthopaedic Department University Hospital of Basel 4031 Basel Switzerland Tapio Videman, M.D., D.Med.Sci. Professor Faculty of Rehabilitation Medicine University of Alberta Edmonton, Alberta T6G 2G4 Canada Sherri Weiser, Ph.D. Research Assistant Professor of Environmental Medicine Occupational & Industrial Orthopaedic Center NYU Hospital for Joint Diseases New York, NY 10014
Sam W. Wiesel, M.D. Professor and Chair Department of Orthopaedic Surgery Georgetown University Medical Center Washington, D.C. 20007 Harriët Wittink, Ph.D., M.S., P.T. Head Physical Therapy Professional Master Program Hogeschool Utrecht 3508 AD Utrecht The Netherlands Joseph D. Zuckerman, M.D. Professor and Chair Department of Orthopaedic Surgery NYU Hospital for Joint Diseases New York, NY 10003
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CHAPTER
1
Introduction to Epidemiologic Concepts in Musculoskeletal Disorders Mary Louise Skovron and Rudi Hiebert
The literature on the epidemiology of occupational musculoskeletal disorders is often confusing because of conflicting evidence on the importance of various potential risk or causal factors. This chapter describes basic epidemiologic methods so the reader can evaluate critically the published literature on occupational musculoskeletal disorders. Most examples are drawn from the literature on occupational low back pain, but the reader should be aware that similar methodologic standards must be applied to the literature on upper extremity disorders. Epidemiology is the study of the distribution and determinants of diseases and injuries in human populations. It consists of a developed methodology for testing scientific hypotheses in groups of individuals rather than in a laboratory setting. With knowledge of the intrinsic strengths and limitations of the design and execution of studies reported in the literature, it is possible to evaluate the strength of the evidence derived from these studies and even to make sense of conflicting results from different studies on the same topic. In this chapter we present an overview of the basic terminology used in epidemiology and the characteristics and generic strengths and limitations of analytic (hypothesis testing) study designs, with an emphasis on observational study designs. There are several types of epidemiologic studies. Descriptive epidemiology is a means of monitoring the health of a population, identifying health problems, and compiling information that can be used for the development of causal hypotheses. Analytic epidemiology is a set of epidemiologic study methods used to test specific hypotheses.
Health Administration (OSHA) by employers, workers’ compensation records, records of visits to the workplace health facility, and surveys of the work force.11 In clinical practice, the simple case count is usually derived by chart review (retrospectively) or by enrollment of patients seen during a given period (prospectively). The frequency of the disorder can also be expressed as a proportionate ratio, a ratio of cases of a particular disorder to cases of all disorders in the population of interest. In 1985 for example, occupational back injuries accounted for 26% of all closed compensation cases in a sample of nine states. By itself, numerator data cannot provide useful information regarding the risk or probability of acquiring the disorder. The case frequency has to be related to the underlying population that could have potentially developed the disorder. For example, the U.S. Bureau of Labor Statistics estimated 303,750 OSHAreportable occupational injuries involving the back in 2003.4 Without reference to the number of people at risk, it is not possible to estimate the risk of back injury in the population or to test hypotheses regarding risk factors for occupational back injury. For this reason, rates are used when the objective is to assess the risk of the disorder or determinants of disorders or their outcomes.
Rates and ratios Rates describe the frequency of a disorder or disorder per unit size of the population per unit time of observation. The rates commonly used in epidemiology are morbidity and mortality rates. The general form of a morbidity or mortality rate is
MEASURES OF DISORDER FREQUENCY The fundamental strategy of epidemiology is the analysis of relative and absolute measures of frequency and a comparison of the characteristics of individuals with and without disorder. The most obvious measures of frequency are case counts and their variations, which are often referred to as numerator data. They describe the frequency of the disorder without reference to the underlying population at risk. Examples of sources of case count data include back injury reports to the Occupational Safety and
Number of cases × 10 0 (1000, etc.) per unit time Number of persons at risk The most frequently used morbidity rates in epidemiologic research are the incidence rate and the prevalence rate. The incidence rate is based on new cases of a disorder or disorders (or new disorder events), whereas the prevalence rate is based on existing cases. Because they are based on new versus existing cases,
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Introduction to epidemiologic concepts in musculoskeletal disorders
incidence and prevalence rates have different uses and different limitations. In a sense, the incidence rate is a rate of change, the frequency with which people change from healthy to injured, sick, or disabled. Therefore the appropriate denominator is the population at risk of acquiring the disorder (i.e., those who are free of the disorder at the start of the time interval). The incidence rate may be quantified in a number of ways, for example, as the number of new events per 1000 persons per year, when the population is stable and the number of new events is counted each year. Alternatively, it may be quantified as the number of new events per 1000 person-years, as is done in prospective studies where a fixed population is followed until the disorder, the end of the study, or loss to follow-up occurs. In practice, although the best denominator for incidence rates is the number of people free of the disorder at the start of the time interval, surveillance incidence rates (and prevalence rates) that are based on case reports often use the total population derived from census data or from work-force estimates. The U.S. Bureau of Labor Statistics’ estimate of 303,750 OSHA-reportable occupational injuries involving the back represents an incidence of 3.46 new cases per 1000 workers.4 The prevalence rate is the number of existing cases of a disorder in a given population in a given time period. For example, the 1-year prevalence of disabling back pain is as high as 25%.14 Point prevalence is the number of cases per unit population at one moment of counting, for example, all persons receiving disability because of back pain in the work force of a metropolitan electrical utility company on January 1, 2005, expressed per 1000 population. For point prevalence, the unit of time is often not expressed because the period of time is effectively instantaneous. Period prevalence is the number of cases existing at one time or another during a definable time interval such as 1-year, 5-year, or lifetime prevalence. Some epidemiologists do not express prevalence as a rate because in practice it is often derived from surveys that are difficult to assign to a specific time interval. A number of factors other than the risk factor under study may affect the incidence and prevalence rates. These include demographic characteristics of the underlying population, most obviously age distribution6 because age is known to be associated with the onset of almost all disorders. Gender and ethnicity distributions must also be taken into account when incidence rates are interpreted. Other influences can distort the apparent incidence rate, including certain company policies, workers’ compensation claims, and health care system influences that affect the likelihood of seeking medical attention, of being diagnosed with a given disorder or disorders, or of having the disorder reported. These factors should be considered when measures of disorder frequency are evaluated, particularly when changes are assessed over time or different populations are compared. To eliminate the effects of differences in these factors, the rates may be adjusted or standardized algebraically. The adjusted rates express the risk of acquiring the disorder in the populations being compared as if they had the same age, sex, and ethnicity distributions. Alternatively, if it is not necessary to have a single summary index of disorder risk, the morbidity rates within population strata defined by age, sex, and ethnicity may be compared. The number of existing cases of a disorder or disorders at any time is a function of both the rate of new cases (incidence) and the duration of that disorder. Therefore, when a population is
stable and the duration of a disorder is also stable, it is possible to estimate prevalence from incidence and vice versa according to the following approximation: ~ incidence × duration Prevalence ~ Thus a change in prevalence may reflect changes in the incidence rate, duration, or both. For example, the prevalence of low back pain in a population may change because of alterations in individual, work-related, or other environmental risk factors affecting incidence rate or because treatment changes alter the duration of back pain episodes and risk of chronicity. It is occasionally the case that improved treatment extends the duration of a disorder, with the result that the prevalence increases in the face of a decreasing incidence, as occurred some decades ago with Down syndrome. The survival of infants with Down syndrome improved because of improved medical and surgical management of their associated disorders. The prevalence of Down syndrome increased, although the incidence declined as a result of prenatal screening programs.
DESCRIPTIVE EPIDEMIOLOGY The first step often undertaken in epidemiology is development of the descriptive epidemiology of a disorder or disorders. Descriptive epidemiology supports the development of causal hypotheses but does not in itself support conclusions about disorder causality or about any hypotheses. In descriptive epidemiology the frequency of a disorder in the population is characterized in terms of person (e.g., age, sex, ethnicity-specific incidence rates, economic, behavioral, occupational, and other factors), place (rural versus urban, type of housing, national variations, type of industry, job requirements), and time (long-term trend, seasonality, occasionally day of the week or time of day). The need to explain variation in descriptive studies drives the formulation of causal hypotheses. Drawing on current available information from various fields (such as anatomy, physiology, psychology, behavioral science, etc.), specific hypotheses are developed by inductive reasoning to explain observed patterns of variation and then evaluated using specific study designs to test these hypotheses. Studies that test specific hypotheses are called analytic. As the results of hypothesis-testing (analytic) studies are accrued, they are added to the basis for causal inference, depending on their strengths and generalizability, and hypotheses are supported, modified, or negated. In interpreting the evidence from all scientific sources, the rules of causal inference are applied.7 Briefly, the hypothesized cause must be demonstrated to have preceded the disorder by a length of time sufficient to allow disorder development and expression (time sequence of events). The disorder should be more common in those with the hypothesized cause than in those without it (increased risk in those exposed to the hypothesized cause), and as the intensity or duration of exposure to the hypothesized cause increases, the frequency of the disorder should increase (dose-response relationship). The association between the hypothesized causal factor and the disorder should be consistently demonstrated in methodologically sound studies and should be biologically plausible. In addition, the specificity of an association (i.e., the extent to which the hypothesized
Chapter 1
causal factor is associated with only one disease or disorder) adds weight to a causal hypothesis, but it is not necessary for causal inference; for example, cigarette smoking is accepted as a cause of lung cancer, although the association is not specific. Cigarette smoking is also associated with a number of other cancers, obstructive pulmonary disorder, heart disorder, and a variety of disorders, including osteoporosis, low back pain, and, in particular, herniated intervertebral disks.
ANALYTIC EPIDEMIOLOGY Analytic, or hypothesis-testing, epidemiology relies on two types of study designs: observational and experimental. In observational studies, exposure to the hypothesized causal factor and development of the disorder in the population under study occur in the natural course of events; the investigator does not cause them to occur. The study is designed and executed to maximize the extent to which it can be seen as a natural experiment, that is, the extent to which all extraneous sources of variation are eliminated and only the exposure to the putative cause and the frequency of disorder vary between populations being compared. It is often the case that once substantial observational evidence has accrued, causality is widely accepted. However, it is desirable in etiologic epidemiology and almost universally required in evaluations of treatment that the final test of the hypothesis is in interventional or experimental studies. In experimental studies, the investigator causes individuals or groups of individuals in the population to receive the treatment in question. To demonstrate ethically the causal role of a risk factor for which there is only observational evidence, the investigator would prevent exposure to the risk factor for a group of people. In both types of interventional design strategies, a comparison group that does not receive the intervention is necessary. All other factors that might influence the outcome of the study (potential confounding factors) can be eliminated or controlled by the investigator. Because the conditions of the study are much more under control of the investigator, interventional studies can more closely approximate true experiments than can observational studies. When such studies are well designed and executed, they provide very strong support (or negation) for a hypothesis. All analytic study designs have potential problems of internal and external validity that must be solved by the investigator either in the study design or in the data analysis. Internal validity is the extent to which a study is a true test of the specific hypothesis, that is, the extent to which all possible biases of measurement or information and all possible confounding variables are eliminated as explaining the observed study result. External validity is the extent to which the study results can be generalized to the population of interest, namely, whether the study subjects are representative of the population at risk. If the potential validity problems have been solved in either the design or analysis of the study, the study evidence is strengthened. Because it is not possible to study the entire universe of potentially eligible subjects, epidemiologic studies are conducted on samples of the population of interest. Even a study of an entire city or the work force of a company constitutes a sample. The method of sampling should not introduce selection biases. For example, a volunteer study is potentially susceptible to selection
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Analytic epidemiology
bias because the health behavior and health status of people who volunteer for research are well documented to be better than those of refusers. No characteristics of the individuals should affect the likelihood of selection for the study, including their knowledge of the question at issue; their beliefs about the risk factors or about the cause of the disorder being studied; or any characteristic such as age, sex, or education that could be independently associated with both the disorder and the hypothesized causal factor. It is important for the internal validity of the study results that the information collected is accurate and complete. If there is inaccuracy (measurement error) in the information collected, the ability to detect the association of interest is reduced. If the accuracy of the information is worse for one exposure group than for another, the effect on the study results may not be predictable. For this reason, an evaluation of the accuracy (or validity) of measurements is necessary for any study. Research reports should describe the validity of the sources of information. Questionnaires or reporting methods that have been validated in the study population or in similar populations or circumstances should be used. The problem of validity of information is particularly important in research on occupational musculoskeletal disorders because the methods of both case diagnosis13 and measurement of work exposure17 have substantial limitations. Before specific study designs can be discussed, the term confounding must be defined. Confounding occurs when the study results can be explained by a factor extraneous to the hypothesis being tested. A potential confounding factor must be associated with both the disorder in question and the hypothesized causal factor. That is, the proportion of persons with the disorder having the confounding exposure must be different from the proportion of persons without the disorder with the confounding exposure. It is also necessary that the proportion of those with the hypothesized causal factor who have the confounding exposure are different from the proportion of those not exposed to the hypothesized causal factor who have the confounding factor. For example, a study that found an association between job satisfaction and the risk of occupational back injury could be confounded by the physical requirements of work if heavy work was a risk factor for back injury and was also associated with lack of job satisfaction in the studied population. Potential confounding factors can be eliminated in the design of the study by restricted or matched sampling or, in the data analysis phase, by stratified or multivariate analysis, for example. If in the study just described the statistical analyses controlled for physical requirements of work or if the researchers conducted an exploratory analysis and found no association between job satisfaction and the physical requirements of work, the potential for confounding would be eliminated. In experimental studies, potential confounding should be successfully eliminated by truly random blind assignment of subjects to the different treatments under study. Comparability of the treatment groups should be confirmed by presentation of the baseline characteristics of each group on entry to the study. Confounding invalidates a study as a test of the hypothesis. The study’s results cannot be taken as evidence of causality or efficacy of treatment. Lack of generalizability, as opposed to confounding, does not invalidate a study’s results but merely restricts inference to populations similar to those under study.
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Introduction to epidemiologic concepts in musculoskeletal disorders
Observational study designs are applicable in both clinical and etiologic epidemiology. In etiologic epidemiology the researcher tests whether a hypothesized factor is a determinant or cause of disorder in previously healthy people, whereas in clinical epidemiology one tests whether particular characteristics, risk factors, or clinical interventions are determinants of the prognosis or outcome. The classic observational analytic study designs are the cohort study, the case-control study, and the cross-sectional study.
Risk factor present
Target population
Risk factor absent
Figure 1.1
Disease or outcome does not occur
Sample
Cohort study (Prognostic study) The cohort study is the observational design that, when well designed and executed, produces the soundest results in terms of incidence rates and disorder etiology or prognostic determinants of all the observational study designs. The hallmark of a cohort study is that a population initially free of the outcome of interest is identified and characterized with respect to the hypothesized risk factor, important covariates, and potential confounders. The population is observed for a period of time adequate for development of the disorder, and the new cases (incident cases) are recorded. Rates of disorder development are compared between those exposed and those not exposed to the hypothesized risk factor. A study of prognostic factors related to return to work after episodes of absence due to work-related low-back-pain sickness is an example of a cohort study. The cohort consisted of all those first presenting to an occupational health clinic at a large municipal transportation agency for medical clearance for sick leave from work because of a complaint of work-related low back pain. These individuals were asked to complete a questionnaire on function, pain, satisfaction with work, and beliefs about pain. The occupational physicians conducting the sickness absence clearance examinations included assessment of gain, posture, and distribution of painful symptoms specific for back pain. Participants in the study were followed for 3 months, at which time the participant’s return to work status was determined. To identify which factors best predicted return to work, rates of return to work were compared between those with high and low scores on clinical signs and symptoms, function, pain, work satisfaction, and pain beliefs. Predictors that showed large differences in rates of return to work were interpreted as being strongly predictive.12 Cohort studies can be prospective in nature, meaning that a disorder-free population or group is initially identified and then subsequently tracked over time (Fig. 1.1). This same model can also be used with historical records. Employment records, for example, can be used to identify a group of new employees at a company. Job status and medical records can then be linked to these employment records to identify work exposures and the development of the disorder of interest. Studies that use historical records are called retrospective. Loss to follow-up is a potential problem in cohort studies. If a substantial proportion of subjects are lost to the study for any reason, for example, having moved out of the region, it would be expected that fewer cases of the disorder in question would arise in the study than originally planned. The number of study cases may ultimately be too small to yield stable estimates of the incidence rates and, consequently, estimates of the relative risk.
Disease or outcome occurs
Disease or outcome occurs Disease or outcome does not occur
Cohort study.
In this case, the observed relative risk would need to be very large to support the causal hypothesis. For example, consider a cohort study examining the causal role of occupational repetitive motion in carpal tunnel syndrome. New workers hired in 1985 through 1990 are enrolled and followed forward for 10 years, with information on new cases of carpal tunnel syndrome coming from the company medical department records. If 30% of the workers retire, take disability pensions, die, get another job, or leave the company for other reasons, there is a substantial loss to follow-up. A bias in loss to follow-up occurs if the workers who leave the company are those with the highest exposure to repetitive work movements and those who leave because upper extremity problems consistent with preclinical carpal tunnel syndrome are making it more difficult for them to do the job. The observed relative risk is an underestimate of the true relative risk because the detected incidence of carpal tunnel syndrome among those with repetitive-motion jobs is lower than the true incidence and the detected incidence among those not exposed is not affected. Biased loss to follow-up leading to underestimates of incidence in the unexposed would produce an inflated observed relative risk. High proportions lost to follow-up or higher proportions lost in one exposure category than another (selective loss to follow-up) leave open the possibility of biased loss to follow-up with consequent distortion of the study findings. Another form of selection bias can occur. This bias, called selective survival or selective attrition, occurs when people who have both the exposure and the disorder have a different probability of dropping out of the population available to be included in the study than do people who are not exposed and get the disorder. This type of bias can easily occur in cross-sectional and case-control studies. It can also occur in a particular variant of the cohort study called the prevalent cohort study. For example, a prevalent cohort study examining occupational repetitive motion as a risk factor for carpal tunnel syndrome that enrolled workers who were first employed between 1985 and 1990 and were still actively employed in 2005 could be affected by selective attrition if carpal tunnel syndrome by and large developed within 15 years of employment and workers tended to leave the company when carpal tunnel syndrome developed.
Chapter 1
Some diseases or disorders take many years to develop after the initial exposure to the presumed causal factor or take many years of exposure. The duration of time between the time of exposure to the presumed causal risk factor and the development of disease or disorder is called latency. Another problem concerns the prevalence of the disorder in the population. If a disorder is rare, many thousands of subjects may be required to identify and collect enough cases where the disorder occurs to be suitable for statistical analysis. Consequently, the cohort study design is not optimal in situations where the disorder of interest is both very rare and also has a long latency period. It can be more efficient in terms of time and the number of subjects studied to address the hypothesis by means of a case-control study, as described in the next section.
Case-control study The essential feature of the case-control study that differentiates it from the other observational study types is that individuals are selected for the study on the basis of the presence of the disorder in question (cases) and compared with individuals selected for the study on the basis of the absence of the disorder under study (control subjects). The presence or absence of the hypothesized causal factor is then ascertained in both case and control subjects. Although this appears on its face to be a simple undertaking, case-control studies present a number of methodologic challenges that must be solved for the study results to be valid (Fig. 1.2). A study of ergonomic risk factors for work absence due to onset of low back pain–related sickness conducted among Baltimore City workers is an example of a case-control study.10 Two hundred cases of absence due to back pain–related sickness were identified from the city’s occupational health department. Four hundred individuals without back pain but matched on gender, job classification, and department served as control subjects. In-person interviews were conducted to collect data on demographics, work history, psychosocial and work organization characteristics,
Risk Factor present? Disease present? Yes
Yes Sample
Cases No
Population Yes No
Sample
Controls No
Figure 1.2
Case-control study.
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Analytic epidemiology
and ergonomic factors related to work. Data on these factors were categorized. To analyze these data, the ratio of those exposed to the risk factor to those not exposed was calculated once for those with back pain and again a second time for those without back pain. A risk factor was interpreted to be associated with the back pain when the ratio of having the risk factor was higher among those with back pain as compared with those without back pain. Case-control studies frequently suffer from information biases. For example, if information on exposure to the risk factor of interest comes from a different source for case and control subjects, biased exposure information is possible. Recall bias, in which a case subject is more or less likely to recall an event in the past than is a control subject, is also possible. There is also the problem of unbiased recall failure, in which subjects are asked to recall events or conditions that took place so long ago they cannot be remembered. Establishing that exposure to the factor of interest took place long enough before the outcome to be a biologically plausible determinant is difficult for certain types of hypotheses; for example, a case-control study examining preexisting degenerative disk disorder as a determinant of chronicity (symptom duration greater than 6 months) in workers with chronic back pain could not establish that the disk problem predated chronicity based on clinical or imaging examinations at the time of study. These problems are avoided if the case-control study uses exposure or prognostic information that was recorded, for example, in medical or prescription records, long enough before the disorder condition being studied to be a biologically plausible cause and to obviate recall problems. Well-designed and well-conducted case-control studies may provide evidence as robust as that of cohort studies at considerably less cost and in considerably less time. However, because of the difficulty in avoiding the problems just described, casecontrol studies often produce weaker causal evidence than do cohort studies.
Cross-sectional study Cross-sectional studies simultaneously ascertain exposure to risk factors (or the presence of prognostic factors) and the presence of the disorder or outcome in question in a population sampled without regard to the presence of either. This type of sampling is sometimes called naturalistic sampling. In contrast to a cohort study, which follows subjects over time and ascertains incidence, a cross-sectional study ascertains conditions present at the moment of study, that is, the prevalence of the disorder or outcome in question at the time of the study. The estimates of relative risk derived from cross-sectional studies are therefore estimates of prevalence relative risk. Population-based crosssectional studies of low back pain often address, among other factors, the association of the type of work (occupation, physical requirements, and so forth) with low back pain (Fig. 1.3).2 Cross-sectional or survey studies are often undertaken because, unlike case-control studies, they require few a priori decisions with regard to the selection of subjects and, unlike cohort studies, it is not necessary to wait for the study outcome. These advantages are offset by their susceptibility to some of the problems of both cohort and case-control studies. When uncommon
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Introduction to epidemiologic concepts in musculoskeletal disorders
Risk factor present disease present
Risk factor present disease absent Study population
Sample Risk factor absent disease present
Risk factor absent disease absent Figure 1.3
Cohort Study
Feature Selective Survival Recall bias Loss to follow-up Time sequence of events Time to complete Expense
+ + − + − −
CaseControl Study + − + − + +
CrossSectional Study − − + − + +/−
Cross-sectional study.
disorders or exposures are being studied, a large number of people must be included, as in cohort studies. If information on exposures or on determinants of interest is collected at the time of the study rather than from previously existing records, there can be recall biases, recall failure, and problems in establishing the time sequence of events, just as in case-control studies. Nevertheless, for relatively common disorders (outcomes) and risk factors (determinants), cross-sectional studies may be a useful first step in exploring a hypothesis. Because of their many limitations, however, cross-sectional studies rarely produce robust results for evaluating the importance of causal or prognostic factors. When the literature on a problem consists predominantly of cross-sectional studies, it is often the case that the analytic epidemiology of that problem is in its infancy. Until recently, much of the epidemiologic information on occupational low back pain was derived from descriptive and cross-sectional studies.16 In the past 5 or 6 years there has been a substantial advance in the quantity and quality of observational analytic studies of work-related back pain. The epidemiologic investigation of upper extremity disorders began later than that of low back pain. Consequently, knowledge of the risk factors for work-related upper extremity disorders is less developed. The intrinsic strengths and limitations of the basic observational study designs are summarized in Table 1.1.
Experimental study designs: clinical trials The distinction between observational and interventional study designs is that in observational designs the investigator does not
Randomize
Patients
Table 1.1 Strengths (+) and limitations (-) of the observational study designs
Eligible
Experimental treatment
Successes/ Failures
Agree
Figure 1.4
Standard treatment Ineligible
Refuse
cause the exposure to the causal factor or treatment for the purposes of the study, whereas in interventional designs the investigator does cause subjects to be exposed to different factors or treatments. Observational study designs are susceptible to treatment assignment biases in which the treatment the patients receive is influenced by certain patient characteristics (e.g., lifestyle or clinical severity) that can confound the results. Clinical trials, in which the treating physicians or the investigators control which treatment patients receive, are also susceptible to such biases. For this reason, randomized controlled trials, where only chance influences which treatment eligible patients receive, are the preferred method of evaluating therapeutic interventions. The validity of randomized controlled trials depends on all the methodologic features described for the observational study designs and more. The study must be confined to those patients who have agreed to participate. Comparisons of treatment outcomes in patients who agree to participate with those in patients who refuse to participate are not valid. Assignment of patients to treatments must be done by using accepted methods of randomization, which are described in the report, and the resulting comparability of the treatment groups on important covariates should be described, usually in a table summarizing the baseline characteristics of the treatment groups. On the occasions when, by chance, randomization does not result in comparable groups, potential confounding must be controlled in the statistical analysis. Figure 1.4 is a schematic representation of appropriate design in a randomized controlled trial. Ordinarily, in randomized trials the treating physician and the patient are blind to which treatment group the patient has been assigned. If this is not possible, assessment of the study
Successes/ Failures
Randomized control trial.
Chapter 1
outcome should be done by an independent evaluator to avoid observer and participant biases in assessing the outcome. This is particularly important when the outcome being assessed is subjective. Information should be collected in the same way and with the same frequency in all treatment groups. Eligibility and exclusion criteria should be described and be appropriate to the question being addressed. Treatments should be clearly described, and patient compliance, dropouts from the study, and complications should be described and equivalent in both groups. Finally, the outcomes studied should be appropriate to the treatment or condition in question. A number of general health status assessment measures are used, for example, the SF-36, a standardized multidimensional assessment instrument that includes functional capacity, pain, locomotion, mental status, and affect. There are numerous assessment instruments for back pain disability, including the Oswestry,5 the Roland-Morris questionnaire,15 the Quebec Back Pain Disability Scale,8 the MaineSeattle back pain disability questionnaire,1 and others.3
STATISTICAL ISSUES Methods of analysis The statistical analysis of any study result should be appropriate to the hypothesis and to the structure of the data collected. When, for instance, the study examines the difference in Oswestry scores associated with a conditioning program as compared with usual care for subacute low back pain, comparisons of the mean scores in the treatment groups may be appropriate. If it is necessary to control for pretreatment differences between the groups, the analysis uses multivariate methods such as analysis of covariance or multiple regression. Occasionally, because of the statistical characteristics of the outcome being assessed, it may be necessary to transform it (e.g., log transformation, square root transformation) and analyze the transformed variable. It is often the case that the outcome variable distribution or the conditions of the study do not conform to the requirements of the usual statistical hypothesis tests such as t-tests, analysis of covariance, and regression analysis. In these cases, a nonparametric method of statistical analysis such as the Wilcoxon method is appropriate. When the hypothesis addresses the relative frequency of an event such as a back injury rate, a ratio can be formed consisting of the risk of development of the disorder among those exposed to the risk factor compared with the risk of the disorder among those not exposed to the risk factor. This ratio is called a relative risk. When the relative risk is 1, then the risk of the disorder is the same among those exposed to the risk factor as those not exposed. However, when the relative risk diverges from 1, then the risk is not the same between the exposed and unexposed groups. This is interpreted as evidence for an association between the risk factor and the disorder. The relative risk may be adjusted for important covariates or to eliminate potential confounding. Relative risks can be calculated only in those studies where the entire study population is tracked or a representative sample is identified, as would be the case in a cohort study. A relative risk cannot be calculated in situations where the study sample is not representative (e.g., as would be the case in a
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Statistical Issues
case-control study). Instead, an alternative to the relative risk needs to be used. The odds ratio is a measure of association that, in certain circumstances, can be used to estimate relative risk. The odds ratio is the ratio of the odds of the disorder in those exposed to the odds of the disorder in those unexposed. It also has valuable statistical properties because it can be estimated by using logistic regression. The effects of confounding variables can be controlled or the simultaneous effects of several causal variables or covariates can be estimated by using multiple logistic regression. Another measure of association can be found in studies that examine the rate of the development of a disorder in a population over time. In these studies, the risk of developing a disorder within a cohort changes for each point in time. As members of the cohort develop a disorder, the total number of individuals in the cohort still free of the disorder becomes smaller and the calculation of risk changes. A survival curve shows the cumulative proportion of cohort members remaining free of the disorder on the vertical axis and time on the horizontal axis (Fig. 1.5). Typically, survival curves show an exponential relationship between cumulative proportion remaining free of the disorder and time. We can examine whether the survival experience is different between members of a cohort with different exposure profiles by using statistical tests specific for this type of analysis, such as the log-rank test.9 Hazard is a term that expresses the rate of change of the cumulative proportion surviving with time. In prognostic studies it is possible to compare whether the rate of change of survival (hazard) is different between exposure groups. A useful property of hazards is that this term can be modeled using logistic regression techniques. The Cox proportionate hazards model is used to evaluate differences in hazard between exposure groups. The hazard ratio is interpreted much like the relative risk or odds ratio. When the hazard ratio is equal to 1, then the survival experience is interpreted to be the same among exposure groups. When the hazard ratio is not equal to 1, the interpretation is that there is an association between exposure to the risk factor and survival experience related to the disorder of interest.9 An advantage of survival analysis is that all study subjects contribute information for as long as they remain in the study. The reader should be aware, however, that if the number of dropouts during the course of the study is substantial, estimates of the hazard ratio toward the end of the follow-up period are based on relatively small numbers and are consequently unstable.
Estimates and confidence limits Research is conducted on a sample of persons or other units of observation drawn from a target population. The results of any given study are estimates of the true means, proportions, relative risks, and so forth in the population from which the samples were drawn. The precision of a study estimate of the population value, or parameter, of a measurement is described by the standard error of estimate. The standard error (SE) is the square root of the ratio of the variance (s2), or variability of the measurement in the sample, to the number of subjects (N) in the study. For example,
SE mean =
s2 N
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Introduction to epidemiologic concepts in musculoskeletal disorders
Percent returning back to any work
100%
75%
50%
Figure 1.5 Return to any work from sick absence because of nonspecific low back pain (n = 225). (From Hiebert R, Skovron ML, Nordin M: Work restrictions and outcome of nonspecific low back pain. Spine 28(7): 722-728, 2003. Reprinted with permission.)
25%
0% 0
90
180
270
364
Time lost from work because of LBP (in days) No restrictions Some restrictions
Variance is affected by a number of factors, including interindividual variability, intraindividual variability (such as diurnal variations), and instrument variability. Designing or executing a study to reduce any of these components reduces the variance of the measurement, thus reducing the standard error and increasing the stability of the estimate of the population parameter. The larger the number of subjects on whom the estimate is based, the smaller the standard error and the more confident we can be in its representation of the population parameter. Because sample results are estimates of population parameters, it is increasingly becoming the standard of reporting to describe the precision of the estimates as a range within which the population parameter probably lies. This is the confidence limit around the estimate and is by convention expressed as the 95% confidence limit. For example, the 95% confidence limit for a mean is approximated by 95% confidence interval = mean ± 2(SEmean)
Statistical hypothesis testing Because there is always sampling error, estimates may be expected to vary from sample to sample. Consequently, study results must be subjected to statistical hypothesis testing; that is, study results must be tested to determine the probability that the observed results from a specific study could have occurred by chance alone. The statistical hypothesis test evaluates the null hypothesis that the observed study results occurred because of sampling error when there was no true association in the population from which the study subjects were sampled. The probability of making this type of error is designated as alpha (α). If the observed association is large enough that this kind of error is improbable, the null hypothesis is rejected. The investigators then accept the alternative hypothesis, that the observed estimates of relative risk
or differences between treatments reflect the true situation in the population from which the samples were drawn. By convention, the cutoff for rejecting the null hypothesis is usually set at 0.05. Then if the probability (p value) that the observed results are due to sampling error is less than 0.05, that is, less than α, the null hypothesis is rejected and the results are declared statistically significant. Thus, statistically significant results are simply results that we have decided, within an acceptable margin of error, probably did not occur by chance. Further, the larger the observed association relative to the underlying variability of the outcome being measured, the more likely that it will be declared statistically significant.
Statistical power and sample size Statistical hypothesis tests actually involve two probabilities. The probability of making a type I error by incorrectly rejecting the null hypothesis, that is, by declaring an observed association to be statistically significant when in fact it is the result of sampling error, is referred to as α, as described in the preceding paragraph. There is also the probability of incorrectly accepting the null hypothesis; that is, declaring that the study results are due to sampling error (not statistically significant) when in fact they reflect a true association in the population from which the study subjects were drawn. This is the type II error and its probability is beta (β). The complementary probability that a study will be able to correctly reject the null hypothesis when it is false, that is, correctly detect an association when there is one in the population at large, is referred to as statistical power (1 – β). Table 1.2 illustrates the different conditions and possible results of a statistical hypothesis test. In the planning phase of research the investigators should make a determination of how strong an association would be clinically significant, that is, how large an estimated relative risk
Chapter 1
Table 1.2 Population conditions, statistical hypothesis test results, error types, and designations Hypothesis Test Result
Population Condition
Accept null hypothesis NULL HYPOTHESIS TRUE No association NO ASSOCIATION Correct Reject null hypothesis Type I error (alpha) Association exists
NULL HYPOTHESIS FALSE ASSOCIATION EXISTS Type II error (beta) Correct
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References
result should be specified, the plan of statistical analysis determined, and the necessary number of study subjects defined. Study management should avoid the introduction of differential loss to follow-up, unblinding, and other potential problems. The statistical analysis should be appropriate to the structure of the data and to the hypothesis. Finally, although the discussion should place the study in the context of other work and what is already known about the question, the specific conclusions should not go beyond what was actually tested.
REFERENCES or how big a difference between treatments. Because the validity of the study requires that it be a true test of the research hypothesis, it is important to design the study so that a clinically significant association will have a good chance of being declared statistically significant, that is, so that the study has sufficient power to detect a clinically significant association. The larger the sample size, the more power the statistical test has to detect associations; in other words, as expected differences or relative risks get smaller, the number of subjects studied must increase to have adequate power to test the hypothesis. Conversely, with very large numbers of study subjects it is possible to declare trivial associations statistically significant. When studies with small sample sizes report results that are not statistically significant, they should also report how large an association would have been required for there to have good power to detect it. The reader should also evaluate whether the observed difference and its upper confidence limit, although not statistically significant, are clinically significant. When studies with huge numbers of subjects report statistically significant results, the reader should decide whether the differences are trivial in clinical terms, even though they are statistically significant.
1.
2.
3.
4. 5. 6. 7. 8. 9. 10. 11.
SUMMARY
12.
The validity of clinical research depends on a number of factors. The hypothesis must be formulated specifically enough to be testable. The appropriate study subjects should be eligible, and there should not be differential participation. The information collected should be appropriate to the hypothesis and accurate. The study design and information sources should avoid potential information biases. Potential confounders should be eliminated in the study design or controlled in the statistical analysis. At the time the study is designed, a clinically significant hypothesized
13.
14. 15.
16. 17.
Atlas SJ, Deyo RA, van den Ancker M, Singer DE, Keller RB, Patrick DL: The Maine-Seattle back questionnaire: a 12-item disability questionnaire for evaluating patients with lumbar sciatica or stenosis: results of a derivation and validation cohort analysis. Spine 28(16):1869-1876, 2003. Bernard BP, ed: Musculoskeletal disorders and workplace factors: a critical review of epidemiologic evidence for work-related musculoskeletal disorders of the neck, upper extremity, and low back. U.S. Dept. of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention. Cincinnati, OH, 1997, National Institute for Occupational Safety and Health. Bombardier C: Outcome assessments in the evaluation of treatment of spinal disorders: summary and general recommendations. Spine 25(24):3100-3103, 2000. Bureau of Labor Statistics, US Labor Department, Annual Survey 2003, Tables R19, 22. Fairbank JC, Pynsent PB: The Oswestry Disability Index. Spine 25(22):2940-2952; discussion 2952, 2000. Gyntelberg F: One-year incidence of low back pain among male residents of Copenhagen aged 40-59. Danish Med Bull 21:30-36, 1974. Kelsey JL, Thompson D, Evans AS: Methods in observational epidemiology. New York, 1986, Oxford University Press. Kopec JA, Esdaile JM, Abrahamowicz M, et al: The Quebec Back Pain Disability Scale: measurement properties. Spine 20(3):341-352, 1995. Lee E: Statistical methods for survival data analysis. Belmont, CA, Lifetime Learning Publications, 1980, Wadsworth Inc. Myers AH, Baker SP, Li G, et al: Back injury in municipal workers: a case-control study. Am J Public Health 89(7):1036-1041, 1999. National Research Council and the Institute of Medicine. Musculoskeletal disorders and the workplace: low back and upper extremities. Panel on Musculoskeletal Disorders and the Workplace. Commission on Behavioral and Social Sciences and Education. Washington, DC, 2001, National Academy Press. Nordin MN, Skovron ML, Hiebert R, et al: Early predictors of delayed return to work in patients with low back pain. J Musculoskel Dis 5(2):5-27, 1997. van den Hoogen HM, Koes BW, van Eijk JT. On the accuracy of history, physical examination, and erythrocyte sedimentation rate in diagnosing low back pain in general practice. Spine 20:318-327, 1995. Praemer A, Furner S, Rice DP: Musculoskeletal conditions in the United States. Rosemont, IL, 1999, American Academy of Orthopaedic Surgeons. Roland M, Morris R: A study of the natural history of back pain. Part I. Development of a reliable and sensitive measure of disability in low-back pain. Spine 8(2): 141-144, 1983. Skovron ML: Epidemiology of low back pain. Baillieres Clin Rheumat 76:559-573, 1992. Winkel J, Mathiassen SE: Assessment of physical work load in epidemiologic studies: concepts, issues and operational considerations, Ergonomics 37:979-988, 1994.
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2
Psychosocial Aspects of Work-Related Musculoskeletal Disorders: Clinical Implications Sherri Weiser
Until recently, attempts to unravel the mystery of work-related musculoskeletal disorders (MSDs) concentrated on the physical demands of the job and the physical vulnerabilities of the worker. It became clear that this problem did not easily lend itself to reductionistic approaches. Although certain physical loads and tasks have been associated with the development of musculoskeletal problems, the strength of these associations has been disappointingly weak.29 Furthermore, a determination of physical vulnerability before injury is nearly impossible. Even when a physical defect such as disk herniation has been established in conjunction with a report of pain, the correspondence with actual disability is often low. Like all human conditions, MSDs can be infinitely complex. A thorough understanding of these disorders requires a consideration of influences beyond the physical. The worker’s psychologic attributes and social reality may have significant bearing on the onset, progression, and outcome of occupational MSDs. A biopsychosocial perspective offers much in the way of understanding these disorders. Adoption of the biopsychosocial model in pain and disability research has resulted in the identification of specific psychologic and social aspects of MSDs. Recently, this research has been summarized in a number of excellent review articles and treatment guidelines, conclusions from which are discussed. The biopsychosocial model implies not just the inclusion of psychologic and social considerations but a new perspective on the part of all stakeholders involved in the prevention and treatment of MSDs. This chapter describes how to achieve the goal of preventing and treating the disorder in practical terms.
THE BIOPSYCHOSOCIAL MODEL The notion of a link between the mind and body has existed throughout history. It was Walter Canon,2 however, who substantiated this idea with his scientific explanation of the “fight or flight” response. His research identified the organism’s physical reactions to psychologic stress. Selye24 later showed how these responses, if left unchecked, can over time cause severe damage
to vulnerable organs and body systems and may even cause death. Today, the relationship between the mind and the body is studied extensively. Psychologic factors have been shown to affect a spectrum of diseases involving virtually all bodily organs and systems.8 First described by Engel in 1977,5 the biopsychosocial model extends beyond mind and body to include the impact of social factors on illness. Influenced by models of stress and illness, Engel concluded that any illness must be viewed from a multidimensional perspective that takes biologic, psychologic, and social factors into consideration.5 Furthermore, these factors are not independent, as a medical model would suggest, but interrelated. It was by understanding this perspective, Engel believed, that physicians would be prepared to take on the complexities of health and illness. The biopsychosocial model soon became the prevailing view among those involved in pain research. In 1965 the gate control theory outlined the channels of pain transmission through neurologic pathways.19 This theory further asserted that pain transmission may be modulated by cognitive and affective states. This model was fundamental in explaining the disparities between physical findings and the phenomenologic experience of pain. The gate control theory laid the groundwork for modern approaches to treating chronic pain. In 1992, Waddell28 presented a detailed analysis of low back pain with the use of a biopsychosocial model (Fig. 2.1). The many levels on which pain is experienced are defined in the model. The physical injury is interpreted cognitively, resulting in a corresponding emotion. A man who believes that he has a herniated disk, for example, is more apt to be anxious and depressed than a man who believes that he has a sprain. The man with the “herniated disk” may also display more avoidance behavior initially than the man who believes he sprained his back. This process takes place within a social context that is constantly providing feedback and modifying the individual’s response. Waddell also pointed out that feedback loops exist among all levels in the model and that a change in one component affects the others. If the man with the supposed herniation sees a physician and is assured that the problem is only a sprain, his belief has changed. As a result, his affect and pain behavior will change,
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Psychosocial aspects of work-related musculoskeletal disorders
Social environment
PSYCHOLOGIC AND PSYCHOSOCIAL FACTORS ASSOCIATED WITH MSDs Illness behavior
Affective
Cognitive
Sensory
Figure 2.1 A cross-sectional analysis of the clinical findings and assessment of low back pain and disability at one point in time. (From Waddell G: Biopsychosocial analysis of low back pain. In M Nordin, TL Vischer, eds: Common low back pain: prevention of chronicity. London, 1992, Bailliere Tindall.)
and nociception may be experienced as less severe. These feedback loops are particularly important in chronic low back pain, wherein the original injury is often resolved. In these cases, psychologic and social variables are even greater determinants of functional status than in cases of acute back pain when nociception is responsible for much of the illness behavior. Occupational musculoskeletal injuries are clearly amenable to biopsychosocial analysis. They either occur at work or are believed to be its result. The cognitive, affective, behavioral, and social elements of such an injury are therefore inextricably related to the workplace. Injuries or disorders that did not occur at work may also be considered work-related if attitudes or beliefs about work affect recovery. If an injured worker fears that returning to work will exacerbate an injury, for example, recovery may be delayed. Recently, a number of studies have demonstrated the impact of psychologic and social factors on occupational musculoskeletal injuries. What has emerged is evidence that these factors have as much, and in some cases more, predictive value as physical and environmental factors. The main findings from recent critical review articles and current studies are discussed below. Most of the articles refer to nonspecific disorders of the spine; research has centered on these conditions because they account for most of the associated costs and suffering caused by the disorder. Some reviews include the upper extremities as well. To date, no high quality study of workrelated lower extremity injuries that explores psychosocial factors has been found.
Psychologic factors refer to cognitions or beliefs about pain and disability and affective or emotional responses, whereas psychosocial factors reflect an individual’s perceptions of others and the environment. Recent systematic evidence-based reviews have concluded that even when measured early in the injury, both these factors are stronger predictors than physical factors of outcomes such as work status. The Clinical Guidelines for the Management of Acute Low Back Pain, published in 2001, state that in addition to social and economic factors, psychologic factors play an important role in the development of chronic low back pain and disability and influence a patient’s response to treatment and rehabilitation.30 Specifically, beliefs that activity and work will make pain worse (fear-avoidance beliefs) and that the patient is not responsible for the pain or treatment along with behaviors intended to communicate that the patient is in pain (illness behaviors) are associated with poor outcome. Using strict inclusion criteria, in 2001 Koes et al13 published a comparison of clinical guidelines for the management of low back pain from 11 different countries that appeared from 1994 until 2000. They found that in most regards the content of the guidelines appeared to be quite similar and that all recognized the importance of psychologic and psychosocial factors, including work perceptions, in the development and maintenance of low back pain. Indeed, the New Zealand Guidelines for assessing acute low backpain, updated in 2003, likewise finds good agreement that beliefs, mood states, and behaviors, such as those identified by Waddell et al,29 consistently predict poor outcome.21 One of these is the belief that work will make the pain worse, evidence for which is so compelling that investigators have labeled this risk factor one of the “yellow flags.” Yellow flags are defined as factors that may increase the risk of developing or perpetuating long-term disability and work loss associated with low back pain. The New Zealand group recommends their assessment as early as 2 weeks after injury. Occupational health guidelines for low back pain were published in 2001. Although the effect size was small, strong evidence was found that psychosocial factors are associated with the risk of onset of low back pain in symptom-free workers. In the workplace, psychosocial factors are stronger predictors of care seeking and disability than clinical symptoms or physical work demands. Specifically, negative work perceptions were risk factors for symptom reports, health care utilization, and work loss. The most important factors associated with delayed recovery and response to treatment were beliefs that work caused the pain and expectations about recovery.29 A comparison of international occupational low back pain guidelines shows them in complete agreement that the early assessment of these risk factors was important if the patient exceeds the expected recovery time.25 Other reviews of factors affecting low back pain outcomes show similar results but call for more stringent scientific investigation of the interrelationships. For example, Hoogendoorn et al10 reviewed the literature and found that low workplace social support and low job satisfaction were related to reports of
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What is the relationship between psychosocial factors and work-related MSDs
back pain, but most studies failed to adjust for psychosocial work characteristics and physical load at work. Crook et al4 determined from their review that among other factors, psychologic distress and work environment characteristics were important prognostic factors. They noted, however, that most studies failed to investigate interactions among psychologic, social, and physical variables. Likewise, Pincus et al23 noted a lack of rigorous prospective studies that evaluated the role of psychologic factors in the development of chronicity. Of 25 publications, only 6 met their acceptability criteria for review. Depression, distress, and to a lesser extent somatization were the psychologic factors most strongly linked to low back pain disability. Catastrophizing by disabled workers as a coping strategy received weak support. The role of coping in conjunction with psychologic factors remains unclear. Although there are fewer studies on upper extremities than on back pain, thus far similar factors seem to be related to both disorders. In another review article, higher levels of perceived job demands and stress were the psychosocial factors most consistently linked to upper extremity disorders. Epidemiologic reviews revealed also that psychosocial factors unrelated to work, such as general worry/psychologic tension, depression/anxiety, general coping style, and response to pain, are likewise associated with both back and upper extremity disorders.15 Systematic reviews on this topic have not, however, been conducted. An interesting study by Ijzelenberg et al11 investigated whether individual, work-related physical, and psychosocial risk factors involved in the occurrence of musculoskeletal complaints also determined musculoskeletal sickness absence. Using a crosssectional study design and self-administered questionnaire, investigators collected data on individual and work-related risk factors and the occurrence of musculoskeletal complaints and musculoskeletal sickness absence among 373 employees of laundry-works and dry-cleaning businesses. Results show that both work-related physical factors and psychosocial factors showed strong associations with low back pain and upper extremity complaints. Workrelated physical factors did not influence sickness absence, however, whereas psychosocial factors showed some associations with it. This finding supports the notion that illness behaviors such as work absence are modified by cognitive and affective responses to physical symptoms in neck and back disorders. Linton15 systematically reviewed numerous studies of variable methodologic quality that looked at the effects of various psychologic factors on neck and back pain and concluded that there is a clear link. Prospective studies indicate, furthermore, that psychologic variables are related to the onset of pain and to all of its phases: Certain factors such as distress, anxiety, cognitive functioning, and pain behavior were found to be significant at all stages from acute to chronic pain. Still, psychologic factors account for only a portion of the variance, underscoring the importance of a multidimensional view. Luo et al16 found a variety of factors, including general stress, depression, and anxiety, to be associated with neck pain disability. Carroll et al3 confirmed the role of depression as a risk factor for pain onset. They followed a population-based random sample of adults and assessed them at 6 and 12 months. Controlling for demographic and socioeconomic factors, health status, comorbid medical conditions, and injuries to the neck or low back,
they found an independent and robust relationship between depressive symptoms and onset of a pain episode. They concluded that depression is a strong and independent predictor for the onset of an episode of intense and/or disabling neck and low back pain.
WHAT IS THE RELATIONSHIP BETWEEN PSYCHOSOCIAL FACTORS AND WORK-RELATED MSDs? There are a number of ways to explain the effect of psychosocial factors on MSDs. Perhaps the most straightforward explanation is that workers who are depressed or dissatisfied at work simply report more symptoms and disability than those who are content at their jobs. Distress in life and work may cause extra attention to be paid to symptoms, and therefore the signs are experienced as more troubling. This does not imply that workers are intentionally making more of symptoms than is warranted but that they are more likely to notice symptoms that can distract them from their daily routines. Another popular explanation is that stress results in increased muscle tension, causing spasms and ischemia, a painful condition resulting from oxygen reduction and the release of painproducing chemicals. Over time this pain may cause more distress, leading to a chronic cycle of stress and pain. Some laboratory studies have demonstrated an increase in muscle activation under stress,18 but findings have been inconsistent among patients with chronic pain. This may be because stress-induced muscle tension has a role in the development of chronic pain, but once patients are chronic their reactivity to stress becomes altered in ways that are unclear at present. The National Research Council and the Institute of Medicine reviewed evidence for the relationship between psychologic and physical factors and concluded that data exist to support a direct role of the central nervous system.20 This may help to explain how psychologic processes such as attention and emotion influence pain and its tolerance, an explanation supported by studies showing that pain is linked to a tendency to somatize or focus on symptoms.17 Other theories mentioned in the review include physiologic changes that occur under stress and result eventually in musculoskeletal pain. Stress hormones may facilitate the transmission of painful stimuli; physically stressful work tasks are associated with an increased release of stress hormones and slower recovery times. One reason for this may be that stress hormones affect the health of muscles, tendons, and ligaments and impede inflammatory or immune responses. Other factors such as behavior or life-style may moderate the effects of stress on muscle tension and biochemical changes. The concept of “work style” has been proposed to define how individuals interact with work demands.6 Originally proposed to explain work-related upper extremity disorders, work style is defined as cognitive, behavioral, and physiologic components of the stress response expressed behaviorally in movement, posture, and activity. Workers who respond to physical or psychologic workplace demands with a “high-risk” work style display excessive attempts to cope with stress and are susceptible to its negative
15
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Psychosocial aspects of work-related musculoskeletal disorders
consequences such as continuous arousal or reactivity. Similarly, Marras et al18 found that characteristic ways of responding to the environment were predictive of spinal loading. During a lifting task, introverts tend to exhibit muscle coactivation and alteration in movement patterns higher than those of extroverts. Stress-related behaviors such as these have been linked to symptom severity, functional limitations, and work disability.9 It is clear that the relationship between psychologic distress and physical responses is not simple. More research is needed to develop detailed models of the stress–pain relationship. Although various pathways have been proposed, there is a need to understand causal pathways and interactions among stresses and responses. Most likely there is no simple explanation of this relationship, and these proposed pathways are not mutually exclusive but work together in an ongoing dynamic way to result in MSDs. It is possible also that the stress pathways discussed here have variable influences in different stages of pain. What began as pain related to muscle tension, for instance, may over time develop into neuropathic pain. In addition, more clarity is needed in defining outcome measures, because different factors may moderate stress and physical complaints, sick absences, and disability.
PSYCHOSOCIAL INTERVENTIONS FOR MSDs
Physicians should share with distressed patients information about treatment philosophies and their possible outcomes. At the very least, physicians should be aware of the treatment philosophy of any facility to which they are referring patients, ideally one that adheres to current guidelines for the treatment of acute low back pain. The occupational health guidelines for the management of low back pain summarize recommendations for physicians to minimize the likelihood of chronic problems29: ● Reassure the worker and provide adequate information about the self-limiting nature and good prognosis of lower back pain. ● Advise the worker to continue normal activity and work or to return to them as soon as possible, even if there is still some pain. ● Because most workers with lower back pain manage to return to more or less normal duties quite rapidly, consider temporary adaptations of work duties or hours only when necessary. ● If a worker fails to return to work within 2-12 weeks (different guidelines vary considerably about the time scale), refer him or her to a gradually increasing exercise program or multidisciplinary rehabilitation (exercises, education, reassurance, and pain management following behavioral principles). These rehabilitation programs should be embedded in an occupational setting.
Most individuals at risk for MSDs can be effectively managed by their usual treatment provider, without the need for referral to a psychologist. Appropriate information and advice from the physician can reduce anxiety and improve patient satisfaction with care. Every encounter with health care professionals and medical management systems provides an opportunity for intervention. Waddell28 astutely observed the powerful effects a physician can have on the patient. Information that is vague, incomplete, or incomprehensible to a lay person can render the patient confused, helpless, and afraid. In the mind of a patient, the diagnosis of a herniated disk, for example, can be a sentence to disability. Diagnostic film results are often held up as proof by patients fearful of permanent disability. It is the health care provider’s responsibility to explain the implications of any diagnosis in terms the patient can understand. In the case of disk herniation, the patient needs to know that pain and disability are often self-limiting and that many people with this condition maintain their usual life-styles. Making sure that the patient has a realistic picture of the diagnosis and the prognosis is the first step. Patients who seem overly distressed can be questioned about other life circumstances. When the injury is work related, questions about work are particularly important. Often, patients feel residual anger toward the employer, sometimes believing that it is the employer’s responsibility to make sure they get well. Even if not responsible for their injuries, patients who understand the normal course of low back pain and are encouraged to take responsibility for their recovery from the onset may be spared the ordeal of becoming a compensation failure. Primary health care professionals have a responsibility also to make appropriate referrals. Information given by the physician can be reinforced or contradicted by secondary caregivers. One of the major causes of distress, contradictory information can lead to endless doctor shopping and prolongation of recovery.
Based on the conclusion that active care is superior to passive therapy, treatment guidelines recommending active and goal-oriented physical therapy should be the first course of treatment. Research has shown that the specific type of exercise prescribed is less important that the overall therapy philosophy. The objective should be to increase gradually the individual’s capacity for work with a balanced strength, flexibility, and cardiovascular program. Specific goal setting ensures that improvement is monitored, whereas positive feedback rewards productive behavior. The easiest program to implement early in treatment, a behavioral approach pioneered by Fordyce,7 consists of time-contingent care in which medication levels, exercise goals, and duration of treatment are preset and not determined by the patient. The idea is to provide environmental contingencies that reinforce “well” behavior and ignore “pain” behavior. In a benchmark study, Fordyce7 compared this approach with traditional care in which patients were told to “let pain be your guide.” Subjects with back pain for less than 10 days were randomly assigned to one of the two protocols and were followed at 6 weeks and 9 to 12 months after treatment. Although no differences were noted at 6 weeks, long-term follow-up showed significantly greater improvement in functioning for the treatment group. Like MSDs, physical therapy may be viewed from a biopsychosocial perspective. In contrast to passive modalities, an active approach shifts the responsibility to patients and provides techniques that they can use themselves to maintain fitness. As such, it increases the patient’s sense of control and may be instrumental in changing negative beliefs about pain. With improvement, the patient’s fears of returning to work should subside. After 2 weeks, patients who are not achieving weekly goals should be referred for a psychosocial evaluation. If warranted, they can begin a multidisciplinary program that addresses psychosocial issues. By their very nature these types of programs address physical, psychologic, and social concerns simultaneously.
Chapter 2
A multidisciplinary approach in treating patients with chronic pain is fairly standard,31 but the application of a biopsychosocial model in the acute and subacute phases of treatment as well is gaining popularity.
EVIDENCE No randomized controlled studies have assessed the use of psychologic interventions alone for MSDs, and high-quality studies that assess the effectiveness of multidisciplinary care for
Onset of pain • Explain the biopsychosocial model • Address concerns about pain, including the course, diagnosis, and prognosis • Emphasize the patient's role in recovery • Make appropriate referral if indicated
Four weeks after • Address concerns again, old and new • Address social factors again • Reinforce patient's role in recovery again • Refer for multidisciplinary evaluation and possible treatment Figure 2.2
●
Evidence
occupational MSDs in general are few. Nonetheless, in line with international opinion, expert panels have recommended the use of multidisciplinary team management for episodes of acute low back pain that is unresolved between 2 and 6 weeks, when patients risk chronic disability. Evidence clearly shows that multidisciplinary teams or networks are effective in managing chronic back pain,14,22,27 but their effectiveness for returning chronic patients to work remains unclear. Some studies showed good outcomes for chronic low back pain patients who are highly motivated to return to work,1 but randomized trials have yet to be done.
Two weeks after • Address concerns again, old and new • Address social factors including attitudes about work, as well as family and friends' responses to pain • Reinforce patient's role in recovery again • Make appropriate referral if indicated
Seven weeks after • Address concerns again • Address social factors again • Reinforce patient's role in recovery • Refer for multidisciplinary evaluation and treatment
Application of the biopsychosocial model: general guidelines for primary health care providers.
17
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Psychosocial aspects of work-related musculoskeletal disorders
Karjalainen et al12 conducted a Cochrane review of multidisciplinary programs for subacute low back pain patients. They concluded that “there is moderate evidence of positive effectiveness of multidisciplinary rehabilitation for subacute low back pain and that a workplace visit increases the effectiveness.” This endorsement is guarded because the only two articles that fit their inclusion criteria were only of moderate quality. However, more support for this treatment in the subacute phase was provided by van den Hout et al.26 In a randomized study, they showed that adding training in problem solving to a graded activity program improved outcome. The Work Loss Data Institute considered but did not recommend multidisciplinary or cognitive-behavioral treatment for upper extremity pain due to lack of studies.32 New studies should consider other MSDs as well. Future research would benefit also from a comprehensive multivariate causal model that would allow the assessment of interactions among psychologic, social, and physical variables. Adjustments for workload could be made when studying the effects of other factors; such a model would also permit an understanding of how these risk factors emerge during the transition from acute to chronic problems.
SUMMARY Traditional treatments for occupational MSDs have fallen short of expectations. The biopsychosocial model goes beyond physical factors to include psychologic and psychosocial elements that affect the worker before and after an injury. Investigations into the practical application of this model are most convincing. Studies have shown that psychosocial factors are at least as important as and often more important than physical factors in determining disability. Programs that have attempted to prevent injury or chronicity associated with occupational low back pain have flourished when they include a biopsychosocial framework. Though more research is needed, it is suggested that our best option is for primary health care providers and all health care practitioners to apply a biopsychosocial model in the same fashion for all MSDs that do not respond to traditional care (Fig. 2.2). Because we all share the burden of disability, we must all share in the solution. Much can be done by all medical professionals to make this process easier and more successful for everyone. For physicians, establishing a good rapport with the patient, giving clear and intelligible information, encouraging an active approach to treatment, and making appropriate referrals at the first sign of delayed recovery can go a long way toward reducing occupational MSDs. Physical therapists can follow a behavior model of active care that encourages patient responsibility for outcome and reinforces function over pain.
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Crook J, Milner R, Schultz IZ, Stringer B: Determinants of occupational disability following a low back injury: a critical review of the literature. J Occup Rehabil 12(4):277-295, 2002. Engel GL: The need for a new medical model. Science 196:129-136, 1977. Feuerstein M: Workstyle: definition, empirical support, and implications for prevention, evaluation, and rehabilitation of occupational upper-extremity disorders. In SD Moon, SL Sauter, eds: Beyond biomechanics: psychosocial aspects of musculoskeletal disorders in office work. Bristol, PA, 1996, Taylor & Francis, pp. 177-206. Fordyce WE: Acute back pain: a control group comparison of behavioral vs. traditional management methods, J Behav Med 9:127-140, 1986. Goleman D, Gurin D, eds: Mind body medicine: how to use your mind for better health. New York, 1993, Consumer Reports Books. Haufler AJ, Feuerstein M, Huang GD: Job stress, upper extremity pain and functional limitations in symptomatic computer users. Am J Ind Med 38(5):507-515, 2000. Hoogendoorn WE, van Poppel MN, Bongers PM, Koes BW, Bouter LM: Systematic review of psychosocial factors at work and private life as risk factors for back pain. Spine 25(16):2114-2125, 2000. Ijzelenberg W, Molenaar D, Burdorf A: Different risk factors for musculoskeletal complaints and musculoskeletal sickness absence. Scand J Work Environ Health 30(1):56-63, 2004. Karjalainen K, Malmivaara A, van Tulder M, et al: Multidisciplinary biopsychosocial rehabilitation for subacute low back pain among working age adults. Cochrane Database Syst Rev (3):CD002193, 2000. Koes BW, van Tulder MW, Ostelo R, Burton K, Waddell G: Clinical guidelines for the management of low back pain in primary care: international comparison. Spine 26(22):2504-2513, 2001. Koopman FS, Edelaar M, Slikker R, Reynders K, van der Woude LH, Hoozemans MJ: Effectiveness of a multidisciplinary occupational training program for chronic low back pain: a prospective cohort study. Am J Phys Med Rehabil 83(2):94-103, 2004. Linton SJ: A review of psychological risk factors in back and neck pain. Spine 25(9):1148-1156, 2001. Luo X, Edwards CL, Richardson W, Hey L: Relationships of clinical, psychologic, and individual factors with the functional status of neck pain patients. Value Health 7(1):61-69, 2004. Main CJ, Wood PL, Hollis S, Spanswick CC, Waddell G: The distress and risk assessment method: a simple patient classification to identify distress and evaluate the risk of poor outcome. Spine 17(1):42-52, 1992. Marras WS, Davis KG, Heaney CA, Maronitis AB, Allread WG: The influence of psychosocial stress, gender, and personality on mechanical loading of the lumbar spine. Spine 25(23):3045-3054, 2000. Melzack R, Wall P: Pain mechanisms: a new theory. Science 150:971-979, 1965. National Research Council and the Institute of Medicine: Musculoskeletal disorders and the workplace: low back and upper extremities. Panel on Musculoskeletal Disorders and the Workplace. Commission on Behavioral and Social Sciences and Education. Washington, DC, 2001, National Academy Press. New Zealand Guidelines Group: New Zealand acute low back pain guide. Wellington, NZ, October 2004, Accident Compensation Corporation. Patrick LE, Altmaier EM, Found EM: Long-term outcomes in multidisciplinary treatment of chronic low back pain: results of a 13-year follow-up. Spine 29(8):850-855, 2004. Pincus T, Burton AK, Vogel S, Field AP: A systematic review of psychological factors as predictors of chronicity/disability in prospective cohorts of low back pain. Spine 27(5):E109-E120, 2002. Selye H: The stress of life. New York, 1956, McGraw-Hill. Staal JB, Hlobil H, van Tulder MW, et al: Occupational health guidelines for the management of low back pain: an international comparison. Occup Environ Med 60(9):617, 2003. van den Hout JH, Vlaeyen JW, Heuts PH, Zijlema JH, Wijnen JA: Secondary prevention of work-related disability in nonspecific low back pain: does problem-solving therapy help? A randomized clinical trial. Clin J Pain 19(2):87-96, 2003. van Tulder MW, Ostelo RWJG, Vlaeyen JWS, Linton SJ, Morley SJ, Assendelft WJJ: Behavioural treatment for chronic low-back pain (Cochrane Review). In The Cochrane Library, Issue 3. Chichester, UK, 2004, John Wiley & Sons, Ltd. Waddell G: Biopsychosocial analysis of low back pain. In M Nordin, TL Vischer, eds: Common low back pain: prevention of chronicity. London, 1992, Bailliere Tindall. Waddell G, Burton AK: Occupational health guidelines for the management of low back pain at work: evidence review. Occup Med (2):124-135, 2001. Waddell G, McIntosh A, Hutchinson A, Feder G, Lewis M: The clinical guidelines for the management of acute low back pain. In Low back pain evidence review. London, December 2001, Royal College of General Practitioners. Weiser S, Cedraschi C: Psychosocial issues in the prevention of chronic low back pain: a literature review. In M Nordin, TL Vischer, eds: Common low back pain: prevention of chronicity. London, 1992, Bailliere Tindall. Work Loss Data Institute: Disorders of the neck and upper back. Occup Environ Med 60:618-626, 2003.
CHAPTER
Neck
3
CHAPTER
3a
A Review of the Epidemiology of Neck Pain in Workers: Prevalence, Incidence, and Risk Factors Pierre Côté, Linda Carroll, J. David Cassidy, Mana Rezai, Vicki Kristman, and the Scientific Secretariat of the 2000-2010 Bone and Joint Decade Task Force on Neck Pain and Its Associated Disorders*
In the past half century, the nature of work has rapidly changed. Once dependent mainly on manufacturing and resource extraction, the economy of industrialized countries increasingly relies on the service sector. This new reality has transformed the nature of work injuries and disability. The shift from manufacturing and resource-based jobs to the service industry led to a sharp reduction in acute and fatal injuries but contributed to the current epidemic of musculoskeletal disorders (MSDs).45 Today MSDs are the most burdensome ailments that affect the health and reduce the productivity of workers.56 Neck pain is one of the most prevalent MSDs in the workingage population48 and a leading source of disability and health care utilization among adults.18,19 During any 6-month period, 54% of adults suffer from neck pain and 4.6% experience significant activity limitations because of neck problems.18 Contrary to popular belief, most adults with neck pain do not experience complete permanent resolution of their discomfort; in fact, it follows an episodic course marked by periods of remission and exacerbation.20 Each year between 14.6% and 18.0% of adults develop a new episode of neck pain,20,21,48 which causes a new episode of disability in 600/100,000 adults annually.20 The etiology of neck pain in workers is complex and multifactorial. Its hypothesized risk factors include demographics, psychosocial and work-related issues, and poor general health.5,7,16,17,20 Although the etiologic contribution of work receives increasing attention, most studies remain cross-sectional and can be used only to hypothesize about the causes of neck pain.5,7 Understanding its etiology in workers is necessary to develop, test, and implement prevention strategies to reduce its burden.
PURPOSE The purpose of this chapter is to review and appraise the recent literature on the epidemiology of neck pain in workers. Specifically, we review the literature to answer the following questions: 1. What is the prevalence of neck pain in workers? We define prevalence as the proportion of workers with neck pain
*Eugene J. Carragee, Jaime Guzman, Scott Haldeman, Sheilah Hogg-Johnson, Lena Holm, Eric Hurwitz, Margareta Nordin, Paul M. Peloso, and Gabrielle van der Velde.
during a specific period of time; its measurement is useful to quantify the burden of a condition in a defined population. 2. What demographic, socioeconomic, health- and workrelated, psychosocial, and societal factors are associated with prevalent neck pain in workers? We refer to “associated factors” to describe variables that are correlated with neck pain in cross-sectional studies. Although these cannot be used to draw causal inferences about its etiology, they are useful to describe the potential risk factors for neck pain. 3. What is the incidence of neck pain in workers? We use the term incidence to describe the average risk of developing neck pain during a time period. A measure of incidence is not only useful to describe the proportion of the workers who will develop a new episode of neck pain during a specific time period but also necessary to quantify the etiologic contribution of risk factors. Incidence is measured from cohort studies. 4. What are the risk factors for neck pain in workers? Risk factors are things that may contribute to on help predict neck pain. We have collected information on risk factors—variables that increase or reduce risk—from case-control and cohort studies.
METHODS We wrote this chapter in collaboration with the members of the scientific secretariat of the 2000-2010 Bone and Joint Decade Task Force on Neck Pain and Its Associated Disorders. The Task Force includes a multidisciplinary scientific secretariat of 12 clinicians and methodologists representing rheumatology, orthopedic surgery, physical and rehabilitative medicine, neurology, physiotherapy, health psychology, chiropractic, epidemiology, clinical epidemiology, and biostatistics. A main objective was to complete a systematic search and critical review of the scientific literature on neck pain and its associated disorders. The literature reviewed in this chapter was critically appraised by members of the Task Force using a standardized critical appraisal methodology.
Definition of neck pain We define neck pain as soft tissue disorders of the cervical spine/shoulder area, including disk lesions and radiculopathy that are experienced by workers. Our definition does not assume a causal link between work and neck pain. It includes neck pain that is caused or aggravated by work, that which interferes with work, and symptomatic neck pain that does not result in disability.
Literature search Having developed our literature search strategy in collaboration with a library scientist (see Acknowledgments), we applied it to two electronic databases: MEDLINE and Embase ( January 1997 to October 2003). For the purpose of this chapter, we used a restricted portion of the exhaustive search undertaken by the Task Force. Our search was based on specific key words (neck pain, neck injury, pain, injury, epidemiology, incidence, prevalence,
26
Chapter 3a
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Prevalence, incidence, and risk factors of neck pain in workers
workplace, worker, work, meta-analysis) and text words (neck pain, cervical pain, neck ache, whiplash, pain, ache, sore, stiff, discomfort, neck, occupational, work-related, review, literature synthesis, literature review). All search terms were limited to the English and French languages and adult subjects. We excluded duplicate articles.
Article selection Each citation found in the search was screened by rotating groups of three Task Force scientific secretariat members to assess its relevance to the epidemiology of neck pain in workers. For the purpose of this review, articles were deemed relevant if they passed the following inclusion and exclusion criteria:
Inclusion criteria 1. Studies that report results relevant to neck pain in workers with or without its associated disorders, which might include radiating arm pain, upper thoracic pain, headache, and temporomandibular joint disorder pain; 2. Studies that examine the prevalence, incidence, risk, and/or prevention of neck pain with or without its associated disorders; 3. Studies of the risk or prevention of neck pain that include at least 20 human subjects at risk for neck pain with or without its associated disorders.
Exclusion criteria 1. Studies that do not include human subjects with neck pain with or without its associated disorders; 2. Studies of neck pain due to fracture, dislocation, tumor, skin lesions, throat disorders, inflammatory disorders, cervical myelopathy, and spinal cord injury; 3. Studies concerning radiating arm pain, upper thoracic pain, headaches, temporomandibular joint disorder, and thoracic outlet syndrome not associated with neck pain; 4. Opinion papers, letters to the editor, traditional narrative reviews, and papers without scientific data; 5. Single-case reports of workers with neck pain with or without its associated disorders; 6. Studies using cadavers or nonhuman subjects, such as crash test dummies, animals, or laboratory simulations; 7. Biomechanical studies without human subjects with neck pain.
to assist reviewers in understanding the impact of bias on the study results and to abstract information. Rotating pairs of scientific secretariat members independently conducted these in-depth reviews of each article, and the remaining members read the studies. The two reviewers presented their critical appraisal to a larger group of members for discussion of the scientific merit of the study. The members decided by consensus whether a study was scientifically admissible or inadmissible, the latter being one in which methodologic flaws were judged to have fatally biased the results and therefore made the paper’s conclusions scientifically invalid.
Data synthesis Each research question was answered by a best-evidence synthesis,52,53 which consists of assembling and qualitatively synthesizing the best evidence relevant to it. We described the strength of evidence for risk factors by adapting a methodology that has been used to rank studies on breast cancer, whiplash injuries, and mild traumatic brain injuries.4,13,19 The methodology distinguishes among three phases of studies. Phase I studies are hypothesis-generating investigations that descriptively explore associations between potential risk factors and disease outcomes. Phase II studies are extensive exploratory analyses that focus on particular sets of risk factors or attempt to discover which ones predict the development of neck pain. Phase III studies are large confirmatory studies of explicit prestated hypotheses that allow for focused examinations of the strength, direction, and independence of the proposed relationship between a risk factor and the development of neck pain. We present the prevalence and incidence of neck pain with 95% confidence intervals. Where these figures were not reported in the article but sufficient information was provided, we computed these estimates and report our computations. We describe the cross-sectional associations between various risk factors and neck pain as positive or negative. We report odds ratios, relative risks or hazard rate ratios, and 95% confidence intervals to describe associations between risk factors and neck pain obtained from case-control or cohort studies. When these estimates did not appear in the paper, they were computed from sufficient data. Confidence intervals for prevalence and incidence rates were calculated using the standard confidence interval formula around proportions described by Kuzma.37 All other analyses were performed using SAS.49
RESULTS
Critical review of the literature
Selection and critical appraisal of articles
All articles meeting the inclusion and exclusion criteria were critically reviewed using standard criteria and computerized critical review forms. Modified for the purpose of the 2000-2010 Task Force, the forms were similar to the ones used by the Quebec Task Force on Whiplash-Associated Disorders and the Best Evidence Synthesis on Traumatic Mild Injury (Appendix 3a.1).12,55 These criteria prompt the reviewers to appraise the methodologic merit of a study by focusing on selection bias, information bias, and confounding. Rather than provide a rating scale for determining scientific acceptability, the forms are used
The results from the literature search and selection of articles are summarized in Figure 3a.1. Overall, we retrieved 162 publications, including 152 articles from the literature search and 10 from our files. Of the 159 nonduplicate articles, 45 met the inclusion criteria and were reviewed. Fifteen articles were excluded by the scientific secretariat after they were appraised as scientifically inadmissible.10,11,15,26,31-34,36,40,41,43,61,63,64 Of the 30 accepted articles, 18 were cross-sectional studies that reported on the prevalence and factors associated with neck pain,1-3,22-25,28-30,39,42,44,46,47,58-60 and 10 reported on its incidence
Chapter 3a
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Results
1. Literature search Medline
Embase
Personal files
109
43
10
Librarian
162 articles
159 non-duplicate articles
2. Screening Scientific secretariat Inclusion criteria
114 irrelevant 45 relevant articles
3. Review Scientific Critical appraisal secretariat
15 rejected
30 articles accepted and reviewed Figure 3a.1
Results of literature search and selection of articles included in the review.
and risk factors.6,8,27,35,38,50,51,54,57,62 Two studies reported crosssectional and prospective results.9,14
Neck pain in general working populations Prevalence We accepted four cross-sectional studies that described the prevalence of neck pain in samples of workers from the general population, in this case in Europe.9,14,23,46 The source population for these studies varied from registers of general practitioners in the United Kingdom to age cohorts of workers under the supervision of occupational physicians in France, workers who participated in periodical health surveys in the Netherlands, and 34-year old workers in Sweden. Overall, these studies suggest that neck pain is highly prevalent and a common source of activity limitations. In the United Kingdom, 34% of workers reported that they experienced neck pain in the preceding year (Table 3a.1).46 During the same period, 11% of workers limited their activities because of neck pain. Overall, 20% of surveyed workers had experienced neck pain in the preceding week. In Sweden, the 1-year prevalence of neck pain was 44% and 61% in 34-year-old men and women, respectively (Table 3a.1).9 In this cohort, 26% of men and 43% of women reported symptoms that lasted more than 1 month. In France during 1990, the prevalence of chronic neck/shoulder pain lasting for at least 6 months and associated with functional limitations was 7.8% in men and 14.8% in women (Table 3a.1).14 In 1995 this same study reported that the prevalence of chronic neck/shoulder pain had increased slightly to 9.5% in men and 17.6% in women.
Factors associated with neck pain All four studies reported that the prevalence of neck pain increases with age and is more common in women (Table 3a.1).9,14,23,46 In Sweden, self-employed males had a higher prevalence of neck/shoulder symptoms in the past month than other workers.9 In the United Kingdom, workers with musculoskeletal comorbidities were more likely to report neck pain. Palmer et al46 reported that the prevalence of neck pain in the preceding week was higher in those with shoulder, elbow, wrist-hand, hip, and knee pain. Similarly, neck pain was more common in workers who had experienced troublesome low back pain in the preceding year and in those who suffered from frequent headaches, fatigue, or stress.9,46 Barnekow-Bergkvist et al9 found that workers with better flexibility of the cervical spine (rotation) reported fewer neck/shoulder symptoms in the preceding month. Three studies reported that ergonomic, physical, and psychosocial factors at work are associated with neck pain (Table 3a.1). Two studies reported on its association with lifting. In Sweden, the prevalence of neck symptoms in the preceding month was lower in workers who performed repetitive or heavy lifting,9 whereas in contrast, Palmer et al46 reported that lifting increased it. Among U.K. workers, the prevalence of neck pain was found to be higher also in workers who reached overhead for more than 1 hour per day and in those exposed to hand and arm vibration.46 Using a keyboard for 4 hours or more in an average working day was positively associated with neck pain in women but not in men.47 A positive association between monotonous work, high decision latitude, and prevalent neck/shoulder symptoms was found among female workers in the Swedish sample.9 Finally, Dutch adult workers who reported a combination of mentally and physically demanding work and those performing heavily
27
Swedish student aged 16 years in 1974
Workers under the supervision of occupational physicians from France in 1990 and 1995
Registers of 163 general practitioners in 34 general practices in England, Scotland, and Wales and members of the British armed services in 1997-1998
Dutch workers who participated in the periodical occupational health surveys between 1982 and 1993
Cassou et al, 200214
Palmer et al, 200146
De Zwart et al, 199723
(−), negative association; (+), positive association; CI, confidence interval.
Inclusion: active workers aged 16-64 years Sample size = 44,486
Regular pain or stiffness in the neck
Not applicable
1-year prevalence: Men: 44% (36-52) Women: 61% (51-71) Prevalence of symptoms > 1/month: Men: 26% (19-33) Women: 43% (33-54) Point prevalence: Men: 1990: 7.8% (7.3-8.3) 1995: 9.5% (8.9-10.1) Women: 1990: 14.8% (14.0-15.6) 1995: 17.6% (16.7-18.5) 1-year prevalence: 34% (33-35) 1-year prevalence of neck pain interfering with normal activities: 11% (10-12) 1-week prevalence: 20% (19-21)
Men: Age (+); shoulder pain (+); elbow pain (+); wrist-hand pain (+); hip pain (+); knee pain (+); low back pain (+); headaches (+); tiredness/ stress (+); working overhead (+); heavy lifting (+); use of keyboard for > 4 hours/day (−); hand-arm vibration (+) Women: Age (+); shoulder pain (+); elbow pain (+); wrist-hand pain (+); hip pain (+); knee pain (+); low back pain (+); headaches (+); tiredness/stress (+); working overhead (+); use of keyboard for > 4 hours/day (−); heavy lifting (+); hand-arm vibration (+) Prevalence varies with occupation Prevalence is higher in women than men Men: Age (+); mentally and physically demanding work (+); heavy physically demanding work (+) Women: Age (+); mentally and physically demanding work (+); heavy physically demanding work (+)
Men: Lifting (−); self-employed (+); worrying (+); neck lateral rotation (−) Women: Monotonous work posture (+); lifting (−); high decision latitude (+); hand grip performance (−); neck lateral rotation (−) Age (+); women (+)
●
Chronic neck pain: self-report of neck/ shoulder pain lasting at least 6 months with functional limitations confirmed by clinical examination Neck pain measured with Standardized Nordic Questionnaire
Neck-shoulder pain measured with Standardized Nordic Questionnaire
Associated factors (95% CI)
Chapter 3a
Inclusion: workers born in 1938, 1943, 1948, or 1953 who underwent an annual medical examination Exclusion: Individuals not employed in 1995 Sample size = 16,950 Inclusion: individuals aged 16-64 years Sample size = 12,907
Inclusion: 34-year-old subjects in 1992 who worked at least 16 hours/week at time of survey Exclusion: maternity/paternity leave, students, long-term sick leave Sample size = 238
Prevalence (95% CI)
BarnekowBergkvist et al, 19989
Case definitions
Source population
Study
Inclusion/exclusion criteria
Studies of prevalence and factors associated with neck pain in workers
Table 3a.1
28 Prevalence, incidence, and risk factors of neck pain in workers
Chapter 3a
demanding work were more likely to report regular pain or stiffness in the neck.23
Incidence Three cohort studies, two conducted in France and one in the United States, provided information about the incidence of neck pain in samples of workers from the general population. The studied populations included workers under supervision of French occupational physicians/medical departments in the early 1990s14 and those covered by the Washington State Department of Labor and Industries state fund (including employees of selfinsured employers) between 1990 and 1998.51 These studies suggested that a significant proportion of the working population experiences a new episode of neck pain each year. These cohort studies offered insights about the “high-risk” groups for the development of an episode of neck pain. In France the 6-month incidence of neck pain among workers with no prior history was 17.4%, whereas it was 44.4% in those who reported a past history of neck disorders.38 Between 1990 and 1995, 12.5% female French workers and 7.3% of male French workers developed chronic neck pain (Table 3a.2).14 In Washington State, 40.1 per 10,000 full-time equivalent workers covered by the state fund developed neck pain.51 However, the reported incidence was only 5.1 per 10,000 full-time equivalent employees in self-insured firms.
Risk factors for neck pain Four phase II studies reported on factors associated with the development of neck pain in general working populations. Three Swedish studies described risk factors for developing neck pain in the past year, and one French study reported on the risk factors for chronic neck pain. In a Swedish cohort of 16-year-old student-workers, bench press performance was negatively associated with the development of neck/shoulder pain 18 years later (Table 3a.2).9 In other words, workers who performed better while bench pressing when 16 years of age in 1974 were protected against developing neck/shoulder pain in 1992. In another study, Fredriksson et al27 found that the development of neck/shoulder pain was associated with physical and psychosocial factors at work, specifically high physical work load for men and frequent hand movement for women. The authors found, moreover, that physical and psychosocial risk factors frequently interact and modify their effects on the incidence of neck/shoulder pain in workers. A third Swedish study found that both physical and psychosocial risk factors contribute to workers seeking health care for neck/shoulder pain.57 A previous episode of neck pain that persisted for more than 3 months and a nonfixed salary strongly predicted seeking health care for this symptom. The risk factors as well as the strength and the direction of association varied between men and women, suggesting that the etiology has a gender-specific component.57 For men, exposure to psychosocial factors such as high job demands or high time pressure reduced the risk of seeking care (Table 3a.2). In women, however, exposure to other psychosocial risk factors such as high degree of hindrance with work increased the risk of seeking care for neck/shoulder pain. Tornqvist et al57 also reported that workers with multiple risk factors were more likely to seek care. In France, the risk of developing chronic neck pain and disability was associated with sociodemographic variables, workplace
●
Results
psychosocial factors, comorbidities, and health risk behaviors (Table 3a.2). In their large cohort, Cassou et al14 found that increasing age, repetitive work, and high job demands were associated with chronic neck pain. Moreover, workers with depressive symptoms and those suffering from MSDs in the preceding year were more likely to develop chronic neck pain.
Neck pain in specific occupational groups Prevalence Twelve cross-sectional studies described the prevalence and factors associated with neck pain in samples of health care workers, including dental personnel, physical therapists and nurses,1-3,22,24,39,58-60 music and nursery school teachers,25,44 and blue collar workers (sewage workers, spinning industry, forestry, and scaffolding).28-30,42 The available evidence suggests that the prevalence of neck pain varies across occupations and tends to be higher for health care workers (Table 3a.3). Among these workers, the 1-year prevalence of neck pain varies from 45.8% in nurses to 47.6% in physical therapists, 64% in dentists, and 72% in dental hygienists (Table 3a.3).1,2,22,39,58-60 In Sweden, it is estimated that 50% of dental hygienists experience neck pain in the preceding week, whereas in Norway, 22.6% of nursing aides report that they experienced intense neck pain in the preceding 2 weeks.2,24 The prevalence of chronic neck pain is 9% among the nursing staff of Greek hospitals.3 In Sweden, most music teachers (59%) experience neck pain every year, and 30% experience an episode each week.25 Similarly, one fourth to one third of Japanese nursery school teachers report neck pain each month.44 Interestingly, except for sewage workers the prevalence of neck pain is lower in industrial, forestry, and construction workers than in health care workers or teachers. In Austrian sewage workers, the annual prevalence of neck pain is 52.4%, and 20.9% of workers suffer from neck pain each day.28
Factors associated with neck pain In health care workers, the presence of neck pain was associated with demographic, ergonomic, and workplace factors. Among nurses, neck pain was more common in older workers and in those with moderate/high physical or psychologic demands.39,58-60 Nurses and nursing aides who worked long hours reported neck pain more frequently.24,39,58-60 Although neck pain was more common in those who worked under strenuous back postures, it was less so in those who used mechanical lifts or received ergonomic training.3,24,39,58-60 In physical therapists, neck pain was positively associated with the pace of work and the type of practice.22 The association between neck pain and physical/psychologic variables was observed also in Japanese nursery school teachers, among whom it was more common in those with poor supervisor support and in those caring for young children.44 Similarly, male Swedish music teachers with low social support and women teachers with high psychologic demands were more likely to report neck pain.25 Neck pain in blue collar workers was associated with age, physical work, and psychologic demands.28,30
Incidence of neck pain Five cohort studies describe the incidence of neck pain in specific occupational groups, including industrial/service companies,6,8
29
Inclusion: individuals living in Sweden in 1993, without a diagnosis of MSD in 1969 and below age 59 in 1993 Sample size = 484
Individuals from Stockholm, Sweden who participated in the REBUS-69 study in 1969
Fredriksson et al, 200027 Nested casecontrol study Phase II
Cases: neck/shoulder Not applicable pain defined by a questionnaire reporting consultation with a physician, physiotherapist, chiropractor, osteopath, or other medical professional or sick leave for more than 7 consecutive days between 1970 and 1992 Neck/shoulder pain defined as pain lasting at least 7 consecutive days during the last year Controls: Individual matched on age, gender, and index year
5-year incidence: Men: 7.3% (6.8, 7.8) Women: 12.5% (11.7, 13.3)
Incidence (95% CI)
Men: Year of birth 1938 vs. 1953 OR = 2.0 (1.6, 2.6); year of birth 1945 vs. 1953 OR = 1.5 (1.2, 1.9); repetitive work before 1990 OR = 1.3 (1.0, 1.7); awkward work OR = 1.3 (1.1, 1.7); high job demand OR = 1.2 (1.0, 1.4); depressive symptoms OR = 1.3 (1.0, 1.8); MSD in past year OR = 1.5 (1.3, 1.8); sporting activities OR = 0.8 (0.7, 0.9); smoking OR = 1.2 (1.0, 1.4) Women: Year of birth 1938 vs. 1953 OR = 1.5 (1.2, 2.0); year of birth 1945 vs. 1953 OR = 1.6 (1.3, 2.0); year of birth 1948 vs. 1953 OR = 1.2 (1.0, 1.5); repetitive work in 1990 OR = 1.3 (1.0, 1.6); repetitive work before 1990 OR = 1.2 (1.0, 1.5); high job demand OR = 1.2 (1.0, 1.4); depressive symptoms OR = 1.5 (1.2, 1.9); MSD in past year OR = 1.7 (1.5, 2.0) Risk factors in the past 5 years. Men: High physical workload index OR = 2.2 (1.1, 4.6); frequent hand/finger work during leisure time OR = 2.1 (1.0, 4.5) Significant interactions: Work with vibrating tools and frequent hand movements; frequent hand work during leisure time and high perceived workload; frequent hand work during leisure time and work with vibrating tools; precision work during leisure time and high physical workload Women: Frequent hand movements at work OR = 1.5 (1.0, 2.3) Significant interactions: High perceived workload and low influence over work condition; high perceived workload outside work and low influence over work conditions; frequent hand work during leisure time and high perceived workload; frequent hand work during leisure time and high physical workload; precision work during leisure time and few possibilities of development; precision work during leisure time and low influence over work conditions
Men: Bench press performance at 16 years old (OR = 0.30 (0.09-0.85))
Risk factors (95% CI)
●
Chronic neck pain: self-report of neck/ shoulder pain lasting at least 6 months with functional limitations confirmed by clinical examination
Neck-shoulder pain measured with Standardized Nordic Questionnaire
Case definitions
Chapter 3a
Cassou et al, 200214 Cohort study Phase II
16-year-old Inclusion: 34-year-old subjects in Swedish student- 1992 who worked at least workers in 1974 16 hours/week at time of survey Exclusion: maternity/paternity leave, students, long-term sick leave Sample size = 238 Workers under Inclusion: workers born in 1938, 1943, the supervision 1948, or 1953 who underwent of occupational an annual medical examination physicians from Exclusion: individuals not employed France in 1990 in 1995 and 1995 Sample size = 16,950
BarnekowBergkvist et al, 19989 Phase II
Inclusion/exclusion criteria
Studies of incidence and risk factors associated with neck pain in workers
Study, design, Source and phase population
Table 3a.2
30 Prevalence, incidence, and risk factors of neck pain in workers
Workers covered by the Washington State Department of Labor and Industries State Fund and employees of self-insured employers between 1990 and 1998 Workers in the municipality of Norrtälje, Sweden from Sept 1, 1994 to June 30, 1997
Silverstein et al, 200251 Cohort study
Inclusion: workers aged 20-59 years who worked more than 17 hours/ week and had worked at least 2 months during the past year Exclusion: seeking health care for neck, shoulder, or low back disorders during the 6 months before enrollment Sample size = 1903
Inclusion: accepted State Fund claims for specific diagnostic or treatment codes. Of the self-insured claims, only those with more than 3 days of lost time were included. Sample size = 392,925
Inclusion: at least 1 year of employment Exclusion: workers with sick leave for more than 3 months in the previous year, pregnancy, temporary work contract, or retirement within the following 12 months Sample size = 511
Men: Suffered from neck or shoulder symptoms > 3 months earlier in life: RR = 4.4 (2.7-7.1); work with vibrating tools: RR = 1.6 (1.0-2.3); nonfixed salary RR = 1.9 (1.1-3.1); high demands RR = 0.7 (0.4-1.0); high time pressure RR = 0.5 (0.3-1.0); high creativity/low routine work profile RR = 0.6 (0.4-1.0); high quantitative demands RR = 0.2 (0.1-0.9); low demands in relation to competence RR = 1.5 (1.0-2.4) Women: Suffered from neck or shoulder symptoms > 3 months earlier in life: RR = 4.1 (3.0-5.7); repetitive hand/finger movements RR = 1.6 (1.2-2.2); nonfixed salary RR = 2.0 (1.0-4.2); nightshift/shift work including night work RR = 1.3 (1.0-1.8); long working hours RR = 0.7 (0.5-0.9); solitary work RR = 1.8 (1.2-2.9); job strain RR = 1.4 (1.1-2.0); high degree of hindrances at work RR = 1.4 (1.0-1.9)
Among 311 workers Not applicable without prior neck pain: 6-month incidence: 17.4% (13.3-22.0) 6-month incidence of disorders that lasted > 30 days: 1.3% (0.0-3.3) Among 27 workers with a prior history neck pain: 6-month incidence: 44.4% (25.5-64.7) 6-month incidence of disorders that lasted > 30 days: 11.1% (2.4-29.2) Cumulative incidence Not applicable (per 10,000 FTE): State fund: 40.1 (39.6, 40.6) Self-insured employers: 5.1 (4.9, 5.3)
Cases were those who Not applicable sought treatment for neck-shoulder disorders Controls were randomly from the population register Control group = 1511
Accepted claims for nontraumatic neck soft tissue disorders with the neck as the primary site of injury
Neck disorder (ache, pain, discomfort) in the past 6 months defined by questionnaire and body diagram Neck disorder for more than 30 days
●
CI, confidence interval; MSD, musculoskeletal disorder; OR, odds ration; RR, relative risk.
Tornqvist et al, 200157 Case-control study Phase II
Hospital, warehouse, office, and airport workers recruited from medical departments in France in 1991
Leclerc et al, 199938 Cohort study
Chapter 3a Results 31
Source population
Dental personnel (dentists, dental hygienists, and dental assistants) from the public health services in the county of Blekinge, Sweden
Nursing staff from six hospitals in Athens, Greece between 2000 and 2001
Physical therapists registered in the state of Victoria, Australia
Norwegian nurse’s aides in 1999
˚Akesson et al, 19991 ˚Akesson et al, 20002
Alexopoulos et al, 20033
Cromie et al, 200022
Eriksen, 200324
Neck pain measured with the Standardized Nordic Questionnaire Chronic neck pain is pain lasting > 3 months Neck pain measured with the Standardized Nordic Questionnaire
Neck pain measured with the Standardized Nordic Questionnaire
Case definitions
Inclusion: vocationally active Neck pain measured Exclusion: sick leave because with the Standardized of illness or pregnancy Nordic Questionnaire Sample size = 6485
Exclusion: therapists not living in Australia Sample size = 536
Inclusion: at least one year of experience in current job Sample size = 351
Exclusion: personnel on leave (other than sick leave) and specialist dentists Sample size = 244
Inclusion/exclusion criteria
2-week prevalence: Any pain: 53.5 % (52.3-54.7) Intense pain: 22.6% (21.6-23.6)
1-year prevalence: 47.6% (43.3-51.8)
1-week prevalence: Hygienists: 50% (33, 67); male dentists: 31% (16, 45); female dentists: 27% (12, 42); general practice dental assistants: 17% (10, 24); specialist dental assistants: 16% (4, 27) 1-year prevalence: Hygienists: 72% (56, 87); male dentists: 64% (49, 79); female dentists: 64% (47, 80); general practice dental assistants: 46% (37, 55); specialist dental assistants: 34% (19, 49) Prevalence at 5-year follow-up for females. 1-week prevalence: Hygienists: 41%; dentists: 38%; dental assistants 31% 1-year prevalence: Hygienists: 73%; dentists: 54%; dental assistants 62% 1-year prevalence: 47% (42-52) Prevalence of chronic neck pain: 9% (6-12) Prevalence of sick leave: 5% (3-7)
Prevalence (95% CI)
Male (+), private practice (+), sports physical therapy (+), manual techniques (+), sedentary work (+), repetitive tasks (+), large number of patients/day (+), few rest periods (+), rest periods (+), work when injured (+), mobilization/manipulation (+), other manual treatment (+) Female (+), marital status/single (+), working >36 hours/week (+), working in old people’s home (+)
Strenuous back posture (+); moderate/bad perceived general health (+)
Not applicable
Associated factors (95% CI)
●
Study
Studies of prevalence and factors associated with neck pain in specific occupations
Chapter 3a
Table 3a.3
32 Prevalence, incidence, and risk factors of neck pain in workers
Molano Workers from a scaffolding company in the et al, 200142 Netherlands from June to September, 1998 Ono et al, Nursery school teachers in a Japanese city, 200244 in October, 1995
Workers from the spinning industry in Lithuania in 1996 Forestry workers from Norway
Exclusion: male workers, nurses, supervisors Sample size = 959
Inclusion: job involving heavy lifting or working while bent over Sample size = 255 Inclusion: production workers Sample size = 363 Inclusion: manual workers, machine operators, and administrative workers who worked for at least 10 months/year during the previous 5 years Sample size = 835 Inclusion: all workers Sample size = 323
Friedrich Sewage workers from Vienna, Austria et al, 200028
Gamperiene and Stigum, 199929 Hagen et al, 199830
Inclusion: all music teachers Sample size = 208
FjellmanMusic teachers in two Wiklund counties of Sweden in 2000 et al, 200325
1-year prevalence: 27% (22, 32)
1-year prevalence: 27.7% (21.9, 33.5)
1-year prevalence: Cumulative: 59% (52-66) Men: 52% (43-61) Women: 67% (57-77) 1-week prevalence: Cumulative: 30% (24-36) Men: 26% (18-34) Women: 36% (26-46) Lifetime prevalence: 67.5% (61.6-73.3) 1-year prevalence: 52.4% (46.0-58.5) 1-week prevalence: 25.7% (20.3-31.3) Point prevalence: 20.9 (15.8-26.0) 1-year prevalence: 16.5% (12.4, 20.8)
Neck/shoulder pain in Not applicable the previous month greater than grade 3/5 on a self-reported scale
Neck pain measured with the Standardized Nordic Questionnaire
Neck pain measured with the Standardized Nordic Questionnaire Neck/shoulder pain for at least 30 days in previous 1 year measured with the Standardized Nordic Questionnaire
Neck pain measured with the Standardized Nordic Questionnaire
Neck pain measured with the Standardized Nordic Questionnaire
Continued
10 years of experience (+); caring for children aged 0 (+); holding/lifting a child/material exceeding 20 kg (+); poor supervisor support (+)
Not applicable
Age (+); physical work (+); low intellectual discretion (+); high psychologic demands (+)
Not applicable
Age (+)
Men: Low social support (+); lifting (+); playing guitar (+) Women: High psychologic demands (+); teaching at 5-12 schools/week (+)
Chapter 3a ●
Results 33
Registers of 163 general practitioners in 34 general practices across Britain in 1997-1998
Palmer et al, 200146
Inclusion: at current job for at least 1 year Exclusion: nurses with non-work related injuries within a 3-month period before onset of workrelated neck pain Sample size = 1163
Inclusion: workers aged 16-64 years employed in nonmanual occupations Exclusion: manual occupations Sample size = 4889
Inclusion/exclusion criteria
(−), negative association; (+), positive association; CI, confidence interval.
Trinkoff et al, Licensed registered nurses from Illinois and 200259 Lipscomb New York state in 1999-2000 et al, 200239 Trinkoff et al, 200358 Trinkoff et al, 200360
Source population
Study
Neck pain measured with the Standardized Nordic Questionnaire Case: neck pain lasting ≥ 1 week and ≥ 3/5 in intensity Symptoms: neck pain without full definition of a case
Neck pain measured with Standardized Nordic Questionnaire
Case definitions 1-week prevalence: Men: Keyboard: 14.8% (12.3-17.4) No keyboard: 13.8% (12.0-15.6) Women: Keyboard: 22.9% (20.3-25.4) No keyboard: 18.3% (16.3-20.3) 1-week prevalence of disability among workers with neck pain: Men: Keyboard: 26% (18-34) No keyboard: 33% (26-39) Women: Keyboard: 33% (27-39) No keyboard: 37% (31-42) 1-year prevalence: Cumulative: 45.8% (43.0-48.7) Case: 20.4% (18.1-22.8) Symptoms: 25.4% (22.9-27.9)
Prevalence (95% CI)
Age (+); mechanical lifting devices (−); training on adjustment of work station (−); training on recognizing workplace hazards (−); working long hours (+); moderate and high physical demands (+); psychologic demands; dependents (+); working long hours (+)
Not applicable
Associated factors (95% CI)
●
Studies of prevalence and factors associated with neck pain in specific occupations—cont’d
Chapter 3a
Table 3a.3
34 Prevalence, incidence, and risk factors of neck pain in workers
Chapter 3a
municipal office workers,35 teaching hospital employees,50 female nurses from acute care hospitals,54 and workers from a large forestry industry.62 Overall, the evidence suggests that the incidence of neck pain varies across occupational group, tending to be higher for those working in hospitals and offices (Table 3a.4). In England, female nurses working in acute care hospital settings developed neck pain at a rate of 17% per year.54 In Canada, 40.5% of employees at a teaching hospital who were asymptomatic in 1996 reported to have experienced an episode of neck pain in the preceding week when followed up a year later.50 In Finnish municipal office workers, the annual incidence of neck pain with or without radiations was 34.4%. Approximately 13% had local neck pain only, and 14.4% had radiating pain without neck pain. The annual incidence of workers reporting both local and radiating neck pain was 6.7%.35 The incidence of neck pain was lower among workers in industrial/service and forestry sectors. In workers from 34 industrial/service companies located throughout the Netherlands, the 3-year incidence of neck pain was 14.4%.6,8 The overall 3-year incidence among Finnish forestry workers was a similar 15.6%62: 9.2% developed mild neck pain, and 6.4% developed severe pain.
●
Relevance
neck pain; specifically, we found its incidence to be higher for nurses and office workers.35,50,51 Studies that quantified the role of risk factors supported that neck pain is more common in workers with high quantitative job demands, low coworker support, repetitive work, nonfixed salary, increased sitting time, poor ergonomics, previous musculoskeletal pain, and depressive symptoms.5,8,14,27,35,54,57 Although we identified several risk factors for neck pain, it is important to note that only one phase III study was designed specifically to test their independence.5,8 This finding indicates that very few risk factors can be considered well established. Efforts should be devoted to designing phase III studies to confirm the results of cross-sectional observations and phase II (exploratory) studies. Moreover, future studies should pay attention to interactions among individual, psychosocial, and workplace risk factors. The growing body of evidence supporting the role of psychosocial and workplace factors in the etiology of neck pain must not be considered in isolation. Because it is very likely that the risk factors for the development of neck pain and disability vary across occupations, as demonstrated in our review, future studies should ensure that the risk profiles of various occupations are explored.
Risk factors for neck pain Two phase II and one phase I study examined the risk factors for neck pain in specific occupational groups (Table 3a.4). Among Finnish municipal workers, females and those with poor keyboard position were more likely to develop neck pain.35 In English female nurses, a new episode of neck pain was associated with previous neck and low back pain and with various physical aspects of care such as moving and transferring patients.54 Only one phase III study supported the observation that physical and psychosocial factors contribute to the development of neck pain.5,8 In their cohort study of industrial and service workers from the Netherlands, Ariens et al5,8 demonstrated that high quantitative job demands, low coworker support, and prolonged sitting are independent risk factors for a new episode of neck pain.
SUMMARY Neck pain is endemic in workers. Our best evidence synthesis demonstrates that it is highly prevalent and a common source of disability. By far, most neck pain in workers is nontraumatic. Its etiology is consequently multifaceted, and although occupational factors may be important contributors to its development, they are neither sufficient nor necessary. This reality clearly emphasizes that the development of an episode of neck pain cannot be attributed entirely to the physical and psychosocial environment of a workplace. Our review of cross-sectional studies supports the view that neck pain is more common in various subgroups of workers. It is more prevalent among older workers, women, and those with musculoskeletal comorbidities.1,2,14,23,24,28,30,39,46,54,57-60 Moreover, it varies significantly across occupations and is associated with ergonomic, physical, and psychosocial factors.3,5,8,9,14,22,23,25,27,30,35,39,44,46,54,57-60 Evidence from case-control and cohort studies confirms that certain occupations pose higher risk of developing an episode of
RELEVANCE Our review has important implications for prevention. First, intervention must target clearly modifiable risk factors. Second, the multifaceted etiology of neck pain highlights the importance of designing preventive interventions focused on multiple rather than individual risk factors. Current research has not yet identified the “necessary” causes for neck pain and disability, and very little is known about the interrelationships among risk factors. Multimodal interventions targeting multiple modifiable risks such as workplace and psychosocial factors may thus prove more promising than one-dimensional approaches targeting a specific one. Finally, the complex etiology of neck pain suggests that the roles of economic and legal factors, work organization, and health care access and delivery are important and must be studied as well.14
ACKNOWLEDGMENTS We are indebted to Emma Irvin and Stephen Greenhalgh, research librarians, for their expertise and guidance with the literature search. The Bone and Joint Decade Task Force on Neck Pain and Its Associated Disorders is supported by a grant to the University of Alberta from the National Chiropractic Mutual Insurance Company and the Canadian Chiropractic Protective Association, Jalan Pacific Inc., Länsförsäkringar Wasa, and the Insurance Bureau of Canada. This article was made possible also through the financial support of the Workplace Safety and Insurance Board of Ontario. Dr. Côté is supported by the Canadian Institutes of Health Research through a New Investigator Award and by the Institute for Work & Health by the Workplace Safety and Insurance Board of Ontario. Dr. Carroll is supported by a Health Scholar Award from the Alberta Heritage Foundation for Medical Research. Dr. Cassidy is supported by an endowed research chair from the University Health Network. Vicki Kristman is supported by a Doctoral Training Award from the Canadian Institutes of Health Research in partnership with the
35
Shannon Employees of a teaching hospital in Hamilton, et al, 200150 Cohort study Ontario, Canada from 1995 to 1997
Korhonen Finnish municipal office workers in et al, 200335 Cohort study 1998-1999 Phase II
Inclusion: workers who worked Neck pain measured by a modified at least 20 hours per week Standardized Nordic Questionnaire and worked at their current Cases were defined as regular or job for at least 1 year prolonged neck pain, with episodes that Exclusion: workers who had another lasted for at least 1 day during the paid job for any substantial previous 12 months on at least amount of time, received a work one of 3 follow-up measurements disability payment for neck pain in the preceding year, and had prolonged neck pain during the year before baseline Sample size = 977 Inclusion: full-time Incident cases were healthy subjects at employees working on baseline (those who reported local or video display units for radiating neck pain for less than 8 days more than 4 hours/week during the preceding 12 months) who Sample size = 180 reported at follow-up local or radiating neck pain for at least 8 days during the preceding 12 months. Question for local neck pain was: “Estimate the total number of days you have had local neck pain (not radiation) during the preceding 12 months: 0 days, 1-7 days, 8-30 days, >30 days but not daily, and daily.” Healthy was defined as 0-7 days, and 8 or more days defined incident neck pain. Inclusion: workers still Neck pain measured by question: “In the employed by the hospital past week, how often have you suffered at the end of the study from neck and/or shoulder pain?” Exclusion: physicians Sample size = 173
High quantitative job demands RR = 2.14 (1.28, 3.58); low coworker support RR = 2.43 (1.11, 5.29); sitting > 95% of the time RR = 2.34 (1.05-5.21)
Incidence of an episode of neck pain in the previous week: 40.5% (33.1, 47.8)
Not applicable
1-year incidence: Female OR = 2.9 (1.3-2.7); poor keyboard Local or radiating neck position OR = 2.1 (1.0-4.5) pain: 34.4% (12.5-41.3) Local and radiating neck pain: 6.7% (3.0-10.3)
1-year incidence: 5.7% (4.3, 7.2) 3-year incidence: 14.4% (12.2, 16.6)
Incidence (95% CI) Risk Factors (95% CI)
Workers from 34 industrial/service companies located throughout the Netherlands from 1994 to 1997
Case definitions
Ariens et al, 20018 Ariens et al, 20015 Cohort study Phase III
Inclusion/exclusion criteria
Source population
Study
●
Studies of incidence and risk factors associated with neck pain in specific occupations
Chapter 3a
Table 3a.4
36 Prevalence, incidence, and risk factors of neck pain in workers
Exclusion: workers with rheumatoid arthritis and part-time workers Sample size = 5180
Viikari-Juntura Workers from a large forest industry et al, 200162 Cohort study enterprise in Finland Phase II from 1992 to 1995
CI, confidence interval; HR, hazard ratio; OR, odds ratio; RR, relative risk.
Inclusion: working at same job throughout the study Exclusion: agency staff, student nurses, and community nurses Sample size = 587
Smedley Female nurses from two acute et al, 200354 Cohort study hospitals in the Phase II south of England
Radiating neck pain measured by a modified version of the Standardized Nordic Questionnaire Mild pain: 8-30 days in previous year Severe pain: >20 days in previous year
Neck pain measured with the Standardized Nordic Questionnaire
Cumulative 3-year incidence: Mild pain: 9.2% (7.9, 10.5) Severe pain: 6.4% (5.3, 7.5)
2-year incidence of neck pain: 34% (30-38)
Previous neck pain: > 1 year before baseline HR = 1.6 (1.1-2.3); < 1 year before baseline HR = 2.8 (2.0-3.9) Duration of previous neck pain: < 1 week HR = 1.7 (1.1-2.5); 1-4 weeks HR = 2.3 (1.5-3.3); > 4 weeks HR = 2.6 (1.7-4.0) Previous low back pain: >1 year before baseline HR = 1.8 (1.2-2.7); < 1 year before baseline HR = 1.9 (1.4-2.7). Duration of previous low back pain: 1-4 weeks HR = 1.8 (1.2-2.7); > 4 weeks HR = 2.3 (1.6-3.3) Assisting patients to mobilize > 4 times/shift HR = 1.6 (1.1-2.3); moving patients around > 4 times/shift HR = 1.6 (1.1-2.4); transferring patients in/out bath HR = 1.4 (1.0-2.0); washing or dressing patients while on chair > 4 times/shift HR = 1.7 (1.1-2.8); washing or dressing patients while on bed > 4 times/shift HR = 1.6 (1.0-2.5) Not applicable
Chapter 3a ●
Relevance 37
38
Chapter 3a
●
Prevalence, incidence, and risk factors of neck pain in workers
Canadian Institute for the Relief of Pain and Disability (formally known as the Physical Medicine Research Foundation) Woodbridge Grants and Awards Program and by the Institute for Work & Health by the Workplace Safety and Insurance Board of Ontario.
25.
26.
27.
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Slavin RE: Best evidence synthesis: an intelligent alternative to meta-analysis. J Clin Epidemiol 48(1):9-18, 1995. Smedley J, Inskip H, Trevelyan F, Buckle P, Cooper C, Coggon D: Risk factors for incident neck and shoulder pain in hospital nurses. Occup Environ Med 60(11):864-869, 2003. Spitzer WO, Skovron ML, Salmi LR, et al: Scientific monograph of the Quebec Task Force on Whiplash-Associated Disorders: redefining “whiplash” and its management [see comment]. [Erratum appears in Spine 20(21):2372, 1995.] Spine (8 Suppl): 1S-73S, 1990. Stewart WF, Ricci JA, Chee E, Morganstein D, Lipton R: Lost productive time and cost due to common pain conditions in the US workforce [see comment]. JAMA 290(18):2443-2454, 2003. Tornqvist EW, Kilbom A, Vingard E, et al: The influence on seeking care because of neck and shoulder disorders from work-related exposures. Epidemiology 12(5):537-545, 2001. Trinkoff AM, Brady B, Nielsen K: Workplace prevention and musculoskeletal injuries in nurses. J Nurs Admin 33(3):153-158, 2003.
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39
Appendix 3a.1
GENERAL METHODOLOGIC ISSUES USED FOR ALL STUDY DESIGN 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.
Research question is clearly stated Source and target population identified and described Inclusion criteria described and appropriate Exclusion criteria described and appropriate Number of excluded or refusals (before study) reported Withdrawals (during study) reported, explained, and reasonable Withdrawals equal in groups Statistical analyses appropriate Adjustment for important variables measured at entry into study Results verifiable from raw data
CRITERIA FOR THE APPRAISAL OF THE METHODOLOGIC QUALITY OF CROSS-SECTIONAL STUDIES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
Similar sampling procedures for all subjects Similar ascertainment of exposure for all subjects Similar referral and diagnostic procedures for all subjects Diagnostic criteria for disease (clear, reliable, and valid) Characteristics of subjects at enrollment reported All aspects of exposure measured (level, dose, duration, etc.) Coexposures measured Recall bias controlled Data collection valid and reliable Selection bias considered Analyses controls for confounding factor
CRITERIA FOR THE APPRAISAL OF THE METHODOLOGIC QUALITY OF COHORT STUDIES 1. Zero time identified 2. Baseline comparability reported (including confounding variables)
3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.
Same data collection for all cohorts Important baseline variables measured, valid, and reliable All aspects of exposure measured (dose, level, duration) Exposure adequately measured (previous, at entry, during study) Regular follow-up periods Coexposures monitored Duration of follow-up adequate Outcome(s) defined and measurable Outcome(s) valid Blind assessment of outcome(s) Analyses controls for confounding
CRITERIA FOR THE APPRAISAL OF THE METHODOLOGIC QUALITY OF CASE-CONTROL STUDIES 1. Similar population sources for cases and controls (time, place, potential for exposure) 2. Referral and sampling independent of exposure 3. Random selection of controls 4. Diagnostic criteria for cases clear, precise, and valid 5. Date of diagnosis for case operationally defined 6. Ascertainment of disease adequate for cases and controls 7. Comparison of cases and controls at enrollment reported (including confounding variables) 8. All aspects of exposure measured (level, dose, duration, etc.) 9. Exposure adequately measured (same in all groups, blinded) 10. Coexposures measured 11. Recall bias controlled 12. Data collection valid and reliable 13. Analysis according to level of exposure 14. Effect of matching assessed
CHAPTER
3b
Biomechanics of the Cervical and Thoracic Spine Jiri Dvorak and Malcolm Pope
BIOMECHANICS OF THE NECK The biomechanics of the cervical spine is determined by the shape of the vertebral bodies and the orientation of the zygapophyseal joints and can accordingly be divided into three sections: ● Upper cervical spine: occiput, atlas, axis; ● Lower cervical spine: C2-C3 to C7; ● Cervical-thoracic junction: C7 to the third thoracic vertebra (Fig. 3b.1). The primary aim of the clinician treating a patient with neck pain is to find the region or even segment responsible for pain symptoms. Because the intersegmental nerve root anastomosis
Upper cervical spine
C2
makes it almost impossible for a patient suffering from neck pain to localize the exact origin of pain,11,12,26 the clinician must base the diagnosis on functional and palpatory examinations of the cervical spine. To do this correctly requires analysis and interpretation of normal and disturbed motion patterns based on a knowledge of clinical biomechanics and an understanding of developmental anatomy. The natural aging process results in many changes in the cervical spine that must be taken into account in the clinical assessment, especially as related to range of motion. It is well established that range of motion decreases with age, mainly in the middle and lower segments of the cervical spine.4 This is due to the ongoing transformation process of the intervertebral disk and the development of uncovertebral joints14,29; later it may also be due to development of osteoarthritis of the zygapophyseal joints. In the first two decades of life, the uncovertebral spaces of the lower part of the cervical spine begin to undergo a lifelong transformation into uncovertebral joints. This transformation is a response to the compressive force of the weight of the head, which the upright posture of the body requires the cervical spine to support (Fig. 3b.2).14,28,29 The result is the formation of lateral tears of the disk annulus beginning in the second decade of life (Fig. 3b.3). These lateral tears continue to develop into the medial center part of the disk until, in the third decade, complete transverse tears commonly occur (Fig. 3b.4).28 The resulting space in the middle of the intervertebral disk partially takes over the function of the zygapophyseal joints during the second and third decades. (At this stage, the nucleus pulposus dries out, appearing on radiographs as a narrowing between the vertebrae of the lower cervical spine, which provides a convenient way for the clinician to monitor these changes.) This new space within the disk significantly reduces the loadabsorbing function of the intervertebral disk in the cervical spine. To support the load of the head, a transformation of the uncovertebral joints starts to occur.28 Instead of the original pointed shape, the uncovertebral processes now become flat
C3
C4
C5
Lower cervical spine
C6
C7
Th1
Th2
Cervical-thoracic junction
Th3
Figure 3b.1
Sections of the cervical spine.
Figure 3b.2 Drawing of the uncovertebral joints. (From Luschka H: Die Halbgelenke des menschlichen Körpers. Berlin, 1858, Reimers.)
42
Chapter 3b
●
Biomechanics of the cervical and thoracic spine
Figure 3b.3 Frontal section of the cervical spine of a 9-year-old child. Remnants of cartilage are still present. The arrow points to a space in the lateral part of the intervertebral disk at level C3-C4.
with a shape like that of a cow horn (Fig. 3b.5) and take over the load of the cranial vertebrae. The overall result is a natural transformation of the structure and shape of the uncovertebral processes that is probably responsible for much of the decreased range of motion that accompanies aging and must be taken into account in any clinical assessment of the cervical spine. In the first two decades of life, the surfaces of the articular processes are covered by a thin layer of cartilage, with the uneven surfaces filled in by a synovial fold in the joint capsule. This synovial fold has been described by Penning and Töndury21 as meniscoid. It is found within the entire cervical spine (Fig. 3b.6) and again degenerates or atrophies with increasing age.
UPPER CERVICAL SPINE: OCCIPUT/C2 The upper cervical spine, which consists of the occiput, atlas, and axis, is responsible for most of the axial rotation and some of the flexion-extension and lateral bending of the head. In addition to allowing large rotations, it must be stable enough to support the weight of the head and protect the delicate spinal cord and intervertebral arteries from injury and is therefore quite a complicated structure. Possible motion in the atlantooccipital and atlantoaxial joints is determined by the orientation of the articular processes. The occipital condyles are an oval-shaped bean-like form with a sagittal orientation of the joint axis of 28 degrees on average (Fig. 3b.7).8,10 The frontal orientation of the joint axis (Fig. 3b.8) averages 124 degrees in males and 127 degrees in females.9,27 The motion axis of the atlantooccipital joints was described by Knese9 (Fig. 3b.9). The atlantooccipital joints are described as a spheroid articulation. They are connected with a tight joint
Figure 3b.4 Frontal section of the cervical spine of a 33-year-old man. In the three lowest segments, each intervertebral disk shows a complete transverse tear; however, the upper two levels have only lateral tears. (From Töndury G, Theiler K: Entwicklungsgeschichte und Fehlbildungen der Wirbelsäule, ed 2, Stuttgart, Germany, 1990, Hippokrates-Verlag.)
capsule that limits the movements possible. The dominant movement in the atlantooccipital joint is flexion and extension of approximately 22 to 24 degrees, according to the author. Lateral bending, again according to the author, is between 5 and 10 degrees. The idea of axial rotation in this joint has long been rejected; however, newer investigations by Dvorak et al7 showed axial rotation in both in vitro and in vivo studies. A summary of movements possible in the atlantooccipital joint is shown in Table 3b.1. The atlantoaxial joint consists of four joint spaces: the two atlantoaxial lateral joints, the atlantoaxial median joint (between the anterior arch of the atlas and the dens axis), and a joint between the posterior surface of the dens and the transverse ligament, which is connected to the anterior joint space. From the medial part arises a large synovial fold in the lateral atlantoaxial joint (Fig. 3b.10).4 This joint capsule is loose, which allows for a great deal of motion. It is here that most of the axial rotation occurs. The movements possible in the atlantoaxial joints are summarized in Table 3b.2. Motion within the upper cervical spine, especially in the atlantoaxial joint, is mainly limited by ligaments that, with exception of the tectorial membrane, consist of nonstretchable collagen fibers.24,25 The tectorial membrane, which consists of elastic fibers, inserts at the great occipital foramen and distally joins the posterior longitudinal ligament. The biomechanical properties of the tectorial membrane have been studied by Oda et al,17 who documented their large elasticity.
Chapter 3b
●
Upper cervical spine: occiput/C2
Figure 3b.5 Cow horn-like shapes (arrows). Changes of the uncovertebral disks at the C4-C5 and C5-C6 levels of the same subject at the age of 47 years (A) and 49 years (B). At the same level on the lateral views, anterior and posterior osteophytes are starting to form (C and D) and narrow the intervertebral foramen at the C5-C6 level (E and F).
A
B
C
D
E
F
43
44
Chapter 3b
●
Biomechanics of the cervical and thoracic spine
Frontal orientation of joint axis 124°
Figure 3b.8 Frontal orientation of the occipital condyles according to Stoff. (From Stoff E: Verh Anat Gesch Jena 70:575, 1976.)
Y-axis
Figure 3b.6 Parasagittal section of the intervertebral joints (zygapophyseal joints) at the level of C4 and C6. The articular processes show an inclination of approximately 45 degrees. The arrow points to the synovial folds in between the intervertebral joint surfaces, which have been described by Penning and Töndury as meniscoid. (Courtesy Professor Doctor W. Rauschning, Uppsala, Sweden.)
Z-axis
X-axis
Figure 3b.9 Possible joint axis of the upper cervical spine according to Knese. (From Knese KH: Z Anat Entwickl 114:67-107, 1949.)
Table 3b.1 Possible movements in the atlantooccipital joint according to different authors Occipto-C1 joint Fick (1904) Poirer and Charpy (1926) Werne (1957)30 Penning (1978)20 Dvorak et al (1985) Clark et al (1986) Dvorak et al (1987)3 Penning and Wilmink (1987)22 Panjabi et al (1988)19
Figure 3b.7 Sagittal orientation of the occipital condyles is 28 degrees on average. (From Ingelmark BE: Acta Anat (Basel) 6:1-48, 1947.)
Flexion/extension (total) rotation Side bending (one side) (one side) Axial 50
30-40
0
50 13 35 — 22.7 —
14-40 8 10 — — —
0 0 0 5.2 4.8 4
— 24.5
— 5.5
1 7.2
Chapter 3b
A Figure 3b.10
●
Upper cervical spine: occiput/C2
B
Dissection of normal left atlantoaxial meniscoid from a fresh cadaveric specimen (A); the surface is covered with meniscoid (B).
The cruciate ligament (Fig. 3b.11) has the important function of restricting potentially dangerous anterior gliding of the atlas during flexion movement of the head while still allowing the atlas to turn freely around the dens during axial rotation. It consists of two main parts: a horizontally oriented transverse ligament and vertically oriented longitudinal fibers. The transverse ligament inserts at the medial portion of the lateral mass of the atlas. The caudal fibers are occasionally fixed at the base of the dens and may additionally stabilize the dens (Fig. 3b.12). At the level of the dens is a thin layer of cartilage covering
Table 3b.2 Summary of possible motions at the atlantoaxial joint according to various authors
C1-C2 joint Fick (1904) Poirer and Charpy (1926) Werne (1957)30 Penning (1978)20 Dvorak et al (1985) Clark et al (1986) Dvorak et al (1987)3 Penning and Wilmink (1987)22 Panjabi et al (1988)19
Flexion/ extension (total)
Side bending (one side)
Axial rotation (one side)
0
0
60
11 10 30 — 10 —
— 0 10 — — —
30-80 47 70 32.2 14.5 43.1
— 22.4
— 6.7
40.5 38.9
the transverse ligament,5 which allows the ligament to move more freely and protects it from damage caused by friction. The transverse ligament consists exclusively of collagen fibers with an interesting fiber orientation similar to a folding lattice (Fig. 3b.13). This allows extensive stretching of the ligament during axial rotation without damage to the fibers. In vitro experiments show failure of the transverse ligament to occur between 170 and 700 N.5 The main limiting structures for the upper cervical spine are the alar ligaments. Consisting exclusively of nonstretchable collagen fibers, the alar ligaments connect the dens axis with the occipital condyles and the anterior arch of the atlas (Fig. 3b.12).1,3,13 Occasionally, a loose connection is also found between the basis of the dens axis and the anterior arch of the atlas3; this has been described by Von Barrow as the atlantodental anterior ligament. According to Werne,30 alar ligaments are of great importance in limiting axial rotation (Fig. 3b.14), a belief that has been confirmed by newer investigations.5,18 In conjunction with the tectorial membrane, the alar ligaments also limit flexion of the occiput. During lateral bending (Fig. 3b.15), the alar ligament is responsible for forced rotation of the second vertebra.5,30 The apical ligament has no functional meaning and is actually a rudiment of the chorda dorsalis.10 Clinical analysis of upper cervical spine motion can be done through the use of functional radiographs. In the anteroposterior view, lateral bending can be assessed.23 Physiologic movements, gliding of the atlas in bending direction, and forced rotation of the axis are presented in Figure 3b.16 as seen on functional radiographs. Axial rotation is currently assessed through measurements of functional computed tomography and may in the future be tested by functional magnetic resonance imaging (Fig. 3b.17).2,6
45
46
Chapter 3b
●
Biomechanics of the cervical and thoracic spine
Clivus
Dura Jugular foramen
Tectorial membrane Hypoglossal canal Transverse occipital ligament Alar ligament Cruciate ligament
Atlantooccipital articulation
Atlantoaxial articulation
Posterior longitudinal ligament
Transverse ligament
Figure 3b.11 Ligaments of the upper cervical spine, posterior view. (From Lang J: Klinische Anatomie der Halswirbelsäule. New York, 1991, Georg Thieme Verlag.)
LOWER CERVICAL SPINE The anatomic structures of the motion segments of the lower cervical spine are different from those in the upper cervical spine. Their particularities include the uncovertebral joints, which support part of the axial load once the intervertebral disk loses its elasticity due to age-related transformations.14,28,29 The articular processes of the cervical spine are inclined approximately 45 degrees from the horizontal plane (Fig. 3b.18), with steeper inclinations in the lower segments. The transverse processes hide and protect the spinal nerve and vertebral artery.
Anterior atlantodental ligament Alar ligament (atlantal portion)
Alar ligament (occipital portion) Transverse ligament Figure 3b.12 Drawing of the ligaments of the upper cervical spine (axial dissection). (From Dvorak J, Froehlich D, Penning L, Baumgartner H, Panjabi MM: Spine 13(7):748-755, 1988.)
The motion segments are connected and stabilized by ligaments, anteriorly by the anterior longitudinal ligament (Fig. 3b.19) and dorsally by the posterior longitudinal ligament. The density of nociceptive and mechanoreceptive innervation of the posterior longitudinal ligament is high in comparison with other cervical spine ligaments and the disk.16 This results in a very sensitive ligament that indirectly controls the innervation of neck muscles through nociceptive and mechanoreceptive reflexes.32 The laminae are connected by the strong ligamentum flavum, which consists almost exclusively of elastic fibers and is a major limiting structure in flexion movement. The dominant motion in the lower cervical spine is flexionextension. Different parameters can be measured with flexionextension x-ray views, including segmental rotation, translatory movement, and the location of the center of rotation (Fig. 3b.20).7 Because a significant motion difference exists between actively and passively performed movements, the use of passively performed radiographs has been recommended in diagnosing segmental instability, such as can occur after trauma (Fig. 3b.21).6,7 The first description of the center of rotation in healthy adults came from Penning and Töndury’s measurements21 of flexion and extension radiographs. The center of rotation has been determined with computer-assisted methods7 and has confirmed Penning and Töndury’s findings (Fig. 3b.22). Table 3b.3 shows the relevant data on flexion-extension movements of healthy adults for in vitro and in vivo examinations. Table 3b.4 presents data on rotation, translation, and center of rotation as measured by computer-assisted methods on a healthy population.7 Lysell15 described the so-called top angle, or segmental arch, as being flat at the level of C2 and steep at the lower cervical spine. Motion of the upper segments during flexion-extension is therefore fairly horizontal, whereas motion of the lower segments is more like that of an arc (Fig. 3b.23).
Chapter 3b
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Lower cervical spine
Figure 3b.13 The orientation of the collagen fibers of the transverse ligament is similar to a folding lattice and allows extensive stretching of the ligament during flexion and axial rotation without damage to the fibers.
Figure 3b.14 Drawing of possible movements in the atlantoaxial joint during axial rotation of the head according to Werne. (From Werne S: Acta Orthop Scand Suppl 23:80, 1957.)
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Left lateral bending –∅z
y
Figure 3b.15 Function of the alar ligaments during side bending of the head. (From Dvorak J, Froehlich D, Penning L, Baumgartner H, Panjabi MM: Spine 13(7):748-755, 1988.)
Right lateral bending y y
y1
+∅z y1
C0
C1 +x
–x + ∅y
+∅y C2
Figure 3b.16 Forced rotation of the axis and gliding of the atlas in the direction of bending as seen from functional radiographs in the anteroposterior view. (From Reich C, Dvorak J: Manual Med 2, 1986.)
Figure 3b.17 Functional computed tomography of the upper cervical spine during axial rotation within the atlantoaxial and atlantooccipital joints.
Chapter 3b
Figure 3b.17
●
Lower cervical spine
Cont’d
Figure 3b.18 Orientation of the articular processes of the lower cervical spine in the frontal plane. (From White AA, Panjabi MM: Clinical biomechanics of the spine, ed 2. Philadelphia, 1990, JB Lippincott.)
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Biomechanics of the cervical and thoracic spine
Figure 3b.19 Ligaments of the anterior and posterior parts at the lower cervical spine. (From White AA, Panjabi MM: Clinical biomechanics of the spine, ed 2. Philadelphia, 1990, JB Lippincott.)
D
G F
A C B E D
H I
G. Facets F. Capsular ligament
E. Intertransverse ligament A. Anterior longitudinal ligament
I. Interspinous and superspinous ligaments
B. Anterior one-half annulus fibrosus C. Posterior one-half annulus fibrosus
H. Ligamentum flavum
D. Posterior longitudinal ligament
Y RX
BY BZ
+Y AY
+RY AZ
+RX +X +Z
+RZ CRY Z X
CRZ
Figure 3b.20 Parameters for measurement of segmental motion using computer-assisted methods. RX is the rotation about the x-axis; CRY and CRZ are the centers of rotation of the Y and Z rotations, respectively; AY, AZ, BY, and BZ are the translations of point A in the Y and Z directions and point B in the Y and Z directions, respectively.
Chapter 3b
A
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Lower cervical spine
B
D
C Figure 3b.21 Female, aged 51, 1 year after injury to the cervical spine. The examination has been performed during active and passive motion (A-D) and measured according to Penning’s method (E and F).
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Biomechanics of the cervical and thoracic spine
35
Figure 3b.21 Cont’d According to the functional diagram, there is a significant difference in segmental motion, especially as related to segments C3-C4 and C6-C7. Drawing the vertebral bodies on a transparent paper (G) makes the difference obvious. (From Dvorak J, Froehlich D, Penning L, Baumgartner H, Panjabi MM: Spine 13(7):748-755, 1988.)
Hypermobile 30 25
Passive
20 15 10 5 0 C1/C2
C2/C3
E
C3/C4
C4/C5
C5/C6
C6/C7
Average + 2 STDV Average + 1 STDV Average Average – 1 STDV Average – 2 STDV Z.A., F, 51y
35 30 25
Active
20 15 10 Hypomobile
5 0 C1/C2a
C2/C3a
F
C3/C4a
C4/C5a
Average + 2 STDV Average + 1 STDV Average Average – 1 STDV Average – 2 STDV Z.A., F, 51y
Active
Active Passive
Passive
Hypermobile
G
Z.A., f, 51Y
C5/C6a
C6/C7a
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53
Table 3b.4 Averages and standard deviations of rotations, translations, and coordinates of center of rotation as measured by computer-assisted methods Parameter* C1-C2 C2-C3 C3-C4 C4-C5 C5-C6 C6-C7 RX (deg) Male RX (deg) Female AZ (mm) AY (mm) BZ (mm) BY (mm) Penning
Dvorak
Figure 3b.22 Determination of the center of rotation by graphic method (Penning, 1960) and by using computer-assisted methods on a normal population. (From Dvorak J, Schneider E, Saldinger P, Rahn B: J Orthop Res 9:828-834, 1991.)
CRZ (mm) CRY (mm)
15.4 6.1 12.9 3.4 –3.8 1.6 6.2 2.3 –1.4 1.4 8.1 3.0 –4.1 4.2 30.0 5.6
11.7 3.1 12.3 3.0 2.4 0.9 1.8 0.8 6.9 1.7 3.0 1.3 4.0 3.5 9.4 4.8
16.0 2.5 18.3 4.7 3.2 1.0 2.3 1.0 8.5 1.8 3.6 1.2 4.3 2.7 9.7 3.4
20.1 2.8 22.1 3.9 3.6 1.2 2.9 0.7 10.0 1.9 4.2 1.0 6.0 2.2 10.4 2.8
21.5 3.9 24.1 4.0 2.9 1.1 3.2 0.8 9.8 1.9 4.3 1.0 6.4 1.8 12.9 2.5
21.0 4.0 21.8 3.5 2.0 0.9 3.1 0.8 8.4 1.9 3.9 0.9 6.4 2.5 17.2 2.1
*See Figure 3b.20 for definitions.
Table 3b.3
Summary of flexion-extension movements of healthy adults in vivo and in vitro
Flexion/Extension (Total) C2-C3 C3-C4 C4-C5 C5-C6 C6-C7
Dvorak (1988) (In Vivo/Passive)
Dvorak (1988) (In Vivo/Active)
10.0 15.0 19.0 20.0 19.0
12.0 17.0 21.0 23.0 21.0
White and Panjabi
(1978)31
8.0 13.0 12.0 17.0 16.0
Penning (1978)20 (In Vivo/Active) 12.0 18.0 20.0 20.0 15.0
C2
C4
C7
Figure 3b.23 Segmental arch of the top angle according to Lysell.9 The flatter the articular surfaces, the flatter the top angle of the motion segments and vice versa.
Left bending
Neutral
Right bending
Figure 3b.24 Coupled axial rotation during lateral bending of the head. (From White AA, Panjabi MM: Clinical biomechanics of the spine, ed 2. Philadelphia, 1990, JB Lippincott.)
Chapter 3b
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Biomechanics of the cervical and thoracic spine
Table 3b.5a Values of main lateral bending according to various authors Main side bending (one side)
Moroney (1988) (in vitro FSU)
C2-C3 C3-C4 C4-C5 C5-C6 C6-C7
4.7 4.7 4.7 4.7 4.7
Table 3b.5b Values of coupled axial rotation according to various authors
White and Penning (1978)20 Panjabi (in vivo/active) (1978)31 6.0 6.0 6.0 6.0 6.0
10.0 11.0 11.0 8.0 7.0
Coupled axial rotation (one side) C2-C3 C3-C4 C4-C5 C5-C6 C6-C7
Dvorak (1987)3 (in vivo/passive) 3.0 6.5 6.7 7.0 5.4
Penning (1978)20 (in vivo/ active) 3.0 6.5 6.8 6.9 5.4
White and Panjabi (1978)31 9.0 11.0 12.0 10.0 9.0
FSU, functional spinal unit.
Lateral bending of the cervical spine is normally coupled with axial rotation to the same side.15,31 This means that the spinal processes are moving in a direction opposite the motion (Fig. 3b.24). This coupled motion is of clinical importance because palpation of the spinal processes can serve as an indirect indicator of disturbed function in motion segments. The lateral bending of the cervical spine below the first cervical vertebra has been variously reported by different researchers. According to Penning,20 the lateral bending is 35 degrees, whereas White and Panjabi31 reported between 4 and 10 degrees per motion segment. Axial rotation, as measured with functional computed tomography, is between 3 and 7 degrees,2,22 but an in vitro study19 showed a higher result, between 8 and 12 degrees. Tables 3b.5a and 3b.5b summarize the segmental motions for lateral bending with coupled axial rotation according to various authors.
10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
20. 21.
REFERENCES
22. 23.
1. 2.
Cave AJE: On the occipito-atlanto-axial articulations. J Anat (Lond) 68:416, 1934. Dvorak J, Hayek J, Zehnder R: CT-functional diagnostics of the rotatory instability of upper cervical spine. Part 2. An evaluation on healthy adults and patients with suspected instability. Spine 12:726-731, 1987. 3. Dvorak J, Panjabi MM: Functional anatomy of the alar ligaments. Spine 12:183-189, 1987. 4. Dvorak J, Antinnes JA, Panjabi M, Loustalot D, Bonomo M: Age and gender-related normal motion of the cervical spine. Spine 17(105):5393, 1992. 5. Dvorak J, Schneider E, Saldinger P, Rahn B: Biomechanics of the craniocervical region: the alar and transverse ligaments. J Orthop Res 6:452-461, 1988. 6. Dvorak J, Froehlich D, Penning L, Baumgartner H, Panjabi MM: Functional radiographic diagnosis of the cervical spine: flexion/extension. Spine 13(7):748-755, 1988. 7. Dvorak J, Panjabi MM, Novotny JE, Antinnes JA: In vivo flexion/extension of the normal cervical spine. J Orthop Res 9:828-834, 1991. 8. Ingelmark BE: Üeber den cranicervicalen Übergang beim Menschen. Acta Anat (Basel) 6:1-48, 1947. 9. Knese KH: Kopfgelenk, Kopfhaltung und Kopfbewegung des Menschen. Z Anat Entwickl 114:67-107, 1949.
24.
25. 26. 27. 28. 29. 30. 31. 32.
Lang J: Craniocervical region, osteology and articulations. Neuroorthopedics 1:67-92, 1986. Lang J: Klinische Anatomie der Halswirbelsäule. New York, 1991, Georg Thieme Verlag. Lang J, Bartram CT: Ueber die Fila articularia der Radices ventrales et dorsales des menschlichen Rückenmarkes. Gegenbaurs Morphol 128:417-462, 1982. Ludwig K: Üeber das Lig. alare dentis. Z Anat Entwickl Gesch 116:442, 1952. Luschka H: Die Halbgelenke des menschlichen Körpers. Berlin, 1858, Reimers. Lysell E: Motion in the cervical spine. An experimental study on autopsy specimens. Acta Orthop Scand Suppl 123:1-61, 1969. Mendel T, Wink CS, Zimny ML: Neural elements in human cervical intervertebral discs. Spine 17(2):132-135, 1992. Oda T, Panjabi MM, Crisco JJ, Bueff HU, Grob D, Dvorak J: Role of tectorial membrane in the stability of the upper cervical spine. Clin Biomech 7(4):201-207, 1992. Panjabi M, Dvorak J, Crisco JJ, Oda T, Wang P, Grob D: Effects of alar ligament transection on upper cervical spine rotation. J Orthop Res 9:584-593, 1991. Panjabi MM, Dvorak J, Duranceau J, Yamamoto I, Gerber M, Rauschning W, Beuff HU: Three-dimensional movements of the upper cervical spine. Spine 13(7):726-730, 1988. Penning L: Normal movement of the cervical spine. AJR Am J Roentgenol 130: 317-326, 1978. Penning L, Töndury G: Entstehung, Bau und Funktion der meniskoiden Strukturen in den Halswirbelgelenken. Z Orthop 98:1-14, 1964. Penning L, Wilmink JT: Rotation of the cervical spine: a CT study in normal subjects. Spine 12:732-738, 1987. Reich C, Dvorak J: The functional evaluation of craniocervical ligaments in sidebending using x-rays. Manual Med 2, 1986. Saldinger PF: Histologische Untersuchung des kraniozervikalen Bandapparates im Hinblick auf Weichteilverletzungen der Halswirbelsöule. Diss. med., Bern, 1987 (Leitung J. Dvorak). Saldinger PF, Dvorak J, Rahn BA, Perren SM: Histology of the alar and transverse ligaments. Spine 15:257-261, 1990. Simmons E, Marzo J, Kallen F: Intradural connections between adjacent cervical spinal roots. Spine 12(10):964-968, 1987. Stoff E: Zur Morphometrie des oberen Kopfgelenks. Verh Anat Gesch Jena 70:575, 1976. Töndury G, Theiler K: Entwicklungsgeschichte und Fehlbildungen der Wirbelsäule, ed 1. Stuttgart, Germany, 1958, Hippokrates-Verlag. Töndury G, Theiler K: Entwicklungsgeschichte und Fehlbildungen der Wirbelsäule, ed 2. Stuttgart, Germany, 1990, Hippokrates-Verlag. Werne S: Studies in spontaneous atlas dislocation. Acta Orthop Scand Suppl 23:80, 1957. White AA, Panjabi MM: The basic kinematics of the human spine. Spine 3:12-20, 1978. Wyke B: Neurological mechanisms in the experience of pain. Acupunct Electrother Res 4:27-35, 1979.
CHAPTER
3c
Evaluation of the Neck Ronald Moskovich and Anthony Petrizzo
Neck, or cervical spine, pain with concomitant disability is a common presentation among injured workers. Neck pain, however, is less prevalent than low back pain as a cause of worker absenteeism and represents less than 2% of all workplace injuries. The 1-year prevalence rate of non–work-related neck pain in most industrialized countries is approximately 20%; the prevalence of neck pain during a 1-month period in the United Kingdom is reported to be 14%.21 In a cohort of patients with neck pain, almost half had persistent neck pain 1 year later.10 Overall, back pain is commonly cited as the second leading cause of absenteeism in workers and the primary cause of workers’ compensation claims. In the Saskatchewan working age population, 10% experience severe neck pain, with up to 5% having neck pain that severely affects their activities of daily living.4 Most of these injuries are diagnosed as either a strain or sprain. For these types of milder neck injuries, analogous to the lower spine, it is a challenge to determine the precise pathoanatomic diagnosis before the initiation of therapy.
STANDARD EXAMINATION Evaluation of the cervical spine requires a history, using standard interviewing principles; a physical examination, focused on elimination of the pertinent negatives; and utilization of functional assessment scales to measure the impact of cervical dysfunction on common daily activities. This crucial assessment of the history with specific questions is used to rule out or determine the need for an urgent workup, a static and/or dynamic physical examination, laboratory studies, and further diagnostic and prognostic evaluations. Although the approach to a patient injured at work should not differ from that of a patient who injured his or her neck during recreational activity, patients referred for work-related cervical spine injury have another aspect added to their evaluation and assessment: critical return of the patient to pre- or near preinjury function to resume prior income-related activities as soon as possible.
DISABILITY EXAMINATION The critical distinction between a standard medical examination and a disability examination or impairment evaluation, lies not only in obtaining the information, but what to do once pertinent information is obtained (Table 3c.1).5 For example, once it is determined that a patient fell at work and is diagnosed and treated for the neck injury, the patient must be further evaluated for his or her ability to attend work and function in the workplace, albeit with possible job modifications.
This is referred to as a disability evaluation or examination. A more comprehensive overview of a disability evaluation is described below.5
IMPAIRMENT EVALUATION An impairment evaluation is another type of assessment tool regarding injury in the workplace. The distinctive contribution of an impairment evaluation is the measure of functional loss or derangement of any body part, organ, or organ system. Another purpose of an impairment evaluation is to measure, define, and determine the status of the patient’s (claimant’s) general health at a particular point in time. Establishing impairment can be accomplished using different objective methods, based on guidelines set by the American Medical Association.3 A diagnosis-related estimate is an impairment method based on eight diagnosis-related categories (i.e., muscle atrophy, guarding, asymmetric motion) for each of the three spinal regions. A second approach in the diagnosis-related estimate method is the diagnosis of a fracture or dislocation of the spine that, after appropriate tests and treatment has been rendered, requires no further verification. Impairment can also be documented based on assessment of the patient’s range of motion (ROM). This method is based on loss of active range of motion (AROM) in addition to an accompanying diagnosis and a spinal nerve deficit. The AROM approach is usually reserved for instances when a diagnosisrelated estimate is not applicable.3 Interestingly, the ability to participate in work activity is not included in calculating impairment percentages. The impairment evaluation is performed after the patient is determined to have achieved the highest possible level of recovery but before they return to work-related activity. Any deviation from predetermined normal criteria or from the patient’s prior health status is translated into an impairment rating. Impairment can then be converted to impairment percentages, which reflect the degree to which the impairment decreases the individual’s ability to perform activities of daily living. The development of an impairment rating is based on clinical decision making, whereas its purpose usually is to determine financial remuneration to the claimant by a third party.5
Table 3c.1 1. 2. 3. 4. 5. 6. 7. 8.
Goals of a disability examination5
Establish a diagnosis Quantify impairment Determine if examinee is capable of performing specified tasks Determine if examinee can attend work Determine if examinee can work in the occupational environment Determine if worker poses a threat to others in the workplace Make a recommendation regarding job modifications Extrapolate into the future a. Recommend treatment(s) b. Derive a time course c. Specify how treatment(s)/time will change points 1 through 7
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Evaluation of the neck
EVIDENCE-BASED MEDICINE In recent years, there has been a shift by research and evaluative bodies to apply evidence-based medicine (EBM) techniques and outcomes as a foundation for clinical decision making.11 The U.S. Agency for Health Care Policy and Research (AHCPR), which convenes expert multidisciplinary nonfederal panels to develop clinical practice guidelines for specific conditions and treatments, has similarly embraced the EBM perspective: Comprehensive evaluation of the results from randomized control studies is the best available scientific evidence on which to base clinical decision making. The working goal of the AHCPR’s musculoskeletal panel is to determine a model for the clinical utility of various diagnostic and therapeutic interventions for low back pain.5 This model for evaluating low back pain, although not interchangeable for cervical issues, has sound principles that can be effectively applied to treat cervical spine disorders. The AHCPR promotes a change in the former paradigm for treating acute low back pain, from focusing care exclusively on the pain itself to improving patients’ activity tolerance once all red flags for critical disorders have been eliminated.1 It is our suggestion that the low back pain model, although not a blueprint for management, can be applied to effectively treat cervical disorders as well. The fact that this approach could be advantageous for both clinician and patient, at minimum, underscores the importance and necessity of excluding red flags through the history and physical examination. The fact that the patient would now be more focused on movement behavior, and perhaps earlier than with prior treatment paradigms, underscores an added relevance to work-related injury cases. An interest in consistent and well-substantiated assessment and treatment paradigms are not limited to clinical medicine settings. A landmark U.S. Supreme Court ruling, in 1993, amended the Federal Rules of Evidence to require experts giving medical depositions to have reliable data to substantiate their testimony.2 Since that ruling, concepts supporting and policies enforcing EBM have expanded through input from epidemiology, outcomes research, policy makers, and clinicians. To adopt an evidencebased approach for the care of patients with neck problems, it is important that practicing clinicians understand the process of critically evaluating the accuracy of individual studies in the literature, know the natural history of cervical spine disorders, and be able to use that knowledge and their clinical experience as a check-and-balance to their practice decisions.
HISTORY Interview A description of the injury and of the precipitating events provides indispensable information for the treating physician. The inciting incident can be acute in onset or chronic with a progressing debility. Documentation must include how and when the precipitating event occurred as well as its duration. The history should begin with the identification and essential demographics of the patient: age, sex, race, and occupation. The chief complaint(s) should be recorded, at least initially, in
the patient’s own words. History of the present illness should include the location, duration, and concise description of symptoms and the timing, setting, any aggravating or relieving factors, and associated manifestations and prior treatments, to include their effects. It is important to establish whether or not there is a relationship between the injury and symptoms and the patient’s work activities and/or work setting. This part of the history may require close attention to draw subtle but meaningful information from the patient, in part because their pain or discomfort can make this information difficult to convey or because they may not be aware of the relationship. From this type of detailed dialogue with the patient, a statement of the probability that the injury is work-related is developed. The primary cause of many injuries can be obvious, whereas causes or etiologies of the injuries require deeper evaluation. Patients commonly present with neck complaints after a vehicular injury, a fall, or rough sport contact. Workers who perform overhead activities or who carry loads that could strain the neck muscles may also develop debilitating neck or arm pain. The symptoms of cervical disease can radiate cephalad to the skull or caudal to the extremities, where repetitive light to moderate work activity may be poorly tolerated and reveal underlying existing pathologies. The presence of a radicular component to the patient’s pathology necessitates documentation of the nature and sources of each of the symptoms. The patient’s prior medical history and a review of systems provide an account of his or her general state of health. A thorough musculoskeletal history should be done to establish the presence or absence of overall joint pain, stiffness, swelling, arthritis, gout, and low back pain. All illnesses and surgeries should be recorded. A history of gastrointestinal diseases, specifically gastritis and ulcerative disorders, should be taken, because patients with cervical ailments may require treatment with nonsteroidal antiinflammatory drugs. Specific hereditary predisposing conditions for inflammatory arthropathies, such as rheumatoid arthritis, psoriatic arthritis, and ankylosis spondylitis, may be discovered in the review of family history. Details of tobacco smoking should also be incorporated into the history. Positive associations between current smoking and nonspecific back pain were found in 18 of 26 studies in men and 18 of 20 studies in women.3 Any history of accidents, at work or home, or occupational exposures must be explored, because they can reveal risky habits or hazardous conditions. Relevant workers’ compensation issues should begin to emerge through the history, but their presence or impact may continue to be revealed during care of the patient. A comprehensive psychosocial history is a valuable but often overlooked part of the evaluation. Nonphysical or psychosocial factors such as job or life satisfaction can affect disability status and treatment outcome. Key features of this review include the patient’s life-style, home situation, and vocational and recreational activities. Notably, a history of mental illness, in particular depression and anxiety, must be addressed. Patients may be reticent to disclose such information, so its importance and practical function for treatment and recovery should be carefully and objectively expressed to the patient and, if necessary, sensitively probed. Finally, a list of the patient’s current medications, including prescription, herbal, holistic, over-the-counter, and “borrowed” must be reviewed.
Chapter 3c
Table 3c.2
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Physical examination
Red flags in cervical spine evaluation
Tumor
Osteomyelitis
Spinal cord compression
Trauma
Age > 50 Cancer history Unexplained weight loss Nocturnal pain
Intravenous drug abuse History of immunosuppression History of fever, night sweats History of urinary tract infection or skin infection
Bowel/bladder dysfunction Gait dysfunction, balance problems Fine motor dysfunction, clumsiness Arm pain, weakness
Trauma in patient < 50 years Low velocity trauma in patient > 50 Corticosteroid use
Modified from Clinical Practice Guidelines, AHCPR.
Red flags After inquiring about the presenting complaint, it is appropriate to focus on “red flags,” the presence of which command urgent evaluation. These red flags include a history of trauma, tumor, or infection, among others. Patients should be questioned regarding changes in any bowel and bladder habits, specifically an inability to fully empty the bladder, a feeling of fullness after urinating, and any history of bladder or bowel incontinence. Again, these may be difficult questions for patients, and they should understand that even quite minimal changes in these behaviors may be important to follow-up if they occur with any frequency or intermittency. Even though a neurologic examination will be done, it is important to question the patient about noticing any loss of manual dexterity as well as the development of headaches. Patients should be specifically questioned regarding recent fever, weight loss, night sweats, and nocturnal pain. Table 3c.2 identifies some of the more common red flags.
PHYSICAL EXAMINATION Inspection The physical examination typically begins with a general visual inspection of the patient’s health and conditioning. It is important to inspect the skin for general and isolated color changes. Warmth and redness are common physical findings with acute musculoskeletal strain. Posture is examined for asymmetry in positions such as lateral bending or rotation and the presence of abnormal sagittal and coronal curves. Ambulation should be observed for an ataxic broad-based gait, commonly seen in myelopathy, and any inability to heel-walk or toe-walk, seen with motor weakness and ability to accomplish tandem gait (walk on a straight line), which may be compromised in myelopathy or cerebellar disorders.
Range of motion A regional evaluation of the spine is part of the overall assessment. The spine has four normal sagittal curves. There is a fixed sacral kyphosis and a primary thoracic kyphosis that are apparent at birth. Cervical lordosis develops when the infant can maintain an upright head posture. The next curve, which typically develops once a child starts to walk, is the lumbar lordosis. Between each
of the sagittal curves is a transition zone where alignment is neutral relative to the vertical sagittal axis of the body. The cervical spine is well balanced in the sagittal plane so that C1 and C7 should be centered over the weight-bearing axis, and a plumb line should descend through T12 and continue caudally through the anterior portion of S1. The cervical lordotic curve normally ranges from 25 to 50 degrees with an apex at C4 (Fig. 3c.1). Assessment of cervical ROM is important from a functional and diagnostic perspective. ROM should be assessed with an inclinometer and recorded during the examination. Inclinometers can be mechanical or electronic, and the use of even a simple home-made device is preferable to a “guestimation.” An inclinometer can easily be made by punching a small hole through the center point of a protractor, passing a string through the hole and through a washer (to act as a weight), and tying the string in a loop. The loop of string indicates the degree of inclination on the protractor scale. A plastic scoliosis protractor can be used or a paper protractor downloaded from www.eece.ksu.edu/∼hkn/ files/protractor.pdf and pasted onto a card for use. C1, C2, and C7 are atypical vertebrae with respect to morphology and function, whereas C3 to C6 are commonly described as typical cervical vertebrae. The atlantooccipital joint acts as a pivot for the flexion/extension motion of the cranium, with 13 degrees average flexion/extension and 8 degrees lateral bending, allowing only a few degrees axial rotation.6 The atlantoaxial complex (C1-C2) has a total axial rotation of approximately 80-90 degrees, coupled with a flexion and extension of approximately 10 degrees and minor lateral bending. The prominent motion of the subaxial cervical spine is flexion/extension with some segmental rotation, the latter being both facilitated and constrained by the alignment of the apophyseal joints and the presence of the uncinate processes. The C5-C6 interspace is generally found to have the greatest range of flexion and extension motion of the subaxial spine.6 Subtle secondary motion, or coupled motion, of the cervical spine occurs in response to the primary motion. The coupled pattern of the cervical spine occurs with motion in the axial, sagittal, or coronal plane, for example, the direction of axial rotation in the subaxial spine is such that the spinous processes rotate into the convexity of the spine on side bending. AROM is performed by the patient at the instruction of the examiner and is one of the cornerstones in the determination of functional limits, assessment of improvement, and demonstration of disability when evaluating permanent impairment.5 AROM is performed by the patient alone on instruction by
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Evaluation of the neck
Figure 3c.1 Lateral radiographs of the cervical spine of various individuals of different ages. Clockwise from top left: A 16-year-old girl with normal cervical spine lordosis and normal disk space. A 46-year-old woman with mild loss of the normal cervical lordosis, noted in the mid-upper cervical spine. A 51-year-old woman with multilevel cervical spondylosis manifesting as narrowing of the intervertebral disk spaces at C4-C5 and C5-C6 with endplate changes and marginal osteophytes. A 73-year-old woman with advanced spondylosis and a frank reversal of the normal cervical lordosis as a result of marked multilevel diskogenic degenerative changes.
the examiner. In passive range of motion (PROM), the patient is assisted by the examiner to reach the maximum range. Often, PROM allows for more ROM in all planes. In the absence of pain, PROM can be performed to the anatomic barrier, whereas AROM is typically hindered by a physiologic barrier created by extant pathology or patterns of disuse not related to the presenting symptoms. ROM of the cervical spine is performed by having the patient rotate the head to the right and to the left. End points of motion should be symmetric. The patient should
be able to bend the head to the right and left, as though attempting to touch the ear to the shoulder but keep the shoulder from rising at the same time. This motion is also referred to as side or lateral bending. Flexion/extension ROM is assessed by having the patient flex or touch the chin to the chest and then extend or bend the neck backward. Neck extension is generally restricted and may be painful for patients with cervical stenosis or nerve root compression, although the opposite may also occur. All these motions should be recorded in degrees using a goniometer
Chapter 3c
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Neurologic examination
or, preferably, an inclinometer. Spurling’s test (see below) may be administered at this time.
Palpation While the patient is lying down, a thorough palpatory assessment of muscle tension, tenderness, and tissue texture abnormalities from spasm or contracture of the superficial anterior and posterior musculature must be performed. The examination of the neck with the patient seated and the examination of the upper thoracic spine are often integrated. The sternocleidomastoid muscle runs obliquely from the mastoid process of the skull to the lateral border of the sternal notch and may be injured in sudden hyperextension injuries of the cervical spine. The trapezius muscle originates from the inion and the spinous processes from C1 (atlas) to T12 (last thoracic vertebra); it flares out to insert on the clavicle, acromion, and spine of the scapula. Spasm in this muscle can best be palpated on the lateral aspect of the neck. The scalene muscles are palpable in the anterior paratracheal area. They originate on the transverse processes of the cervical vertebrae and insert bilaterally on the first and second ribs. These muscles function to laterally flex the neck (side bend) and help the attached ribs elevate during forced inspiration. Within this region, three anatomic sites of neural compression have been implicated in thoracic outlet syndrome: between the anterior and middle scalenes, between the clavicle and first ribs, and between the pectoralis minor and the upper ribs. The levator scapula originates on the rib’s posterior tubercles and inserts on the upper medial border of the scapula. This muscle is tender to palpation when in spasm. Anomalous cervical ribs may be palpated and can be confirmed radiologically; they may be involved in thoracic outlet obstruction but usually exist only as an anatomic anomaly. The cervical spine has an abundant supply of superficial and deep interconnected lymphatics to return the lymph to the vascular compartment in the thorax. Palpation of the cervical lymph nodes can elicit tenderness in adenopathy caused by tumor or infection.
NEUROLOGIC EXAMINATION The neurologic examination provides both direct and indirect methods of determining damage to the spinal cord and nerves by examination of their sensory, motor, and reflex distribution. The aim is to identify an anatomic level for possible neurologic deficit.
Sensory examination and dermatome testing The sensory component for each spinal nerve originates in a dermatome, a segmental portion of the skin. Each cutaneous innervation generally follows the distribution of the underlying muscle innervation (Fig. 3c.2). However, there are exceptions and variations to this generalization in the cervical spine. The suboccipital nerve (dorsal ramus of C1) exits the spine between the skull and C1 and has no cutaneous distribution. The dorsal branch of C2 is the greater occipital nerve, which distributes
Figure 3c.2 The cervical dermatomes are indicated. The C5 to T1 dermatomes are expressed in the upper extremity and develop as the embryonic limb bud does, extending from the trunk.
cranially upto provide sensation to the vertex of the scalp. The lesser occipital nerve of the cervical plexus (ventral ramus of C2) supplies sensation to the skin of the scalp behind the ear as well as the skin of the ear. Pathologic conditions affecting the C2 nerve result in occipital neuralgia. The dorsal ramus of C3 (third occipital nerve) distributes cutaneous sensation to the upper neck and scalp. The dorsal rami (sensory) of C4-C6 provide sensation to the posterior neck in a cephalad to caudal direction. The cutaneous nerves of the upper limb, on the other hand, are derived from branches of the brachial plexus, and thus each one is comprised of more than one nerve root.24 The dermatomal pattern in the extremities is patterned on orderly embryologic limb development. Clinical differentiation between dermatomal sensory loss and a peripheral nerve deficit helps distinguish cervical radiculopathy from other neurologic problems. The upper lateral cutaneous nerve of the arm is the termination of the lower branch of the axillary nerve. Its cutaneous distribution is the lower half of the deltoid muscle and the long head of the triceps brachii. The sensory branches of the radial nerve are the posterior cutaneous nerve of the arm that distributes to the middle third of the back of the arm, the posterior cutaneous nerve of the forearm, and the superficial branch of the radial. All the above arise from the posterior cord of the brachial plexus. The lateral cutaneous nerve of the forearm distributes into the lower lateral and the anterior surface of the arm. This nerve is the cutaneous branch of the musculocutaneous nerve which arises from the lateral cord of the brachial plexus. The medial cutaneous nerve of the arm provides sensation to the posterior surface of the lower third of the arm, as low as the olecranon, and the medial cutaneous nerve of the forearm covers the ulnar aspect of the forearm down to the hand. These are sensory branches of the ulnar which arises off the medial cord of the brachial plexus. The shoulder receives its cutaneous sensation proximally from the cervical plexus, specifically from the supraclavicular nerves of C3 and C4.
Motor strength examination The dorsal and ventral rootlets at each level unite to form a mixed spinal nerve. The motor roots arise from the anterior horn
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C4 Dorsal scapular n. Suprascapular n.
Axillary n. Radial n. Median n. Ulnar n.
C8
rior ste Po
T1 l T2 ia ed M Medial Long pectoral n. thoracic n.
To subscapularis teres major latissimus dorsi
Medial cutaneous nerves to the arm and forearm
Figure 3c.3 Diagram of the brachial plexus. There is a complex interconnection of nerve tissue. Note the differentiation between the nerve roots, which arise segmentally, and the ultimate peripheral nerves, which are usually an amalgam of two or more nerve roots.
cells and thus lie ventral to the sensory rootlets; they exit the spinal cord through the foramen above the named cervical vertebrae and carry their fibers to the striated muscles. Because there are eight cervical nerves and seven cervical vertebrae, the C8 nerve root exits below the C7 body. From C5 to T1, these nerves separate and recombine to form the brachial plexus where the fibers are reconfigured into trunks, divisions, and cords before finally forming independent branches (Fig. 3c.3). The resulting nerves are thus of mixed root origin and are named musculocutaneous, axillary, radial, median, and ulnar, innervating muscles in the upper extremity. Evaluation of the efferent nerves is achieved by testing the muscles they innervate. Motor strength is objectively evaluated using a six-point grading system (Table 3c.3). Testing begins with assessment of the patient’s breathing. The phrenic nerve (C3-C5) is the motor nerve to the diaphragm, although it also contains many sensory and sympathetic fibers. If the patient is breathing adequately without the use of accessory musculature, the diaphragm is functionally intact.19 The C5 nerve root innervates the deltoid muscle, and along with C6 it also innervates the biceps muscle. The C6 nerve root also innervates the wrist extensors. The C7 motor distribution includes the triceps muscle, the wrist flexors, and finger extensors.
Table 3c.3
Reflex examination
C7
l era Lat
Musculocutaneous n.
C5 C6
Lateral pectoral n.
These demonstrate the overlapping character of upper limb innervation (Fig. 3c.4).
Evaluation of motor strength15
5 - Normal 4 - Able to overcome moderate resistance (not symmetric to contralateral side) 3 - Able to accomplish full range of motion against gravity 2 - Able to accomplish full range of motion with gravity eliminated 1 - Only trace muscle contraction 0 - Flaccid
Pathologic alterations in the basic stretch reflexes are important findings in neurologic disease. Deep tendon reflexes are a misnomer, because they are actually muscle stretch reflexes initiated by excitation of the afferent muscle spindle fibers. These 1a afferent fibers synapse directly onto the proximal dendrites and soma of the motor neurone, completeing the reflex arc, resulting in a reflex muscle contraction. These monosynaptic reflexes are helpful for localizing the level of pathology in the cervical spine or nerve root and for differentiating a lower motor neuron lesion from an upper motor neuron lesion. Although some examiners grade the intensity of reflexes on a scale of 0 to 3, we believe it is more realistic to grade them as absent or present, because there are variable individual reactions to reflex testing. Deep tendon reflexes can be influenced by age, metabolic factors, and anxiety levels in the patient. Brisk, or hyperreflexic responses, however, may be abnormal findings on reflex testing. Typically, upper motor neuron lesions involve the spinal cord and cause hyperreflexia. Lower motor neuron lesions depress reflexes. For example, the nerve of C5 mediates the biceps reflex and that of C6 can be tested through the brachioradialis reflex and C7 through the triceps reflex (Table 3c.4 and Figs. 3c.5, 3c.6, and 3c.7).
Long-tract signs After injury to the corticospinal tract of the spinal cord, abnormal reflexes, or long-tract signs, can be elicited that are not typically found in normal individuals. These reflexes suggest the presence of lesions proximal to the anterior horn cells and represent clinical signs of myelopathy. Below are select examples. ● Clonus is elicited by the examiner rapidly dorsiflexing the ankle and maintaining slight pressure while counting the pulsed contractions on resistance. Greater than four beats of clonus is considered abnormal. ● Lhermitte’s sign (a.k.a. the barber’s chair phenomenon) is a symptom of radiating shock-like sensation down the back with neck flexion. ● Babinski’s sign is an abnormal reflex elicited by stroking the lateral border of the plantar surface of the foot with a blunted pointy object, which elicits dorsiflexion of the great toe with fanning and dorsiflexion of the small toes (Fig. 3c.8). A normal response is plantar flexion of all toes. A positive Babinski sign indicates damage to the corticospinal tract or injury to the spinal cord. ● Oppenheim’s sign is indicative of disease of the pyramidal tract and is performed by sliding the pointed back of the reflex hammer up the crest of the tibia. A positive test elicits a response similar to a positive Babinski sign; the great toe extends whereas the small toes flex and splay. ● Hoffman’s sign is a pathologic reflex elicited by flicking and flexing the distal phalanx of the patient’s middle finger. When the sign is present, there is prompt adduction of the thumb and flexion of the index finger on the ipsilateral side (Fig. 3c.9).
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B
A
C
D
E
F
G
Figure 3c.4 Testing a full array of individual muscles permits the examiner to form an accurate assessment of the affected nerve roots and to assess whether the injury is due to a specific peripheral nerve injury. Comprehensive examination is necessary because of the overlapping neural supply to individual muscles. A: infraspinatus (suprascapular nerve; C5, C6): external rotation of the upper arm at the shoulder. B: deltoid (axillary nerve; C5, C6): abduction of the upper arm. C: biceps brachii (musculocutaneous nerve; C5, C6) flexion of the supinated forearm. D: triceps (radial nerve; C6, C7, C8): extension of the forearm at the elbow. E: bracioradialis (radial nerve; C5, C6): flexion of the forearm at the elbow with the forearm in neutral rotation. F: extensor carpi ulnaris (posterior interosseous nerve; C7, C8): extension and abduction of the hand at the wrist. G: extensor digitorum (posterior interosseous nerve; C7, C8): extension of the fingers at the metacarpophalangeal joints.
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H
I
J
K
L
M
Figure 3c.4 Cont’d H: Flexor carpi radialis (median nerve; C6, C7): flexion and abduction of the hand at the wrist. I: abductor pollicis brevis (median nerve; C8, T1) abduction of the thumb at right angles to the palm. J: flexor digitorum profundus I and II (anterior interosseous nerve; C7, C8): flexion of the distal phalanges of the index and middle fingers. K: third and fourth palmer interossei (ulnar nerve; C8, T1): finger adduction by the patient on the left as the examiner pulls a card. L: dorsal interosseous muscle (ulnar nerve; C8, T1): abduction of the fingers. M: abductor digiti minimi (ulnar nerve; C8, T1): abduction of the little finger.
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An inverted brachioradialis reflex is elicited by tapping the brachioradialis tendon and observing ipsilateral finger flexion. In the finger escape sign, the patient is asked to hold his or her fingers in an extended and adducted position. If the two ulnamost digits drift into abduction and flexion within 30-60 seconds, the patient is deemed to have a positive finger escape sign. In a grip and release test, the patient should be able to rapidly make and release a fist 20 times within 10 seconds.
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A scapulohumeral reflex is elicited by tapping the vertebral border of the scapula at the tip of the scapula spine or the base of the inferior angle. A normal response should be retraction of the scapula by the rhomboid muscles (C4-C5). Absence of retraction is abnormal. A pectoralis reflex is an indication of hyperreflexia. The reflex is present when tapping the pectoralis tendon elicits flexion of the elbow or dorsiflexion of the wrist (Fig. 3c.10).
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Table 3c.4
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Muscle nerve root origins
Upper extremities
Root level tested
Nerve foramen
Pectoralis Biceps Brachioradialis Triceps
C5-T1 C5-C6 C5 C7 (C8)
— C4-C6 C5-C6 C6-C7
Figure 3c.6 The brachioradialis reflex is tested by a direct tap on the muscle tendon.
Figure 3c.5 Biceps reflex: Support the forearm with the patient’s elbow at a right angle and apply light tension to the biceps tendon with your thumb, which should then be hit lightly with the reflex hammer.
Figure 3c.7 The triceps reflex can be more easily elicited if the arm is supported so that the forearm hangs freely or by supporting the arm in the horizontal gravitational plane.
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Specialized physical tests
Figure 3c.8 A positive or extensor plantar response, also known as a Babinski sign. The sole is scratched from the lateral aspect of the heel forward and then medially across the ball of the foot.
The distraction test is an example of a provocative maneuver that can relieve symptoms of spondylosis or radiculopathy. While the patient is sitting or lying down, the palm of the examiner’s dominant hand is placed under the base of the skull and the nondominant hand placed under the chin. The head is gently distracted, increasing the pressure to about 5-7 kg. A positive sign provides symptomatic relief of neck or arm pain. An axial compression test is a provocative maneuver intended to elicit the neck or arm pain a patient may be experiencing intermittently. This is performed by placing up to 5-7 kg of pressure on the top of the head, preferably while the patient is sitting. A positive response precipitates or increases the patient’s symptoms. A distraction test can be performed after this test to attempt to provide some relief. Spurling’s sign is a maneuver to provoke symptom radiation. The patient laterally flexes and extends the neck (rotating the head to the symptomatic side), after which the examiner applies axial compression to the spine. A positive result causes pain or tingling that starts on the ipsilateral side of the neck or shoulder and radiates distal to the elbow (Fig. 3c.11). Spurling’s test has been shown to have a sensitivity of 30% and a specificity of 93% when confirmed with electrodiagnostic studies.17 Pronator reflex (a.k.a., ulnar reflex) is produced by tapping the volar aspect of the distal radius, or alternatively the styloid process of the ulna, with the forearm in a neutral position and the elbow flexed. The normal response is forearm pronation and adduction of the hand. The pronator reflex represents a muscle stretch reflex of the pronator teres that would make it helpful in evaluating C6 and C7 root lesions.14 The Valsalva maneuver is a provocative test that exacerbates arm pain when a patient bears down or coughs. These symptoms result from the increase in intrathecal pressure.
Figure 3c.9 Hoffman’s sign is positive or present if the act of flicking (flexing) the distal phalanx of the index or middle finger (black arrow) elicits a flexion of the thumb (white arrow) and/or other fingers.
Chapter 3c
Figure 3c.10 Position of the examiner’s fingers over the pectoralis tendon to test for a pectoralis reflex.
Tests for thoracic outlet syndrome include maneuvers that are presumed to tighten the thoracic outlet, such as arm hyperabduction, the “elevated arm stress test,” or the Adson test, all of which may provoke the patient’s typical symptoms of pain and/or paresthesia or affect the radial pulse. The Adson test, also called Adson’s maneuver, is performed with the patient in a sitting position. The patient’s hands rest on the thighs, the examiner palpates both radial pulses as the patient rapidly fills his or her lungs by deep inspiration, and, holding his or her breath, hyperextends the neck and turns the head toward the affected side. If the radial pulse on that side is decidedly or completely obliterated, the result is considered positive. In the Allen test, which is sometimes also described in the literature as the Adson test, the arm in which the patient is experiencing symptoms is raised and rotated while the head is turned away from the affected side. If the strength of the pulse is reduced in either of these two tests, it indicates compression of the subclavian artery. All the above are nonspecific tests. If they are positive, however, there may be an indication to perform further studies.
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Evaluating the impact of neck pain
Figure 3c.11 Spurling’s test: Hold the patient’s neck in extension for a few moments. Typical symptoms of brachialgia may be elicited, and if not, the test can be augmented by adding a lateral tilt of the head toward the symptomatic side as shown above. These maneuvers increase the degree of foraminal compression.
EVALUATING THE IMPACT OF NECK PAIN The standard history and physical examination provide objective findings that support subjective complaints to develop an overall assessment of cervical spine disorders. This “standard” examination does not often assess the impact of the disability on a patient’s life quality. Functional scales can be potentially useful to measure the impact of disease on the performance of common daily activities. Defining a standard evaluation for functional disability is difficult, because functional activity can be influenced by many factors independent of symptoms and signs such as age, psychologic ability to cope with disease, and the demands of professional activity.8 Well-validated instruments for evaluating neck dysfunction are widely available (Table 3c.5). For individual patient follow-up evaluation, the Patient-Specific
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Table 3c.5 Standard instruments for evaluating neck dysfunction Medical Outcomes Study 36-Item Short Form Health Survey Neck Disability Index18 Copenhagen Neck Functional Disability Scale12 Northwick Park Neck Pain Questionnaire13 Patient Specific Functional Scale22 Neck Pain and Disability Scale23
Functional Scale has high sensitivity to change and thus represents a good choice for clinical use.16 The MOS 36-Item Short Form Health Survey (SF-36), developed for the Medical Outcomes Study, is an example of a traditional scale for functional assessment.20 This questionnaire has demonstrated an overall usefulness in the general reporting of musculoskeletal ailments; however, it does not report on specific neck pain or disability. The Neck Disability Index is a 10-item questionnaire designed to assess pain-related limitations in activities of daily living. The test is scored as a percentage of maximal pain and disability. The scale is categorized by activity; however, some questions are not pertinent for all patients. The Copenhagen Neck Functional Disability Scale is a 15-item questionnaire requiring yes, no, or occasional as responses. The Northwick Park Neck Pain Questionnaire has nine five-part questions requiring responses of 0-4. The Patient Specific Functional Scale is unique in that it requires the patient to generate a specific list of problems emphasizing the limitations most affecting the patient. The Neck Pain and Disability Scale is a unique 20-item questionnaire in which a visual analog scale is assigned to each discomfort. The 20 items measure intensity of pain and its interference with the vocational, recreational, social, and functional aspects of living and the impact of emotional factors.
SPECIAL TESTS Imaging studies of the spine After the development of a working pathologic and anatomic diagnosis, appropriate imaging studies should be selected to demonstrate and confirm the diagnosis. Routine spinal imaging is not recommended during the first month of symptoms except in the presence of red flags.
Radiographs Plain radiography is the most widely available modality for imaging the cervical spine. The cervical (C) spine series consists of anteroposterior and lateral views to visualize the entire cervical spine and an open-mouth odontoid view to assess the odontoid and C1-C2 joint (Figs. 3c.12 and 3c.13). A swimmer’s view may be required to assess the cervicothoracic junction if the C7-T1 level is obscured by the patient’s shoulders on the lateral cervical radiograph. Lateral flexion and extension radiographs should also be obtained in patients with a history of trauma and patients with extensive degenerative disease. These radiographic views permit assessment of cervical alignment, degenerative changes, assessment of bony architecture in the vertebral bodies, and gross evaluation of the soft tissues. Oblique radiographs can be used to assess encroachment of the neural foramina (Fig. 3c.14). Radiographs should be the first-line diagnostic modality for patients presenting with neck pain when any of the following red flags are present: recent significant trauma or recent mild trauma in patients over 50, prior cancer or recent infection, neck pain worse at night or worse with rest, and history of intravenous drug abuse or corticosteroid use. Radiographs are the least sensitive of the imaging modalities in predicting symptomatology once tumor, trauma, or infection is excluded. A cervical sprain or strain leave no direct radiographic
Figure 3c.12 Lateral and anteroposterior radiographs of the cervical spine of a 34-year-old patient who had a disk herniation at C6-C7 with a clinical radiculopathy. The plain lateral film shows narrowing of the C5-C6 disk space (arrow) with a bony bar between the two vertebrae. That was not appreciated on the MRI. Note also the loss of cervical lordosis. The C5-C6 uncovertebral joint is indicated by an arrow on the anteroposterior radiograph.
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evidence, nor does a herniated disk. Although the presence of degenerative disk disease can be visualized on radiographs, it cannot predict symptoms or disability status.9 As much as 25% of the population has radiographic degenerative changes by age 50, and 75% have degenerative changes by age 70.7 It is the strength of this literature that persuades against the use of routine cervical spine radiographs alone to evaluate disability.
Computed tomography
Figure 3c.13 Open mouth view: A frontal view of the atlantoaxial (C1-C2) joint can be obtained radiographically with the patient’s mouth open as the teeth no longer obscure the direct view. In this example, both right and left C1-C2 facet joints are clearly seen, the dens is clearly visualized equidistant from both facet joints, and a partial view is even obtained of the occipitocervical articulations.
Figure 3c.14 Oblique cervical radiograph: The right-sided neural foramina can be clearly visualized. The black arrow indicates the right C4-C5 intervertebral or neural foramen; the C5 nerve root traverses the foramen. The small osteophytes arising from the right C3-C4 uncovertebral joint (joint of Luschka) are identified by the white arrow. The mild foraminal stenosis can be appreciated when comparing the foraminal dimensions with the normal adjacent foramina.
Computed tomography (CT) is a noninvasive diagnostic modality that provides excellent visualization of the cervical bony anatomy, helps evaluate osseous pathology, and assesses the integrity of the spinal canal. When CTs are supplemented with myelography, one can also evaluate soft tissue structure and impingement of nerve elements. That being said, studies directly comparing magnetic resonance imaging (MRI) and CT myelogram with respect to identifying pathology can yield conflicting results. However, general consensus points to the advantage of the CT myelogram in identifying osseous pathologies such as fractures, osteophytes, and bony foraminal encroachment. MRI studies better demonstrate soft tissue impingement, spinal cord edema, and myelomalacia. The ability of current multiplanar CTs has greatly enhanced the detail of the spine but also escalates the risk of false positivity. Scans can be reconstructed electronically in any desired plane to better visualize pathoanatomy (Fig. 3c.15).
Figure 3c.15 Midsagittal reconstructions of the cervical spine of a 56-year-old man who has an os odontoideum. Note the very short dens (odontoid process) that results in multiplanar atlantoaxial instability. The anterior ring of C1 (arrow) is normally aligned in neutral; there is posterior C1-C2 subluxation in the extended position and marked anterior C1-C2 subluxation in flexion. Note the marked anterior reposition of the C1 ring in flexion resulting in the posterior arch of C1 approaching the C2 body and causing severe spinal stenosis.
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Three-dimensional multiplanar CTs are extremely useful to demonstrate the complex anatomy of fractures and spinal deformity, be it congenital or other (Fig. 3c.16).
Magnetic resonance imaging MRI uses radiofrequency pulses within a strong magnetic field to produce an image without the use of ionizing radiation. MRI is a potentially useful modality for evaluating spinal cord pathology in the presence of brachialgia. MRI is also an excellent imaging modality to assess the soft tissues in the cervical spine and their contribution to compression of the nerves and spinal cord (Figs. 3c.17, 3c.18, and 3c.19). MRI provides excellent visualization of the spinal cord for masses or lesions and cysts as well as for the myelomalacia seen in chronic compression and edema seen in various acute pathologies. Spinal pathology, such as diskitis or local abscess, can be well identified with MRI. However, many of the abnormalities seen on MR images may be incidental, resulting in the potential for over-diagnosis. Nevertheless, in the presence of many of the red flags for pathology, MRI provides indispensable information that can rapidly help confirm or rule out serious clinical problems.
Myelography Myelography uses nonionic contrast injected intradurally to indirectly visualize soft tissues in the canal. Filling defects are an
A
Figure 3c.16 Three-dimensional reconstruction of the cervical spine of a child with a congenital hemivertebra (arrow). There is also a split or butterfly vertebra at C5.
indicator of spinal cord or nerve root compression. Plain myelography is typically enhanced with the addition of a CT. Myelography is a good test for patients in whom spinal root or cord compression is suspected and for patients who have received metallic
B
Figure 3c.17 Cervical magnetic resonance imaging (MRI) of a 26-year-old woman who has a large C6-C7 disk herniation. (A) Sagittal MRI. (B) The axial image through the C6-C7 disk (D) shows the large herniation (H) and the compressed spinal cord (SC).
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A
B Figure 3c.18 Cervical magnetic resonance imaging (MRI) of a 34-year-old woman who had a left C7 radiculopathy. (A) Midsagittal and parasagittal MRIs show the apparently small disk herniation. (B) Axial MRI at C5-C6 demonstrates normal anatomy, whereas at C6-C7 there is a large disk herniation (white arrow) extending into the left neural foramen and compressing the C7 nerve root. Note the normally patent right-sided neural foramen.
implants, which render an MRI ineffective. Myelographic studies also permit acquisition of (dynamic) images of the spinal cord and nerves taken with the neck flexed, extended, laterally tilted, or rotated (Fig. 3c.20). Soft tissue or bony impingement on the neural elements may be demonstrated in positions other than neutral. Note that there are now MRI scanners that also permit a full range of movement and the opportunity to obtain dynamic scans.
Barium swallow Visualizing swallowed radiographic contrast fluoroscopically can demonstrate mechanical compression on the esophagus from anterior osteophytes and differentiate dysphagia from other pathologies.
Bone scans A bone scan uses the technique of scintigraphy (diagnostic technique of recording the distribution and uptake of radioisotopes
injected into various body systems) to gauge the chronicity of a bony lesion such as a fracture, neoplasm, or a focus of osteomyelitis and to monitor disorders affecting bones. Scintigraphy is a very sensitive imaging modality; however, it is not very specific. The bone scan detects the distribution of a radioactive agent injected throughout the venous system. After injection, a scintillation camera detects the radioisotope’s distribution in the body, most importantly its concentration in the skeleton. Areas of increased metabolic activity are imaged as increased isotope uptake on a full body scan.
Electrodiagnostic studies Examination by electrodiagnostic methods is useful to document radiculopathy and to confirm nerve root impingement. These studies additionally facilitate the diagnosis of peripheral
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A
B Figure 3c.19 Cervical magnetic resonance imaging (MRI) of a 51-year-old man who had cervical myelopathy. (A) The sagittal scans show multilevel spinal stenosis. T1- and T2-weighted scans are shown. (B) Axial scans through the disks show central spinal stenosis from C3-C4 to C6C7 with spinal cord compression.
entrapment syndromes and peripheral neuropathy. The tests commonly include needle electromyography, nerve conduction studies, and somatosensory evoked potentials.
Electromyography Measuring the electrical activity of muscle fibers at rest and when active provides diagnostic information on the degenerative or healthy status of muscles and their innervation and distinguishes neurogenic from myopathic disorders. The electromyographic evaluation in chronic cervical radiculopathy shows a
partial denervation pattern that manifests as increased amplitude and a longer duration of the motor unit potential. Fibrillations, or small-amplitude, single muscle fiber potentials, may also be present but are nonspecific and usually seen in the acute stage. Insertional activity from movement of the electrode is normal in electromyographic studies, but if it persists after electrode motion ceases, it is described as prolonged insertional activity and can be a sign of radiculopathy. When these tests are done within the first 2-3 weeks after injury, the results are falsely negative as it takes time to develop denervation.
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Figure 3c.20 Cervical myelogram. (A) Lateral (left) and anteroposterior (right) views of the cervical spine of a 56-year-old man with neck and arm pain and early signs of cervical myelopathy. Compression of the thecal sac is well seen on the lateral view at the C4-C5 and C5-C6 levels when his neck is extended. The anterior-posterior view demonstrates a paucity of contrast at those levels and truncation of the exiting nerve roots. Normal nerve root filling is noted at C6-C7 and distal levels. (B) Postmyelogram axial computed tomography images clearly demonstrate bilateral foraminal stenosis at C4-C5, whereas at C6-C7 the nerve root sleeves can be seen to fill well with the contrast (arrow).
Nerve conduction studies Using nerve conduction studies to evaluate how well nerves transmit electrical signals provides an assessment of the overall condition of both individual nerves and whole nerve structures. Measured electrical parameters are usually the signal amplitude and signal onset latency. These measured values are then compared with established normal parameters to determine the site of a compression. Nerve conduction studies are useful to evaluate acute and chronic peripheral entrapment neuropathies that mimic radiculopathy. Nerve conduction velocity and latency changes are not typically found in cervical radiculopathy unless there is extreme demyelinization of axons. The F-wave response tests electrical conduction through motor roots (Table 3c.6). The F-wave is recorded after maximal stimulation of a motor nerve. The amplitude, shape, and latency should change with each stimulation. Clinical parameters usually evaluated are response time, or latency. Because the F-wave is dependent on the integrity of the entire motor unit, it can assess proximal neuropathies. Another parameter with which to document nerve abnormalities is through the recording and measurement of sensory nerve action potentials. Abnormal sensory nerve action potentials are noted with damage to the nerve from the dorsal root ganglion while they are normal in pure radiculopathy, as the presumed lesion is proximal to the sensory ganglion. In patients with sensory deficit in the hands, recordings of sensory nerve action potentials make a differentiation between lesions of dorsal roots and peripheral nerves possible.
Somatosensory evoked potentials Somatosensory evoked potential recordings can be used to evaluate the integrity of the central nervous system and peripheral sensory neurons. Because most peripheral nerves in the upper extremity carry fibers from multiple roots, somatosensory evoked
potentials are not specific in elucidating spinal root dysfunction but can be useful in determining spinal cord abnormality that affect cord pathways.
Laboratory screening Laboratory studies provide valuable clinical evidence for patients presenting with atypical neck complaints or those suspected of tumor or infection. A complete blood count with differential can help detect a response to infection, blood dyscrasias, and medication side effects. The erythrocyte sedimentation rate and C-reactive protein are categorized as acute phase reactants commonly used in orthopedics to detect evidence of an infection or a connective tissue disorder. Although both indices serve the same primary function, clinicians often use them simultaneously, because the C-reactive protein is quicker to respond to either improvement or worsening of a clinical course. A comprehensive metabolic panel, including Ca+, phosphorus, uric acid, alkaline phosphatase, and acid phosphatase, can help detect metabolic bone disease.
CONCLUSION Evaluation of the cervical spine in workplace injuries requires a multidimensional workup that facilitates, first, ruling out serious pathology before initiating therapy for the work-related injury and, second, evaluation of the patient’s work setting relative to the patient’s recovery process for a rapid and safe return to work activity. The trend in evaluating cervical spine injuries increasingly involves more emphasis on EBM to guide treatment. Using EBM as a guide facilitates a rapid evaluation with concise elimination of red flags for spinal pathology. Returning to work
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Table 3c.6
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Evaluation of the neck
Nerve and main root supply of muscles Spinal roots
Spinal accessory nerve Trapezius C3, C4 Brachial plexus Rhomboids C4, C5 Serratus anterior C5, C6, C7 Pectoralis major Clavicular C5, C6 Sternal C6, C7, C8 Supraspinatus C5, C6 Infraspinatus C5, C6 Latissimus dorsi C6, C7, C8 Teres major C5, C6, C7 Axillary nerve Deltoid C5, C6 Musculocutaneous nerve Biceps C5, C6 Brachialis C5, C6 Radial nerve Long head Triceps Lateral head C6, C7, C8 Medial head Brachioradialis C5, C6 Extensor carpi radialis longus C5, C6 Posterior interosseous nerve Supinator C6, C7 Extensor carpi ulnaris C7, C8 Extensor digitorum C7, C8 Abductor pollicis longus C7, C8 Extensor pollicis longus C7, C8 Extensor pollicis brevis C7, C8 Extensor indicis C7, C8 Median nerve Pronator teres C6, C7 Flexor carpi radialis, C6, C7 Flexor digitorum superficialis C7, C8, T1 Abductor pollicis brevis C8, T1 Flexor pollicis brevis C8, T1 Opponens pollicis C8, T1 Lumbricals I and II C8, T1 Anterior interosseous nerve Flexor digitorum profundus I and II C7, C8 Flexor pollicis longus C7, C8 Ulnar nerve Flexor carpi ulnaris C7, C8, T1 Flexor digitorum profundus III and IV C7, C8 Hypothenar muscles C8, T1 Adductor pollicis C8, T1 Flexor pollicis brevis C8, T1 Palmar interossei C8, T1 Dorsal interossei C8, T1 Lumbricals III and IV C8, T1 Abductor digiti minimi C8, T1
See Figure 4
activity or to normal daily activities, in general, is therapeutic; if necessary, they can be modified to minimize exacerbations and maximize productivity. Once neck pain shifts from acute to subacute or chronic, there exists a comprehensive panel of tests and studies that help to continue to delineate pathology and further guide patient treatment.
REFERENCES 1.
A 2. 3.
B
4.
C
5. 6. 7.
D
8.
E
9. 10. 11.
F G
12. 13. 14. 15. 16.
H I
17. 18. 19. 20.
J
21.
22.
23.
24.
K L M
Adapted from Medical Research Council: Aids to the examination of the peripheral nervous system. London, 1980, Her Majesty’s Stationary Office.
Bigos S, Bowyer OR, Braen GR, Brown K, Deyo R, Haldeman S, et al: Acute low back problems in adults. Rockville, MD, 1994, Agency for Health Care Policy and Research, Public Health Service, U.S. Department of Health and Human Services. Bigos SJ, McKee JE: Data-driven Daubert defendable care code—activity paradigm and reliable data for back problems. Semin Spine Surg 15:68-90, 2003. Cocchiarella L, Andersson GBJ: Guides to the evaluation of permanent impairment. AMA Press, 2004. Co^té P, Cassidy JD, Carroll L: The Saskatchewan Health and Back Pain Survey. The prevalence of neck pain and related disability in Saskatchewan adults. Spine 23:1689-1698, 1998. Demeter S, Anderson G: Disability evaluation. St Louis, MO, 2003, Mosby. Dvorak J, Panjabi MM, Novotny JE, Antinnes JA: In vivo flexion/extension of the normal cervical spine. J Orthop Res 9:828-834, 1991. Friedenberg ZB, Miller WT: Degenerative disc disease of the cervical spine, J Bone Joint Surg Am 45:1171-1178, 1963. Goldberg MS, Scott SC, Mayo NE: A review of the association between cigarette smoking and the development of nonspecific back pain and related outcomes. Spine 25:995-1014, 2000. Gore DR, Sepic SB, Gardner GM: Roentgenographic findings of the cervical spine in asymptomatic people. Spine 11:521-524, 1986. Hill J, Lewis M, Papageorgiou AC, Dziedzic K, Croft P: Predicting persistent neck pain: a 1-year follow-up of a population cohort. Spine 29:1648-1654, 2004. Holland JP, et al: How to critically evaluate the clinical literature on low back problems: the foundation for an evidence-based approach to care. Semin Spine Surg 15:54-67, 2003. Jordan A, et al: The Copenhagen Neck Functional Disability Scale: a study of reliability and validity. J Manip Physiol Ther 21:520-527, 1998. Leak AM, et al: The Northwick Park Neck Pain Questionnaire, devised to measure neck pain and disability. Br J Rheumatol 33:469-474, 1994. Malanga GA, Campagnolo DI: Clarification of the pronator reflex. Am J Phys Med Rehabil 73:338-340, 1994. Medical Research Council: Aids to the examination of the peripheral nervous system. London, 1980, Her Majesty’s Stationary Office. Pietrobon R, Coeytaux RR, Carey TS, Richardson WJ, DeVellis RF: Standard scales for measurement of functional outcome for cervical pain or dysfunction: a systematic review. Spine 27:515-522, 2002. Tong HC, Haig AJ, Yamakawa K: The Spurling test and cervical radiculopathy. Spine 27:156-159, 2002. Vernon H, Mior S: The Neck Disability Index: a study of reliability and validity. J Manip Physiol Ther 14:409-415, 1991. Wagner R, Jagoda A: Spinal cord syndromes. Emerg Med Clin North Am 15:699-711, 1997. Ware JE Jr, Sherbourne CD: The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care 30:473-483, 1992. Webb R, Brammah T, Lunt M, Urwin M, Allison T, Symmons D: Prevalence and predictors of intense, chronic, and disabling neck and back pain in the UK general population. Spine 28:1195-1202, 2003. Westaway MD, Stratford PW, Binkley JM: The patient-specific functional scale: validation of its use in persons with neck dysfunction. J Orthop Sports Phys Ther 27:331-338, 1998. Wheeler AH, Goolkasian P, Baird AC, Darden BV: Development of the Neck Pain and Disability Scale. Item analysis, face, and criterion-related validity. Spine 24:1290-1294, 1999. Woodburne RT, et al: The Netter Collection of Medical Illustrations: Volume 8 Musculoskeletal System. New Jersey, 1997, Novartis Pharmaceutical Corporation.
CHAPTER
3d
Treatment Options for Disorders of the Cervical Spine James N. DeBritz and Sam W. Wiesel
As with any pathophysiologic condition, treatment of neck pain depends on the proper diagnosis. Neck pain has multiple etiologies (Table 3d.1) that may result from trauma as well as from chronic atraumatic conditions. Understanding these etiologies requires detailed knowledge of both the anatomy of the cervical spine and its relationship to neurovascular structures as well as comprehension of the natural history of cervical spondylosis and myelopathy. Diagnosis of neck pain can be more easily accomplished by dividing clinical complaints into several main categories, including axial neck pain, neck pain with an associated radiculopathy, and neck pain with signs and symptoms of myelopathy. Once the proper diagnosis is established, treatment can be directed in a focused and individualized manner. This chapter summarizes some of the most common cervical spine disorders to aid in their diagnosis. The reader is instructed on how a pertinent history, directed physical examination, and diagnostic findings can be used to establish a diagnosis. Treatment options are discussed in detail, and finally a diagnostic and treatment algorithm is presented that integrates the information into a usable format.
ANATOMY A detailed understanding of the osseous and soft tissue structures of the neck is a prerequisite to fully understand the pathophysiology of neck pain and cervical spine disease. Once a pathologic process temporarily or permanently distorts the normal anatomy of the neck, a compensatory response may occur that often presents to the individual as pain. With the exception of C1, each cervical vertebra articulates with the adjacent vertebra through the facet, or zygapophyseal, joints. These are gliding joints characterized by capsules and synovial membranes in addition to ligamentous support. The facet joints are innervated by the dorsal ramus of the associated nerve roots. Axial neck pain can be produced by facet joint injections in asymptomatic individuals, providing evidence that it can originate from the facet joints themselves.2 This information can be used to direct treatment in certain cases, as discussed. The amphiarthrodial joints that join each vertebral body through intervertebral disks play an important role in the pathologic process of the spine as well. Although varying in size depending on the level of the spinal column, all intervertebral disks are identical in their structural organization. The internal portion of the disk is comprised of the nucleus pulposus that is contained around its periphery by the annulus fibrosus.
Table 3d.1 Causes of neck and neck-related pain syndromes Localized neck disorders Osteoarthritis (apophyseal joints, C1-C2-C3 levels most often) Rheumatoid arthritis (atlantoaxial) Juvenile rheumatoid arthritis Sternocleidomastoid tendinitis Acute posterior cervical strain Pharyngeal infections Cervical lymphadenitis Osteomyelitis (staphylococcal, tuberculosis) Meningitis Ankylosing spondylitis Paget disease Torticollis (congential, spasmodic, drug involved, hysterical) Neoplasms (primary or metastatic) Occipital neuralgia (greater and lesser occipital nerves) Diffuse idiopathic skeletal hyperostosis Rheumatic fever (infrequently) Gout (infrequently) Lesions producing neck and shoulder pain Postural disorders Rheumatoid arthritis Fibrositis syndromes Musculoligamentous injuries to the neck and shoulder Osteoarthritis (apophyseal and Luschka) Cervical spondylosis Intervertebral osteoarthritis Thoracic outlet syndromes Nerve injuries (serratus anterior, C3-C4 nerve root, long thoracic nerve) Lesions producing predominantly shoulder pain Rotator cuff tears and tendinitis Calcareous tendinitis Subacromial bursitis Bicipital tendinitis Adhesive capsulitis Reflex sympathetic dystrophy Frozen shoulder syndromes Acromioclavicular secondary osteoarthritis Glenohumeral arthritis Septic arthritis Tumors of the shoulder Lesions producing neck and head pain with radiation Cervical spondylosis Rheumatoid arthritis Intervertebral disk protrusion Osteoarthritis (apophyseal and Luschka joints, intervertebral disk, osteoarthritis) Spinal cord tumors Cervical neurovascular syndromes Cervical rib Scalene muscle Hyperabduction syndrome Rib-clavicle compression From Wiesel SW; Neck pain, ed 2. Charlottesville, VA, 1992, The Michie Company, pp. 60-61.
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Figure 3d.1 Cross-sectional view showing the cervical nerve root, dorsal and ventral primary rami, recurrent meningeal or sinuvertebral nerve, and sympathetic plexus. Note the proximity of the disc space, vertebral artery, and facet joints. (From Rao R: Instr Course Lect 84A(10):1872-1881, 2002.)
Both the nucleus pulposus and the annulus fibrosus share a similar composition and are comprised mainly of water, proteoglycans, and collagen. They differ, however, in their organization and in the type of collagen present. Type II collagen is found in the nucleus pulposus, and type I collagen is present in the annulus. The cervical intervertebral disks are wedge-shaped to accommodate the uncinate processes and the corresponding joints of Luschka, a bony articulation between the vertebral bodies. The blood supply and innervation of the intervertebral disks of the cervical spine have been well defined. Branches of the sympathetic plexus and the ventral nerve root form the sinuvertebral nerve that innervates the intervertebral disk, supplying portions of the annulus, the posterior longitudinal ligament, the periosteum of the vertebral body and pedicle, and the adjacent epidural veins (Fig. 3d.1). In a review of clinical findings of cervical diskography, Grubb and Kelly5 showed a correlation between reliable patterns of pain and each cervical disk. These pain patterns and axial pain patterns produced by facet joint injections are summarized in Figures 3d.2 and 3d.3, respectively. In addition to the major articulations of the cervical spine and their innervations, the soft tissue structures of the cervical spine and the neck play an important role in neck pain. The vertebrae are bound together by many ligaments. The anterior longitudinal ligament and the weaker posterior longitudinal ligament bind the vertebral bodies along the anterior and posterior surfaces, respectively, and run from the skull to the sacrum. The segmental denticulate configuration and intricate association with the intervertebral disk is characteristic of the posterior longitudinal ligament, and a prolapsed nucleus pulposus is most likely to be permitted lateral to these expansions. The ligamentum flavum is a strong elastic ligament that connects the laminae of each of the vertebrae and runs from C2 to the lumbosacral interval. A continuation of the supraspinous ligament, the ligamentum nuchae, runs from C7 to the occiput and along with the interspinous and intertransverse ligaments serves to stabilize further the spinal column architecture.
Muscles in the neck are divided into anterior and posterior groups. Anterior muscles are comprised mainly of the strap muscles and the sternocleidomastoid. The neck musculature forms several distinct layers posteriorly. From dorsal to ventral
Figure 3d.2 Axial pain patterns provoked during discography at each cervical level. A: level between second and third cervical vertebrae; B: level between third and fourth cervical vertebrae; C: level between fourth and fifth cervical vertebrae; D: level between fifth and sixth cervical vertebrae; and E: level between sixth and seventh cervical vetebrae. (From Rao R: Instr Course Lect 84A(10):1872-1881, 2002.)
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Acute herniated disk
will usually reveal only some local tenderness lateral to the bony spine. The loss of motion in individual patients is variable and tends to correspond directly with the intensity of the pain. True muscular spasm, defined as continuous muscular contraction, is rare, except in severe cases of torticollis in which the head is tilted to one side. Because radiographic studies in neck strain are usually normal, plain films are generally not warranted on the first office visit. If the pain persists for more than 2 weeks, however, a radiograph should be obtained to rule out other more serious causes of neck pain such as instability or neoplasia.
Treatment
Figure 3d.3 Composite map of axial pain patterns produced by injections into the facet joints at the second through seventh cervical levels. (From Rao R: Instr Course Lect 84A(10):1872-1881, 2002.)
are the trapezius and levator scapulae, splenius and longissimus, semispinalis, and suboccipital muscles. These muscles assist in scapular rotation (trapezius and levator scapulae) and rotation, flexion, and extension of the neck. Strain of these muscles can also contribute to neck pain.
The prognosis for patients with cervical strain is excellent because the natural history of this disorder is complete resolution of all symptoms over a period of several weeks. Therapy consists primarily of rest and immobilization, often with the use of a soft cervical orthosis. Certain medical interventions such as antiinflammatory agents and/or muscle relaxants may aid in the acute phase of pain management, but they do not appear to alter the natural course of the syndrome. Although no good randomized, prospective, clinical trials have studied their efficacy, trigger point injections do seem empirically to work well. The purpose of a trigger point injection is to decrease inflammation in a specific anatomic area, with apparently superior results the more localized the trigger point. These injections can be repeated at 1- to 3-week intervals.
ACUTE HERNIATED DISK NECK SPRAIN The condition of nonradiating neck pain with a concomitant loss of motion has been referred to incorrectly as neck sprain. Correctly termed cervical strain and one of the most common neck disorders, this often occurs in the absence of a distinct traumatic episode. Most commonly, the pain is located in the middle to lower part of the neck, and although the pain is not secondary to trauma, its onset can be acute. The pain associated with cervical strain is often a dull ache that is exacerbated by movement. In addition, a component of referred pain may be involved. This is not, however, true radicular pain secondary to mechanical compression of a nerve root. The pain is referred generally to other mesenchymal structures derived from a similar sclerotome during the process of embryogenesis. The most common referral patterns include the posterior of the shoulder, the occipital area, the scapular region, and the anterior chest wall, also known as cervical angina pectoris. The source of the pain is most commonly believed to be the ligaments and musculature of the cervical spine.14 As previously illustrated, however, both facet and disk disease can contribute to axial neck pain and should be considered as a source of the inciting complaint (Figs. 3d.2 and 3d.3). Once the precise location, frequency, and quality of the pain have been determined, careful questioning should then address the presence, if any, of subtle long-tract signs, including bowel or bladder dysfunction and gait abnormalities, to avoid missing the diagnosis of myelopathy. Physical examination of the patient
A herniated disk results when the nucleus pulposus protrudes through the fibers of the surrounding annulus fibrosus and occurs around the fourth decade of life while the nucleus pulposus remains gelatinous. Stookey15 and Rothman and Marvel13 described three types of soft disk herniations (Fig. 3d.4), with the posterolateral herniation being the most common due to the anatomy of the posterior longitudinal ligament, as previously mentioned. Herniations occurring posterolaterally produce predominantly motor signs and symptoms. As opposed to those in the lumbar region, disk herniations occurring centrally may cause myelopathy because of the presence of the cord in the cervical region. The most common levels for herniation are at the C6-C7 and C5-C6 levels. Those at the C7-Tl and C3-C4 levels are uncommon, and those at the C2-C3 level are extremely rare. Interestingly, not every disk herniation is symptomatic. The presence and severity of symptoms depend on the individual’s spinal reserve capacity, the presence or absence of associated inflammation, the size of the herniated fragment, and the presence of concomitant disease processes such as uncovertebral joint osteophytes. In general, a herniated disk affects the nerve root of the next lowest cervical level: A C3-C4 disk affects the C4 nerve root, a C4-C5 disk affects the C5 nerve root, and so on. The radicular symptoms then correspond to the involved nerve root. In addition, as previously stated, a herniated disk may cause some long-tract signs because of the presence of the spinal cord at the cervical level.
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Figure 3d.4 Types of soft disk herniations. (From Boden SD, et al: The aging spine: essentials of pathophysiology, diagnosis, and treatment. Philadelphia, 1991, WB Saunders.)
Most patients have symptoms consisting primarily of arm pain. Although it may begin in the neck region, the pain radiates down into the shoulder, arm, forearm, or hand along a clearly defined dermatome. The onset of pain may be gradual, although acute tearing or snapping sensations may occur. The arm pain may vary in intensity from a dull cramping pain in the arm with
use to pain so severe as to preclude use. In addition, attacks of sharp pain may radiate into the hand and fingers with associated paresthesias. Pain severe enough to awaken the patient at night is common. The differential diagnosis of radicular pain must be considered. Pathologies that range from tumors to nerve entrapment syndromes share the common trait of mechanically compressing a nerve root and imitating radicular symptoms. Other neurologic diseases can masquerade as a radicular process, however, and should also be contemplated. Classic differential diagnoses include a Pancoast tumor, which is an apical lung tumor often accompanied by Horner syndrome because of disruption of the sympathetic chain, and thoracic outlet syndrome, which can be diagnosed on physical examination. Physical examination may reveal some decreased motion of the neck that may be so severe as to manifest as frank torticollis. Any maneuver (such as the Valsalva maneuver) that stretches the involved nerve root may recreate the pain pattern. Spurling’s test, in which the neck is extended, may often make the pain worse by further narrowing the involved intravertebral foramina. Additionally, coughing, shoulder abduction, and axial compression tests are often positive in patients with compression radiculopathy. The axial compression test is performed by pressing down on a patient’s head while he or she is either sitting or lying down. A positive finding consists of worsening or reproduction of radicular symptoms. The shoulder abduction relief test is positive if radicular symptoms are decreased when a seated patient elevates one hand above the head with the elbow flexed and the shoulder abducted to 90 degrees. An axial manual traction test is performed with the patient supine. A positive finding consists of a decrease or complete absence of radicular symptoms when 20 to 30 pounds of axial traction is applied. The finding of a neurologic deficit on physical examination greatly aids in the diagnosis, although in the setting of a chronic radiculopathy, the neurologic examination may be normal. Because subjective sensory changes are often difficult to interpret, the neurologic examination must show a diminution of reflexes, motor weakness, or atrophy to be significant. Henderson et al6 found a diminished deep tendon reflex in 71% and a demonstrable motor deficit in 65% of 846 patients with cervical radiculopathy. The specific motor and deep tendon reflex changes noted depend on the cervical nerve root that is compressed by the herniated disk. Because the C3 and C4 nerve roots do not have a uniquely testable reflex or motor innervation, involvement of these roots corresponds to sensory changes in their respective dermatomes. The remaining cervical nerve roots do exhibit testable motor and reflex changes in addition to sensory deficits in their corresponding dermatomes (Table 3d.2). The specific motor innervation of the individual nerve roots allows the examiner to pinpoint the level of disease with good accuracy. Because plain films are most often normal they are nondiagnostic, leaving the clinician to rely on the history and physical examination to arrive at the diagnosis of an acute herniated cervical disk. Occasionally, disk space narrowing is seen at the involved interspace, or oblique films may show foraminal narrowing. Plain films are useful primarily for ruling out other causes of arm and neck pain, such as instability and neoplasia. Other diagnostic tests, such as electromyography (EMG) or myelography, are not useful as screening tests and should be
Chapter 3d
Table 3d.2
Neurology of the upper extremity
Disk
Root
Reflex
Muscles
Sensation
C4-C5
C5
Biceps reflex
C5-C6
C6
C6-C7
C7
Brachioradialis reflex (biceps reflex) Triceps reflex
Deltoid Biceps Wrist extension Biceps
Lateral arm Axillary nerve Lateral forearm Musculocutaneous nerve Middle finger
C7-T1
C8
T1-T2
T1
Wrist flexors Finger extensions Triceps Finger flexion Hand intrinsics Hand intrinsics
Medial forearm Med. Ant. Brach. Cutaneous nerve Medial arm Med. Brach. Cutaneous nerve
used more to confirm diagnoses based on a detailed history and physical examination. In addition, the routine use of computed tomography (CT) or magnetic resonance imaging (MRI) is not warranted. These sensitive studies may reveal herniated disks that are clinically insignificant: In a study of 63 asymptomatic individuals, 10% showed evidence of cervical disk herniation on MRI.1
Treatment The primary mode of treatment for an acute herniated disk is rest and immobilization. A cervical orthosis greatly improves the chance that the patient will remain at rest. The collar must fit properly and hold the head in a neutral to slightly flexed position. If the neck is held in hyperextension, the patient often is uncomfortable and therefore noncompliant in its use. Once the acute pain starts to subside, the patient should be weaned slowly from the orthosis and should likewise increase activity gradually. If the patient complies with the rest and immobilization, the use of analgesics is often not necessary, although a brief course of analgesic medicine may occasionally be required in severe cases. Benzodiazepines and muscle relaxants can act as central nervous system depressants but as such have a limited role in the treatment of acute herniated disk disease. Drug therapy does, however, have an important role in combination with rest and immobilization. Evidence now suggests that herniated disks are capable of eliciting an immune response characterized by the secretion of cytokines such as interleukin-1, interleukin-6, nitric oxide, and prostaglandins, which have multiple effects on tissues, including direct stimulation of nerve ending and sensitization of nociceptors.7 By inhibiting the production pathway of some of these mediators, antiinflammatory medications such as nonsteroidals have a role to play in symptomatic relief. Many such medications can have adverse gastrointestinal side effects but can generally be well tolerated for brief periods. The patient should be educated on these side effects, however, and should be instructed to stop taking the medication immediately if side effects occur. Routine use of oral systemic
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Cervical degenerative disk disease
steroids is not necessary but may prove useful in the more refractory cases. In this case, a tapering dose schedule over a period of 7 days can be used. Injections of local anesthetic and steroid into the cervical epidural space may provide some pain relief. This again is based on the premise that inflammation plays a significant role in the production of radicular symptoms. This procedure, however, requires considerable experience and technical competence and carries with it a risk of complications. Some authors have had limited success with this procedure, but we do not routinely use cervical epidural steroids. The prognosis for patients with an acute herniated cervical disk is generally very good. If patients are compliant with the rest and immobilization program as outlined, most are able to return to work within a period of 1 month, at least under light duty conditions. Indications for surgical intervention in the treatment of an acute herniated disk include persistent radicular pain unresponsive to at least 3 months of conservative therapy, progressive neurologic deficit, static neurologic deficit in the presence of radicular-type pain, and radiographic studies such as CT or MRI with a myelogram confirmatory of clinical signs and symptoms (Fig. 3d.5). Diskectomy for pain relief has been shown to be greater than 90% effective when performed for the proper diagnosis.
CERVICAL DEGENERATIVE DISK DISEASE Cervical degenerative disk disease can produce cervical spondylosis in isolation or in concert with a number of syndromes, including myelopathy, radiculopathy, myeloradiculopathy, and associated visceral or vascular encroachment. Radiculopathy secondary to spondylosis is not discussed separately because it does not significantly differ from radiculopathy secondary to acute herniated disk disease as previously described.
Spondylosis The human cervical spine has a high degree of mobility and flexibility. It has paid the price for this mobility with an almost universal propensity for degenerative change. Cadaveric studies have revealed that nearly everyone will demonstrate some degree of degenerative change in the cervical spine by age 55. Cervical spondylosis is a term used to describe the chronic process of degenerative changes that occur as part of natural aging. These include changes in the vertebral body, intervertebral disk, uncovertebral joints of Luschka, zygapophyseal joints, ligamentum flavum, dura, and soft tissues. The primary cause of cervical spondylosis appears to be agerelated changes that occur in the intervertebral disks, including loss of annulus fibrosus elasticity, desiccation of the nucleus pulposus, and narrowing of the disk space with or without associated disk rupture. Narrowing of the disk space creates excessive motion between vertebral segments, causing secondary changes such as osteophyte formation, facet joint and ligamentum flavum hypertrophy, inflammation of synovial joints, and possibly microfractures. Ultimately, spinal canal and lateral recess stenosis may result. These changes are seen in varying degrees in patients with spondylosis and to a lesser extent in asymptomatic
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JS
C5
A
B
Figure 3d.5 Magnetic resonance images of a 45-year-old man with unilateral C6 radiculopathy. (A) Midsagittal view showing more pathologic anatomy than a parasagittal view of the unaffected side (arrows). (B) Parasagittal view of the affected side showing hard disk pathology (arrow). (From Boden SD, Rothman RH, Wiesel SW, Laws ER, Boden SD: The aging spine: essentials of pathophysiology, diagnosis, and treatment. Philadelphia, 1991, WB Saunders.)
elderly individuals and can produce a variety of clinical signs and symptoms depending on the severity. However, not everyone has clinically symptomatic complaints. Friedenberg and Miller4 showed a lack of correlation between symptoms and degenerative changes seen on plain radiographs of the cervical spine. These changes become clinically significant only when directly related to symptoms. Historically, the typical patient with cervical spondylosis is over 40 years of age and has a complaint of neck ache. Referred pain patterns discussed above include shoulder pain, suboccipital referred pain, occipital headaches, intrascapular pain, anterior chest wall pain, or other nonspecific symptoms such as blurred vision and tinnitus. Physical examination of a patient with cervical spondylosis often reveals little in the way of objective clinical findings. Neurologic findings are generally normal in isolated spondylosis without radiculopathy or myelopathy. Some decrease in motion of the cervical spine may be evident. Point palpation may reveal some tenderness along the midline of the neck and in areas of referred pain. Plain radiographs are obtained primarily to rule out more serious causes of neck pain. Plain films in the anteroposterior, lateral, and oblique planes reveal varying degrees of change, including disk space narrowing, osteophyte formation, foraminal narrowing, facet degeneration, or instability patterns. Once again, these changes do not directly correlate with the presence or severity of clinical symptoms.
Treatment The mainstay of therapy for patients with cervical spondylosis is conservatism. In the presence of acute exacerbation of symptoms
against a background of chronic disease, rest and immobilization are generally beneficial. Aspirin or other nonsteroidal antiinflammatory medications may be helpful also for an acute exacerbation and may be needed on a chronic basis to abate symptoms. As previously described, trigger point injections may be of value also both diagnostically and therapeutically. A soft cervical orthosis may assist in resting and immobilizing the cervical spine. Cervical isometric exercises and changes in the patient’s daily activities such as work habits, sleeping positions, and automobile driving may be useful adjuvant therapies in the treatment of these chronic patients. In this patient population, the use of manipulative techniques and traction protocols should not be performed.
Spondylosis with myelopathy When the previously described degenerative changes of the cervical spine become so severe as to impinge on the spinal cord, a pathologic process termed myelopathy is produced. Spinal cord and nerve root compression produces myeloradiculopathy. Having been described already in detail in relation to acute herniated disk disease, radiculopathy is not addressed here. Those patients with developmental cervical stenosis are more prone to the development of spondylitic myelopathy at a younger age. Etiologic factors in the reduction of canal reserve volume include hypertrophy of the ligamentum flavum, facets, lamina, and dura with redundant annulus fibrosus; foraminal osteophyte compression of radicular vessels; vertebral osteophyte cord compression; tethering of the cord by dentate ligaments; and ossification of the posterior longitudinal ligament or ligamentum flavum.
Chapter 3d
A reduction in volume of the spinal canal can result in direct canal compression and intrinsic or extrinsic ischemia. Edward and LaRocca3 demonstrated that development of myelopathy with spondylosis is almost certain with canal diameters of less than 10 mm. Patients with canals 10-13 mm in diameter are at risk, and those with canals 13-17 mm are myelopathic prone. Myelopathy rarely develops with canal diameters greater than 17 mm. In addition to these static considerations, dynamic changes in the cervical spine may result in myelopathy. Penning and van der Zwaag described the pincer mechanism in 1966. In this mechanism, the spinal cord becomes compressed between the anterosuperior margin of the lamina of the inferior vertebrae and the posteroinferior osteophyte (i.e., hard disk disease) of the superior level. Flexion of the spine causes stretching of the cord over vertebral body osteophytes, with extension possibly resulting in retrolisthesis of one vertebral body on another or buckling of the hypertrophied ligamentum flavum. All these dynamic changes can cause compression of the cord as it passes through the cervical canal. Clinically, most patients are between 40 and 60 years of age when initially seen, with males affected more often. Myelopathy develops in fewer than 5% of patients with cervical spondylosis. Although a history of trauma may occasionally be given, the onset is more often insidious. Acute myelopathy generally reflects a central soft disk herniation producing a high-grade block. The natural history is one of deterioration initially, followed by a plateau in deficit lasting for several months. The exact clinical picture is variable, with a patchy distribution of deficits. This distribution depends on the number of levels involved and the severity of cord impingement at each level. Typically, patients have a gradual onset of numbness and paresthesias with associated weakness and clumsiness. Often, a history of difficulty writing is elicited. Lower extremity symptoms may precede those in the upper extremity and include gait disturbances, peculiar leg sensations, weakness, hyperreflexia, spasticity, and clonus. Upper extremity findings that may initially be unilateral often progress bilaterality. These include hyperreflexia, a brisk Hoffmann sign, and muscle atrophy, particularly of the hand intrinsics. Abnormalities in micturition are seen in approximately one third of cases and connote a more severe cord impingement. Sensory changes are a less reliable sign of myelopathy. Spinothalamic tract signs may be seen with disturbances in pain and temperature sensation in the upper extremities, thorax, or lumbar region. These may be characterized by a stocking-glove distribution. Dorsal column function can be affected with resultant vibratory and proprioceptive disturbances. Impingement on the dorsal division of the nerve root may produce unusual dermatomal sensory changes. In the event of a severe myelopathy, one of several spinal cord syndromes may develop. These include (1) Brown-Sequard syndrome with ipsilateral motor dysfunction, contralateral pain, and temperature dysfunction one to two levels below the motor involvement; (2) central cord syndrome with upper extremity involvement greater than lower extremity involvement; (3) transverse lesion syndrome, which occurs most commonly with involvement of the posterior columns, spinal thalamic tracts, and corticospinal tracts; (4) brachialgia cord syndrome with upper extremity radicular symptoms and long-tract signs; and (5) motor
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Rheumatoid arthritis
system syndrome with corticospinal tract involvement and weakness of both the upper and lower extremities. The differential diagnosis for patients with cervical spondylitic myelopathy includes such disorders as multiple sclerosis, amyotrophic lateral sclerosis, spinal cord tumors, syringomyelia, disk herniation, intracranial lesions, low-pressure hydrocephalus, and subacute combined degeneration. Each of these should be ruled out with appropriate history, physical examination, and diagnostic studies. Plain radiography in these patients generally demonstrates typical degenerative findings, including spinal canal narrowing by prominent posterior osteophytes, variable foraminal narrowing, disk space narrowing, facet joint arthrosis, and instability. MRI can demonstrate structural and parenchymal changes (Fig. 3d.6). The myelogram also is valuable in demonstrating the typical washboard appearance (Fig. 3d.7) with multiple anterior and posterior dye column defects. The posterior defects are produced by facet joint arthrosis and ligamentum flavum buckling.
Treatment Studies looking at the natural history of cervical spondylitic myelopathy are inconsistent and often difficult to compare because of the lack of a universal classification system. Some common factors, however, can be identified. The age at onset and duration of symptoms before the onset of treatment are prognostic factors. Increased age at diagnosis and delay in treatment for longer than 1 year indicates a poor prognosis. Most patients in these series had periods without progression, or plateau phases, interspersed with periods of rapid deterioration. Some patients had a steady progression of the disease with resultant severe disability. Conservative therapy rarely reverses the myelopathy, although in a patient who is a poor surgical candidate because of concomitant medical conditions, conservative measures such as immobilization and rest with a cervical orthosis are viable options. In general, however, management of patients with myelopathy requires surgical decompression of the spinal canal and prevention of further spinal cord impingement and vascular compromise. Progression of the myelopathy after surgical decompression is uncommon. Both anterior and posterior surgical procedures have been reported to lead to improvement in the myelopathy of patients with cervical spondylosis.
RHEUMATOID ARTHRITIS Approximately 2% to 3% of the general population is affected with rheumatoid arthritis. Of these, 86% show radiographic evidence of cervical spine disease, and 60% have clinical signs and symptoms of cervical spine involvement reflecting the erosive inflammatory changes characteristic of this systemic disease process. The clinical variable that is the most consistent indicator of cervical spine involvement is the presence of hand deformities.11 Involvement of the cervical spine consists of three distinct syndromes: atlantoaxial instability, basilar invagination, and subaxial instability. Although atlantoaxial instability is the most common of these syndromes, Ranawat et al12 showed that they tend to occur in combination. They found that 60% of patients had atlantoaxial instability, 16% had basilar invagination, and 60% had subaxial instability. Risk factors for the development
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Figure 3d.6 (A) A sagittal 500-ms TR/17-ms TE image in a patient who sustained a cervical extension injury. Note the disruption of the anterior longitudinal ligament at multiple levels (solid white arrows) and the traumatic disk herniations (open arrows). Pinching occurs at the C5-C6 level (black arrows). (B) A parasagittal 500-ms TR/17-ms TE image shows anterior longitudinal ligamentous disruption (arrows) and prevertebral soft tissue swelling. (C) The midline sagittal 2000-ms TR/30-ms TE 7-mm image demonstrates ligamentous disruption (white arrows), prevertebral edema (e), and pinching at C5-C6 (black arrows). The canal compromise appears more serious on this 7-mm sagittal image, most likely because of a partial volume effect from the lamina laterally. (D) A 2000-ms TR/60-ms TE midline sagittal image shows similar findings, again with prevertebral edema (e), ligamentous disruption (white arrows), and some increase in signal intensity of the spinal cord at the site of compression (black arrows). (E and F) 2000-ms TR/90- and 120-ms TE images with similar findings, although the increased signal intensity within the spinal cord secondary to edema is more obvious on those more T2-weighted scans. The absence of any significant focal areas of decreased signal intensity indicates a relative absence of intramedullary hemorrhage (contusion) and a more favorable prognosis. Despite the initially severe neurologic deficit, this patient eventually recovered significant function. (From Modic MT, Masaryk TJ, Ross JS: Magnetic resonance imaging of the spine, ed 2. St. Louis, 1994, Mosby Year Book.)
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3 4 5 6 B Figure 3d.7 (A) Lateral roentgenogram of a 43-year-old man with complaints of left shoulder pain, gait abnormality, and leg weakness. He had mild spondylotic changes and a congenitally narrow cervical canal (12 mm). (B) Lateral myelogram showing significant extradural defects at C3-C4, C4-C5, and C5-C6. (C) A computed tomography myelogram shows large uncovertebral spurs (arrows) plus soft disk material protruding at C3-C4. (D) Severe spinal cord flattening at C4-C5 from the disk and an osteophytic ridge. (From White AH, Schofferman JA: Spine care, vol. 2. St. Louis, 1995, Mosby Year Book.)
of atlantoaxial instability include prolonged systemic steroid use, long disease duration, older age, and erosive peripheral joint involvement. Patients with cervical spine involvement secondary to rheumatoid arthritis often have occipital neuralgia caused by compression of the greater occipital branch of C2. This gives the typical complaint of headaches when upright that is relieved by
recumbency. Range of motion may be limited, and crepitation or sensations of frank instability may be present, in which case Lhermitte’s sign may be elicited with motion. Neurologic changes can be variable and are often difficult to interpret in rheumatoid patients, who may have severe involvement of the upper and lower extremities. Physical examination should be performed very carefully to rule out upper motor neuron signs, such as
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hyperreflexia and spasticity, and the presence of abnormal reflexes, such as the Babinski and Hoffmann signs. Brainstem involvement by compression of the invaginated dens and/or associated pannus can result in symptoms of vertebrobasilar insufficiency. Other nonspecific findings may include the onset of bowel or bladder incontinence or retention, development of spasticity, and a change in ambulatory status. Evaluation of patients with any of these clinical symptoms should first begin with plain radiographs of the cervical spine. Common findings include osteopenia, facet erosion, disk space narrowing, and subluxation of the lower cervical spine (step ladder). Clinical management and operative indications can be defined by five radiographic measurements: (1) the anterior atlantodens interval, (2) the posterior atlantodens interval, (3) the McGregor line, (4) the Ranawat measurement, and (5) the Redlund-Johnell measurement10 (Fig. 3d.8). Basilar invagination occurs with upward migration of the odontoid process into the foramen magnum with resultant brainstem impingement. Radiographic evaluation includes a measurement of the distance from the tip of the odontoid to beyond the MacGregor line. This is seen on the lateral view of the cervical spine and represents a line drawn from the tip of the hard palate to the posterior base of the foramen magnum. Normally, the dens should not protrude more than 4.5 mm above this line. Protrusion more than 8 mm in females or 9.7 mm in males may be an indication for surgery. A CT may be helpful in determining radiographic landmarks, which tend to become more diffuse in the rheumatoid patient. Subaxial subluxations are also evaluated on dynamic flexion-extension views of the spine. Significant subluxation is defined as translation of one vertebral body on another of 3.5 mm or more or disk space angulation of 11 degrees or more.
Treatment Most of these patients can be managed conservatively despite the fact that cervical spine involvement may develop in a significant number. The mainstay of nonoperative therapy is a hard cervical orthosis (Philadelphia collar), which produces symptomatic relief without actually affecting the atlantoaxial interval. Medical treatment of these patients plays a crucial role in nonoperative management. Medications such as oral steroids, methotrexate, leflunomide, and other disease-modifying antirheumatic drugs are administered under the supervision of a rheumatologist.
Prognostically, these patients tend to do very well with conservative measures, and only a small percentage die of medullary compression from significant atlantoaxial disease. Atlantoaxial disease gradually worsens with time, with only 2% to 14% of patients exhibiting progressive neurologic symptoms. To summarize, surgical intervention should be considered in the presence of (1) more than 3.5 mm of mobile subaxial subluxation on flexion-extension views, (2) atlantoaxial subluxation greater than 8 mm in the presence of spinal cord compression on flexion-extension radiographs, or (3) cranial settling indicative of basilar invagination in the presence of radiographic evidence (MRI) of cord compression. Additionally, in the absence of these findings, the presence of a progressive neurologic deficit is a strong indication for surgical intervention.
HYPEREXTENSION INJURIES (WHIPLASH) Most hyperextension injuries to the cervical spine result from rear-end automobile accidents, which cause acceleration hyperextension injuries in the drivers of the struck cars. Falls and sports injuries contribute to the remainder of the hyperextension injuries. This injury has great economic considerations. The term whiplash injury was introduced by H. E. Crowe in 1928, and since that time it has become a major source of litigation potential. The pathophysiology behind a hyperextension injury involves the soft tissues of the neck region.9 Usually, the driver of the struck automobile is relaxed and unaware of the incipient collision. When struck from behind, the automobile accelerates forward acutely. If no headrest is present, the driver’s head is thrown back and the neck forced into hyperextension as the torso continues onward with the automobile. The sternocleidomastoid, scalenes, and longus coli muscles are extended beyond their elastic limit and are severely stretched or torn. Tears of the longus coli muscles may be associated with a concomitant tear of the sympathetic trunk and result in Homer syndrome. Further hyperextension may result in injury to the larynx or esophagus with subsequent hoarseness or difficulty in swallowing, respectively. Injury to the anterior longitudinal ligament may result in hematoma formation with cervical radiculitis or injury to the intervertebral disk. Furthermore, when the head is thrown backward, the jaw generally lags behind, resulting in injury to the temporomandibular joint as the jaw falls open. When the head recoils forward, the skull may strike the driver’s wheel or windshield, resulting in a head injury.
Figure 3d.8 (A) Measurement of anterior atlantodens interval and posterior atlantodens interval. (B) The Ranawat method for measurement of vertical setting. (C) The Redlund-Johnell method for measurement of vertical setting. (From Monsey RD: J Am Acad Orthop Surg 5:240-248, 1997.)
Chapter 3d
Hyperextension injuries in elderly patients with preexisting cervical spondylosis may acutely compress the spinal cord as the already limited spinal reserve volume is overcome. This cord compression can take the form of a frank paralysis or a central cord syndrome. Patients with a hyperextension injury are generally examined 12 to 24 hours after the initial traumatic event. It is at this point that the patient starts to feel stiffness in the neck and pain at the base of the neck made worse by motion. The pain becomes progressively worse, and eventually the slightest head or neck movement elicits severe pain. The anterior cervical musculature may be tender to palpation, and the patient may have hoarseness, dysphagia, or pain with chewing or opening the mouth. Pain may radiate into both shoulders and arms and upward into the base of the skull. Other pain patterns may include the anterior of the chest, interscapular region, and vertex of the skull. The potential for a closed-head injury even in the absence of visible head trauma should not escape the examiner. Concussion can occur secondary to mechanical deformation during the acceleration-deceleration phase of the injury. This may result in headache, photophobia, mild transient confusion, fatigue, tinnitus, or transient concentration abnormalities. Physical examination must be complete from head to toe so that other associated injuries are not overlooked. The potential for a “chance fracture” of the lumbar spine exists if the patient was wearing a lap seatbelt. The head should be examined for any evidence of a closed-head injury. A unilateral dilated pupil may suggest an injury to the sympathetic chain as it travels along the longus coli muscles with resultant Horner syndrome. It may also indicate significant intracranial pathology in a patient with an altered level of consciousness. Temporomandibular joint tenderness should be assessed as well as suboccipital tenderness, which may indicate that the head struck the top of the seat. A careful and thorough neurologic examination should be performed. Again, particular attention should be paid to elderly patients, who may have baseline spinal stenosis secondary to cervical spondylosis with resultant cord injury or central cord syndrome. If any objective neurologic deficit is identified, further diagnostic tests, including CT and/or MRI, are necessary. CT is better at providing bone detail, whereas MRI is better at demonstrating soft tissue disruption such as intervertebral disk protrusion. In most cases of hyperextension injury, only soft tissue disruption occurs. Plain radiographs should be obtained, however, to rule out unsuspected facet dislocations, facet fractures, odontoid fractures, or spinous process fractures. In most cases, these films are normal or may show some straightening of the cervical spine. As noted, other diagnostic studies such as a head CT should be obtained as the history and physical findings dictate.
Treatment Treatment involves primarily rest and immobilization. Rest consists of a soft cervical orthosis that assists in relieving muscle spasms and prevents quick movements of the head. Collar wear beyond 2 to 4 weeks should not be encouraged, because this may result in weakening of the neck musculature and, in turn,
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development of a long-term psychoneurosis. Strict bed rest may be necessary for 3 to 5 days if the symptoms are severe. Heat in the form of hot soaks or heating pads may be useful. Although narcotics should be avoided, medical therapy in the form of nonnarcotic analgesics, nonsteroidal antiinflammatory medications, and muscle relaxants is helpful. Activity should be restricted according to symptom severity. Characteristically, improvement should occur after 2 weeks of treatment as outlined earlier. If improvement does not occur, an additional 2 weeks of rest and immobilization should be prescribed with the addition of home cervical traction. Lowweight traction consisting of 7 to 10 pounds for 20 to 30 minutes per day generally gives symptomatic improvement. Persistence of symptoms past 4 weeks should alert the physician to search for another etiology. If headaches persist, a CT of the head should be obtained to rule out a closed-head injury. If arm or shoulder pain persists, CT of the spine and/or EMG should be performed. In general, symptoms should be resolving by 6 weeks, although complete resolution may take as long as 1 year.8 Persistence of symptoms beyond 6 weeks of severity equal in intensity to that in the initial period may alert the physician to secondary gain from pending litigation, and compensation neurosis should be suspected. Before assigning this diagnosis, the physician should certainly rule out any significant pathology by a careful history, physical examination, and appropriate diagnostic testing. The physician should not, however, over-treat the patient and encourage a retreat into a life of incapacitating neck pain. The point at which the patient is able to return to the work force depends on both the severity of the hyperextension injury and the type of work involved. Patients performing heavy manual labor may require 3 to 4 weeks of treatment before returning to work, whereas those in less demanding positions may be able to return after only 2 weeks. Limitations on the work performed should consist of no lifting of objects heavier than 50 pounds, no bending, and no prolonged periods of stooping. These restrictions should remain in effect for the first 3 weeks that the patient has returned to work. Depending on the severity of the injury, the prognosis is generally good for complete recovery. Occasionally, a 5% to 10% disability rating is appropriate in an honest patient in whom symptoms persist during hard manual labor.
CERVICAL SPINE TREATMENT ALGORITHM The goal for patients with neck pain is to obtain an accurate diagnosis and administer the correct therapy at the appropriate time. The previously presented clinical entities have been organized into a standardized approach,16 a graphic display of which is presented in the form of an algorithm in Figure 3d.9. The algorithm aids in establishing the proper diagnosis and guides in the delivery of the proper treatment. A summary of treatments categorized by pathology is listed in Table 3d.3. The algorithm begins with evaluation of those patients seen for neck pain with or without associated arm pain. Patients with a history of trauma and associated fractures and/or dislocations are excluded. The first task is a thorough medical history and physical examination to rule out the presence of cervical myelopathy, as discussed earlier.
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Figure 3d.9
Treatment options for disorders of the cervical spine
Cervical spine algorithm. (From Wiesel SW, et al: Neck pain. Charlottesville, VA, 1988, The Michie Company.)
Chapter 3d
Table 3d.3 Treatment options for cervical spine pathology Neck sprain
Spondylosis
Hyperextension/ whiplash Rest Soft orthosis Moist heat Activity modification Physical therapy NSAIDs Rheumatoid arthritis
Rest Soft orthosis Activity modification NSAIDs Muscle relaxants Trigger point injections Acute herniated disk Rest Soft orthosis NSAIDs Oral steroids Epidural injections ↓ Diskectomy
Rest Soft orthosis Activity modification Isometric exercises NSAIDs Trigger point injections Spondylosis with myclopathy Rest/immobilization (nonoperative candidate)
Hard orthosis Steroids/DMARDs
↓ Surgical decompression
↓ Surgical fusion
DMARDS, disease modifying antirheumatic drugs, NSAIDs, nonsteroidal antiinflammatory drugs.
If a myelopathic process is confirmed, surgical intervention should be considered in a timely fashion. The best results are obtained with only one- to two-motor unit involvement and relatively short duration of symptoms. Further studies, including myelography or MRI, should be performed to define precisely the neural compression. Adequate surgical decompression should then be performed. If cervical myelopathy is ruled out, most patients should then be started on a course of conservative management. Regardless of the etiology of the neck pain, all patients are treated equally in this regard. Initially, this nonoperative management consists primarily of immobilization and drug therapy. A well-fitted soft cervical collar should be worn for 24 hours per day to prevent awkward positioning and movements during sleep and while awake. In addition, antiinflammatory medications, analgesics, and muscle relaxants will improve patient comfort. Most patients will symptomatically improve with this protocol within approximately 10 days and should then start to be weaned over the next 2 to 3 weeks. Additionally, their level of activity should be gradually increased, and they should start a series of exercises aimed at strengthening the paravertebral musculature. If the condition remains unimproved, patients should continue full-time collar wear and pharmacologic management. If no significant improvement in symptoms is seen after 3 to 4 weeks, a trigger point injection at the point of maximum tenderness should be considered. This is performed with a combination of 10 mg of corticosteroid and 3 to 5 ml of 1% lidocaine. If this is likewise not successful at 4 to 5 weeks, a trial of home cervical traction may be considered. For patients with neck pain, a total period of 6 weeks of conservative management should be pursued. Most patients respond to this program and return within 2 months to their previous life-styles. If, on the other hand, the symptoms fail to resolve within 6 weeks of conservative therapy, the patients are
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then divided into two groups depending on whether neck or arm pain (brachialgia) is the predominant complaint. For those patients whose main complaint is neck pain and for whom conservative therapy for 6 weeks has failed, plain radiographs, including flexion-extension films, should be obtained. Several of these patients will have evidence of instability, the criteria for which include horizontal translation of one vertebra on another of 3.5 mm or an angular difference of 11 degrees between adjacent vertebrae. Most of these patients do well with nonoperative management consisting of education and bracing, but those who do not may require segmental spinal fusion. A second group of patients have changes characteristic of degenerative disease. Radiographic findings include osteophyte formation, loss of intervertebral disk height, narrowing of the neural foramina, and zygapophyseal joint osteoarthritis. As previously mentioned, degeneration of the cervical spine may be a normal part of the aging process. The difficulty arises in determining which of the degenerative changes are clinically significant. The most significant change has been found to be narrowing of the intervertebral disk height, particularly at C5-C6 and C6-C7. Treatment of these patients consists primarily of antiinflammatory agents, support braces, and trigger point injections. During quiet periods, isometric exercises should be used. Reexamination is necessary to monitor for the development of myelopathic symptoms or signs. Most patients who have normal plain films receive a preliminary diagnosis of neck strain. After failure to improve with conservative therapy, these patients should have a thorough medical evaluation and a bone scan to rule out infection, neoplasia, or inflammatory arthritis as the etiology of the neck pain. If this workup proves negative, they should then undergo psychosocial evaluation and receive treatment, if appropriate, for depression or substance dependence, both of which can frequently be found in patients with neck pain. If the psychosocial findings prove normal, the patient is considered to have a diagnosis of chronic neck pain. Treatment therefore consists of thorough education and support, detoxification from narcotics, and institution of an exercise program. Antidepressant agents may prove to be useful, and frequent reevaluations are necessary to avoid overlooking any serious pathologic process. Other large groups of patients in this algorithm are those in whom arm pain is the predominant symptom. The etiology of this pain may be either direct pressure from a herniated disk or inflammation about a nerve on hypertrophic bone (hard disk disease). Other causes of extrinsic compression of the vascular or nervous structures supplying the upper extremity, including pathologic processes of the chest and/or shoulder region, may imitate brachialgia also and must therefore be ruled out. A thorough history and physical examination, including an Adson test, shoulder examination, and Tinel’s test of the carpal, cubital, and ulnar tunnels, should be performed, with additional appropriate studies possible, based on the results. If an Adson test is positive, vascular studies and EMG should be performed to evaluate causes of thoracic outlet syndrome. Compression of the brachial plexus may occur secondary to vascular structures, cervical ribs, muscular or fibrous bands, or neoplastic processes. Additionally, an apical lung carcinoma can cause brachial plexus compression with or without Horner syndrome from sympathetic chain involvement (Pancoast tumor).
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If plain films of the chest and shoulder are negative and fail to reveal a source of extrinsic compression, EMG studies should be performed. If these indicate peripheral nerve compression, surgical decompression at the site should be performed. In the presence of radicular symptoms, a myelogram or MRI should be performed, and if the results are consistent with the neurologic deficit, history, and physical findings, surgical decompression of the nerve root should be undertaken because conservative treatment results in persistent symptoms. This algorithm is applicable to all patients with nonspecific neck or arm pain and provides a rational approach to the therapeutic and diagnostic sequence of events. The goal of this approach must always be to treat appropriately the etiology of the pain while avoiding unnecessary tests and therapeutic interventions and, most importantly, to minimize the chance of overlooking other serious pathologic processes.
REFERENCES 1.
2. 3. 4. 5. 6.
7.
8.
CONCLUSION
9. 10.
This chapter summarizes some of the major pathologic processes that affect the cervical spine. A detailed description of the anatomy and of the pathophysiology is provided to aid in the understanding of these clinical entities. In addition, the clinical workup of each disease process is discussed, covering the presenting signs and symptoms, corresponding physical examination, and pertinent diagnostic studies. A special emphasis is placed on the treatment of cervical spine disease, which is individualized for each pathologic process. Finally, a treatment algorithm is presented that provides a coherent clinical decision-making process combined with a standardized approach to treatment of cervical spine disease.
11. 12. 13. 14. 15. 16.
Boden SD, McCowin PR, Davis DO, Dina TS, Mark AS, Wiesel S: Abnormal magneticresonance scans of the cervical spine in asymptomatic subjects: a prospective investigation. J Bone Joint Surg 72(8):1178-1184, 1990. Dwyer A, Aprill C, Bogduk N: Cervical zygapophyseal joint pain patterns. I. A study in normal volunteers. Spine 15:453-457, 1990. Edward WC, LaRocca SH: The developmental segmental sagittal diameter in combined cervical and lumbar spondylosis. Spine 10:43-49, 1985. Friedenberg ZB, Miller WT: Degenerative disc disease of the cervical spine. J Bone Joint Surg 45A:1171-1178, 1963. Grubb SA, Kelly CK: Cervical discography: clinical implications of twelve years of experience. Spine 25:1382-1389, 2000. Henderson CM, Hennessy R, Shuey H: Posterolateral foraminotomy for an exclusive operative technique for cervical radiculopathy: a review of 846 consecutively operated cases. J Neurosurg 13:504-512, 1983. Kang JD, Stefanovic-Racic M, Mcintyre LA, Georgescu HI, Evans CH: Toward a biochemical understanding of human intervertebral disc degeneration and herniation: contributions of nitric oxide, interleukins, prostaglandin E2 and matrix-metallo-proteinases. Spine 22:1065-1073, 1997. McNab I: Acceleration injuries of the cervical spine. J Bone Joint Surg 46A:1797-1799, 1964. McNab I: The whiplash syndrome. Orthop Clin North Am 2:289-403, 1971. Monsey RD: Rheumatoid arthritis of the cervical spine. J Am Acad Orthop Surg 5:240-248, 1997. Oda T, Fujiwara K, Yonenobu K, Azuma B, Ochi T: Natural course of cervical spine lesions in rheumatoid arthritis. Spine 20:1128-1135, 1995. Ranawat CS, O’Leary P, Pellici P, Tsairis P, Marchisello P, Dorr L: Cervical spine fusion in rheumatoid arthritis. J Bone Joint Surg 61A:1003-1010, 1979. Rothman RH, Marvel JP: The acute cervical disc. Clin Orthop 109:59-68, 1975. Rothman RH, Marvel JP: The spine, ed 4. Philadelphia, 1999, WB Saunders. Stookey B: Compression of spinal cord and nerve roots by herniation of nucleus pulposus in the cervical region. Arch Surg 40:417-432, 1940. Wiesel S: Neck pain, ed 2. Charlottesville, VA, 1992, The Michie Company.
CHAPTER
3e
Workplace Adaptation Thomas J. Armstrong
The deviation of neck, shoulder, and elbow postures from neutral positions is associated with adverse health effects such as fatigue and chronic muscle, tendon, and nerve disorders. The effects of these disorders range from minor discomfort and degraded performance to disability. Available data suggest that the time at onset of adverse effects decreases with increasing exertion duration, frequency, and force. This does not mean, however, that some postures can or should be maintained indefinitely without interruption. Also, it does not mean that brief exposures to extreme postures are not desirable. The relationship between certain work activities and adverse health effects is referred to as the “dose-response” relationship (see Chapter 1). The dose-response relationship provides insight into how work can be designed to minimize the risk of possible adverse health effects or to facilitate the return to work of persons in whom an adverse effect may have developed. Unfortunately, sufficient data are not yet available to specify job designs that provide a specific level of risk. For example, it cannot be said how many times a group of workers can exert a horizontal force of 50 N to engage the bit of a powered screwdriver weighing 15 N at an elevation of 1.5 m before unacceptable health effects would develop in a given fraction of them. It is extremely important that the work equipment and procedures be evaluated at all stages of design and implementation. Workplace adaptation entails three basic steps14: 1. Evaluation of the proposed or existing job; 2. Specification of adaptations; 3. Evaluation of adaptations. It may be necessary to repeat one or more of these steps one or more times to achieve a desired level of control.
EVALUATION Evaluation entails documentation of the process, equipment, procedures, and environment and assessment of stressors, including posture, force, duration, and frequency.1,7 The documentation is performed from available job descriptions, time studies, workplace inspections and measurements, equipment specifications, and interviews with workers and supervisors. This information is then used to identify stressful postures and forces necessary to reach, hold, and use work objects and the duration and frequency of these exertions. Tables 3e.1 and 3e.2 and Figures 3e.1 and 3e.2 illustrate evaluation summaries of two jobs: claims processor and assembler. An assessment of stressful postures and forces entails examining each step of the operation for extreme neck, shoulder, and elbow
postures and forces (Fig. 3e.3). These elements should be recorded along with their duration, frequency, and cause. For example, in the claims processor job described in Table 3e.1, extreme reaches to the workers’ side are required 80 times per day to get unfinished files and 80 times per day to put aside finished files. Workers must reach over the files and rotate their forearms to use the keyboard 6 hours per shift. In the assembler job described in Table 3e.2, the workers must reach for parts beside and behind them 2400 times per 8-hour shift; they must elevate their elbow above shoulder height and rotate their forearm 14,400 times per shift, and so forth. The analysis should also include an inspection of infrequent or irregular elements. For example, in the claims processor job (Table 3e.1), 3 of 10 claims are set aside to await additional information that must be retrieved by telephone. In the assembler job (Table 3e.2), 1 of 12 screws is defective and requires additional movements and time to replace. By their very nature, it may be hard to identify irregular elements from existing job descriptions or observations. Often they are identified via worker and supervisor interviews.
SPECIFICATION OF ADAPTATIONS The causes of the physical stressors should be apparent from the work evaluation. The tabulation of stressors and their causes illustrated in Tables 3e.1 and 3e.2 provide a systematic format for developing possible adaptations. This format also provides insight into how the overall stressfulness of the job is affected by the proposed control measures and how one adaptation may affect other stressors. For example, in Table 3e.1 it can be seen that the claims processors are exposed to 2 hours of a stressful shoulder-neck posture per day to hold the phone handset. It can also be seen that a headset or a bracket attached to the handset could reduce this exposure. Yet another adaptation might be passing uncompleted files to another worker who does all the phoning; however, this solution could result in increased keyboard times and other undesirable effects. Reaching for documents is associated with cart location and design. It follows that locating the carts close to the workers’ side and modifying them with a fold-down side would reduce reaching. Because these reaches occur an average of only once every 3 minutes, it can be argued that this work element is by itself unlikely to produce adverse health effects; however, it can also be argued that when combined with other factors, this reaching could result in an adverse effect or could aggravate an existing case. An analysis of the low cost associated with parking the carts close to the workers versus the possible cost of medical treatment and lost work for disabled workers would support locating carts close to the workers. Such an analysis would probably also support a modification of the cart with drop sides. Workplace adaptations may involve modification of ● Work processes; ● Work standards; ● Design of methods; ● Workplace layout; ● Equipment; ● Training.
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Table 3e.1 Sample documentation and analysis of “claims processor” job for identifying and controlling shoulder and neck stressors TITLE Claims processor STANDARD Complete 80 claims per day EQUIPMENT Computer, keyboard, 13-inch color monitor and claim processor software Desk Staple remover Stapler Telephone with handset Adjustable-height chair Carts for holding files METHOD 1. Get file from cart—place on lap in front of keyboard 2. Remove staples 3. Sort documents 4. Perform keystrokes to open file 5. Perform keystrokes to update file 6. Call for information as necessary—3 calls per 10 claims 7. Perform keystrokes to close file 8. Staple documents 9. Stamp and date file 10. Place finished file in cart 11. Note: occasionally claims processor cannot finish file and will set it aside at the front of desk until someone calls back with necessary information MATERIALS Files weighing 5-50 N ENVIRONMENT Inside overhead fluorescent lights with diffusers
Work processes refer to the technologies used for completing the work objectives. In the claims processor example (Table 3e.1), the technologies are keyboards and telephones. Alternative technologies include scanners and electronic mail. In the assembler example (Table 3e.2), the technologies include threaded fasteners; alternative technologies include clips and adhesives. Work standards refer to the quantity and quality of work produced in a given time. In the claims processor example, the standard is 80 claims per 8-hour shift; in the assembler example, the standard is 2400 motor assemblies per 8-hour shift. The work standard is an important factor in how many times per day workers must assume a given posture or exert a given force. Reducing work standards is generally considered an adaptation of last resort; however, it may be shown that the lost productivity is more than offset by the reduced cost of medical treatment and lost work for a disabled worker. Work methods refer to the procedures or sequence of movements used to perform the job. In the assembler example, the method entails getting motors from a bin, placing them on the line, and driving six screws. A methods change to reduce reaching would be to unload one corner of the bin and then rotate it 90 degrees so that the workers are always working from the
WORKER Skilled male and female keyboard operators Fifth percentile female to 95th percentile male stature ERGONOMIC STRESSORS Stressor POSTURE Reaching for unfinished files (80 times per shift) Reaching over file on lap to use keyboard (6 hr/shift) Looking down at file (4 hr/shift) Extending the neck to see monitor through bifocals (2 hr/shift) Reaching to put aside finished files (80 times per shift) Inward forearm rotation and wrist deviation to position hands over keyboard (6 hr/shift) Holding phone between neck and shoulder (2 hr/shift) Proposed Adaptation Provide access for carts so that it can be positioned to minimize reaching Provide adjustable tray to hold file above keyboard Provide corrective lenses that do not require worker to extend neck Investigate variable geometry keyboard to reduce forearm rotation Provide headset for phone Investigate adjustable keyboard holder Investigate wrist rest Provide adjustable monitor holder Stressor FORCE Lifting files weighing up to 50 N from cart to lap (80 times per shift) and from lap to cart (80 times/shift) Proposed Adaptation Provide access for cart so that it can be positioned to minimize reaching Investigate drop side for cart
corner closest to them. A methods change may also require an equipment change and worker training. Workplace layout refers to the position of equipment and work objects in the workplace. In the claims processor example, the workplace layout includes the position in space of the carts with files, the keyboard, the monitor, the phone, and the active file with respect to the worker. Adaptations include repositioning the carts to reduce reaching, adding equipment to allow repositioning of the keyboard, and supplying adjustable document and monitor holders. In the assembly example, adaptations include equipment to reposition the parts bin and adjustment of the suspender so that the tool can be positioned to minimize reaching. Anthropometric data may be used to estimate reach distances.3,11 Average link length proportions can be used with population stature data to estimate vertical, horizontal, and lateral reach limits (Fig. 3e.4). Caution should be used in interpreting reach predictions based on link length data. A reach distance based on average proportions and a given percentile stature may correspond to a different percentile reach. Work locations should be made as adjustable as possible to accommodate individuals and should be tested with user trials.8,12,14 Reach data for U.S. civilian populations are available from U.S. National Health surveys.13
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Table 3e.2 Sample documentation and analysis of “assembler” job for identifying and controlling shoulder and neck stressors TITLE Assembler STANDARD Assemble 2400 motor assemblies per 8-hour shift EQUIPMENT Assembly line (1 m above floor level) Power screwdriver suspended above line Rack and bin for holding parts METHOD 1. Get motor assembly from bin (weight, 40 N) and position on subassembly 2. Get handful of screws with one hand 3. Get screwdriver with other hand 4. Position screw in screwdriver × 6 5. Drive screw (1 of 12 screws is defective and must be backed out and replaced) ENVIRONMENT Inside overhead fluorescent lights with diffusers WORKER Males and females Fifth percentile female to 95th percentile male stature ERGONOMIC STRESSORS Stressor POSTURE Reaching for motor assemblies located to side and behind worker (300 times/hr)
Equipment refers to hardware such as tools to drive fasteners or shape and smooth surfaces, containers, jigs, fixtures for holding parts, and seating to support the worker. A proposed adaptation in the claims processor example includes modification of the cart; adjustable holders for the keyboard, monitor, and files; and a headset for the phone. In the assembly example, equipment changes include an in-line screwdriver with articulating arm, an indexing assembly line, and a turntable for the parts bin. Training entails instructing workers on the hows and whys of arranging and performing their work. In the claims processor example, it should be explained to the workers where they should position the carts and why this is necessary to prevent possible shoulder problems. Follow-up training and evaluations should be performed to determine whether the workers understand and follow the specified procedures. If procedures are not followed, further evaluations should be performed to determine why they are not followed. The design of adaptations should draw on all available resources. Available resources vary from one situation to another, depending on the size and type of industry. Possible resources include ● Job designers, such as engineers, facilities people, and setup people; ● Safety and health personnel, such as doctors, nurses, industrial hygienists, and safety personnel; ● Supervisors;
Reaching for parts located to side and behind worker (300 times/hr) Reaching for screwdriver located overhead (300 times/hr) Driving 1800 screws/hr with pistol-shaped driver requires elevation of elbow and forearm rotation Reaching upstream and downstream to keep up with production line (50% of time, but 90% of time when bad screws are encountered) Proposed Adaptation Position trays close to worker and production line to minimize reaching Unload trays one corner at a time and then rotate tray 90 degrees to minimize reaching Adjust tool suspender to minimize tension and locate tool as close as possible to point of use Investigate use of in-line tool with articulating arm to control torque Investigate indexing production line in which work object stops until released by worker Position work object as close to edge of production line as possible to minimize reaching Investigate quality control program to avoid defective screws that take extra motions to try and to reject Stressor FORCE Lifting motor assemblies weighing 40 N from bin (300 times/hr) Pulling down power tool into work position (300 times/hr) Proposed Adaptation Investigate small hoist or air balancers to facilitate transferring motors to line (See above recommendations for tool suspender)
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Workers or work representatives; Purchasing; Sales and technical representatives from suppliers; Catalogs, brochures, and technical specifications; Scientific papers, books, and magazines.
In general, the team approach is the most effective way to mobilize the resources necessary to develop and implement workplace adaptations. On occasion, however, the problems are conspicuous and the solution is clear so organizing a special team is not merited. Development of adaptation is not an exact process. Consequently, all adaptations should be evaluated to ascertain their effectiveness.
EVALUATION OF ADAPTATIONS Ideally, adaptations should be evaluated in terms of their effects on upper limb disorders. Unfortunately, such evaluations are difficult. Upper limb disorders develop over long periods of time. To determine the effect of a given adaptation on the occurrence of disorders would require identification of a group of several hundred workers, implementation of the adaptation in a random subset of these people, and some kind of comparison adaptation in the others.6 The population would then have to be tracked for
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Figure 3e.1 (A) Illustration of a claims processor job. (B) Major stresses include reaching for documents, holding the telephone, reaching for the keyboard, looking down at documents, and reaching to get and put aside documents. (C) Possible claims processor job interventions include an adjustable document holder (a), adjustable monitor holder (b), adjustable keyboard holder (c), drop-side cart (d), headset for phone (e), and optically correct glasses (f).
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1 or more years. Unfortunately, such studies are extremely difficult and expensive. It is difficult to find large groups in which adaptations can be randomly assigned. Work activities are generally dictated by production schedules that may cause the work population to shrink or swell. In addition, non–health-related factors may cause a turnover in the work population. Although evaluation of health patterns is an important means of identifying workers and jobs that merit further evaluation and assessing an overall program, in most cases it provides only limited feedback about specific adaptations. Adaptations can be evaluated by using the same methods that were used for the initial job evaluations. This analysis should begin as the adaptations are developed on paper and continue through the prototype, pilot testing, and implementation phases.8 In some cases it may be possible to identify and evaluate other jobs at that work site or other work sites where the proposed
adaptations have already been implemented. In other cases it may be necessary to develop prototypes and conduct pilot testing on a small number of the proposed interventions. Worker feedback can be obtained through interviews; however, care should be taken to avoid leading questions.9 The questions should be structured in such a way as to provide guidance on how to enhance the adaptation. For example, one of the proposed adaptations for the assembly job was the use of another tool and locating it to minimize reaching. In this case, workers could be permitted to try several tools and then rank them in order of preference. They could also be asked to try the tools at several locations and rate them on a scale of 0 to 10 where 0 is “too low,” 5 is “just right,” and 10 is “too high.”2,12 Even though these measures do not ensure that future shoulder, neck, or elbow problems will not develop, they do provide a basis for selecting a work configuration that minimizes stress on the worker.
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Figure 3e.2 (A) Work station layout for an assembler. (B) Proposed interventions for the assembler example include using a narrower conveyor to reduce reaching over line “dead space,” using an indexing line so that the worker does not have to “chase” the assemblies, and using a smaller box of parts mounted on a turntable to reduce reaching to the side and behind the worker.
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Neck deviation
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Figure 3e.3 Shoulder and neck stressors include extreme neck, shoulder, and elbow postures and force. (Modified from Armstrong TJ: Hand Clin 553-565, 1986.)
Discomfort patterns can also be used to evaluate work designs before and after they are implemented.4,5,10 Workers are shown pictures of the body and asked to identify and rate areas of discomfort. Discomfort patterns provide information about many parts of the body, as well as those parts likely to be affected by the stress of concern and the proposed adaptation. Often, the variation from within and between workers is considerable, and rigorous statistical conclusions may not be possible.
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The available data are not yet sufficient to develop design specifications that can be used to achieve a given level of risk of neck, shoulder, and elbow disorders; however, the data do provide insight into some of the things that can be done to reduce risk. Control of disorders entails three basic steps: (1) evaluation of
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Figure 3e.4 (A) Average link length proportions can be used with population stature data to estimate vertical, horizontal, and lateral reach limits. (B) The outer arc represents maximum reach without bending. The inner arc represents maximum reach without bending and not flexing the shoulder more than 30 degrees to minimize loads on shoulder tissues.
Chapter 3e
the job to determine the frequency, duration, and cause of extreme reaches and forces; (2) specification of adaptations; and (3) evaluation of the adaptations. It may be necessary to repeat these steps before the desired level of control is achieved. Development of workplace adaptations should be integrated into an ongoing program that includes health surveillance, job surveys, evaluation of affected workers and jobs, medical management, training, and a team approach with participation from all levels of the organization.
5.
6. 7.
8.
9. 10.
REFERENCES
11. 12.
1. Armstrong TJ: Ergonomics and cumulative trauma disorders. Hand Clin 2(3):553-565, 1986. 2. Armstrong TJ, Punnett L, Ketner P: Subjective worker assessments of hand tools used in automobile assembly. Am Ind Hyg Assoc J 51(12):639-645, 1989. 3. Armstrong TJ, et al: Repetitive trauma disorders: job evaluation and design. Hum Factors 28(3):325-336, 1986. 4. Corlett EN, Bishop RP: The ergonomics of spot welders. Appl Ergonom Mar:23-31, 1978.
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References
Harms-Ringdahl K: On assessment of shoulder exercise and load-elicited pain in the cervical spine. Biomechanical analysis of load-EMG-methodological studies of pain provoked by extreme position. Scand J Rehab Med Suppl 14:1-40, 1986. Hennekens CH, Buring JE, Mayrent SL, eds: Epidemiology in medicine. Boston, 1987, Little, Brown. Keyserling WM, Armstrong TJ, Punnett L: Ergonomic job analysis: a structured approach for identifying risk factors associated with overexertion injuries and disorders. Appl Occup Environ Hyg 6(5):353-363, 1991. McClelland I: Product assessment and user trials. In JR Wilson, EN Corlett, eds: Evaluation of human work: a practical ergonomics methodology. New York, 1990, Taylor & Francis, pp. 218-247. McCormick E: Job and task analysis. In G Salvendy, ed: Handbook of industrial engineering. New York, 1982, John Wiley & Sons, pp. 2.4.1-2.4.21. Saldana N, et al: A computerized method for assessment of musculoskeletal discomfort in the workforce: a tool for surveillance. Ergonomics 37(6):1097-1112, 1994. Ulin SS, Armstrong TJ, Radwin RG: Use of computer aided drafting for analysis and control of posture in manual work. Appl Ergonom 21(2):143-151, 1990. Ulin SS, et al: Effect of tool shape and work location on perceived exertion for work on horizontal surfaces. Am Ind Hyg Assoc J 54(7):383-391, 1993. U.S. Department of Health, Education and Welfare: Weight and height of adults 18-74 years of age: United States, 1971-1974. Vital Health Stat 11(211), Hyattsville, MD, 1979, National Center for Health Statistics. Wilson JR: A framework and a context for ergonomics methodology. In JR Wilson, EN Corlett, eds: Evaluation of human work: a practical ergonomics methodology. London, 1990, Taylor & Francis, p. 6.
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Lower Back
4
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4a
Epidemiology: Incidence, Prevalence, and Risk Factors Michele Crites Battié, Tapio Videman, and Douglas Gross
The high prevalence and social and economic impact of low back pain and related disability are well recognized. Low back pain is one of four musculoskeletal conditions specifically targeted by the Bone and Joint Decade (2000-2010) initiative endorsed by the World Health Organization.15,106 Related to the workplace, back injury claims comprise the most expensive category of industrial injuries40,65 and are one of the most common causes of disability in adults under 45 years of age.24,90 In response to this problem, many workplace programs and medical services have been designed to prevent back problems or to minimize their negative consequences. Limited progress has been made, however, in alleviating this common condition and its consequences. When the underlying condition and risk factors for an ailment are understood, prevention and treatment strategies can be rationally based and well directed. In such situations, interventions are likely to be successful. Unfortunately, medical science still lacks information sufficient to guide the prevention and treatment of common back pain. Epidemiologic studies have sought to gain information that could be helpful in guiding these efforts. Epidemiology generally refers to the study of occurrence rates of diseases and especially factors associated with disease occurrence or nonoccurrence. A primary goal of such studies is to obtain information about the disease cause. However, challenges of the most basic nature have hindered epidemiologic studies of back problems.
CHALLENGES FACING EPIDEMIOLOGIC STUDIES OF BACK PAIN PROBLEMS Definition of the problem A central challenge of epidemiologic studies of back pain problems is that in the vast majority of cases the underlying pathology or condition is unknown.29,89 Current clinical examination methods rarely identify the underlying pathology of either acute or recurrent back pain in the absence of major trauma. Despite this reality, there is a tendency to approach back pain as though it were a specific disease or injury state. Miettinen and Caro67 cautioned that epidemiologic studies based solely on a complaint have limited value and that inferences to pathology can be misleading. A complaint is a voluntary behavior and as such can be influenced by a variety of factors other than physical pathology. Further problems encountered in studying any type of pain
include defining and quantifying the pain experience and controlling the effects of individual and cultural factors on pain perception and interpretation. Studies can be complicated also by uncertain reliability in a person’s recall of symptoms and by variations in how researchers define their presence.83 Back pain problems, moreover, are identified through numerous different reporting systems, primarily health surveys and symptom complaints noted in clinical or workplace settings. In North America, for example, in contrast to some other industrialized countries, pain in the workplace becomes known or registered through the filing of an incident report or workers’ compensation claim, and back pain is labeled a “back injury.” Taylor91 described a complex chain of events that leads to the production of industrial insurance and sickness data and makes it clear that the occurrence of back pain incidents registered in the industrial setting cannot be equated to the occurrence of morbidity. Failure to distinguish between studies of different back-related outcomes such as spine pathology, back symptom complaints, industrial injury claims, absenteeism, and long-term disability may lead to misleading generalizations and inaccurate conclusions. Along with different low back pain problem case definitions themselves are the influences and potential biases of the systems through which they are registered. An example of the potentially large effect of health system differences has been provided by Cherkin et al,23 who compared rates of back surgery in 11 developed countries and examined the association between these rates and the number of neurologic and orthopedic surgeons per capita. They found that the rate of back surgery was at least 40% greater in the United States than in any of the other countries investigated and more than four to five times that of England and Scotland. They also found that the rate of back surgery was positively correlated with the number of surgeons per capita (Fig. 4a.1).
Assessment of occupational and other relevant exposures In addition to the challenges posed by definitions, influences, and biases involved in back pain are the methodologic challenges of measuring occupational and other relevant exposures. Occupational exposures that appear frequently on lists of suspected risk factors are vehicular vibration and physical loading involving heavy lifting, bending, twisting, and sustained nonneutral postures. Virtually all inhabitants of developed countries are exposed to these factors during leisure time and work. Exposure is therefore a matter of degree and requires reliable valid methods of measurement. Unfortunately, practical tools to identify and quantify the different exposures in epidemiologic studies of large populations are not fully developed. Further complicating measurement is that for many outcomes such as structural changes of the spine, data are needed on lifetime loading rather than simply on current conditions. Most studies have used the job title as an indicator of occupational loading. This simple method of estimating occupational exposure can be highly inaccurate. The activities and environments of persons with similar job titles can vary substantially, and the loading profiles of workers who remain in one occupation for many years can change greatly. Moreover, most persons
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1.2 Back surgery rate (as compared to the United States)
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hold several different types of jobs during their working years, and their current positions may poorly reflect the physical loading experienced over their working lives. It has also been shown that workers in sedentary jobs tend to engage in more physically loading leisure-time activities than do workers with physically heavy jobs, which can confound attempts to investigate the effects of occupational loading.50 Conceptually, studies designed with the aim of understanding the effects of physical loading on back pain problems should be assessing total loading exposures both within and outside the work environment. Such studies are very seldom performed. Identifying factors associated with risk can give clues about causation, but an understanding of the basis for associations is required to formulate optimal prevention strategies. Leino58 showed that greater exercise activity was associated with fewer back symptom reports and back findings, for example, and Videman et al95 found that former elite athletes had significantly fewer back pain complaints than did nonathletes. If exercise has a protective effect and decreases the risk of back symptoms or spine pathology, then exercise participation could be expected to help prevent back pain. Exercise is also a marker for other healthy life-style behaviors, as well as higher education, higher life satisfaction, and lower occupational physical demands and psychosocial problems,85 all of which can affect back pain reporting. Because physical loading from certain forms of exercise and sports can increase spine pathology, exercise itself may not be directly beneficial and may even have some harmful effects on the spine, so that the apparent benefits are produced instead by factors not associated with exercise. If this were the case and exercise were only a risk indicator, exercise without other changes in life-style would be unlikely to decrease back troubles. Before interventions are planned, it would be important to sort out whether exercise is a beneficial factor or only an indicator of “healthier” life conditions. An odd paradox exists in perceptions of the effects of physical loading at work and at leisure. Physical loading associated with work and with leisure or sport activity share many dimensions
such as frequency, intensity, and duration, yet adaptation to loading, which is an expected result of regular exercise, receives little attention in studies of occupational loading. It is often stated that one reason for disability is that work demands exceed the capacity of the worker. The level of physical demands over prior months, however, is a primary determinant of individual capacity, which should include an adaptation of strength to routine daily work demands, as is the case with exercise training. Yet perhaps the greatest challenge in studies of the association between workplace exposures and back pain incidents and “injury” claims in the developed countries of the world is the injury model commonly used to explain the presence of back pain. Under the injury model, occupational physical loading exposures are believed to be primarily responsible for damage to the back and related pain. This belief naturally leads to greater attribution of symptoms to occupational exposures as workers search for possible causes of their problem. Attributing back pain to work activities may be further enhanced within a workers’ compensation system that offers clear benefits to causation lying with work. These inherent problems to studying back pain reporting in the workplace and its association with work activities greatly complicate, and in some cases may invalidate, study findings and their interpretation.
Causation versus exacerbation Another unresolved issue is that of back pain causation versus exacerbation. Certain occupational exposures, like heavy materials handling in bent and twisted postures, awkward sustained postures, or other forms of physical loading, play a role in the conditions underlying back symptoms that is not well understood. Whether physical loading contributes to the pathology underlying common back pain or simply exacerbates symptoms from an already present underlying condition is a matter of current controversy.
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Incidence and prevalence
high estimates, whereas low back pain that is defined as prolonged or disabling yield estimates toward the lower end of the range. What is clear is that back pain problems are ubiquitous in the general adult population. Work-related low back pain must be viewed against this high baseline. Whether or not a back “injury” has occurred at the workplace, back pain among workers is common, and many believe that their work is to blame. This is a natural and expected consequence of beliefs fostered by the injury model that back pain problems are the result of structural damage caused by physical demands. Further complicating the determination of occurrence rates is the recognition that back pain cannot be neatly categorized as acute or chronic. Instead, it is a fluctuating condition characterized by recurrences or exacerbations of varying severity and pain-free periods.103 In many cases an underlying condition appears to influence propensity for symptoms and occasional flare-ups loosely related to a variety of individual and environmental factors. This recurrent variable nature of back pain within individuals commonly leads to misclassification of the presence or absence of contributing conditions and influences occurrence rates and observed associations with suspected risk factors. Also important to the incidence and prevalence of low back pain reporting in the workplace are significant overall trends in industrial injury reporting. The mix of industrial injury claims has changed dramatically over past decades, with increasing dominance of back and other ill-defined musculoskeletal complaints over traumatic accident-induced injuries. Ostry78 clearly depicted this trend in a summary of short-term work loss claims from 1952 to 1996 in British Columbia. He presented the relative number of claims attributable to strains, which includes the categories of back strain, overexertion, and other strains and sprains, as compared with claims for impact (falls, slips, blows from objects, and so forth) and other miscellaneous injuries (Fig. 4a.2). During the years studied, a dramatic decline occurred in the proportion
Some evidence suggests that routine physical loading exposures, such as seen in occupations with heavy physical demands, may have a modest role in influencing underlying pathology and a role in exacerbating such pathology. Videman et al99 controlled for spine pathology and found that a history of back symptoms was correlated with physical loading. This finding supports the belief that loading exacerbates symptoms from existing conditions. The same study found that annular tears were more commonly found in subjects who engaged in occupations involving heavy physical loading, which suggests that it can lead also to increased risk of some structural failures. The role of occupational loading in degenerative changes and pathology, however, appears to be considerably less than previously thought.
INCIDENCE AND PREVALENCE As mentioned previously, there are no standard definitions for determining the presence or absence of back pain problems in the general population; instead, various definitions and methods for collecting such data are used. This leads to wide variations in prevalence and incidence estimates. A systematic review of the scientific literature from 1966 to 1998 presenting data on the prevalence of low back pain yielded point prevalence estimates from 12% to 33%, 1-year prevalence estimates from 22% to 65%, and lifetime prevalence estimates from 11% to 84%.102 Another review of the literature on low back pain prevalence estimated the point prevalence specifically in North America at 5.6%, but similarly broad ranges were noted in prevalence estimates as in the aforementioned review.63 These wide ranges are influenced by many factors, not the least of which is the definition of low back pain used in terms of pain severity, duration, and associated disability. Responses to such questions as “Have you ever had low back pain?” result in
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of impact injuries from over 80% of all injury claims in the late 1960s to slightly over 30% in 1996. Conversely, claims for strains rose from approximately 10% of all injury claims to 50%. Overall, in recent years occupational injury and illness rates in North America have shown a downward trend. The U.S. Survey of Occupational Injuries and Illnesses, generated by employer workplace incident logs, revealed a decline in nonfatal injuries in private industry from a high of 9.2 cases per 100 full-time workers in 1978 and 1979 to a low of 6.6 cases per 100 full-time workers in 1997, the last year for which data were analyzed.30 Similar trends were observed in Ontario, Canada from 1993 to 1998, where a 29% reduction in lost-time compensation claims was seen.72 The reasons for the decline are unclear. It has been speculated that it could be due to more effective prevention or treatment programs that influenced incidence or time loss, greater reluctance by employees or employers to report incidents, or changes in criteria for the diagnosing of some of these conditions by health care providers.12 The reduction may be due also to shifts in dominant industries and more generalized economic, social, cultural, or legislative trends that have affected injury reporting. Of the approximately 5.7 million injuries reported in 1997, representing 93% of all injuries and illnesses documented in employer records, however, the category of “strains, sprains, and tears” accounted for a disproportionately large share of cases with days away from work. Nearly half of these involved the back.30 Looking specifically at low back pain claims and associated disability and costs in North America, a downward trend has been noted since the late 1980s. Using a large sample of claims from the privately insured U.S. workers’ compensation market, Hashemi et al44 examined length of disability for low back pain claims and associated costs during the period of 1988 to 1996. As in previous studies,88 the distribution in terms of disability and costs was highly skewed. Depending on the year, 4.6-8.8% of claims with a disability duration lasting over 1 year accounted for 78-90% of the total disability days and 65-85% of the claims costs. Over the study period from 1988 to 1996, the mean length of disability decreased by 61%, whereas the mean and median cost per claim decreased by 41% and 20% respectively, suggesting that the most influential changes occurred through a reduction in long-term disability claims. Concurrently, a 34% decrease in the annual low back pain claim rate was reported in the United States from Bureau of Labor and Statistics data between 1987 and 1995, although it was noted that the trend was not monotonic. There was a sharper decrease in costs, one of 58%. Yet in 1995 the rate of low back claims in the United States was 1.8 per 100 employees, still representing a major health problem in the workers’ compensation system.71 These changes in back incident and claims rates seem to be a part of the larger trend for declines in all work-related injury and illness reporting. In Washington state, for example, there was a decrease of approximately 24% in the incidence rate of back claims from 1989 to 1996 and a similar decrease of 27% in all claims during the same period.44 Although a significant variation exists among industry sectors, Yamamoto107 reported a trend for a decline in the number of recognized occupational low back pain cases in Japan as well. In a large study of over 730,000 claims initiated from 45 U.S. states in 1989, available through a Liberty Mutual Insurance Company database, back-related claims constituted 16% of all
claims and 33% of all costs.104 Medical costs were overshadowed by indemnity costs that represented nearly 66% of total claims costs. These figures are similar to those from other studies reported from the United States at around the same time88 and somewhat lower than figures from Australia from the early 1990s.77
RISK FACTOR ASSOCIATIONS Structural pathology and tissue injury Back pain is commonly used as a synonym for spinal illness or, in the case of the workplace, spinal injury, although it is obvious that they are not the same and that the causal factors for the underlying pathology and reporting of back pain can be different. Some pain could originate from a metabolic disturbance such as muscle fatigue, which could be expected to recover fully without remaining identifiable pathology. Physical loading exceeding the tolerance of a structure produces a structural pathology with pain. This true injury and other factors, such as severe degeneration or infections, could lead to irreversible pathologic conditions, the symptoms of which could be triggered by routine or “physiologic loading.” This could be one explanation for the result that previous history of back pain is one of the most consistent predictors of later back pain.13 Commonly used “disability” scores estimate avoidance of defined functions due to back pain (the modifying effect of reported physical loading on pain). The correlations of underlying illness with sickness absenteeism, permanent disability pension, and use of health care due to back pain, however, are generally low.
Clinical relevance of spine pathology Studies of factors associated with the pathology of spinal structures have received relatively little attention, although the disk has been commonly thought to be responsible for most back symptoms and has been a primary target for diagnostic and therapeutic interventions related to spinal disorders. Knowledge of the macropathoanatomy and micropathoanatomy of the spine is consequently limited with respect to painful conditions. For example, we do not know the clinical value of osteophytes, disk space narrowing, disk bulges, end-plate changes, intervertebral foramina and spinal canal anthropometry, or facet joint degeneration. In the past decade even our understanding of the clinical relevance of disk herniation and annular ruptures has changed. Some studies have shown an association between disk pathology and back pain reporting, but degenerative findings are also common among asymptomatic subjects.14,16,99,105 Certain mechanisms have been suggested to explain associations between disk pathology and back pain. Full annular ruptures reaching innervated disk structures could be associated with back pain through several mechanisms. Annular tearing can lead to disk herniation with nerve compression, has been shown to produce pain by biochemical effects, and is the pathology allowing nerve ingrowth into the disk.5,33,34,76 Disk degeneration could make the disk mechanically incompetent, allowing abnormal motion between neighboring disks and leading to pain in innervated structures in the functional unit.73 Several other structures in the spine, such
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as muscles and tendon insertions, are possible sources of back pain. The condition underlying most back pain remains unknown, however, and the structural changes mentioned are currently of little clinical value.
Hereditary influences on disk degeneration There has been a dramatic paradigm shift over the past decade with respect to determinants of disk degeneration and pathology. This shift is clearly depicted by the contrasting conclusions of two reviews on the topic of “degenerative disk disease” written a decade apart. After an extensive review of the literature in 1992, Frymoyer35 concluded, “Among the factors associated with its occurrence are age, gender, occupation, cigarette smoking, and exposure to vehicular vibration. The contribution of other factors such as height, weight, and genetics is less certain.” A decade later in 2002, Ala-Kokko1 concluded, “Even though several environmental and constitutional risk factors have been implicated in this disease, their effects are relatively minor, and recent family and twin studies have suggested that sciatica, disk herniation and disk degeneration may be explained to a large degree by genetic factors.” Traditionally, degeneration of the spine has been viewed as an outcome of the accumulation of lifetime mechanical insults and injuries imposed on normal aging changes. During the 1990s the dominant effect of hereditary factors became clear, but the traditional view still maintains wide support.1,35 The traditional view, however, makes it difficult to explain the very high concordance in degenerative signs observed in lumbar spine magnetic resonance images in monozygotic twin pairs highly discordant for occupational exposures. In a study of determinants of disk degeneration in 115 pairs of identical twins, occupational physical loading explained from 0 to 7% of the variance in disk degeneration in the lumbar spine and age (ranging from 35 to 70 years) below 10%, whereas the combined effect of genes and shared environmental factors accounted for 30-60% of the total variance in disk degeneration.11 The observed significant individual differences at all ages in the degree of disk degeneration support a conclusion that there are crucial individual differences in predisposition to this problem. Using a classic twin study, Sambrook et al84 reported that heritability estimates explained 74% of the variance of the “overall score of disk degeneration” of the lumbar spine. The results from these twin studies suggest that heredity has a dominant role in disk degeneration compared with the importance of all commonly suspected adulthood exposures. The role of genetics has been confirmed additionally in several studies identifying gene forms associated with disk degeneration.4,51-53,97 It is likely that more genes associated with disk degeneration and symptoms will be found over the coming years, enhancing our chances to investigate so-called gene-environment interactions and leading to better understanding of the etiopathogenesis of disk degeneration.
Occupational and other influences on disk degeneration Most epidemiologic studies in the area of common spinal disorders have been of back symptoms, and the literature related to the epidemiology of spine pathology is limited. In an exceptional study of musculoskeletal findings based on 1000 consecutive autopsies, the occurrence rate of “spondylitis deformans”
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increased linearly from 0 to 72% between the ages of 39 and 70 years.45 Although these findings relate to people and work conditions around the turn of the century and the definition of “spondylosis” is not clearly stated, the rapid linear increase is notable. In a review article, Miller et al68 reported a similar increase in grades II to III disk degeneration from 0% at age 20 to about 90% at age 70 years. The authors also concluded that radiographic data are corroborated by macroscopic findings. Frymoyer et al37 compared the radiographs of three groups of men between the ages of 18 and 55 years: men with no history of back pain, men with moderate back pain, and men with severe back pain. In these three groups the frequency of Schmorl’s nodes, claw spurs, disk heights at the L3-L4 and LS-S1 levels, the disk vacuum sign, and transitional vertebrae were similar. The radiographic findings that differed in the three groups were traction spurs and/or disk space narrowing between L4 and L5, but these findings did not correlate with occupation, occupational lifting, or whole-body vibration. Specifically with respect to driving and associated whole-body vibration, findings have been somewhat conflicting, but the current weight of evidence suggests no notable effect on disk degenerative findings. Arguably the most well-controlled study to date on the subject did not find lumbar disk degeneration or pathology to be associated with lifetime driving.9 Riihimaki82 found that concrete reinforcement workers had a relative risk of 1.8 for disk “space narrowing as compared with house painters and a relative risk of 1.6 for ‘spondylophytes’.” They concluded that heavy physical work enhanced the degenerative process in the lumbar spine. An autopsy study of 86 subjects by Videman et al99 showed that occupations that involved sitting, standing, and walking without heavy physical loading were associated with the least degeneration. Workers with heavy physical loading had the highest incidence of annular ruptures, and sedentary work was associated with the highest degree of general disk degeneration. Studies using magnetic resonance imaging reported risks of 0.35 and 0.57 at the age of 20 years among asymptomatic and symptomatic subjects and 0.09 among asymptomatic subjects at the age of 11 years.79,86 In addition, Boos et al17 demonstrated histologically verified annular tears in a group of subjects aged 11-16 years and endplate cartilage pathology among 3 to 10 year olds. The adjusted disk signal intensity reflecting the water content of nucleus pulposus has been shown to change rapidly in early years between the ages of 9 and 77 years.68,98 Obviously, degeneration begins before individuals are exposed to workplace factors. All adults have disk degeneration, and only the degree of spine degeneration varies. That degenerative changes are present already in childhood further underlines our limited understanding of the etiology of spinal degeneration. Many researchers have studied spine degeneration based on radiography, which provides good measures of disk space narrowing and annular insertions to vertebrae (osteophytes), although its overall relevance for the intervertebral disk is not clear. A study of more than 15,000 adults did not show that heavy work was associated with spine degeneration in radiographs, although men had more degenerative signs than women. Lawrence56 reported that lumbar disk degeneration was most common in persons with physically heavy tasks compared with more sedentary workers, but only in men. Hult49 showed the
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prevalence of disk degeneration to be nearly 100% by age 59 in workers with heavy physical work, and similar degenerative findings were noted about 10 years later among those engaged in light work. Interestingly, however, important differences between the groups with heavy and light physical work were observed at baseline, and firm conclusions about the relative role of occupational physical loading on disk degeneration cannot be made. Conflicting findings in the scientific literature and failure to identify a dose-response relationship have not led to a convincing demonstration of the primacy of workplace factors in causing anatomic abnormalities.10,96
SUMMARY In principle, the determinants of all degenerative processes are similar. A function of individual constitutional factors, including genetics, they are modified by behaviors and extrinsic exposures. As studies progress in the area of spinal degeneration and structural variation, genetic influences appear to play a dominant role. Occupational exposures, representing different loading conditions, alone appear to have only modest affects on disk degeneration and pathology. Virtually all humans are exposed to the types of physical activities that have been suspected of accelerating lumbar degeneration during either work or leisure, with exposure being simply a matter of degree. Their influences vary due to recovery times, adaptation level, and stage of degeneration, among other factors. It is likely also that there are as yet unknown factors contributing to degeneration. In the end, both environmental and constitutional factors have some role in all degeneration, and only their relative magnitudes vary.21
Work-related back pain reporting Industrial back “injury” incident reports and claims filing involve specific definitions of back problems to be distinguished from structural pathology, symptom complaints solicited on surveys, or problems identified through health care visits. Most developed countries have systems for filing complaints of work-related injuries and illnesses with their own sets of rules, costs, and benefits. In discussing such systems in the United States, Hadler41 emphasized that filing a complaint forces the person to conform to the workers’ compensation paradigm. He stated, “By definition, work task description is causal. By inference, the illness is a manifestation of major structural damage.” As we have discussed, both of these assumptions are highly controversial. We found 13 prospective longitudinal studies that investigated predictors of industrial back pain reports.13,19,22,31,38,46,48,55,69,70,81,83,93 Early studies focused largely on physical factors, whereas more recent research attempted to account for other factors influencing back pain reports. Chaffin and Park22 performed some of the earliest prospective research in this area. In the early 1970s, they conducted a study of back incident reports in 411 men and women who engaged in manual lifting in their work at an electronics manufacturing company. The study focused on the effects of occupational lifting and mismatches between individual strength and job requirements. They reported an association between low back pain and jobs
with higher lifting strength requirements. They also found a higher incidence of back pain reporting in persons who demonstrated less strength on isometric strength testing than that deemed necessary to meet job demands, as compared with those whose strength met or exceeded demands, although the association was not statistically significant. Limitations of this study were that only 25 low back incidents were reported and controls for other factors influencing back pain reports were not undertaken. Cady et al19 later reported on physical fitness as an indicator of risk in 1652 firefighters over a 3-year period. Fitness was defined by a composite score based on aerobic capacity, strength, and flexibility measures. They found that firefighters with low “fitness” levels were about nine times more likely to report a back injury than those in the “most fit” group. The few injuries reported among the highly fit were the most serious, however, in terms of cost. Again, the effects of age, previous back pain, and other potentially confounding factors were not reported, making interpretation of the results difficult. Isokinetic lifting strength was investigated as a predictor of low back injury claims among nurses in a study by Mostardi et al,70 who concluded that lifting strength was a poor predictor of subsequent back symptoms and injury reports. Another prospective study of back injury reports in nurses reported by Ready et al81 reached similar conclusions about isometric lifting strength and other general fitness parameters. The factors that discriminated most between the nurses who did and did not report subsequent back injuries were previous receipt of compensation, smoking status, and poorer job satisfaction. In the Boeing study, a prospective cohort study of industrial back pain complaints in 3020 aircraft manufacturing workers, isometric lifting strength, maximal aerobic capacity, and lumbar range of motion were among the factors that were not associated with subsequent complaints. Other than having had current or recent back problems at the onset of the study, the strongest predictors of future back pain reports were negative perceptions of the workplace, including low job task enjoyment and social support and emotional distress.13 The only factor from the baseline physical examination that was strongly associated with future reporting was back pain elicited on straight leg raise testing, which probably represents another aspect of recent or current back problems also known to influence future risk.7 Yet in multivariable analysis, considering the numerous suspected risk factors under investigation, less than 10% of the variance in the reporting of work-related back pain was explained. The study findings underline the multifaceted nature of back pain reporting in industry and the limited predictive ability of most suspected risk factors. A later extension of the Boeing study looked specifically at back incident reports that resulted in the formal filing of industrial insurance claims. Lower job satisfaction and a poorer employee appraisal rating by the employee’s immediate supervisor were associated with back injury claims. Given the findings of the earlier analysis of back incident reports, this result was not surprising. A more notable finding of the later analysis was that these psychosocial factors were similarly associated with non–back injury claims as well. It would appear that certain psychosocial factors may predispose to the filing of injury claims, but the study did not provide evidence of significant differences between those who filed back injury claims and those who filed other types of injury claims.9 Such findings caution against
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stereotyping persons who file back injury claims as being distinctly different from those filing other injury claims with respect to “preinjury” psychosocial factors. As Leavitt57 stated, “The unfortunate problem is that stereotypes have consequences. Doubts raised by labels often shape evaluation and treatment of industrial workers in problematic ways, to the extent that their integrity and status as patients is challenged.” Since the Boeing study, researchers have continued to search for risk indicators and have expanded the investigation more fully into multiple domains including the physical, social, and psychologic. Numerous potential risk indicators, including exposure to repetitive trunk rotation, low supervisor support, and lack of control over work duties, have been reported. Many of these indicators have been found through exploratory studies, however, and few results have been taken to the next crucial stage of confirmation or replication in a separate cohort. Exploratory investigations have many inherent risks, including observing statistically significant associations by chance that do not actually exist or are biologically implausible.2 More trust can be placed in findings that have been validated through confirmation studies. Although confirmation studies in this area of research are rare, six indicators have been reported in multiple studies to increase the probability of future back pain reports: low job satisfaction,13,48,55,81,83 heavy physical work requirements,31,38,55,69 low social support at work,13,93 previous low work performance ratings,13,55,93 smoking status,8,81,93 and previous history of low back problems.13,83,93 The magnitudes of each of these associations have been relatively low, with odds or rate ratios typically ranging between 1.5 and 3.0 and accompanied by confidence intervals approaching 1.0. It is clear also that individual worker strength levels do not predict future injury.7,69,70,81 Although the above results have been substantiated in multiple investigations, it is unknown whether the associations observed indicate causal relationships, especially regarding the psychosocial and physical indicators. Although theories abound for how both psychosocial and physical stressors could result in reports of back pain, it is possible that indicators from within one domain influence indicators within the other. It has been theorized that individuals with higher workloads may be more likely to have lower job satisfaction.27 Alternatively, individuals under psychologic stress may be exposed to altered biomechanical forces through changes in posture or movement strategies.66 Further research is required to clarify the potential interactions arising between physical and psychosocial indicators. One study in which interaction effects between predictor variables were studied found independent effects of both psychosocial and physical variables, possibly indicative of unique effects for each.55 Although some work has been done to elucidate which factors are associated with industrial back pain reporting, the practical value of predictive models or preemployment screening for identifying specifically who will or will not experience or report symptoms is questionable. The magnitude of associations for individual predictor variables and overall predictive accuracy of created models has been relatively low, and practical difficulties arise when attempting to apply results from large samples to individual workers. Additionally, attempts at prevention based on knowledge of suspected risk factors such as workplace ergonomic modification have been largely unsuccessful.26,64,94 In fact, authors of one systematic review evaluating the effectiveness
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of multiple prevention strategies stated, “The results concerning prevention for subjects not seeking medical care are sobering. Only exercises provided sufficient evidence to conclude that they are an effective preventive intervention.”60
Subsequent disability Evidence suggests that back symptoms have always been present to some degree among humans and likely always will be. Episodes of these symptoms are, however, typically manageable and relatively short-lived. A systematic review of the prognosis of acute (<3 weeks) low back pain indicated that the prognosis of this condition is largely positive.80 Although back pain is a recurring phenomenon, most individuals recover from episodes quickly and experience little disability. The vast majority (68-86%) of individuals off work due to back pain returns to work within 1 month, and further improvements are seen for up to 3 months. In the small minority experiencing pain and disability for 3 consecutive months, however, little further improvement in important clinical outcomes is seen. Although some chronic back pain sufferers are able to cope with their pain and continue to work, a portion remains off work and experiences extended time loss.20 Within the workplace, it has been reported that approximately 10% of back injury claimants with extended work loss account for approximately 10% of back-related industrial insurance costs.88 Long-term disability is therefore the outcome that poses the greatest threat to the individual and the greatest cost to society. Disability is typically represented in the work environment as absenteeism. An examination of factors associated with illness absenteeism led Backenheimer6 to conclude that “absence behavior is, in considerable measure, a cultural and social phenomenon.” He claimed also that “a biological frame of reference is too narrow to explain the condition of being ill.” There is now a large body of evidence that these notions apply also to absenteeism and disability from back problems. Great variability is observed in back pain disability and work loss durations among nations and disability systems that would not be expected if disability were purely a biologic phenomenon.47,100 Long-term back pain disability is a relatively new phenomenon in the history of Western civilization, and its dramatic growth since World War II suggests that factors other than physical pathology are influencing its development. This is not to say that many working people do not genuinely experience back pain or that severe symptoms do not cause physical limitations of some duration. On the contrary, numerous health surveys indicate that back symptoms are extremely common in both developed and Third World countries.3,75,101 What appears to have changed in many societies, however, is the public perception of back pain as an “injury” or medical problem and its effect on work life in terms of disability. One striking example of the tremendous growth in back pain disability seen in many of the developed countries comes from the U.S. Social Security Disability Insurance System, where from 1957 to 1976 the incidence of disability awards increased by approximately 270%, a rate 14 times that of the population growth (Fig. 4a.3).87 Similarly striking increases in the incidence of disability awards have occurred in Finland, Sweden, and England.74 Although there is some evidence that the increasing
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Figure 4a.3 Social Security Disability Insurance awards by diagnosis: percent increase from 1957 to 1976. (From Fordyce WE: Back pain, compensation, and public policy. In JC Rosen, LJ Solomon, eds: Prevention in health psychology. Hanover, NH, 1985, University Press of New England.)
trends have leveled or reversed, disability associated with back pain remains widespread.71 Factors other than just the presence of back symptoms influence back symptom reporting and long-term disability. Multiple literature reviews have been published examining what factors are related to prolonged disability or work loss.25,59,92 Consistently, a multifactorial model of disability incorporating factors from physical, social, psychologic, and occupational domains is advocated. Of likely importance to the onset and persistence of disability are cultural norms; socioeconomic conditions, including unemployment rates and opportunities for compensation; and physical and psychosocial work environments.25,54,59,101 Many studies seeking to identify predictors of prolonged disability have enrolled subjects already in subacute or chronic states, however, thus confounding results and reducing generalizability to more acute cases. The authors of a systematic review of acute back pain prognosis reported identifying only one study of high methodologic quality that included a clinically relevant predictor.80 Clearly, further research is needed to accurately identify acute back pain patients at risk of developing chronic conditions. Compensation availability appears to affect the length of disability in the case of both surgical intervention32,43 and conservative care.39,42 However, Leavitt57 noted that most studies citing an association between compensation and back pain reporting and disability failed to take into account the effects of physical demands of the job; these can affect the outcome and differ significantly between compensation and noncompensation groups. He attempted to disentangle the effects of these factors and found that work-related back symptom reports were associated with more time loss than were non–work-related back symptoms, even after controlling for the degree of physical job demands. In addition, a related literature synthesis by Loeser et al62 concluded that when all other factors are held constant, the existing economic studies imply a positive relationship between the level of wage replacement benefits and both the incidence and duration of workers’ compensation claims. The relative effect of benefit
level appeared to be greater on claim duration than on claim incidence. This suggests that a key issue for workers’ compensation systems to contend with may be determining an optimal wage replacement ratio. Inappropriate medical management has been implicated also as a contributor to the growing disability problem. The rise in disability and increasing health care costs and utilization despite advances in medical technology led Frymoyer and Cats-Baril36 to raise the question, “Have medical professionals of all types become part of the problem rather than part of the solution?” Erroneous back pain beliefs of both health care professionals and the general public, including frequent suspicions of and investigations for major pathology and fear-avoidant beliefs in cases of simple back pain, appear to influence back pain disability.61 In regards to the desynchrony between current evidence-based treatment guidelines and popular opinions, Deyo28 stated, “The new back pain guidelines represent such a substantial shift from the traditional approach that the public will need to be re-educated.” Indeed, a recent public reeducation attempt through a social marketing campaign in Victoria, Australia, which portrayed the positive prognosis of back pain and conveyed the importance of staying active, was effective in altering beliefs and reducing workrelated disability.18
CONCLUSION AND IMPLICATIONS Back pain continues to be a major burden for developed countries. Since the earlier version of this chapter was written for the first edition of this book, further epidemiologic studies have been undertaken in an attempt to understand the prevalent and costly condition of low back pain. Because they substantially alter the conceptualization of occupational back pain, several discoveries are particularly noteworthy. First, lumbar spine degeneration, long considered a consequence of the accumulation of mechanical insults and injuries,
Chapter 4a
mainly from occupational exposures, has been found to be influenced in large part by heredity. The clinical implications of these findings include an altered conceptualization of the etiology of lumbar spine degeneration. Medical imaging findings that were once commonly attributed to occupational exposures can no longer be explained as such. Current evidence suggests that the role of occupational loading exposures is relatively minor in comparison with genetic influences. Second, the search for risk indicators has continued to result in inconsistent findings, identifying relatively small roles for environmental factors in explaining work-related back pain reporting and associated disability. These findings are contrary to earlier views that ascribed back pain incidents to excessive occupational physical loading requirements (either peak or repetitive). Thus it is not currently possible to predict which workers will experience back pain in a given occupation and which will experience delayed recovery. Finally, although the global experience of work-related back pain reporting and associated disability varies markedly by country or jurisdiction, over the past decade or so, for which figures are available, there has been an overall decline in some countries. This decline comes after many decades of growth. Recent trends in North America indicate that incidence and disability related to back injury claims, and time loss claims in particular, have declined over the past 10 years or so that data have been analyzed. However, this decline is part of one observed in all industrial injury and illness claims. The phenomena of work-related back pain incident reports, claims, and disability are influenced by socioeconomic, cultural, and broad legislative and jurisdictional factors. When comparing incidence and prevalence figures between nations and jurisdictions, great variations are thus observed. For this reason, the role of dominant paradigms through which back pain is viewed, particularly as it pertains to work, and the systems through which persons file related complaints must be acknowledged. Such factors constitute inherent biases in studies of the role of occupational exposures that must be recognized in planning epidemiologic studies and interpreting resulting data.
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Hashemi L, Webster BS, Clancy EA: Trends in disability duration and cost of workers’ compensation low back pain claims (1988-1996). J Occup Environ Med 40:1110-1119, 1998. Heine J: Uber die Arthritis deformans. Virch Arch Pathol Anat 260:521-663, 1926. Hemingway H, Shipley MJ, Stansfeld S, Marmot M: Sickness absence from back pain, psychosocial work characteristics and employment grade among office workers. Scand J Work Environ Health 23:121-129, 1997. Hestbaek L, Leboeuf-Yde C, Manniche C: Low back pain: what is the long-term course? A review of studies of general patient populations. Eur Spine J 12:149-165, 2003. Hoogendoorn WE, Bongers PM, de Vet HC, Ariens GA, van Mechelen W, Bouter LM: High physical work load and low job satisfaction increase the risk of sickness absence due to low back pain: results of a prospective cohort study. Occup Environ Med 59:323-328, 2002. Hult L: Cervical, dorsal and lumbar spinal syndromes; a field investigation of a non-selected material of 1200 workers in different occupations with special reference to disc degeneration and so-called muscular rheumatism. Acta Orthop Scand Suppl 17:1-102, 1954. Ilmarinen J, Louhevaara V, Korhonen O, Nygard CH, Hakola T, Suvanto S: Changes in maximal cardiorespiratory capacity among aging municipal employees. Scand J Work Environ Health 1(17 Suppl):99-109, 1991. Jones G, White C, Sambrook P, Eisman J: Allelic variation in the vitamin D receptor, lifestyle factors and lumbar spinal degenerative disease. Ann Rheum Dis 57:94-99, 1998. Kawaguchi Y, Kanamori M, Ishihara H, Ohmori K, Matsui H, Kimura T: The association of lumbar disc disease with vitamin-D receptor gene polymorphism. J Bone Joint Surg Am 84A:2022-2028, 2002. Kawaguchi Y, Osada R, Kanamori M, et al: Association between an aggrecan gene polymorphism and lumbar disc degeneration. Spine 24:2456-2460, 1999. Krause N, Frank JW, Dasinger LK, Sullivan TJ, Sinclair SJ: Determinants of duration of disability and return-to-work after work-related injury and illness: challenges for future research. Am J Ind Med 40:464-484, 2001. Krause N, Ragland DR, Fisher JM, Syme SL: Psychosocial job factors, physical workload, and incidence of work-related spinal injury: a 5-year prospective study of urban transit operators. Spine 23:2507-2516, 1998. Lawrence JS: Rheumatism in coal miners. III. Occupational factors. Br J Ind Med 12:249-261, 1955. Leavitt F: The physical exertion factor in compensable work injuries: a hidden flaw in previous research. Spine 17:307-310, 1992. Leino PI: Does leisure time physical activity prevent low back disorders? A prospective study of metal industry employees. Spine 18:863-871, 1993. Linton SJ: A review of psychological risk factors in back and neck pain. Spine 25:1148-1156, 2000. Linton SJ, van Tulder MW: Preventive interventions for back and neck pain problems: what is the evidence? Spine 26:778-787, 2001. Linton SJ, Vlaeyen J, Ostelo R: The back pain beliefs of health care providers: are we fear-avoidant? J Occup Rehab 12:223-232, 2002. Loeser JD, Henderlite SE, Conrad DA: Incentive effects of workers’ compensation benefits: a literature synthesis. Med Care Res Rev 52:34-59, 1995. Loney PL, Stratford PW: The prevalence of low back pain in adults: a methodological review of the literature. Phys Ther 79:384-396, 1999. Maher CG: A systematic review of workplace interventions to prevent low back pain. Aust J Physiother 46:259-269, 2000. Maniadakis N, Gray A: The economic burden of back pain in the UK. Pain 84:95-103, 2000. Marras WS, Davis KG, Heaney CA, Maronitis AB, Allread WG: The influence of psychosocial stress, gender, and personality on mechanical loading of the lumbar spine. Spine 25:3045-3054, 2000. Miettinen OS, Caro JJ: Medical research on a complaint: orientation and priorities. Ann Med 21:399-401, 1989. Miller JA, Schmatz C, Schultz AB: Lumbar disc degeneration: correlation with age, sex, and spine level in 600 autopsy specimens. Spine 13:173-178, 1988. Mooney V, Kenney K, Leggett S, Holmes B: Relationship of lumbar strength in shipyard workers to workplace injury claims. Spine 21:2001-2005, 1996. Mostardi RA, Noe DA, Kovacik MW, Porterfield JA: Isokinetic lifting strength and occupational injury. A prospective study. Spine 17:189-193, 1992. Murphy PL, Volinn E: Is occupational low back pain on the rise? Spine 24:691-697, 1999. Mustard C, Cole D, Shannon H, Pole J, Sullivan T, Allingham R: Declining trends in work-related morbidity and disability, 1993-1998: a comparison of survey estimates and compensation insurance claims. Am J Public Health 93:1283-1286, 2003. Nachemson A: The future of low back pain research. In JW Frymoyer, SL Gordon, eds: New perspectives on low back pain. Illinois, 1989, AAOS. Nachemson AL: Problemets omfatting. In Ont i ryggen, orsaker, diagnostik och behandling. Stockholm, 1991, SBU, pp. 18-28.
75. Nayha S, Videman T, Laakso M, Hassi J: Prevalence of low back pain and other musculoskeletal symptoms and their association with work in Finnish reindeer herders. Scand J Rheumatol 20:406-413, 1991. 76. Olmarker K, Rydevik B, Nordborg C: Autologous nucleus pulposus induces neurophysiologic and histologic changes in porcine cauda equina nerve roots. Spine 18:1425-1432, 1993. 77. Osti OL, Cullum DE: Occupational low back pain and intervertebral disc degeneration: epidemiology, imaging, and pathology. Clin J Pain 10:331-334, 1994. 78. Ostry A: The history of injury and industrial disease rates in British Columbia from 1950 to 1996. Can J Public Health 91:36-40, 2000. 79. Paajanen H, Erkintalo M, Kuusela T, Dahlstrom S, Kormano M: Magnetic resonance study of disc degeneration in young low-back pain patients. Spine 14:982-985, 1989. 80. Pengel LH, Herbert RD, Maher CG, Refshauge KM: Acute low back pain: systematic review of its prognosis. BMJ 327:323, 2003. 81. Ready AE, Boreskie SL, Law SA, Russell R: Fitness and lifestyle parameters fail to predict back injuries in nurses. Can J Appl Physiol 18:80-90, 1993. 82. Riihimaki H: Low-back pain, its origin and risk indicators. Scand J Work Environ Health 17:81-90, 1991. 83. Rossignol M, Lortie M, Ledoux E: Comparison of spinal health indicators in predicting spinal status in a 1-year longitudinal study. Spine 18:54-60, 1993. 84. Sambrook PN, MacGregor AJ, Spector TD: Genetic influences on cervical and lumbar disc degeneration: a magnetic resonance imaging study in twins. Arthritis Rheum 42:366-372, 1999. 85. Sarna S, Sahi T, Koskenvuo M, Kaprio J: Increased life expectancy of world class male athletes. Med Sci Sports Exerc 25:237-244, 1993. 86. Smith F, Jeffrey J, Porter RW: unpublished data. 87. Social Security Statistical Supplement (1977-1979), HE 3.3/ 3:979. Washington, DC, 1979, Government Printing Office. 88. Spengler DM, Bigos SJ, Martin NA, Zeh J, Fisher L, Nachemson A: Back injuries in industry: a retrospective study. I. Overview and cost analysis. Spine 11:241-245, 1986. 89. Spitzer WO: Scientific approach to the assessment and management of activity-related spinal disorders: a monograph for clinicians. Report of the Quebec Task Force on Spinal Disorders. Spine 12(Suppl):S12-S15, 1987. 90. Stewart WF, Ricci JA, Chee E, Morganstein D, Lipton R: Lost productive time and cost due to common pain conditions in the US workforce. JAMA 290:2443-2454, 2003. 91. Taylor PJ: International comparisons of sickness absence. Proc R Soc Med 65:577-580, 1972. 92. Truchon M, Fillion L: Biopsychosocial determinants of chronic disability and low-back pain: a review. J Occup Rehab 10:117-142, 2000. 93. Tubach F, Leclerc A, Landre MF, Pietri-Taleb F: Risk factors for sick leave due to low back pain: a prospective study. J Occup Environ Med 44:451-458, 2002. 94. van Poppel MN, Koes BW, Smid T, Bouter LM: A systematic review of controlled clinical trials on the prevention of back pain in industry. Occup Environ Med 54:841-847, 1997. 95. Videman T, et al: Elite sport as a predictor of back-related outcomes. American College of Sports Medicine Annual Meeting, Seattle, 1993. 96. Videman T, Battié MC: The influence of occupation on lumbar degeneration. Spine 24:1164-1168, 1999. 97. Videman T, Leppavuori J, Kaprio J, et al: Intragenic polymorphisms of the vitamin D receptor gene associated with intervertebral disc degeneration. Spine 23:2477-2485, 1998. 98. Videman T, Nummi P, Battié MC, Gill K: Digital assessment of MRI for lumbar disc desiccation. A comparison of digital versus subjective assessments and digital intensity profiles versus discogram and macroanatomic findings. Spine 19:192-198, 1994. 99. Videman T, Nurminen M, Troup JD: 1990 Volvo Award in clinical sciences. Lumbar spinal pathology in cadaveric material in relation to history of back pain, occupation, and physical loading. Spine 15:728-740, 1990. 100. Volinn E: The epidemiology of low back pain in the rest of the world. A review of surveys in low- and middle-income countries. Spine 22:1747-1754, 1997. 101. Waddell G: 1987 Volvo Award in clinical sciences. A new clinical model for the treatment of low-back pain. Spine 12:632-644, 1987. 102. Walker BF: The prevalence of low back pain: a systematic review of the literature from 1966 to 1998. J Spinal Disord 13:205-217, 2000. 103. Wasiak R, Pransky GS, Webster BS: Methodological challenges in studying recurrence of low back pain. J Occup Rehab 13:21-31, 2003. 104. Webster BS, Snook SH: The cost of 1989 workers’ compensation low back pain claims. Spine 19:1111-1115; discussion 1116, 1994. 105. Wiesel SW, Tsourmas N, Feffer HL, Citrin CM, Patronas N: A study of computer-assisted tomography. I. The incidence of positive CAT scans in an asymptomatic group of patients. Spine 9:549-551, 1984. 106. Woolf AD, Pfleger B: Burden of major musculoskeletal conditions. Bull World Health Org 81:646-656, 2003. 107. Yamamoto S: A new trend in the study of low back pain in workplaces. Ind Health 35:173-185, 1997.
CHAPTER
4b
Clinical Biomechanics of the Spine Malcom H. Pope
The spine is an important structure with many conflicting functions. The first function, mobility, provides the motion necessary for the activities of daily living. The second function is one of support for the body segments and any load moments that are applied by the worker. The third function is housing, in which the spinal cord and nerve roots are protected. The last function is control, with the muscles acting through the vertebrae to precisely control the posture.
FUNCTIONAL SPINAL UNIT The functional spinal unit (FSU) consists of two adjacent vertebrae, the interposed vertebral disk, and adjoining ligaments. The motion segment can be divided into anterior and posterior components. The anterior components are the vertebral bodies, the disk, and the attached ligaments; all the remaining structures are posterior components.19 The FSU is a structure in which the disk acts as a spring, the facet joints as a pivot, and the posterior ligamentous complex as another spring. Experiments have shown that the FSU exhibits coupled motion in which vertical translation also results in complex movements in other directions. The anterior elements of the FSU have a support function and a function of impact absorption, whereas the posterior elements control motion.
Anterior portion The major structural part of the anterior portion of the FSU consists of the vertebral bodies. These bear mainly compressive loads and are progressively larger caudally as the weight of the upper body increases (Fig. 4b.1). Therefore, the vertebral bodies in the lumbar region are bigger than those in the thoracic and cervical regions. Compressive strength concomitantly gradually increases from the cervical spine down to the lumbar spine. Overall, the vertebrae are six times stiffer than the disks, three times thicker than the disks, and suffer half the deformation of the disks. The vertebrae are very important in shock absorption. Under compression, endplate deformation precedes the expelling of hematopoietic contents from the vertebrae themselves. The vertebrae are an expression of Wolff’s law inasmuch as the trabeculae are oriented to resist the vertical compression forces and tensile forces through the spinous and transverse processes caused by muscle and ligament attachments. There is a zone of relative weakness anteriorly because of a lack of trabeculae.
Compressive failure, particularly in an osteoporotic individual, occurs in this region. The other major component of the anterior portion of the FSU is the intervertebral disk. The function of the disk is to distribute loads and restrain excessive motion. The disk is composed of the annulus fibrosus and nucleus pulposus. The annulus is made up of a series of sheets of collagen fibers, with the fibers of one sheet at a 30-degree angle relative to the neighboring sheet. Mathematical models show that with removal of the nucleus, interval stresses ensue as a result of the compressive forces being carried through the annulus. The inner portion of the disk, the nucleus pulposus, is rich in hydrophilic glycosaminoglycans in young adults, but with age the nucleus pulposus becomes progressively less hydrated. Animal experiments have shown that disks are avascular structures and that endplate permeability decreases with age, thereby decreasing disk nutrition. Motion is beneficial for intervertebral disks. Solute transport and metabolism are both improved by spinal motion, and intermittent motion is less effective than continuous motion. Aging usually results in disk degeneration. Degeneration of a disk reduces its proteoglycan content and thus its hydrophilic capacity. As the disk becomes drier, its elasticity and its ability to store energy and to distribute loads gradually decreases. Most disk herniations occur in the fourth decade of life, and herniations are found in 15 to 30 of autopsy specimens. The intervertebral disk exhibits creep, which means that the disk continues to deform under a constant load. This timedependent behavior comes from the fluid flow of the disk under an applied load and from the inherent viscoelastic behavior of the collagen and proteoglycan matrix. Time-dependent behavior has been demonstrated both in vivo by Keller et al8 and in vitro by Kazarian.7 The studies of Eklund and Corlett3 and Krag et al10 indirectly measured the change in overall height of the subjects. The diurnal loss was about 17 mm. Kazarian7 noted that a degenerate disk had a higher rate of deformation and the creep curve stabilized sooner. Virgin17 was the first to suggest that the nucleus pulposus acts hydrostatically to pressurize the disk and thus stabilizes the FSU. In a nondegenerate disk, nucleus pressure is redistributed as tension in the annulus layers. Normal disk pressure is about 1.5 times the compressive load divided by the cross-sectional area. Pressure is higher in the disk center and decreases toward the exterior. Nachemson15 reported that disk pressure is different in various positions or maneuvers (Table 4b.1). Andersson et al1 found in vivo that intradiskal pressure increased linearly with an increase in both trunk load and trunk moment. Disk pressure was found to be high in unsupported sitting but decreased significantly with the use of a backrest inclination greater than 110 degrees, with the use of lumbar supports, and with the use of armrests. The tensile stress in the annulus fibrosus due to disk pressure in the thoracic spine is less than that in the lumbar spine because the higher ratio of disk diameter to height in the thoracic disks reduces the circumferential stress.11
Posterior portion The posterior portion of the FSU has a primary role of guiding its movement. The type of motion possible at any level is
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C3 C4 C5 C6 C7 T1 T2 T3 T4 T5 Vertebral level
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T6
Messerer, 1880
T7
Perry, 1957
T8
Bell et al, 1967
T9 T10 T11 T12 L1 L2 L3 L4 L5
0
2000 (450 lbf)
4000 (900 lbf)
6000 (1350 lbf)
8000 (1800 lbf)
Compression strength in newtons (pound force) Figure 4b.1 Vertebral compression strength at a slow loading rate. (Modified from White AA, Panjabi MM: Clinical biomechanics of the spine. Philadelphia, 1991, WB Saunders.)
determined by the orientation of the facets of the FSU to the transverse and frontal planes. This orientation changes throughout the spine (Fig. 4b.2). Other structures that influence motion of the spine are the rib cage, which limits thoracic motion, and the pelvis. The cervical spine, the most mobile region of the spine, affords the head a
large range of motion, which is necessary for the activities of daily living. Except for the facets of the two uppermost cervical vertebrae (C1 and C2), which are parallel to the transverse plane, the cervical facets are oriented at 45 degrees to the transverse plane and are parallel to the frontal plane (Fig. 4b.2). The loadbearing function of the facets at all spinal levels is significant.
Chapter 4b
Load (N)
Supine (awake) Supine (semi-Fowler) Supine (traction, 500 N) Sitting (unsupported) Standing (relaxed) Coughing Straining
250 100 0 700 500 600 600
Functional spinal unit
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joints play an important role in resisting shear forces. In addition, Farfan5 showed that 40% of the torsional strength of the FSU come from the facet joints, and Lorenz et al12 suggested that 25% of the axial load bearing is from these structures.
Table 4b.1 Loads on the L3 disk calculated from intradiskal pressure measurements in a 70-kg man Position, Maneuver
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Ligaments The spine ligaments function in conjunction with other elements of the FSU as stabilizers and check reins. They are tensile elements that can fatigue, and they do contain pain fibers. The overall load deflection curve on the FSU is nonlinear, being reflective of ligament behavior. Extension loads the anterior ligaments and flexion loads the posterior elements. During flexion, the interspinous ligaments have the greatest strain, followed by the capsular ligaments and the ligamenta flava, whereas in extension the anterior longitudinal ligament bears the greatest strain. During lateral flexion, the contralateral transverse ligament is strained the greatest, followed by the ligamenta flava and the capsular ligaments. The capsular ligaments bear the most
Load sharing between the facets and the disk varies with the position of the spine. The loads on the facets are very high, peaking at about 30% of the total load when the spine is hyperextended.9 They are also quite high during forward bending coupled with rotation.4 The facets through the vertebral arches and intervertebral
Cervical (C3-C7)
0˚ A
45˚
20˚ Figure 4b.2 Orientation of the facets of the intervertebral joints. (A) In the lower cervical spine the facets are 45 degrees to the transverse plane and are parallel to the frontal plane. (B) The facets of the thoracic spine are oriented at 60 degrees to the transverse plane and at 20 degrees to the frontal plane. (C) The facets of the lumbar spine are oriented at 90 degrees to the transverse plane and at a 45 degree angle to the frontal plane. (From White AA, Panjabi MM: Clinical biomechanics of the spine, 1991, JB Lippincott.)
Thoracic
B – 60˚
45˚ C
90˚
Orientation of the facets to the transverse plane
Orientation of the facets to the frontal plane
Lumbar
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strain during rotation. The ligamentum flavum, which connects two adjacent vertebral arches longitudinally, is an exception in its behavior because it contains a large percentage of elastin. The elasticity of this ligament is therefore very high. This allows it to contract during extension of the spine and elongate during flexion. In a neutral position, the ligamentum flavum is under tension as a result of its elastic properties. Because it is located at a distance from the center of motion in the disk, it prestresses the disk and thus adds to overall stability.
independently of the rest of the cervical spine, but motion below C1 involves the entire cervical spine. The facets guide the motion, and as a result flexion-extension is coupled with transverse translation, lateral flexion with rotation (Fig. 4b.4), and rotation with axial translation. In the thoracic region, rotation is associated with lateral flexion, especially in the upper thoracic region. In this case, the vertebral bodies generally rotate toward the concavity of the lateral curve.18 Coupling of rotation and lateral flexion occurs in the lumbar spine, with the vertebral bodies rotating toward the convexity of the curve.13
KINEMATICS KINETICS The range of motion of the spine varies from level to level. White and Panjabi19 summarized these data (Fig. 4b.3). Flexion and extension are about 4 degrees in the upper thoracic, about 6 degrees in the midthoracic, and about 12 degrees in the lower thoracic segments. This increases in the lumbar motion segments to a peak of 20 degrees at L5-S1. Lateral flexion varies from level to level quite markedly but is greatest in the lower thoracic segments and L3-L4 (8 to 9 degrees). In the upper thoracic segments the range is 6 degrees. Rotation is greatest in the upper segments of the thoracic spine (9 degrees). The range of rotation is minimal in the lumbar spine because of facet orientation. The lumbar spine is susceptible to injury from rotation. There have been reports of coupled motion throughout the spine. Coupling refers to a primary motion in one direction leading to a secondary motion in another. For example, C1 moves
0˚
10˚ 20˚
0˚
10˚
20˚
The basic building materials of the spine are the vertebral bodies, which take the loads of compression, shear, and bending, and the muscles which act as the building blocks in tension. The muscles position and stabilize the spine. Without muscles, the ligamentous spine buckles under loads of as small as 2 kg. In general, the muscle electrical activity electromyographic (EMG) amplitude is directly proportional to the moment arm of the muscle line of action from the center of rotation. We can investigate the role of muscle around the periphery through a free-body analysis in which, mathematically at least, the body is cut in two and the forces and moments are resolved across that cut surface. Forces are estimated from the electromyographic signals. In complex postures, very high antagonistic activity occurs. Loads are also produced by body weight, prestress from ligaments, and externally applied loads.
0˚
10˚ 20˚
OC - C1 C1 -2 2-3 3-4 4-5 5-6 6-7 C7 - T1 T1 - 2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9 - 10 10 - 11 11 - 12 T12 - L1 L1 - 2 2-3 3-4 4-5 L5 - S1
Figure 4b.3 A composite of representative values for type and range of motion at different levels of the spine. (Modified from White AA, Panjabi MM: Clinical biomechanics of the spine. Philadelphia, 1991, JB Lippincott.)
Flexionextension
Lateral flexion
Rotation
Chapter 4b
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Kinetics
Neutral: OCC – C1 1.3 Nm (0.6 – 1.5) C7 – T1 1.2 Nm (0.5 – 2.2)
Left lateral flexion
Neutral
Right lateral flexion
Figure 4b.4 Coupled motion during lateral flexion is depicted schematically. When the head and neck are flexed to the left, the spinous processes shift to the right, indicating rotation. The converse is also illustrated. (Modified from White AA, Panjabi MM: Clinical biomechanics of the spine. Philadelphia, 1991, JB Lippincott.)
Because the lumbar spine is the main load-bearing area and the most common site of pain, studies have focused on this region. Loads on the cervical spine are mainly produced by the weight of the head, the activity of the surrounding muscles, the inherent tension of adjacent ligaments, and the application of external loads. Investigations in vivo confirm that physiologic loads are lower than those on the thoracic and lumbar spines. However, quite large loads on the cervical spine have been calculated during neck flexion, particularly in the lower cervical motion segments. Harms-Ringdahl6 calculated the bending moments generated around the axes of motion of the atlantooccipital joint and the C7-T1 motion segment with the neck in flexion, neutral position, and extension (Fig. 4b.5). The load on the junction between the occipital and C1 was lowest during extreme extension and highest during extreme flexion. The load on the C7-T1 motion segment was low with the neck in the neutral position but tucked in (ranging from an extension moment of 0.8 Nm to a flexion moment of 0.9 Nm). The load increased substantially during slight flexion (reaching 6 Nm). Moroney et al14 studied subjects who resisted loads. Calculation of the maximum (compressive) reaction forces on the C4-C5 motion segment ranged from 500 to 700 N during flexion, rotation, and lateral bending and rose to 1100 N during extension. Body position also affects the magnitude of the loads on the lumbar spine. These loads are minimal during well-supported reclining, remain low during relaxed upright standing, and rise during sitting (Fig. 4b.6). Trunk flexion increases the load by increasing the forwardbending moment on the spine. The forward inclination of the spine also makes the disk bulge on the concave side of the spinal curve and retract on the convex side. Hence when the spine is flexed, both compressive and tensile stresses on the disk increase.1 Nachemson and Elfström16 and Andersson et al2 also showed that during relaxed unsupported sitting, the loads on the lumbar spine are greater than during relaxed upright standing. In this position the pelvis is tilted backward and the lumbar lordosis straightens the upper body, thereby creating a longer lever arm for the weight of the trunk.
Slight flexion: OCC – C1 1.4 Nm (0.8 – 1.7) C7 – T1 3.7 Nm (3.0 – 6.2)
Figure 4b.5 Extension and flexion moments around the axes of motion of the atlantooccipital (OCC-C1) joint and the C7-T1 motion segment (marked with Xs) are presented for five positions of the head: extreme flexion, slight flexion, neutral, head upright with the chin tucked in, and extreme flexion. Values shown are the medial and range for seven subjects: Negative values indicate extension moments. The arrows represent the force vectors produced by the weight of the head. (Modified from Harms-Ringdahl K: On assessment of shoulder exercise and load-elicited pain in the cervical spine. Biomechanical analysis of load-EMG-methodological studies of pain provoked by extreme position. Thesis, 1986, Karolinska Institute, University of Stockholm.)
Figure 4b.6 The relative loads on the third lumbar disk for living subjects in various body positions are compared with the load during upright standing, depicted as 100. (Modified from Nachemson A, Elfström G: Intravital dynamic pressure measurements in lumbar discs: a study of common movements, maneuvers and exercises. Stockholm, 1970, Almqvist & Wiksell.)
111
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A
B
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Clinical biomechanics of the spine
C
D
Figure 4b.7 Influence of backrest inclination and back support on loads on the lumbar spine in terms of pressure in the third lumbar disk during supported sitting. (A) Backrest inclination is 90 degrees, and disk pressure is at a maximum. (B) The addition of lumbar support decreases disk pressure. (C) Backward inclination of the backrest to 110 degrees but with no lumbar support produces less disk pressure. (D) The addition of lumbar support with this degree of backrest inclination further decreases the pressure. (E) Shifting support to the thoracic region pushes the upper part of the body forward, moves the lumbar spine toward kyphosis, and increases disk pressure. (Modified from Andersson GBJ, Ortengren R, Nachemson A: Clin Orthop 129:156-164, 1977.)
E
Disk pressure
The loads on the lumbar spine are lower during supported sitting than during unsupported sitting because part of the weight is supported by the backrest. Backward inclination of the backrest and a lumbar support further reduce the loads (Fig. 4b.7).2 Because user requirements vary, the kinds of chairs available also vary widely. Regardless of use, however, it is important to be able to adjust any chair to meet the basic anthropometric dimensions of the worker. A proper seat height is desirable and should be adjustable for the individual user. The seat surface should be 3 to 5 cm below the knee-fold when the lower limb is vertical. Foot supports can be used with higher chairs. The width of the seat should be sufficient to accommodate the user. It must be possible to use the backrest, so the seat pan should not be too deep. Pressure should be avoided on the back of the thigh near the knees. Lifting creates the highest loads on the lumbar spine, and these are the occupational exposures with the greatest incidence of low back pain injury reports. The key to prevention is to reduce the load moment, which means reducing either the magnitude of the load, the distance from the body, or both. Therefore, if objects of the same weight, shape, and density but of different sizes are held, the lever arm for the force produced by the weight of the object is longer for the larger object and the bending moment on the lumbar spine is greater (Fig. 4b.7).
REFERENCES 1.
2.
3. 4.
5. 6.
7.
8. 9. 10. 11. 12.
DISCUSSION
13. 14.
The spine has functions of load bearing, protection of neural elements, and mobility yet stability. The FSU, which is the basic unit, exhibits coupled motion. It is composed of the anterior components (vertebral body, disk, pedicles, and ligament), and the remainder make up the posterior elements. Motion, which is largely controlled by the facet, varies between regimes. Flexion-extension is high in the lumbar spine, but rotation is minimal. Loads in the spine are a function of body mass, muscle activity, prestress, and external loads. The latter is particularly important in the lumbar spine.
15. 16.
17. 18. 19.
Andersson GBJ, Ortengren R, Nachemson A: Intradiscal pressure, intra-abdominal pressure and myoelectric back muscle activity related to posture and loading. Clin Orthop 129:156-164, 1977. Andersson GBJ, Ortengren R, Nachemson A, Elfstrom G: Lumbar disc pressure and myoelectric back muscle activity during sitting. I. Studies on an experimental chair. Scand J Rehabil Med 6:104, 1974. Eklund JAE, Corlett EN: Shrinkage as a measure of the effect of load on the spine. Spine 9(2):189-194, 1985. El-Bohy AA, King AI: Intervertebral disc and facet contact pressure in axial torsion. In SA Lantz, AI King, eds: Advances in bioengineering. New York, 1986, American Society of Mechanical Engineers, pp. 26-27. Farfan HF: Mechanical disorders of the low back. Philadelphia, 1973, Lea & Febiger. Harms-Ringdahl K: On assessment of shoulder exercise and load-elicited pain in the cervical spine. Biomechanical analysis of load-EMG-methodological studies of pain provoked by extreme position. Thesis, 1986, Karolinska Institute, University of Stockholm. Kazarian L: Dynamic response characteristics of the human vertebral column: an experimental study of human autopsy specimens. Acta Orthop Scand Suppl 146, 1972. Keller L, et al: In vivo creep behavior of the normal and degenerated porcine intervertebral disc-a preliminary report. J Spinal Disorder 1(4):267-278, 1989. King AI, Prasad P, Ewing CL: Mechanism of spinal injury due to caudocephalad acceleration. Orthop Clin North Am 6:19, 1975. Krag MH, Cohen MC, Pope MH: Load-induced changes in human intervertebral disc height in-vivo: a new and closer look. Orthop Trans 9(3):516, 1985. Kulak RF, Schultz AB, Belytschko T, Galante J: Biomechanical characteristics of vertebral motion segments and intervertebral discs. Orthop Clin North Am 6:121, 1975. Lorenz M, Patwardhan A, Vanderby R: Load-bearing characteristics of lumbar facets in normal and surgically altered spinal segments. Spine 8:122, 1983. Miles M, Sullivan WE: Lateral bending at the lumbar and lumbosacral joints. Anat Rec 139:387, 1961. Moroney SP, Schultz AB, Ashton-Miller JA: Analysis and measurement of neck loads. J Orthop Res 6(5):713-720, 1988. Nachemson A: Lumbar interdiscal pressure. In MIV Jayson, ed: The lumbar spine and back pain. London, 1987, Churchill Livingstone, p. 191. Nachemson A, Elfström G: Intravital dynamic pressure measurements in lumbar discs: a study of common movements, maneuvers and exercises. Stockholm, 1970, Almqvist & Wiksell. Virgin WJ: Experimental investigations into the physical properties of the intervertebral disc. J Bone Joint Surg 33B:607-611, 1951. White AA: Analysis of the mechanics of thoracic spine in man. An experimental study of autopsy specimens. Acta Orthop Scand Suppl 127:1-105, 1969. White AA, Panjabi MM: Clinical biomechanics of the spine. Philadelphia, 1991, JB Lippincott.
CHAPTER
4c
Initial Evaluation of the Low Back Region
have some specific properties (sensitivity and specificity) as well as those depending on the prevalence of the disease considered (predictive value) in the population being evaluated. Basically, signs and symptoms (or any other test) with very high sensitivity allow the clinician to rule out the target disease when the test is negative. On the contrary, when the specificity of a test is extremely high, a positive result “rules in” the target disease.21
Marek Szpalski, Federico Balagué, Robert Gunzburg, and Dan M. Spengler
HISTORY
Although patient evaluation and management have been clearly improved by the explosive growth in technology over the past decades, the hallmark of patient assessment continues to reside in the fundamentals of the history and physical examination. The information provided in this chapter emphasizes the importance of these basic skills to attempt to motivate the reader to continue to improve and update this important knowledge area. The focus of this chapter is the clinical assessment of patients who seek an evaluation of low back pain, with an emphasis on occupational aspects. Another relevant aspect that has become increasingly important in the last decades is the point of view of the patients. An important volume of literature devoted to this topic has been reviewed recently. In their systematic review of qualitative and quantitative studies, Verbeek et al72 highlighted the major patient expectations, specifically diagnosis, instructions, and interpersonal management. This information is important for the individual clinician. It is important to remind the clinician that the variables elicited by history taking and through a clinical examination
Two reviews of patient histories reported that although 2% to 3% of the causes of low back pain are nonmechanical, these etiologies must be considered most seriously and diagnosed quickly.20,22 All the factors that might be relevant because of their association with increased risk of cancer, infection, or other complications should be included in the history.20 In a study of almost 2000 back pain patients, Deyo21 found that no cancer was identified among those under age 50 without a history of cancer, unexplained weight loss, or failure of conservative therapy (combined sensitivity of 100%). The elements suggesting a diagnosis of specific low back pain are commonly designated in the literature as red flags (Table 4c.1).6 Concluding that a patient suffers from “nonspecific low back pain” once the clinician has reasonably excluded red flags seems to be rather unsatisfactory for most health care providers, who do not believe nonspecific low back pain to be one condition.42 It has been shown, moreover, that a comprehensive medical assessment is not predictive of return to work after an episode of occupational low back trouble.34 For all patients who are examined for an evaluation of low back pain with or without sciatica, a history of the present illness should be completed, including information regarding the nature
Table 4c.1
Red flags for potentially serious conditions
Possible fracture
Possible tumor or infection
Possible cauda equina syndrome
Age over 50 or under 20 History of cancer Constitutional symptoms such as recent fever or chills or unexplained weight loss Risk factors for spinal infection: recent bacterial infection (e.g., urinary tract infection) intravenous drug abuse, or immune suppression (from steroids, organ transplantation, or human immunodeficiency virus infection) Pain that worsens when supine; severe nighttime pain
Saddle anesthesia Recent onset of bladder dysfunction such as urinary retention, increased frequency, or overflow incontinence Severe or progressive neurologic deficit in the lower extremity
From medical history: Major trauma such as vehicle accident or fall from a height Minor trauma or even strenuous lifting (in older or potentially osteoporotic patients)
From physical examination: Unexplained laxity of the anal sphincter Perianal/perineal sensory loss Major motor weakness: quadriceps (knee extension weakness); ankle plantar flexors, evertors, and dorsiflexors (footdrop)
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of symptom onset. The absence of sciatica or femoral nerve radicular pain makes a clinically important disk herniation very unlikely (sensitivity about 0.95 and specificity 0.88).21 In addition, the examiner should document various treatment approaches and the effects of the treatments on symptoms. The reason for the evaluation and any anticipated outcomes must be understood in advance by both the physician and the patient. If the evaluation is for an independent medical evaluation, for example, the patient needs to understand its purpose of providing an independent objective assessment for a third party and that treatment is not included. The evaluation may be to assist another physician in patient management or solely to provide an insurance company or a workers’ compensation carrier with a diagnosis and recommendations. When related to swirling litigation and compensation issues, a history must usually be more detailed than one obtained solely to diagnose symptoms and manage a patient. If a patient falls at home and seeks evaluation, for example, the history might be succinct and relate only the type and distance of the fall. In a contested on-the-job injury encounter, the details may be more important for dispute resolution. Was the fall witnessed? Did the employee return to work? For how long? Is an attorney involved? Who are the physicians or others who have evaluated the patient? Has the employee had a previous injury? Has an impairment been recorded previously? An interview with a patient who is involved in litigation can be facilitated by having the referring person summarize the outcomes desired from the consultation. In addition, a succinct summary of the events to date should be provided to serve as a template for review during the patient interview. Information provided by the referral source does not replace the need for a good history; it only highlights the issues from another perspective. The opening aspects of the history should focus on the present illness. The examiner must not lead patients into answers by the use of “closed” questions, such as “Does your back pain radiate to the posterior of your thigh, calf, and foot?” Patients may often answer yes to these questions even though they may not understand what was asked or the relevance. A much better strategy is to ask the patient to describe the pain. What makes the pain better or worse? These questions can amplify the pain drawing that is gathered before the history and physical examination.9 This tool is helpful to maintain in the patient’s file to compare over time or to establish the patient’s pain pattern at the time of evaluation. In addition, recording a few notes for later dictation, the physician should also observe the psychologic, physical, and emotional behavior of the patient throughout the interview and examination. Loss of eye contact, change in voice tone, or excessive movement on the examining table should be noted, because these nonverbal cues may be equally or more important than the actual words spoken. Signs suggesting a clinical depression should be noted also because depression can be commonly encountered as both a primary and a secondary disorder in patients complaining of low back pain. Slurred speech or an impressive knowledge of pain medications should be noted also to provide clues to potential alcohol or medication abuse, the latter of which is quite common in patients who complain of chronic back symptoms.9,61 Pain patterns should also be noted. Does the pain intensity stay the same throughout the 24-hour day, or is it better or worse
in the morning or in the evening? Is the pain predictable or erratic? Is the patient’s sleep pattern disrupted because of night pain? Although night pain can be associated with various forms of malignancy or inflammatory disorders, it can also reflect clinical depression or be associated with psychosocial issues. The relationship of various activities to the pain complaints should be discussed as well. Pain that increases with walking short distances yet disappears rapidly with sitting or lying can represent a typical pattern in a patient with lumbar spinal stenosis. A clinical diagnosis cannot be advanced solely on the basis of the pain pattern, however, because of the wide variability of clinical symptoms in most disorders that result in low back pain. When interviewing a patient with low back pain that has been present for more than 3 months, the physician should completely review the patient’s systemic symptoms, including fever, chills, night sweats, weight loss, and lethargy, along with any sources of infection, whether systemic or not, such as a localized cutaneous abscess. Gastrointestinal symptoms are relevant because such disorders can actually occur concomitantly with low back symptoms and because so many patients take large doses of salicylates or nonsteroidal antiinflammatory agents, which can lead to significant gastrointestinal bleeding.53 Genitourinary symptoms are reviewed also, because bladder dysfunction can be associated with pressure on the spinal cord or cauda equina. Although such symptoms are more commonly related to causes other than neural compression, an early recognition of a change in bladder habits may signal a subtle increase in pressure on the neural elements.5 When genitourinary symptoms are present, the physical examination should include a well-documented rectal examination. A cystometrogram and a urologic consultation may be necessary to clarify the nature of these problems.5 Female patients should be questioned regarding any changes in bleeding patterns or pain related to menstruation, and those with persisting back complaints should be evaluated by their gynecologists. Medications taken by the patient should also be recorded. If the patient has been taking multiple medications in the past for back pain, the associated clinical response should be noted. Other back treatment approaches, including the patient’s pain-free interval after an intervention such as steroid dose packs, epidural steroid injections, or physical therapy, should be noted as well. Psychosocial and economic issues associated with the low back symptoms should be reviewed. Life stressors, litigation, compensation, and other secondary gain parameters would likely not have “caused” the pain, but such issues can certainly maintain the chronicity of symptoms in specific cohorts of patients. A systematic review of psychologic factors as predictors of chronicity or disability highlight the limits of the available evidence, but the roles of distress/depressive mood and, to a lesser extent, somatization are underlined. As discussed in greater detail in Chapter 2, the role of coping strategies and fear avoidance deserve further research.52,73 In recent years a list of red flags and treatment matrices have been enlarged to include cognitive and behavioral approaches into the early management of acute low back pain. “Yellow flags” can be evaluated by means of six open questions that should be phrased in the health care provider’s own words: 1. Have you had time off from work in the past with back pain? 2. What do you understand to be the cause of your back pain? 3. What are you expecting will help you?
Chapter 4c
4. How are your employer, coworkers, and family responding to your back pain? 5. What are you doing to cope with back pain? 6. Do you think that you will return to work? When?40 Moreover, “blue” flags (psychosocial aspects of work) and “black” flags (employer-specific and global) aimed at evaluating other socioeconomic environmental factors have been described in the last few years.31 The past medical history should be completed to include any diagnostic assessments, treatment approaches not previously noted, and doctors or others who have evaluated or treated the patient for low back and other medical problems. The length of any pain-free interval after previous surgical procedures should also be documented. Short-term relief after major surgery may occur after procedures that may not have been clearly indicated. Other causes can include an operation performed at the wrong spinal level, an inaccurate diagnosis, an associated medical disorder with referred low back symptoms, and a pain-prone patient who tends to amplify symptoms. A comparison of the existing occupational health guidelines for the management of low back pain revealed that all the published guidelines distinguished specific and nonspecific cases and consistently recommended a clinical history to identify relevant physical and psychosocial workplace factors and a physical examination including neurologic screening. Red and yellow flags are highlighted by most of the guidelines.63
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Physical examination
patient and doctor. They must be understood in the context of the patient’s history and offer only a psychologic “screener,” not a complete psychologic assessment. Finally, they are not on their own a test of credibility or veracity, nor are they a reason to deny appropriate physical treatment.48 A study showed that with regard to return to work in patients with acute low back pain, the predictive value of the nonorganic symptoms or signs (independently or combined) was rather poor.28 The patient should be suitably attired for the examination to provide for privacy but also to facilitate a complete musculoskeletal evaluation. Together with a sheet for the supine and prone portions of the examination, the standard patient gown that is open in back is quite appropriate. The physical examination should be complete but also age and complaint related. Although not an essential portion of the examination in an 80-year-old patient with back pain after a minor fall, chest expansion, for example, is clearly important in a 20-year-old man with an insidious onset of low back pain over a long period of time. Decreased chest expansion (less than 2.5 cm) in such a patient could suggest the diagnosis of ankylosing spondylitis. A study showed that a screening system led by two physiotherapists resulted in a clinical and economic improvement in the care of those suffering from acute low back pain.49 The physical examination is divided into five components based on the position of the patient, beginning with the patient standing.
Patient standing PHYSICAL EXAMINATION A physical examination is one among many patient expectations72 that permits the physician to assess the patient and record the observations. Objective findings, including deep tendon reflexes and circumferential measurements of the calf and thigh to determine swelling or atrophy, represent the most important parameters. Less helpful, subjective, physical examination findings include supine straight leg raising (unless done in the sitting position as well) and range of motion, the least reliable of all determinants.3 Unfortunately, range of motion is still used, although to a lesser degree, for impairment ratings as suggested in the American Medical Association guidelines. Inappropriate physical examination findings are important to record also. A certain number of inappropriate physical signs have been described and are often referred to as “Waddell’s signs.” Too often, physicians consider the presence of three or more of these findings as an alert that the patient may be attempting to amplify them for secondary gain. It is important to note, however, that the presence of inappropriate physical findings does not exclude the presence of a pathologic process and may be due to factors other than attempted malingering. This illness behavior may be linked to fear of reinjury, misunderstanding of instructions, other psychologic issues, and other incident issues. The onus is therefore on the physician to recommend the appropriate diagnostic studies. Main and Waddell48 discussed the theoretical misunderstandings of the behavioral signs in clinical practice and in the medicolegal context. We reproduce here some of the authors’ conclusions and recommendations. As “behavioral responses to examination,” these signs are a form of communication between
The lumbar spine examination begins with the patient standing. The physician should observe the general configuration of the spine to detect any lateral curvatures, kyphosis, or excessive lordosis. Patients with lumbar paraspinous spasms frequently have a pelvic list that should be noted. In patients with lumbar disk herniation, it has been demonstrated that although not associated with the location of nerve root compression, the direction of lumbosacral scoliotic list is related to the side of disk herniation.64 In young adult males with low back pain, chest expansion should be measured with a cloth tape because expansion less than 2.5 cm suggests an inflammatory process such as ankylosing spondylitis. After observing the spine orientation in the erect patient, the physician should ask him or her to flex forward, a step particularly important in adolescents to detect early lateral curvatures of the spine. To assess the range of motion of the lumbosacral spine, the physician should stand behind the patient and observe the lumbar paraspinous muscles. Any eccentric contractions of the musculature suggest lumbosacral paraspinous spasms; limited motion without evidence of such eccentric contractions might suggest a lack of patient cooperation even though there are other possibilities (such as a congenital block or previous fusion). Forward and lateral flexion and extension of the lumbar spine should be observed. Normal patients should be able to bend forward nearly to touch their toes and to the sides to touch the fibular heads, but extension of the spine is extremely variable. In general, pain increased by flexion suggests lumbar disk abnormalities and pain with extension suggests degenerative changes involving posterior elements of the spine, lumbar spinal stenosis, or both. Occasionally, patients with lumbosacral paraspinous
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spasm can flex forward reasonably normally but have difficulty returning to the erect position. Such patients may accomplish this move in a two-phase recovery by flexing the knees and extending the hips without motion in the lower back. The true value and reliability of flexibility assessment is, however, dubious. The reliability of lumbar flexion and extension measured with an electronic inclinometer within a complete physical examination was evaluated in a group of normal volunteers. The intrarater and interrater reliability for flexion were, respectively, 0.48 and 0.56, whereas the same values for extension were 0.53 and 0.37, respectively.33 In older patients, the range of motion of the cervical spine should also be assessed because degenerative osteoarthritis of the cervical spine occasionally results in low back complaints. A study including 27 patients suffering from lower back pain and unilateral single nerve root symptoms, 14 patients with multilevel nerve root symptoms, and 10 control subjects showed that low back pain correlated significantly with restriction of anteroposterior spinal flexion measured with a computerized triaxial potentiometric analysis system.54 After observing the range of motion, the physician should percuss the spine to detect any localized tenderness, a subjective reaction. This test has little value if the patient has tenderness at multiple areas, but consistent localized tenderness over the midline of the spine may suggest inflammatory diskitis (or fractures, tumors, and so forth). The costovertebral angle should be palpated; tenderness in this area suggests a genitourinary problem such as pyelonephritis. Patients should next be asked to walk on their heels and then toes to assess the overall strength of the dorsiflexors (L5) and plantar flexors (S1) of the ankle. In particular, the extensor hallucis longus muscles should be observed when the patient is walking on the heels, because discrepancies can be detected between this act of walking and later passive strength testing. To assess and detect weakness of the triceps surae muscles, which are innervated primarily through the S1 nerve root, the physician should ask the patient to hop several times on the left foot, then on the right foot, and note any discrepancies in the two abilities. The patient should be observed also while walking in the examining room. Extreme staggering from side to side and other bizarre gait patterns suggest symptom amplification. Patients with true herniated disks often have a gait pattern slightly antalgic on one side but with no bizarre abnormalities.
Patient sitting The patient should next sit on the edge of the examining table so the physician can perform the knee and ankle reflex tests and determine the strength of the extensor hallucis longus muscle. This latter examination is critical in all patients complaining of back and leg pain because many have weakness of the extensor hallucis longus but not the tibialis anterior. Weakness of the extensor hallucis longus in a patient who complains of back and leg pain suggests involvement of the L5 nerve root. The extensor digitorum brevis muscle should be checked; however, some authors remain unconvinced that observation of this muscle has any diagnostic significance in patients with lumbar disk disease. Asymmetry is often observed in patients who have never had low back and/or leg pain.
Figure 4c.1 Sitting straight leg raise test. The patient leans back in the “tripod” sign, indicative of true sciatic tension.
The most important portion of the sitting examination is the distracting straight leg raise (SLR) test (Fig. 4c.1). The SLR test has shown to be adequate in healthy subjects when performed within a complete physical examination.33 During this lifting of an extended symptomatic leg in the sitting position, patients with herniated disks and true symptoms of sciatic tension arch backward and complain of pain in the buttock, posterior of the thigh, and calf. Patients who do not have true sciatic tension do not recognize this as a sciatic tension test and therefore have no symptoms. For the patient who complains of pain in the neck as well as the lower back, the strength and reflexes of the upper extremities can be evaluated while he or she is sitting.
Patient supine With the patient supine on the examining table, the physician uses a standard tape to measure the true length of the limbs from the anterior superior spine to the medial malleolus on both sides. Although significant discrepancies (more than 2.5 cm) in limb lengths can result in mild compensatory scoliosis and low back discomfort, these associations are uncommon. The physician should observe the thigh and leg muscles for early signs of atrophy. In addition, the physician should use a cloth tape to measure the circumferences of both thighs one handbreadth above the patella and those of both calves one handbreadth below the patella. Discrepancies greater than 2 cm again are probably significant and suggest muscle atrophy. For the standard ipsilateral SLR maneuver, the physician stands to the patient’s right, places the left hand on the patient’s patella to extend the knee, places the right hand under the os calcis, and then lifts the leg while keeping the knee extended (Fig. 4c.2). Because patients often describe their discomfort in different locations in the extremity, the objectivity of the test results are qualified. If the patient complains of radicular discomfort
Chapter 4c
Figure 4c.2 Supine straight leg raise (SLR) test. For maximum accuracy in identifying sciatic tension, this test must be compared with the sitting SLR test.
during the test, the limb should not be lifted any higher. At that moment, plantar flexion of the ankle should be performed as a distracting test. Because plantar flexion of the ankle should not increase back pain, exacerbation of pain may suggest amplification of symptoms by the patient. Dorsal flexion, on the contrary, should increase sciatic tension and pain (Fig 4c.3). The physician should perform the crossed SLR test also by lifting the nonsymptomatic extremity as in the ipsilateral SLR test. If the patient complains of discomfort radiating into the symptomatic extremity when the well extremity is lifted, this test is positive, almost invariably indicating lumbar disk herniation. During both the SLR test and the crossed SLR test, the patient must be allowed to state where the discomfort is occurring. Specifically, asking the patient whether lifting the well extremity causes pain in the symptomatic extremity invalidates the test. It is important to note that in patients with L4-L5 and L5-S1 disk herniations, the SLR test has very high sensitivity (95%) but lower specificity, whereas the cross SLR has much lower sensitivity (25%) but significantly higher specificity (90%).20
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Patrick’s test should then be performed bilaterally. In this test, the shear force applied across the sacroiliac joint helps detect early abnormalities. Many patients with osteoarthritis of the hip complain of buttock pain rather than the classic groin discomfort, causing the hip joint often to be overlooked because of the apparent back problem. Patients with abnormalities of the hip joint cannot tolerate Patrick’s test, however, because of the discomfort when the limb is fully externally rotated into the abducted position. While the patient is supine with the limbs extended, the physician should therefore gently rotate the lower extremity both internally and externally, a gradual rotation that reveals early irritability in the hip joint. If internal and external rotations cause pain, it may arise from that area. Brown et al14 reported on the clinical signs that may be helpful to distinguish between a hip disease and a spinal origin of pain: “the presence of a limp, groin pain, and limited internal rotation of the hips more often was associated with and predictive of a hip disorder than a spine disorder.” The abdomen should be examined by palpating the four quadrants to detect any intraabdominal masses. Abdominal lesions may erode into the lumbosacral plexus and cause symptoms identical to those of lumbar spinal stenosis or disk disease (Fig. 4c.4). The strength of the abdominal muscles should be assessed by having the patient flex the knees while keeping the feet flat on the table and then perform a sit-up. Patients who have extreme difficulty completing even one sit-up are theoretically excellent candidates for a vigorous rehabilitation program. In addition, the patient should be asked to hold the lower extremities 15 to 20 cm off the table. In general, a patient with an established herniated disk can easily perform this maneuver, so the primary value of this test is to assess the strength of the abdominal musculature rather than determine the likelihood of a disk herniation. With the patient supine, the motor strength of the iliopsoas, quadriceps, and hamstrings, along with Babinski’s reflexes and proprioception, should all be assessed. A sensory examination also should be performed and recorded. A study demonstrated significant elevations of warm, cool, and touch perception thresholds correlated with leg pain in patients with unilateral L5 or S1 nerve root pain. However, dermatomal quantitative sensory tests require some specific tools that are not part of the routine clinical equipment.54
Patient on side
Figure 4c.3 Dorsiflexion of the ankle during a straight leg raise test increases pain.
The supine patient is then asked to turn on one side and to raise and maintain the superior extremity against resistance by the physician (Fig. 4c. 5). In most patients, the gluteus medius is innervated primarily by L5, so patients with L5 radiculopathy often have weak abductors, as do patients with significant hip disease. The trochanter should be palpated to test for trochanteric bursitis. These same tests should be repeated with the patient lying on the opposite side. With the patient on one side, perianal sensation and but-tocks sensation also should be evaluated. All patients over the age of 40 and any patient suspected of a neurologic deficit should have a rectal examination. In males, anal sphincter tone and the size of the prostate may be assessed. Female patients with chronic back pain should have a pelvic examination by a gynecologist.
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A Figure 4c.4 on an MRI.
B (A) CT of a calcified arthrosynovial cyst (circled) causing left nerve root entrapment. (B) The same pathology is less obvious
Figure 4c.5
Gluteus medurs strength testing with the patient on the side and abducting against resistance.
Chapter 4c
Patient prone With the patient prone on the examining table, the lumbar spine, sacrum, and sacroiliac joints should then be reexamined for any localized tenderness. A reverse SLR maneuver can easily be accomplished by the physician simply by lifting both of the patient’s lower extremities off the table, although quite often just bending the knees in the prone position is enough to elicit pain in the L3 or L4 dermatome. The patient should next flex the knees 90 degrees so that the physician can observe internal and external rotation of the hips. In most patients, the amount of internal and external rotation is quite similar. Patients with femoral anteversion, however, have excessive internal rotation and limited external rotation and often experience discomfort in the low back area and buttocks while running. When the patient is prone, ankle jerks often are easier to reexamine and compare; the absence of one or both reflexes should be noted. Finally, the patient should extend first one lower extremity and then the other by using the gluteus maximus muscle. Increased low back discomfort during this maneuver suggests a more superficial myofascial source of the symptoms.
ADDITIONAL INVESTIGATIONS After careful history taking and physical examination (and only then), a number of technical examinations can be ordered based on the results. None of those examinations should be considered as a screening tool, “to see how they come out.” A specificity of low back pain is that in most cases a precise cause of nociceptor cannot be precisely determined despite the increasing sophistication of investigations. Specialized examinations should serve to confirm or pinpoint a suspected diagnosis, and the precision of each should be known. That precision can be determined by statistical measures of sensitivity (the proportion of subjects with the disease in whom the examination is positive), the specificity (the proportion of subjects without the disease in whom the examination is negative), the accuracy, and the predictive value. The two latter measures are not always available in all cases, and in the context of back pain the specificity of imaging is often poor due to a wide range of abnormal images that are asymptomatic. With more sophisticated examinations, more asymptomatic abnormal images are found. In contrast to severe osteoarthritis of the hip or knee, which does not affect everyone and is seldom asymptomatic, marked degenerative changes in the spine seem to affect nearly all human beings with aging and are often asymptomatic. The patient should be told the reason for which an examination is ordered and advised that it may show some meaningless “pathologic images” that are irrelevant to the present symptoms. Those incidental findings are usually nonsignificant and not what was suspected and researched. We all see patients coming with multiple radiology reports where statements about “black disk,” “bulging disk,” or “degenerative changes” have been strongly underlined or highlighted by the patient (or sometimes the doctor). Those misconceptions can lead patients to further impressions of seriousness and prolonged disability. Early and complex imaging
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Additional investigations
with precise description of nonsignificant abnormalities facilitates the “medicalization” of low back pain,12 and duration of disability is associated with its early increased use.47 Patients’ perceptions, expectations, and demands play a major role in the use of imaging modalities to diagnose low back pain. A myth common among patients is that radiographs will show the exact cause of their back pain,36 so they expect to have radiographs when seeing doctors for such complaints.43 They wish to have an x-ray examination ordered, moreover, and physicians’ attitudes are often correlated to patient wishes.77 It appears then that patient education is necessary, although physician education is perhaps even more acutely needed.74 Although many guidelines about diagnostic procedures in back pain have been published in several countries, multiple studies show that most are not followed in the United States,27,56 Canada,8 Norway,77 and Spain.29 All those studies reveal that physicians, mainly in primary care settings but also specialists, still order too many examinations that are of little use.
Plain radiograph Plain radiographs have been the standard (and only widely available) imaging technique in assessment of back pain for decades. They show the bony structures precisely, displaying spondylolysis, spondylolisthesis, deformities, tumors, fractures, and degenerative changes such as disk narrowing, disk vacuum, and traction osteophytes. The latter, however, appear to be a normal evolution of the spine and are very common in symptom-free middle-aged and aged subjects. Instability can be assessed on dynamic (flexion/extension/lateral flexion) radiographs, but the relation of radiologic “instability” to back pain is subject to discussion.65 For these reasons plain films have very low specificity and therefore low diagnostic precision38 and make no difference to the outcome for back pain,78 especially in elderly subjects.10,71 In the case of acute low back pain in a subject between 18 and 50 years of age, plain films are indicated only if there is a history of trauma, malignant disease, or symptoms of infection. In the case of neurologic symptoms, magnetic resonance imaging (MRI) (or computed tomography [CT] if it is unavailable) might be a better diagnostic tool. If no clinical improvement is observed after 6 weeks, plain films may be taken to help exclude a diagnosis of tumor, infection, spondylolysis or olisthesis, and osteoarthritis of the hip, and along with simple laboratory tests will rule out systemic diseases.37 Some studies suggest, however, that in the absence of red flags, radiographs should not be ordered even after 6 weeks of symptoms.41 In chronic low back pain, the same pathologies should be ruled out, but preferably by MRI.10
Myelography Until the advent of CT, myelography was the only examination that enabled physicians to assess spinal neural structures, the dural sac, and the roots. Myelography is still the only widely available examination permitting a dynamic view of the dural sac during flexion and extension in the upright posture (Fig. 4c.6). Given the decrease of the dural sac diameter during extension, some cases of
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stenosis can be underestimated during examinations like CT or MRI that are performed in a supine position. Although upright MRI is becoming available, it is very expensive, uncommon, and constrained in patient positioning and acquisition time, making it inappropriate for this kind of assessment in stenotic patients. Upright myelography examination appears useful also in the diagnosis of position-related disk herniations35 and those in the lateral recess where MRI may underestimate root compression in nearly 30% of cases.2 Indeed, some authors have demonstrated similar sensitivity and specificity in myelography and MRI.55 Myelography is an invasive procedure, however, and neurologic or infectious complications, although very rare, are possible. Combined with CT (myelo-CT), myelography still has a place in cases of strong clinical suspicion of stenosis or herniated disk not clearly demonstrated on other imaging modalities. It also enables the laboratory analysis of the cerebrospinal fluid to be performed to rule out a number of neurologic diseases.
Computed tomography
Figure 4c.6 Myelogram showing multiple level central degenerative stenosis (arrows). Myelogram remains the only widely available examination enabling dynamic and upright assessment.
A
CT is the first examination to provide axial and three-dimensional representations of the spine and the first noninvasive examination to provide a view of spinal neural structures. When it appeared in the 1970s, it was a true revolution. It has now been widely replaced by MRI for the assessment of neural structures but still remains the best examination for the visualization of bony elements. It is also the only examination available for claustrophobic patients or for those with pacemakers or ferrous metallic implants. CT also offers more precise views of calcified disk protrusions.24
B
Figure 4c.7 (A and B) Spondylolysis and olisthesis are best investigated by computed tomography. In this case the pars defect is partially filled by Gill’s nodules (ossified fibrous tissue), which when associated with a disk bulge provoke a lateral stenosis.
Chapter 4c
CT shows more precisely the patterns of fractures in trauma cases and investigates pars fracture in spondylolysis or olisthesis (Fig. 4c.7). In the case of spinal stenosis, if MRI allows a better view of neural elements, CT is still invaluable to investigate the osseous participation in the stenotic process. We believe that it complements MRI before surgical treatment of lumbar stenosis. Spiraled helical CT allows a three-dimensional view of long spinal segments and as such may be very interesting for the accurate description of deformities.
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Additional investigations
MRI has become the standard investigation tool for spinal disorders. The precision of this examination handicaps its specificity, however, because it demonstrates a high frequency of clinically irrelevant abnormal images without associated symptoms. Some studies have shown a prevalence of 28% of disk herniations, at an average age of 42, in asymptomatic subjects,11,39 up to 52% of
which presented at least one bulging disk.39 With MRI, degenerative intervertebral disk disease is present in one third of subjects between 20 and 39, over half of those between 40 and 59, and in nearly all subjects over that age.11 Apparently, a normal physiologic evolution of the decrease of disk hydrophilic properties, dark or black disks, appear in almost everyone. These findings underline that to avoid misunderstandings by patients, MRI results must be interpreted with great care and meticulously related to clinical presentation. Even in the presence of symptoms, the correlation between the severity of clinical findings and MR images of mild to moderate compression due to bulging or stenosis is poor.4 Keeping these limitations in mind, MRI is nevertheless the best tool to investigate compromise of neural elements of the spine. In spinal stenosis it is especially useful in determining the extent of the narrow canal. In presence of a suspicion of neural compression, the addition of MR-myelography, realized through specific acquisition sequences, complements the results of the standard MRI in many cases (Fig. 4c. 8,9).26
Figure 4c.8 Voluminous extruded disk herniation provoking a cauda equine syndrome. In this case magnetic resonance imaging is the examination of choice. The patient had a full recovery after surgery.
Figure 4c.9 Magnetic resonance image of a lytic spondylolisthesis showing root entrapment in the foramen. The root (A) is hampered by the disk bulge in the foramen (B) consecutive to the sliding and flattening of the disk.
Magnetic resonance imaging
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Because it is usually performed in the supine position, MRI may underestimate images of compression in position-related stenosis or sciatica, as is the case with neurogenic claudication. Devices enabling axial compression during supine MRI (or CT) appear to add useful information about the decrease of the spinal canal diameter that appears during upright weight-bearing positions76 and also to enable more precise surgical strategies to be performed.32 MRI is highly specific and sensitive also in the research of malignant and infectious spinal diseases, warranting the use of gadolinium-enhanced MRI in acute low back pain when one of those pathologies is suspected.30 The results in MRI investigation of back pain are more subject to caution. An example is the high intensity zone, the presence of which has appeared to show much promise as a marker of discogenic low back pain. The high intensity zone is a high T2 signal in the posterior and/or posterolateral annulus that seems to increase during axial loading.59 Some authors have found a high correlation of this finding with pain and annular penetration of the dye during diskography, which they believe demonstrates a very high positive predictive value.1,60 Other authors, however, have shown a high prevalence of high intensity zone in asymptomatic subjects,15 whose reaction to diskography is similar to that of symptomatic patients.20 The sensitivity of the sign is low,58 and although it seems that the high intensity zone may show an annular fissure, that fissure is not a reliable sign of painful disk disease. In patients without active symptoms, furthermore, annular disruption is a weaker predictor of future low back pain than psychologic distress.19
have proposed ultrasonic imaging combined with pain provocation by vibrations to diagnose internal annular tears,79 but this technique has not gained widespread acceptance. Investigation of nerve roots and facets has been abandoned due to the lack of accuracy.51 Those examinations do not play a major role in spinal imaging.
Diskography Provocative diskography, which aims at back pain reproduction, has been a controversial subject for many years. It has been considered by some authors to be the best indicator of discogenic pain and has been widely used to confirm surgical indications of fusion and, more recently, disk replacement. Even after positive diskography, however, fusion results remain unpredictable.75 Furthermore, the frequency of positive responses to diskography among asymptomatic subjects challenges the value of this examination as a predictor of clinically relevant discogenic pathology.16,18 Although diskography is indeed a good indicator of annular tears, the latter do not appear to predict a clinically relevant spinal pathology.16 Specificity of diskography appears low,17 and pain intensity during injection is influenced strongly by the patient’s psychologic factors and compensation claims.16 In any case, diskography has no place in the initial assessment of low back troubles.
Electromyography Radionuclide bone scan Radionuclide bone scan (isotopic) is a highly sensitive but poorly specific examination. Of the different radionuclides that can be used, technetium-99m is the most common in spinal indications because it is highly sensitive for malignant diseases and infections. Bone scans using markers such as gallium or marked leucocytes show better specificity for infections. Nearly 40% of subjects with spinal metastasis and normal plain films have a positive bone scan.50 The test might help also to determine whether a vertebral or pelvic fracture is recent or old. Single photon emission CT has been suggested as useful for identifying patients with facet joint disease more likely to benefit from facet injections.23 Single photon emission CT also reveals many abnormalities not detected on a standard radiograph,57 but here again one might wonder about the clinical relevance of those findings. Whereas either the planar bone scan or single photon emission CT reveals areas of increased bone turnover, these tests lack the specificity necessary to determine the true nature of the “lesion” and serve only as indicators for further studies in accordance with the clinical presentation.
Ultrasonography Ultrasonograms may be useful in cases of paraspinal soft tissue infections or tumors or to rule out other sources of lumbar pain, such as urinary tract calculus or kidney diseases. Some studies
Electromyography may be useful in specifying the level of symptomatic compression and ruling out peripheral neuropathies (diabetic, ethylic, or other). One must bear in mind that electromyography shows abnormal signals only several weeks after the occurrence of a nerve compression. Although interesting as an adjunct examination, electromyography is not an essential tool in the initial assessment of spinal troubles.
Mechanical testing The inability to correlate low back pain to anatomic findings and the difficulties in quantifying pain have directed much effort toward measurement of spinal performance through the assessment of function across various dimensions such as flexibility, strength, speed, endurance, and coordination. Goniometers and isokinetic and isoinertial dynamometric devices are currently used. Isoinertial testing seems to be the most physiologic and clinically relevant approach. Useful for prescribing musclestrengthening therapy precisely, it enables the physician to follow up on the patient’s progress and can also be used to assess the efficacy of diverse treatments.44,46,68 In certain pathologies like spinal stenosis, specific patterns of motion have been demonstrated,69 and early decrease of spinal function has been shown in subjects with Parkinson disease.13 The use of neural network technique analysis of motion patterns has enabled researchers satisfactorily to assign back pain patients to pathologic categories based on the Quebec Task Force classification.7 These tests can also provide insight into the maximum effort exerted by the subjects62,66 but
Chapter 4c
despite the hopes of their proponents are by no means back pain “lie detectors.” The measure of flexibility is of limited value in the assessment of the spine,70 and the current American Medical Association guidelines for evaluating disability, heavily based on spinal range of motion, can lead to irrelevant results.45 More elaborate protocols, based on more complex analysis of kinematic profiles, appear to be much more promising.25
Other diagnostic studies Laboratory evaluation should be recommended for patients who are not responding to treatment or who have severe pain. Although many of these tests are indicated in specific situations, a useful screening evaluation for patients with persistent symptoms should include a complete blood count, sedimentation rate, coagulation survey, sequential multiple analysis-18, and urinalysis. Patients who show diminished bone density should be evaluated more thoroughly with thyroid studies, protein electrophoresis, urinary calcium, and evaluation of parathyroid hormone levels. Should one proceed this far in the evaluation, a referral to an endocrinologist with an interest in calcium metabolism is clearly warranted. In young male patients suspected of having ankylosing spondylitis, an HLA-27 antigen study can be ordered.
DIFFERENTIAL DIAGNOSES When evaluating patients with complaints of low back pain, the physician must remain vigilant to identify those whose symptoms result from referred pain unassociated with the intervertebral Differential diagnosis disk or spinal nerves. In this of low-back pain time of intense focus on cost, the physician must also remain Trauma dedicated to a proper evaluaInfections tion for the patient and not Inflammations succumb to managed-care Neoplasms bureaucrats who are interested Developmental abnormalities primarily in the cost rather Metabolic diseases than the quality of care. Patients with low back pain Degenerative disorders represent an interesting group. Neurologic disorders A list of differential diagnoses Referred pain is provided in the box to the Psychological disorders right. Approximately 2% of Miscellaneous patients who come to a low back specialty clinic have evidence for neoplasms as the source of the symptoms.10 A list of suspected causes coupled with the knowledge of appropriate testing aid the physician in formulating a proper workup. A complete history and careful physical examination must underlie any assessment for low back pain. Physicians should remember that their most effective and readily available tools are their hands and brains. Only after this meticulous first stage has been completed can specialized examinations be ordered to answer precise questions and to confirm or eliminate specific pathologies.
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References
Evidence-based medicine principles apply to diagnostic investigations, but there are no screening tests for back pathologies. The poor specificity of the most common imaging techniques is inversely proportional to the frequency of their use. Radiographs and now MRI, which seem to be used almost as routine investigations in low back pain patients, provide a huge quantity of clinically irrelevant information. In a world in which health care resources are decreasing while the population ages and increasing technology costs demand further funding, physicians will be held accountable for unjustified practice costs. Patients should be educated and alerted that technology will not invariably uncover the precise reason of their pain, but physicians too require education, as the failed implementation of many guidelines painfully shows.
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Pincus T, Burton AK, Vogel S, Field AP: A systematic review of psychological factors as predictors of chronicity/disability in prospective cohorts of low back pain. Spine 27:E109-E120, 2002. Pincus T, Griffin M: Gastrointestinal disease associated with nonsteroidal anti-inflammatory drugs. Am J Med 91:209-212, 1991. Quraishi NA, Taherzadeh O, McGregor AH, Hughes SPF, Anand P: Correlation of nerve root pain with dermatoma sensory threshold and back pain with spinal movement in single level lumbar spondylosis. J Bone Joint Surg 86B:74-80, 2004. Ramsbacher J, Schilling AM, Wolf KJ, Brock M: Magnetic resonance myelography (MRM) as a spinal examination technique. Acta Neurochir (Wien) 139:1080-1084, 1997. Rao JK, Kroenke K, Mihaliak KA, Eckert GJ, Weinberger M: Can guidelines impact the ordering of magnetic resonance imaging studies by primary care providers for low back pain? Am J Manag Care 8:27-35, 2002. Ryan PJ, Evans PA, Gibson T, Fogelman I: Chronic low back pain: comparison of bone SPECT with radiography and CT. Radiology 182:849-854, 1992. Saifuddin A, Braithwaite I, White J, Taylor BA, Renton P: The value of lumbar spine magnetic resonance imaging in the demonstration of anular tears. Spine 23(4): 453-457, 1998. Saifuddin A, McSweeney E, Lehovsky J: Development of lumbar high intensity zone on axial loaded magnetic resonance imaging. Spine 28(21):E449-E451, 2003. Schellhas KP, Pollei SR, Gundry CR, Heithoff KB: Lumbar disc high-intensity zone: correlation of magnetic resonance imaging and discography. Spine 21(1):79-86, 1996. Spengler DM, Loeser JD, Murphy TM: Orthopaedic aspects of the chronic pain syndrome. Instr Course Lect 29:101-107B, 1980. Spengler DM, Szpalski M: Newer assessment approaches for the patient with low back pain. Contemp Orthop 21:371-378, 1990. Staal JB, Hlobil H, van Tulder MW, et al: Occupational health guidelines for the management of low back pain: an international comparison. Occup Environ Med 60: 618-626, 2003. Suk KS, Lee HM, Moon SH, Kim NH: Lumbosacral scoliotic list by lumbar disc herniation. Spine 26:667-671, 2001. Szpalski M: The mysteries of segmental instability. Bull Hosp Jt Dis 55:147-148, 1996. Szpalski M, Federspiel CF, Poty S, Hayez JP, Debaize JP: Reproducibility of trunk isoinertial dynamic performance in patients with low back pain. J Spinal Disord 5:78-85, 1992. Szpalski M, Gunzburg R: Methods of trunk testing. Semin Spine Surg 10:101-111, 1998. Szpalski M, Hayez JP: Objective functional assessment of the efficacy of tenoxicam in the treatment of acute low back pain: a double-blind placebo-controlled study. Br J Rheumatol 33:74-78, 1994. Szpalski M, Michel F, Hayez JP: Determination of trunk motion patterns associated with permanent or transient stenosis of the lumbar spine. Eur Spine J 5:332-337, 1996. Szpalski M, Parnianpour M: Trunk performance, strength and endurance: measurement techniques and applications. In JN Weinstein, SW Wiesel, eds: The lumbar spine. Philadelphia, 1996, WB Saunders. Tress BM, Hare WS: CT of the spine: are plain spine radiographs necessary? Clin Radiol 41:317-320, 1990. Verbeek J, Sengers MJ, Riemens L, Haafkens J: Patient expectations of treatment for back pain: a systematic review of qualitative and quantitative studies. Spine 29: 2309-2318, 2004. Waddell G, McCulloch JA, Kummel E, Venner RM: Nonorganic physical signs in low back pain. Spine 5:117-125, 1980. Werner EL, Laerum E, Ihlebaek C: How is the general practitioner managing the back pain? Tidsskr Nor Laegeforen 122:1800-1803, 2002. Wetzel FT, LaRocca SH, Lowery GL, Aprill CN: The treatment of lumbar spinal pain syndromes diagnosed by discography: lumbar arthrodesis. Spine 19(7):792-800, 1994. Willen J, Danielson B: The diagnostic effect from axial loading of the lumbar spine during computed tomography and magnetic resonance imaging in patients with degenerative disorders. Spine 26(23):2607-2614, 2001. Wilson IB, Dukes K, Greenfield S, Kaplan S, Hillman B: Patients’ role in the use of radiology testing for common office practice complaints. Arch Intern Med 161(2):256-263, 2001. Yelland M: Diagnostic imaging for back pain. Aust Fam Physician 33:415-419, 2004. Yrjämä M, Tervonen O, Vanharanta H: Ultrasonic imaging of lumbar discs combined with vibration pain provocation compared with discography in the diagnosis of internal anular fissures of the lumbar spine. Spine 21(5):571-575, 1996.
CHAPTER
4d
Treatment Options Margareta Nordin, Federico Balagué, and Christine Cedraschi
More than 17 guidelines drawn from large evidence-based systematic literature reviews have been published in different countries on low back pain (LBP),8,79,96 a topic that the World Health Organization included in their report, the Bone and Joint Decade 2000-2010.38,59,98 LBP remains a common affliction that is debilitating for the patient and expensive for the working individual and for society.31,70 This chapter gives an overview of treatment modalities for returning an individual to work during the course of acute to chronic LBP. The focus is on LBP that is nonspecific, where causality cannot be established and which is treated by a structured evidence-based approach to prevent disability and chronicity.
SPECIFIC AND NONSPECIFIC LBP The classification for pain in the lumbar spine used by clinicians is “specific” or “nonspecific,” depending on which of more than 60 diagnoses applies.
TREATMENT MODELS Two treatment models are commonly used in treating back pain: the medical model and the biopsychosocial model. Modern medicine uses the classic scheme, which implies that an interaction between the patient and an exposure leads to an illness complex.99 This model works well in dealing with SLBP. The procedures are to 1. Recognize patterns of symptoms and signs by history and examination; 2. Identify underlying injury or disease by investigation and diagnosis; 3. Treat underlying injury or disease by specific intervention; 4. Expect the patient to recover. Preferably applied to NSLBP, the biopsychosocial model identifies factors associated with delayed recovery for return to activity and, most often, return to work. The model calls for identification of symptoms and signs outside the traditional medical field such as beliefs, high perception of disability, kinesophobia, depression, stress, job dissatisfaction, anxiety, somatization, or lack of control.22,94 These contributing factors are treated with nontraditional medical approaches such as cognitive behavioral therapy (CBT) or ergonomic or occupational intervention. The biopsychosocial model in occupational health care helps to 1. Recognize the nonspecific nature of the back pain; 2. Identify underlying psychosocial and/or environmental factors; 3. Treat these factors with appropriate interventions; 4. Empower the patient to assume responsibility for managing a condition with possibly frequent recurrence.
Specific low back pain The common feature for specific low back pain (SLBP), the diagnosis in up to 2% of all early back pain cases, is a causal link between a structural pathology and the described experience of the patient (see Chapter 4c). SLBP may result from systemic disease, infection, injury, trauma, cauda equine, or structural deformity. Additionally, nerve root pain, which occurs in about 5% of the individuals seeking care early, includes diagnoses such as a disk prolapse or spinal stenosis. These conditions are treated with or without surgery and should be referred to a specialist for determination of care.6,8,57
Nonspecific low back pain Nonspecific low back pain (NSLBP), which afflicts 85-90% of all individuals seeking care, is a diagnosis of exclusion: No precise structure is identified as the cause. NSLBP is attributable to common diagnoses such as lumbago, myofascial syndromes, muscle spasms, mechanical LBP, back sprain, and back strain. These conditions all include pain in the lumbar region that may or may not radiate to one or both thighs but not below the knee(s). The following International Classification of Diseases diagnostic codes are suggested to best represent NSLBP: lumbago (724.2) and sprains of the lumbosacral region (846.0-3/8-9, 847.2-3).24
The first occupational health guidelines for the management of LBP at work were published in 2001 (see also www.facoccmed. ac.uk).96 These guidelines are based on an extensive systematic review of the scientific literature primarily in terms of occupational settings or outcomes.
PATIENT EXPECTATIONS A patient approaches a physician with expectations and preconceptions. The patient expects diagnostic explanation, pain relief, referral for treatment, instructions for coping with pain and disability, and, in an occupational environment, help with sickness certification or light duty assignment. Some patients expect imaging or special tests and specific medication. In one cross-sectional study (n = 1942), for example, 77% of the responders believed that if back pain exists, a wrong movement could lead to a serious problem. Forty percent believed also that radiographs and imaging could always identify the cause of back pain.40 It takes time to explain inappropriate concepts and expectations. The first encounter addresses such misconceptions, whereas at subsequent visits the important concepts for recovery are discussed and reinforced.69,91 Evidence-based information educates the patient that selective treatments may take time; some treatments may pose higher risks, and the effects of new treatments
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are not entirely known. The patient and clinician discuss the proposed treatment and the prospect of harm when work is resumed and agree on a regimen including compliance and return to work. Patient education about treatment choice and expected outcome is a key factor for success.49,97
NATURAL HISTORY AND RECURRENCE OF NSLBP Acute NSLBP has a favorable prognosis. Some authors argue that NSLBP is a lifetime disease if recovery has not occurred during the first 3 months,10,84,92 as is true for a large subgroup of individuals.48 Von Korff et al93 found that 20% of the U.S. population suffers from chronic LBP each year and that about 30% of them suffer chronic pain over their lifetimes. Studies focusing on the natural history of LBP report that 80% of patients who consult a health care provider for acute NSLBP can expect to resume normal activities within 4 to 6 weeks. By 12 weeks, the rate of recovery rises to almost 90%. Compared with approximately 35% to 40% of patients with SLBP, 10% or fewer of NSLBP patients experience chronic pain and work incapacity.1,11,70 The recurrence rate in NSLBP varies considerably from 5% to 70%, with up to 2 years follow-up in studies of both general and specific occupational populations.18,92 Recurrence or episode rate is difficult to estimate, however, because the definition of an episode is not standardized in different studies.29 We diagnose recurrent NSLBP when the employee has returned to regular work pain free for at least 8 weeks since the previous episode.71
on exercises and NSLBP, the authors concluded that “exercise therapy is as effective as either no treatment or other conservative treatments” in 11 trials involving 1192 adults.1,45,88 A series of five to six manipulations in the acute stage of NSLBP reduces pain and disability for up to almost 3 weeks.4,8,14,33 Alternatively, the patient may have a short course in pain management involving five to six encounters with a therapist trained in the biopsychosocial approach.61 In a comparison of manipulation and pain management in patients with acute NSLBP, the outcomes at 3 months and 12 months were almost identical (difference 0 [95% confidence interval (CI), -1.3-1.4]), with a decrease in disability score of about 8.8/24 points.44 With the patient maintaining tolerable activity, manipulations and pain management in acute NSLBP are superior to all passive modalities (mobilization, diathermy, massage, heat) over the long term.21,33 Continued passive longterm treatment of NSLBP is harmful because it precludes patient involvement, increases fear that the condition is serious, decreases cardiovascular conditioning, and reinforces the role of sick person.94 For the employee seeking care, the message is sometimes difficult to understand, particularly if the injury or back pain started at work. “Why should I go back to work, where I was injured, if it may hurt my back?” he or she asks. This legitimate question needs to be answered in relation to the type of job involved and the availability of modified work for a limited period if necessary. The occupational health care provider is best placed to answer this question and to adapt the employee’s duties if necessary.
Self-care for acute NSLBP DURATION OF PAIN AND TREATMENT GOALS The following definitions of LBP and duration since onset are used and well accepted: The duration of acute NSLBP is 0-4 weeks and that of subacute NSLBP is 4-12 weeks.1,8,33 Although episode definition is not standardized, intermittent or recurrent NSLBP is diagnosed when the patient is pain free or almost pain free between the bouts of pain.1 Chronic NSLBP is defined as a duration of pain longer than 12 weeks.1,8,17,33 The most important goal for acute LBP is a continuum of occupational care and identification of factors to prevent chronicity during the first 3 months after the patient seeks help. Management in occupational medicine can make a difference by providing regular follow-up and using a multidisciplinary approach to reinforce return to work with temporary job accommodations or, in some cases, job change.
ACUTE NSLBP AND EVIDENCE FOR TREATMENT Because acute NSLBP is largely self-limiting, minimal or no medical interventions are recommended for most patients.1,26,33,67,88,95 The most important message is for the patient to keep as active as tolerable without bed rest.1,33,67,73,74,88 Specific exercises are not needed and may also have a negative effect. In two systematic reviews and a recent meta-analysis
Self-care implies that the NSLBP patient can control symptoms and engage in behaviors necessary to reduce or alleviate them. Playing an active role in recovery, the patient decides what behaviors are tolerable. The message to remain as active as possible cannot be overemphasized.1,88 Self-care techniques include (but are not limited to) stretching and/or walking or using heat and/or ice or relaxation techniques72 when convenient for shortterm relief. Written evidence-based information is helpful to reinforce the good prognosis of NSLBP, explaining the biopsychosocial factors influencing recovery and offering instructions for self-care.16 Company-specific information may have a better impact than a generic pamphlet.46,75 In summary, systematic literature reviews, randomized controlled trials, and meta-analysis of acute NSLBP show that selfcare in the form of maintained activity, education, and medication as needed is as effective as manipulation or a short course of pain management based on the biopsychosocial model. Bed rest and passive treatment should be avoided. If patients demand treatment, it is prudent to ask about their expectations and goals, educate them, and reinforce the positive prognosis. The natural history of acute NSLBP measured as return to work is altered only marginally by prescribed treatment at this early stage, but together with self-care it provides shortterm relief from pain. Patients should be followed until they resume work.
Chapter 4d
INTERVENTIONS FOR SUBACUTE NSLBP The interval of 4-12 weeks in the management of NSLBP has been called “the window of opportunity.” The occupational health care professional can become instrumental in preventing work disability and recommending alternative and more intensive regimens of evidence-based treatment. A clinical reevaluation at 4 weeks includes a careful orthopedic and neurologic examination along with imaging and other diagnostics if warranted to exclude any ongoing process in the spine.8,33 If the diagnosis remains NSLBP, screening for psychosocial factors is warranted.
Yellow flags “Yellow flags”56 indicate psychosocial barriers to recovery and predict poor outcomes related to occupational health care because the patient does not return to any kind of work.55 Yellow flags are employee misconceptions (that back pain is harmful or can be severely disabling), avoidance of movement or activity due to fear of pain, tendency toward depression, withdrawal from social interaction, or expectation of continued passive treatment rather than belief that active participation will help.55,61 Six open-ended questions are helpful for revealing yellow flags: 1. Have you had time off work in the past with back pain? 2. What do you understand to be the cause of your back pain? 3. What do you expect will help you? 4. How is your employer responding to your back pain? Your coworkers? Your family? 5. What are you doing to cope with your back pain? 6. Do you believe you will return to work? When?
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In one study from a primary care cohort (n = 800) over 5 years, not recognizing psychosocial issues early on has been shown to account for an increase of 10 consultations per year per patient.52
Blue flags In occupational health care it is also helpful to recognize so-called “blue flags” that are related to possible work problems. Initially proposed by Main and coworkers,7,65,66 blue flags represent occupationally related predisposing factors for delayed recovery and return to work. Blue flags include factors such as fear of losing one’s job, monotony at work, lack of job satisfaction, and poor relationships with peers and supervisors. Occupational health care professionals are particularly well placed to address these issues. Appropriate intervention such as CBT aims to strengthen the employee’s coping skills and problem solving. In collaboration with the occupational physician, a discussion with supervisors or a workplace visit can occur early in the course of back pain to prevent chronicity. An active approach combining patient participation with involvement by the health care provider, the management, and the union is beneficial.60,62,81
Management of NSLBP The management of subacute NSLBP treatment should proceed in a stepwise fashion from least to the most invasive treatment (Fig. 4d.1). There is weak to moderate evidence in randomized controlled trials for efficacy of a treatment regimen including exercise, behavioral therapy, and ergonomic intervention.33,70 The employee must be convinced to participate actively to prevent long-term chronicity and disability. Meaningful outcomes for the patient that need to be discussed are those of taking control of
Work disability in %
100
50
• Convey optimism • Stay active • Pain medication • Self care techniques • Follow-up • Pamphlet/information
0
1 month Acute
Figure 4d.1
• Convey optimism • Exercise • Pain medication • Psychological evaluation and possible cognitive behavoral treatment • Work conditioning program • Ergonomic and/or occupational intervention
>6 months
3 months Subacute
Suggested management of occupational nonspecific low back pain.
• Exercise • Aggressive pain management • Cognitive behavoral treatment • Multidisciplinary conditioning program with focus on return to work • Workplace intervention • Surgery (?)
Early chronic
Chronic
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the condition; feeling better; resuming activities, including work; and avoiding recurrences. Because compliance with regimens requires the patient’s active participation, management of subacute NSLBP is demanding. Compliance rates for different regimens have been reported to vary from 13% to 85%,2,61 and a patient’s decision to adhere to a treatment regimen is complex.50 Patients may prefer passive treatment that may delay the course of recovery.83 One study has shown, for example, that patient compliance with video watching for back education (70-80%) in a physical therapy practice was significantly higher than compliance with a more demanding exercise regimen (40-50%).2 Linton and Andersson61 indicated an adherence rate of 53% and 72% for six and four CBT sessions, respectively. Adherence appears to be influenced by both the type of treatment and its frequency. The stepwise active approach includes an exercise regimen or a CBT program as a single intervention or a combination of the two as a bimodal treatment if no recovery occurs.
Exercise regimens The message here is for the patient to “start moving” with or without help from a coach. There are many different types of exercise regimens for LBP, each with its own proponents. Exercise programs evaluated in randomized controlled trials include the McKenzie regimen, walking programs, Williams flexion exercises, endurance-strength-stabilization training, and other less frequently described regimens.23,27,43,47,54 Different types of exercises appear to be equally effective.1,87 A recent meta-analysis of five exercise studies involving about 800 patients resulted in pooled weighted difference decrease in pain of about two points (1.89 [95% CI, -1.13 to 4.91) on a scale of 100. Pooling four trials demonstrated an improvement of 1.07 (95% CI, -3.18 to 5.32) points on a scale of 100 for perceived functional outcomes.45 The authors concluded that the evidence is insufficient to refute or support the effectiveness of regimens involving exercise alone without a behavioral component.
Cognitive behavioral therapy CBT interventions include creative visualization, imagery, progressive muscle relaxation, problem solving, and other techniques. The clinician uses the components in various combinations to have the patient understand, accept, and take control of the back pain. Moderate to strong evidence indicates that CBT should be used early if biopsychosocial signs or symptoms are present, and strong evidence exists for using CBT in patients with chronic NSLBP.33,87,96 The European Guidelines 2005 stated, “We recommend cognitive-behavioural treatment for patients with chronic LBP,” and summarized as follows: There is strong evidence that behavioural treatment is more effective for pain, functional status, and behavioural outcomes than placebo/no treatment/waiting list control. There is strong evidence that a graded activity programme using a behavioural approach is more effective than traditional care for returning patients to work, and finally there is strong evidence that there is no difference in effectiveness between the various types of behavioural therapy.33
Combination therapy in occupational settings Three studies in occupational settings have found that a behaviorally oriented graded-activity exercise program provides moderate to excellent reduction of days lost at work. This type of program has been compared to usual care in the Netherlands and in Sweden.60,81,86 These studies had highly structured interventions with an unambiguous primary goal of returning the patient to work. A behaviorally oriented graded-activity exercise program includes the following components: 1. The occupational or treating physicians advise workers on ergonomics, prevention, and return to work schedules; 2. The clinicians also advise and communicate with interested parties such as health care providers and workplace representatives; 3. The programs use gradually progressive exercises adapted to patient needs; 4. The clinical team is trained, and all caregivers provide the same message to the patient to avoid ambiguity; 5. There is ample communication and discussion with the patient; 6. An ergonomic intervention such as a workplace visit or a discussion with the occupational physician may be included.60,62 The studies showed significant reduction in days of work loss. Lindstrom et al,60 for example, showed an average return to work in the intervention group at 10 weeks (standard deviation, 12.7) and in the control group at 15.1 weeks (standard deviation, 15.6). Staal et al80 showed an effect on work loss days (HR 1,9; CI, 1.2-3.2) at 50 days after randomization in favor of the graded-activity program. However, the results were not significant in early follow-up less than 50 days after treatment for the two interventions (an exercise program and a graded operant conditioning program). One randomized controlled trial in an occupational setting in the Netherlands added problem-solving therapy conducted by a trained therapist to a behaviorally oriented graded-activity exercise program for patients with subacute and chronic NSLBP. The combination group showed significantly favorable results, including fewer work loss days and fewer patients receiving disability pensions 1 year after the intervention.86 In all studies, self-reported pain and function were affected marginally.60,80,86 Usually measured by a pain score or visual analog scale, pain itself appeared not to be a major determinant for return to work. Possibly the highly structured positive environment in an occupational setting provides a better venue for problem solving, educating the patient, and monitoring progress.
Ergonomic intervention Using the Sherbrooke model of occupational/ergonomic intervention and clinical rehabilitation, Loisel et al62 found that a consultation with an occupational physician or a low-cost ergonomic intervention contributed the most to the success of return to work. In a follow-up study of cost effectiveness 6.4 years later, the same authors found that the Sherbrooke model yielded the highest savings in work loss days compared with standard care or rehabilitation alone.64 The authors assessed participatory ergonomics in workers
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suffering from subacute LBP (>6 weeks of work disability). Performed 6 months after the ergonomic intervention, the assessment included all parties: management, union, and afflicted worker. About half of the recommended ergonomic solutions were implemented with a substantial agreement among all respondents.63 The Cochrane review of multidisciplinary biopsychosocial rehabilitation concluded, “There is moderate evidence showing that multidisciplinary rehabilitation for subacute LBP is effective and that a work site visit increases the effectiveness.”53 These findings must be interpreted with caution, however, because the few studies reviewed contained methodologic flaws and need to be confirmed. Based on several studies of patients with chronic back pain, the European Guidelines 2005 recommend an occupational intervention.33
MULTIMODAL PROGRAMS FOR CHRONIC LBP Two recent reviews and one systematic Cochrane review of chronic NSLBP showed the importance of multimodal active programs.9,10,19,39,42 The Cochrane review covered 18 trials, including 1964 chronic NSLBP patients (Fig 4d.2).53,87 The comparison included treatment such as back training, exercise only, education, standard care, assessment by specialist with or without a nurse and/or advisement (oral and printed), waiting lists, and other factors. Like the European Guidelines 2005, the review concluded, “There is strong evidence that intensive multidisciplinary biopsychosocial rehabilitation for chronic NSLBP with a functional restoration approach reduces pain when compared with inpatient or out-patient nonmultidisciplinary treatments and moderate evidence when these programs are compared to usual care. There is contradictory evidence regarding global vocational outcomes.”42 The authors cautioned about the lack of definition concerning content, duration, and intensity of the programs but found that those longer than 100 hours of therapy with a focus on functional restoration seem to be more effective than less intensive programs or nonmultidisciplinary control groups. The review indicated significant and favorable results for pain ratings, functional status, employment status, and sick leave up to 60 months.
MANIPULATION Manipulation has been evaluated extensively for chronic LBP and studied less in the subacute phase. A recent pragmatic randomized trial, however, included 181 general practices in the United Kingdom with 1334 patients, most of whom had subacute NSLBP. Patients were randomized to groups of standard best care or manipulation, each with or without exercise, and followed for 1 year.85 Results on the Roland Morris disability questionnaire76-78 improved with a mean of 3.3 (standard deviation, 4.5) and 3.5 (standard deviation, 4.7) points out of a total score of 10 points at 3 and 12 months, respectively. A score change of 20% is deemed clinically significant.10 The difference between the groups was nonsignificant. Manipulation for chronic NSLBP was reviewed extensively by Assendelft et al,4 Bronfort and Bouter,13 and Cherkin et al.25 In a
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meta-analysis, Cherkin et al compared sham manipulation, traction, corset, bed rest, home care, topical gel, diathermy, massage, general practitioner care, analgesics, physical therapy, exercises, back training, no treatment, or some combination thereof. They found no evidence that spinal manipulation is substantially more or less effective than other conventional therapies for chronic NSLBP. The expected gain in pain reduction is 4-5 points (ranging from -4 to 12) on a 100-mm visual analog scale for pain of longterm duration and somewhat less for self-reported disability. These measures were reported for both the short and the long term.25 A UCLA study (n = 681) included about 50% patients with chronic NSLBP in a managed care health organization. The patients were randomized to chiropractic, medical, or physiotherapy care, and at a 6-month follow-up the results were comparable.51 Chiropractic care in combination with physical modalities or physical therapy modalities provided in combination with medical care did not produce clinically significant improvements in outcome.58 The European Guidelines 200533 recommend a short course of spinal manipulation/mobilization as a treatment option for chronic LBP. They also summarize the evidence for medication use as follows.
MEDICATION Nonsteroidal antiinflammatory drugs (NSAIDs) The usefulness of nonsteroidal antiinflammatory drugs (NSAIDs) was reviewed systematically by van Tulder et al,89 who highlighted the methodologic problems they encountered. Most of the published trials reported on acute LBP. In comparison with placebo, the authors found “conflicting evidence” that NSAIDs provided better pain relief, but patients on NSAIDs exhibited significantly less use of analgesics. There were no significant differences in terms of side effects. In the same review, “conflicting results” were found among studies comparing NSAIDs with paracetamol. Included in the same systematic review were six studies comparing NSAIDs with narcotic analgesics or muscle relaxants. The authors found “moderate evidence” that NSAIDs are not more effective than other drugs. van Tulder et al89 highlighted the impossibility of making any statement about the relative effectiveness of different NSAID types because no studies comparing the same two drugs for acute or chronic LBP were available.
Muscle relaxants Benzodiazepine and nonbenzodiazepine muscle relaxants, either isolated or combined with other drugs, have been extensively investigated in LBP. A systematic review of this literature was published by van Tulder et al.90 Limited evidence from one study favored diazepam (an intramuscular injection followed by 5 days of oral treatment) versus placebo. The authors found strong evidence both that oral nonbenzodiazepines are more effective than placebo for short-term pain relief and that both types of muscle relaxants are associated significantly more than placebo with central nervous system side effects. Because the number of high-quality studies comparing different muscle relaxants is
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Treatment options
Trial characteristics
Time since treatment
Pain record
Functional status
Days on sickness leave
Employment status
Intensive (>100h) daily MBPSR with functional restorative: Alsants 1994* v >100h inpatient rehabilitation
3 months 12 months
Bendix 1995:1* v < 30h outpatient rehabilitation
4 months 12 months 24 months 60 months
Bendix 1990 v usual care
4 months 24 months 60 months
Michel 1994* v usual care
4 months 12 months 24 months
Less intensive (<30h) once or twice daily outpatient MBPSR: Bazier 1997 v outpatient rehabilitation
At treatment completion
Bendix 1995:2* v <10h outpatient rehabilitation
6 months 12 months 24 months 30 months
Nichols 1991* v < 30h outpatient rehabilitation
6 months 12 months
Nichols 1992* v < 30h outpatient rehabilitation
6 months
Martapea 1989:2 v usual care
3 months 12 months 30 months 54 months
Other types of MBPSR: Martapea 1989:1 Inpatient MBPSR >108h (no functional restoration) v usual care
3 months 12 months 30 months 54 months
Juckel 1990 Sμ type MBPSR v waiting list
At treatment completion
Uritias 1989* Individualized inpatient MBPSR v usual care
12 months
–2 –1
0
1
Standardized mean difference
2
–2 –1
0
1
Standardized mean difference
2
0.1
1 Relative risk
10
–2 –1
0
1
2
Standardized mean difference
Figure 4d.2 Treatment effect sizes for 12 randomized comparisons of multidisciplinary biopsychosocial rehabilitation and a control condition. Bars represent standardized mean differences and 95% confidence intervals for comparison of intervention and control groups, except for employment status, where bars represent relative risks. Treatment effect sizes entirely to the left of the vertical line indicate statistically significant differences in favor of the intervention. *, High quality trial; I1, intervention 1 testing more than one multidisciplinary intervention; I2, intervention 2 testing more than one multidisciplinary intervention; MBSPR, multidisciplinary biopsychosocial rehabilitation.
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rather limited, it seems very difficult to make general recommendations in this area. There is strong evidence that combining tizanidine plus paracetamol or tizanidine plus NSAIDs is more effective for short-term pain relief than placebo plus paracetamol or plus NSAIDs. Two high-quality trials offer strong evidence that temazepam 50 mg 3 times a day is more effective than placebo for short-term pain relief and overall improvement. When the literature review was published, however, this drug was available only in some European countries and Mexico. Among the nonbenzodiazepines, there is moderate evidence that flupirtine and tolperisone are more effective than placebo for short-term improvement.90
Opioids Breckenridge and Clark12 and Fillingim et al35 independently showed that the use of opioids in chronic LBP patients was not predicted by pain intensity. Therefore, the factors influencing health care providers to prescribe opioids probably deserve more research.
Antidepressants The efficacy of antidepressants in chronic LBP was systematically reviewed by Staiger et al.82 Based on the seven studies reviewed, the authors concluded that tricyclic and tetracyclic antidepressants can produce moderate symptom reductions. Inhibition of norepinephrine reuptake seems important for the analgesic effect. Benefits appear to be independent of a patient’s depression. Selective serotonin reuptake inhibitors were evaluated in three studies that failed to show any analgesic effect. It remains unclear whether these drugs affect functional status.
Corticosteroids In their review, Atlas and Nardin5 stated that evidence supporting the use of oral corticosteroids is lacking. Because these drugs have potential significant side effects, the authors therefore advised against their use in patients with chronic pain.
SURGERY Chronic NSLBP would imply LBP without sciatica in patients with degenerative disk diseases.30 Although shown to be controversial, the diagnosis itself is usually made by provocative diskography at the level of the disk possibly causing the pain.19,20 An et al3 discussed disk degenerative progressive changes as part of normal aging. Studies today cannot confirm what starts and what influences progression if no trauma or disease is present. There is also debate about the disk as a pain source; from a clinical perspective, however, severe disk degeneration on several levels is shown to cause pain. Moderate to less visible disk degeneration changes are more debatable. The authors argued for investigating other sources of pain as well as its enhancers or modifiers. A systematic literature review in 1999 concluded that there was insufficient evidence for lumbar spine fusion in lumbar
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Surgery
spondylolysis and back pain.39 Three randomized trials have since shown that long-term benefits for surgery over 2 years is comparable with those of nonsurgical treatments.15,35,37 In a large randomized controlled study, Fritzell et al36,37 compared fusion with usual conservative care in patients (n = 294) with one- or two-level disk degeneration and pain duration of at least 1 year. The surgical group had a greater improvement in pain relief, function, depressive symptoms, and return to work at 1-year follow-up compared with those who had common conservative treatment prescribed by a physician. At 2-years follow-up, the difference between the groups had diminished, suggesting that the results of fusion are intermediary rather than long term. The heterogeneous therapy in the nonsurgical treatment may also have contributed to a less favorable result in the nonsurgical group. The nonsurgical group received a variety of treatments according to individual physician preferences such as acupuncture, physical therapy, injections, electrical stimulation, and CBT. The study did not have blinded evaluators. In a smaller randomized trial, 64 patients aged 25-60 years with NSLBP lasting longer than 1 year and evidence of disk degeneration at L4-L5 and/or L5-S1 at radiographic examination were randomized to either lumbar fusion with posterior transpedicular screws and postoperative physiotherapy or cognitive intervention and exercises.15 The cognitive intervention consisted of a lecture to help patients understand that ordinary physical activity would not harm the disk and a recommendation to use the back and bend it. This was reinforced by three daily physical exercise sessions for 3 weeks. The main outcome measure was the Oswestry Disability Index. At a 1-year follow-up visit to 97% of the patients, the Oswestry Disability Index was significantly reduced from 41/100 to 26/100 points after surgery, compared with 42/100 to 30/100 points after cognitive intervention and exercises. The mean difference between the groups of 2.3 points (-6.7 to 11.4; p = 0.33) was not significant. Improvements in back pain, use of analgesics, emotional distress, life satisfaction, and return to work were not different. Fear-avoidance beliefs and fingertip-floor distance were reduced more after nonoperative treatment, and lower limb pain was reduced more after surgery. According to an independent observer, the success rate was 70% after surgery and 76% after cognitive intervention and exercises. The early complication rate in the surgical group was 18%. The authors concluded that the main outcome measure showed equal improvement in patients with chronic LBP and disk degeneration randomized to lumbar fusion or cognitive intervention and exercises.15 The risk for the nonsurgical group was considerably lower, however, because no complications occurred. Although the evidence is less compelling than it might have been, in the future these patients may be offered surgery or CBT with similar results. This study needs to be confirmed by other and larger studies, but it may provide an alternative to surgery when expected outcomes from that treatment are uncertain. In a multicenter study from Great Britain,34 349 patients with chronic back pain lasting more than 1 year were randomized to surgery (spinal fusion) or to an intensive rehabilitation program for 5 days a week for 3 weeks continuously and followed for 2 years. The team included a physician, a physical therapist, and a psychologist. The program was individually tailored to each patient with progressive exercises and CBT to overcome fears and negative beliefs about back pain. Both groups reported
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reductions in disability, and the only primary outcome measure that marginally favored surgery was the Oswestry Disability Index, which showed a clinically insignificant decrease of about four points on a scale of 100 (-.1 [95% CI, -4.1 to -0.1; p = 0.045). No clear evidence emerged that primary spinal fusion was any more beneficial than intensive rehabilitation. Randomized controlled trials on novel technology such as artificial disks, electrothermal therapy, analgesic pumps, and implanted stimulators are lacking. One systematic literature review stated, “There is no evidence that disk replacement reliably, reproducibly, and over longer periods of time fulfills the three primary aims of clinical efficacy, continued motion, and few adjacent segment degenerative problems. Total disk replacement seems to be associated with a high rate of re-operations, and the potential problems that may occur with longer follow-up have not been addressed.”28 Arthroplasty and fusion or laminectomy have been compared in randomized clinical trials with similar outcomes.41,68 In these studies no nonsurgical groups were included for comparison, as is greatly needed. In patients with chronic NSLBP, the current evidence points to improved triage and a stepwise active approach in which the patient and clinician discuss goals, outcomes, and compliance with the proposed treatment.
COMPLICATIONS AND TREATMENT CHOICE
REFERENCES 1.
2.
3. 4.
5. 6. 7.
8.
9. 10. 11.
12.
We could not find any complications reported in therapies including exercise, CBT, or workplace intervention. The complication rate for spinal surgery varies by type from 2% to 15%, including instrument failure, prosthetic migration, infection, chronic pain, and neural injuries or/and pulmonary embolus. When advising a patient, this information can be used for education to help with choice of treatment.
13.
SUMMARY
17.
This chapter summarizes evidence-based management and treatment regimens for patients seeking care for LBP and diagnosed with NSLBP. In acute NSLBP there is strong to moderate evidence for self-care by taking over-the-counter medication and maintaining activity as tolerated or engaging in limited sessions of manipulative therapy. In subacute NSLBP, there is weak to moderate evidence for a graded activity program, including a combination of exercise and CBT. Strong evidence indicates that these programs reduce work absenteeism. In NSLBP of more than 12 weeks’ duration, a variety of regimens seems to be available with limited and similar efficacy on pain and disability reduction. There is weak to moderate evidence that interventions, including CBT, exercise, and education about chronic NSLBP, are as effective as surgery after 2 years of followup. Surgical indications for chronic NSLBP are ill-defined.
14.
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25.
26.
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ACKNOWLEDGMENT 29.
We thank Chaitrali Gore, M.S., for her excellent help with references and figures.
30.
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Fritzell P, Hagg O, Jonsson D, Nordwall A: Cost-effectiveness of lumbar fusion and nonsurgical treatment for chronic LBP in the Swedish Lumbar Spine Study: a multicenter, randomized, controlled trial from the Swedish Lumbar Spine Study Group. Spine 29:421-434, 2004. Fritzell P, Hagg O, Wessberg P, Nordwall A: Lumbar fusion versus nonsurgical treatment for chronic LBP: a multicenter randomized controlled trial from the Swedish Lumbar Spine Study Group, 2001 Volvo Award Winner in Clinical Studies. Spine 26: 2521-2532, 2001. Garfin SR, Andersson G, Gronblad M, et al: The Bone and Joint Decade, 2000-2010, for prevention and treatment of musculoskeletal disorders. Spine 24(11): 1055-1057, 1999. Gibson JN, Grant IC, Waddell G: The Cochrane review of surgery for lumbar disc prolapse and degenerative lumbar spondylosis. Spine 24:1820-1832, 1999. Goubert L, Crombez G, De Bourdeaudhuij I: Low back pain, disability and back pain myths in a community sample: prevalence and interrelationships. Eur J Pain 8: 385-394, 2004. Guyer RD, McAfee PC, Hochschuler SH, et al: Prospective randomized study of the Charite artificial disc: data from two investigational centers. Spine 4:252S-259S, 2004. Guzman J, Esmail R, Karjalainen K, et al: Multidisciplinary rehabilitation for chronic LBP: systematic review. BMJ 322:1511-1516, 2001. Hansen FR, Bendix T, Skov P, et al: Intensive, dynamic back-muscle exercises, conventional physiotherapy, or placebo-control treatment of low-back pain. A randomized, observer-blind trial. Spine 18:98-108, 1993. Hay EM, Mullis R, Lewis M, et al: Comparison of physical treatments versus a brief pain-management programme for back pain in primary care: a randomised clinical trial in physiotherapy practice. Lancet 365:2024-2030, 2005. Hayden JA, van Tulder MW, Malmivaara AV, Koes BW: Meta-analysis: exercise therapy for nonspecific LBP. Ann Intern Med 142:765-775, 2005. Hazard RG, Reid S, Haugh LD, McFarlane G: A controlled trial of an educational pamphlet to prevent disability after occupational low back injury. Spine 25: 1419-1423, 2000. Helmhout PH, Harts CC, Staal JB, Candel MJ, de Bie RA: Comparison of a high-intensity and a low-intensity lumbar extensor training program as minimal intervention treatment in LBP: a randomized trial. Eur Spine J 13:537-547, 2004. Hestbaek L, Leboeuf-Yde C, Engberg M, et al: The course of LBP in a general population: results from a 5-year prospective study. J Manip Physiol Ther 26:213-219, 2003. Heymans MW, van Tulder MW, Esmail R, Bombardier C, Koes BW: Back schools for nonspecific low-back pain. Cochrane Database Syst Rev, CD000261, 2004. Hiebert R: Factors influencing patient compliance with medically recommended care for work disabling, non-specific, low back pain during acute and subacute phases. Masters of Science (Sc.M.) thesis. Baltimore, 2004, Johns Hopkins School of Hygiene and Public Health, Department of Health Policy and Management. Hurwitz EL, Morgenstern H, Harber P, et al: A randomized trial of medical care with and without physical therapy and chiropractic care with and without physical modalities for patients with LBP: 6-month follow-up outcomes from the UCLA LBP study. Spine 27:2193-2204, 2002. Kapur N, Hunt I, Lunt M, et al: Psychosocial and illness related predictors of consultation rates in primary care—a cohort study, Psychol Med 34:719-728, 2004. Karjalainen K, Malmivaara A, van Tulder M, et al: Multidisciplinary biopsychosocial rehabilitation for subacute LBP in working-age adults: a systematic review within the framework of the Cochrane Collaboration Back Review Group. Spine 26:262-269, 2001. Kellet J: Support groups: caring about each other. Nurs Stand 5:46, 1991. Kendall NA: Psychosocial approaches to the prevention of chronic pain: the low back paradigm. Baillieres Best Pract Res Clin Rheumatol 13:545-554, 1999. Kendall NA, Linton S, Main C: Guide to assess psychosocial yellow flags in acute LBP: risk factors for long-term disability and work loss. Wellington Accident Rehabilitation and Compensation Insurance of New Zealand, 1997, National Health Committee. Koes BW, van Tulder MW, Ostelo R, Kim BA, Waddell G: Clinical guidelines for the management of LBP in primary care: an international comparison. Spine 26: 2504-2513, 2001. Kominski GF, Roby DH, Kincheloe JR: Cost of insuring California’s uninsured. Policy Brief: UCLA Cent Health Policy Res 1-6, 2005. Lidgren L: The bone and joint decade 2000-2010. Bull World Health Org 81(9):629, 2003.
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Lindstrom I, Ohlund C, Eek C, et al: Mobility, strength, and fitness after a graded activity program for patients with subacute LBP: a randomized prospective clinical study with a behavioral therapy approach. Spine 17:641-652, 1992. Linton SJ, Andersson T: Can chronic disability be prevented? A randomized trial of a cognitive-behavior intervention and two forms of information for patients with spinal pain. Spine 25:2825-2831, 2000. Loisel P, Abenhaim L, Durand P, et al: A population-based, randomized clinical trial on back pain management. Spine 22:2911-2918, 1997. Loisel P, Gosselin L, Durand P, et al: Implementation of a participatory ergonomics program in the rehabilitation of workers suffering from subacute back pain. Appl Ergon 32:53-60, 2001. Loisel P, Lemaire J, Poitras S, et al: Cost-benefit and cost-effectiveness analysis of a disability prevention model for back pain management: a six year follow up study. Occup Environ Med 59:807-815, 2002. Main C, Glozier N, Wright I: Validity of the HSE stress tool: an investigation within four organizations by the Corporate Health and Performance Group. Occup Med (Lond) 55:208-214, 2005. Main CJ: Early psychosocial interventions for LBP in primary care. BMJ 331:88, 2005. Malmivaara A, Hakkinen U, Aro T, et al: The treatment of acute LBP—bed rest, exercises, or ordinary activity? N Engl J Med 332:351-355, 1995. McAfee PC, Fedder IL, Saiedy S, Shucosky EM, Cunningham BW: Experimental design of total disk replacement-experience with a prospective randomized study of the SB Charite. Spine 28:S153-S162, 2003. McGuirk B, King W, Govind J, Lowry J, Bogduk N: Safety, efficacy, and cost effectiveness of evidence-based guidelines for the management of acute LBP in primary care. Spine 26:2615-2622, 2001. Nachemson A, Jonsson E: Neck and back pain: the scientific evidence of causes, diagnosis and treatment. Philadelphia, 2000, Lippincott Williams & Wilkins. Nordin M, Skovron ML, Hiebert R, et al: Early predictors of delayed return to work in patients with LBP. J Musculoskel Pain 5:5-27, 1999. Nordin M, Weiser S, Campello MA, Pietrek M: Self care techniques for acute episodes of LBP. Best Pract Res Clin Rheumatol 16:89-104, 2002. Oleske DM, Neelakantan J, Andersson GB, et al: Factors affecting recovery from workrelated, low back disorders in autoworkers. Arch Phys Med Rehabil 85:1362-1364, 2004. Proper KI, Staal BJ, Hildebrandt VH, van der Beek AJ, van Mechelen W: Effectiveness of physical activity programs at worksites with respect to work-related outcomes. Scand J Work Environ Health 28:75-84, 2002. Roberts L, Little P, Chapman J, et al: The back home trial: general practitioner-supported leaflets may change back pain behavior. Spine 27:1821-1828, 2002. Roland M, Morris R: A study of the natural history of back pain. Part I: development of a reliable and sensitive measure of disability in low-back pain. Spine 8:141-144, 1983. Roland M, Morris R: A study of the natural history of low-back pain. Part II. Development of guidelines for trials of treatment in primary care. Spine 8:145-150, 1983. Roland M, Fairbank J: The Roland-Morris Disability Questionnaire and the Oswestry Disability Questionnaire. Spine 25:3115-3124, 2000. Spitzer WO, Leblanc FE, DuPuis M: Scientific approach to the assessment management of activity-related spinal disorders: a monograph for clinicians. Report of the Quebec Task Force on Spinal Disorders. Spine 12(7 Suppl):S1-S59, 1987. Staal JB, Hlobil H, Twisk JW, et al: Graded activity for LBP in occupational health care: a randomized, controlled trial. Ann Intern Med 140:77-84, 2004. Staal JB, Hlobil H, van Tulder MW, et al: Return-to-work interventions for LBP: a descriptive review of contents and concepts of working mechanisms. Sports Med 32:251-267, 2002. Staiger TO, Gaster B, Sullivan MD, Deyo RA: Systematic review of antidepressants in the treatment of chronic LBP. Spine 28:2540-2545, 2003. Thomas E, Croft PR, Paterson SM, Dziedzic K, Hay EM: What influences participants’ treatment preference and can it influence outcome? Results from a primary carebased randomised trial for shoulder pain. Br J Gen Pract 54:93-96, 2004. Thomas E, Silman AJ, Croft PR, et al: Predicting who develops chronic LBP in primary care: a prospective study. BMJ 318:1662-1667, 1999. United Kingdom back pain exercise and manipulation (UK BEAM) randomised trial: effectiveness of physical treatments for back pain in primary care. BMJ 329(7479): 1377, 2004. van den Hout JH, Vlaeyen JW, Heuts PH, Zijlema JH, Wijnen JA: Secondary prevention of work-related disability in nonspecific LBP: does problem-solving therapy help? A randomized clinical trial. Clin J Pain 19:87-96, 2003. van Tulder MW et al: Behavioural treatment for chronic LBP. The Cochrane Library, Issue 3. Chichester, UK, 2004, John Wiley & Sons, Ltd. van Tulder MW, Ostelo R, Vlaeyen JW, et al: Behavioral treatment for chronic LBP: a systematic review within the framework of the Cochrane Back Review Group. Spine 25:2688-2699, 2000. van Tulder MW, Scholten RJ, Koes BW, Deyo RA: Nonsteroidal anti-inflammatory drugs for LBP: a systematic review within the framework of the Cochrane Collaboration Back Review Group. Spine 25:2501-2513, 2000.
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van Tulder MW, Touray T, Furlan AD, Solway S, Bouter LM: Muscle relaxants for nonspecific LBP: a systematic review within the framework of the Cochrane Collaboration. Spine 28:1978-1992, 2003. Verbeek J, Sengers MJ, Riemens L, Haafkens J: Patient expectations of treatment for back pain: a systematic review of qualitative and quantitative studies. Spine 29:2309-2318, 2004. Vingard E, Mortimer M, Wiktorin C, et al: Seeking care for LBP in the general population: a two-year follow-up study: results from the MUSIC-Norrtalje Study. Spine 27: 2159-2165, 2002. Von Korff M, Crane P, Lane M, et al: Chronic spinal pain and physical-mental comorbidity in the United States: results from the national comorbidity survey replication. Pain 113:331-339, 2005.
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Waddell G: The back pain revolution. New York, 1999, Churchill Livingstone. Waddell G, Burton AK: Concepts of rehabilitation for the management of LBP. Best Pract Res Clin Rheumatol 19:655-670, 2005. 96. Waddell G, Burton AK: Occupational health guidelines for the management of LBP at work: evidence review. Occup Med (Lond) 51:124-135, 2001. 97. Weinstein JN: Doctor and patient: advocacy for informed choice vs. informed consent. Spine 30(3):269-272, 2005. 98. Weinstein SL: 2000-2010: the bone and joint decade. J Bone Joint Surg 82A(1): 1-3, 2000. 99. Wood P: The basis of rheumatological practice, including nomenclature and classification. In JT Scott, ed: Copeman’s textbook of Rheumatic Diseases. New York, 1986, Churchill Livingston, p. 59.
CHAPTER
4e
Workplace Adaptation for the Low Back Region Shrawan Kumar and Steve Konz
THE NATURE OF LOW BACK PAIN The nature of low back pain (LBP) and even its broad categorization into acute, subacute, and chronic categories defy scientific precision. In many cases, its insidious onset, relief without medical intervention, recurrence despite all precautions, and eventual chronicity have not only perplexed medical practitioners but also posed an intellectual challenge even for a scientific conception of the phenomenon. Although many risk factors have been associated with LBP, its etiology remains obscure. Kumar14 categorized all known risk factors into four broad categories: (1) morphologic, (2) genetic, (3) biomechanical, and (4) psychosocial. He stated that whereas morphologic and genetic factors are hardly manipulable, the biomechanical and psychosocial factors lend themselves to manipulation. It was, however, conceded that all strategies must take into account the genetic and morphologic data for optimal results. Many studies have been conducted to examine the possible impact of different risk factors, but the human back is like a multilink chain that is only as strong as its weakest link. Unfortunately, the weakest link is most elusive, being different in different people and also at different times in the same individual because of varying internal and external circumstances.
CAUSAL MECHANISMS AND CONTROL Humans have evolved over millions of years into what they are today. Evolutionary pressures and consequent speciation resulted in an upright biped creature with dextrous upper limbs and a highly evolved brain. For a large duration of its existence, the species relied on hunting and gathering as its primary means of sustenance.5 With the advancement of science, technology, and industrialization, the physical occupational stresses have changed dramatically in an evolutionary “flash” so that none of the body systems that one uses today was either designed or evolved for the current purpose. As a result, demand for force exertion, activity repetition, or posture assumption for prolonged periods places stress on human physical systems that is inherently unnatural. This is further aggravated by many psychologic stresses emanating from financial or interpersonal factors. In addition, most human occupations have become complex, requiring significant organization and thereby enhancing the chances of errors. As a function of a multivariate complex system (in many cases under multiple partial controllers), significant
chances emerge for unplanned events. These then result in various kinds of accidents with property damage and/or personal injuries. A meaningful attempt to control such injuries makes it imperative to understand them. Most cases compensated by the Workers’ Compensation Board are regional musculoskeletal problems. Workers in different economic sectors generally have injuries characteristic of those sectors. People in forestry, construction, and manufacturing have a higher proportion of back injuries. Those working in office jobs involving keyboarding have cumulative trauma disorders (also called musculoskeletal disorders and repetitive strain injuries). Because heavy physical workers do not develop repetitive strain or injury of the upper extremity and office workers do not injure their backs, the argument can be made that the nature of the physical stress and the region enduring the load largely determine the affected area and probably the nature of injury. If therefore one could delineate the mechanisms of injuries and the quantitative details of the relevant variables, one might develop a more effective intervention. An effective intervention would result in better control of injuries, which clearly has a significant payoff. Thus, the long-term success in controlling these injuries depends on understanding their causality. Because for ethical reasons human beings cannot be subjected to controlled experiments exposing them to risk of injury, Kumar et al16 performed an integrative synthesis of information in the scientific literature to formulate biologically plausible theories as to the mechanisms of injury causality. Through this exercise they proposed four theories of musculoskeletal injury causality described briefly below. 1. The Cumulative Load Theory16: Because biologic tissues are composed of both solid and liquid, their combined mechanical behavior or viscoelasticity is determined largely by the proportion of these components. Biologic tissues therefore deform partially like solids and partially like liquids in a blended manner. Such properties are time dependent: a longer exposure to the same load will produce larger deformation and vice versa. As a result, recovery from deformation takes time also. If the succeeding load does not allow sufficient recovery time, the tissue begins to deform further from its compromised stage. As demonstrated by Kumar13 in an epidemiologic study, repeated loading results in a cumulative effect of reduced threshold to failure. 2. The Differential Fatigue Theory16: Occupational tasks are kinesiologically complex and hardly ever performed in one plane. Asymmetric activities requiring the use of many body parts of the bilaterally symmetric human organism result in differential unequal loads on various muscles, joints, and connective tissue. One task may stress one tissue element to 80% of its capacity, whereas another one is stressed only 10%. Additionally, this distribution is not determined by the tolerance of the tissue concerned. Such diverse distribution of stress results in one muscle becoming more fatigued than others.15,16 This differential fatigue causes loss of coordination resulting in sudden and significant stress concentration that precipitates an injury. 3. The Overexertion Theory16: The basic tenet of this theory is that even a rested and normal tissue can, and probably will, fail when the stress/load exceeds its tolerance time. Although stressed and fatigued tissues cannot withstand stress concentration, it is not necessary for tissues to reach that stage to fail.
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4. The Multivariate Interaction Theory16: Over and above the three previous theories, the variability in the individual threshold indicates also that a precipitation of musculoskeletal injury may be modulated by the interaction of genetic, morphologic, psychosocial, and biomechanical factors. Within each of these categories are many variables that may potentiate an injury. Interaction between the relative weights of the variables and the extent to which these have been stressed in any given individual determines the final outcome. Although these four theories have been presented as distinct, all four are simultaneously operative but to a different degree depending on the circumstances and individuals. As pointed out above, humans have not evolved over the past 250 million years to be industrial workers. Humans will therefore always find themselves in the middle of a conflict between their nature and an industrial requirement. Such a backdrop clearly makes occupational injury prevention not only a daunting and lofty goal but an unachievable objective. Control of injuries to reduce their incidence and severity, however, remains a goal that may be achieved to varying degrees. With this in mind, Kumar12 presented a strategy to quantify the risk based on the discrete physical elements of the task in question.
THE EXTENT OF THE PROBLEM As a medical condition LBP has only one redeeming feature—it is not fatal. In spite of the obscurities associated with its etiology, classification, and treatment, human and economic impacts have been approximately quantifiable. Chapter 4a on the epidemiology of LBP offers a comprehensive picture of the problem; suffice it to say here that it is a large social and economic one. Although it occurs in less developed countries also, the impact of LBP is much more recognized in Western and industrialized countries. To put the extent of the problem in perspective, a brief description follows. Andersson1 stated that national statistics from the European countries reveal 10% to 15% of all sickness absence to be due to back pain, with the number of work days lost per worker increasing steadily. An annual prevalence of 25% to 45% was reported, and chronic back pain was present in 3% to 7% of the adult population. The lifetime prevalence of LBP has been variously reported as between 70% and 80%. In Canada, LBP has steadily constituted approximately 27% of all industrial injuries; these have been reported to cost disproportionately higher amounts than all other injuries. In the United States, the annual prevalence has been reported to be in the 15% to 20% range. Khalil8 reported that on any given day, roughly 75 million Americans have back pain, 6.5 million of whom are in bed. Webster and Snook23 reported the cost of LBP in 1989 incurred by Liberty Mutual, the largest insurer in the United States; it constituted 16% of the claims and accounted for 33% of the total expense. They reported also that the mean cost per case of LBP was $8300 compared with $4100 for all other claims combined, whereas the median cost was $396 ($168 for other claims). In these claim settlements, 34% of the total cost for LBP was medical, whereas 66% was indemnity cost for lost time and wages.23 No matter which way one looks, LBP is prevalent and expensive. Some of the socioeconomic aspects of our society may accentuate
the problem because of the alleged secondary gain. We have been able to reduce neither the incidence nor the severity of LBP; a cure neither exists nor is likely to emerge in the foreseeable future. No difference in long-term outcome between aggressive and conservative treatments has been identified, and we seem unable to control the problem in a significant or meaningful way. LBP is clearly here to stay. It is therefore of utmost importance to focus on workplace adaptations to reduce human suffering and economic cost. Our endeavor to identify these adaptations must try to reduce the magnitude of identified risk factors and the exposure of workers to them, decrease the incidence of LBP in healthy people, and reduce stress in patients who already have the condition. Such adaptations will be helpful in returning workers to work after injury.
DISABILITY CAUSED BY LBP LBP is associated with considerable disability that results in work loss, its most important social and economic consequence despite the influence by many other factors. A direct correlative scale between LBP, disability, and work loss has not been established. A simple clinical and subjective assessment of disability, however, has been claimed to have considerable relevance to quality of life as well as industrial performance. This assessment is focused on loss of function rather than pain. The emphasis is on whether an activity can be performed by an individual or is restricted because of LBP. Implicit in this assumption is that the restriction must have its onset coincident with that of the back pain and must therefore be the functional limitation. The specific criteria used by Waddell et al21 are as follows: 1. Bending and lifting 2. Sitting 3. Standing 4. Walking 5. Traveling 6. Social life 7. Sleep 8. Sex life 9. Dressing/undressing The aforementioned criteria combine postural, strength, metabolic, and everyday living activities that are involved also in occupational activities. LBP and loss of function through disability are results of biomechanical (kinematic and kinetic) perturbation of the human system. These demands are covered in Chapter 4b, but we note here that the functional activities accentuating these demands are divided into two main categories: static load (sitting, holding) and dynamic load (pushing/pulling, carrying, and lifting/ lowering). The concentration must therefore be on those activities that reduce hazards for initial injury and subsequent recurrences.
ADAPTATIONS Static work Spitzer et al20 report the LBP incidence in Quebec, Canada of individuals required to do heavy work but also include sedentary
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work areas such as “government, wholesale and retail, and finance and insurance.” Magora17 reported on LBP for bank tellers and for those who perform heavy work.
Seated work Problem Because intervertebral disks are avascular, their nutrition depends entirely on diffusion. Intervertebral disks also are viscoelastic. While an individual is sitting, the load on the intervertebral disk is 140% of that imposed by standing. This static load progressively decreases the water content of a disk; an increased load accelerates this process. Loss of water from a disk makes the diffusion process more difficult and results in reduced oxygen tension and lack of nourishment, leading to disk degeneration. Sedentary occupations involve prolonged exposure to static loads, hastening this process and making the disk more vulnerable to injuries. A constant static load also deforms the viscoelastic disk and causes compression creep. Because creep is time dependent, elimination of a load does not immediately restore either the preload disk configuration or the water content. The reduction in water and oxygen is therefore prolonged, interfering with disk metabolism by decreasing the amount of glycosaminoglycans (which have a strong affinity for water) and increasing the content of keratan sulfate (which is amorphous with far less capacity to imbibe water). In the short term, the viscoelastic deformation may lead also to laxity of the ligament and lack of coordination, potentiating injury through biomechanical perturbations. Over the long term, it leads to degenerative and permanent changes that are a hazard to the back. The problem of seated sedentary work worsens considerably when prolonged sitting is combined with whole-body vibration, such as with truck driving. The frequencies of many vehicles are close to the natural frequency (4 to 8 Hz) of the human spine, causing resonance and thus amplification of the motion amplitude. Truck drivers must contend not only with this vibration but also with the static loading of the disk while driving. In addition, often they have periodic acute loading of the back when they load or unload their vehicles.
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stools; both conventional and sit/stand chairs should have backrests. Sit/stand chairs should have a forward tilt of 15-30 degrees and a fabric seat.4 Another technique to encourage movement is job rotation. A chair is the key component of seated work, but because not all seated work is the same, chairs should be matched to specific jobs. Of course, people vary in height and weight, and many of them often sit in the same chair because of multiple shifts, parttime workers sharing a shift, and holiday or vacation replacements. Thus chairs should be easily adjustable in terms of seat pan height, back rest height and forward/back location, and armrest width and height. The seat should be padded with a breathable fabric; avoid plastic and leather. It should not be contoured, because this reduces micropostural changes. A curved front edge (waterfall front) maximizes contact with the underside of the thigh; avoid upholstered beading on the front edge. Normally, the seat should tilt backward 1-5 degrees and permit swiveling. For seat width, the wider the better; for depth, the most common problem is a seat that is too deep. A deep seat forces the sitter forward (losing support of the backrest) or back (with the legs dangling). The ideal backrest is adjustable both horizontally and vertically and has a spring action so that it “tracks” the angle of the back as the person moves. It should be concave to give area support to the back, especially in the lumbar region. Armrests should be adjustable in width and height. Avoid long armrests that hit the table edge and preclude good chair location with respect to the task. The legs/pedestal normally should permit swiveling and thus micropostural changes. The sitter’s legs should be able to tuck under the seat to shorten the hamstrings (reducing their pull) and decrease stress on the back. If the seated worker moves about the work station, the chair should have casters; otherwise, they are inadvisable because they force the operator to use leg muscles to keep the chair still. Design modifications to truck seats should reduce vibration at the point of origin or dampen it before transmission to the driver. Trucks should be equipped with hoists and dollies to reduce acute stress on the back by doing the work.
Holding work Problem
Control strategies The two strategies for addressing this problem are personal compensations and job design. From a personal viewpoint, people in sedentary jobs should lead active lives outside the workplace. In addition, at work they should be encouraged to change postures frequently, move around, and mix nonseated with seated work. (Naturally, the job design should not just permit this movement but also encourage it.) Job designs of seated workers often include either machines or other workers to bring supplies and remove finished products. By not allowing the worker to move, this practice creates a “straight jacket” that precludes movement. Permitting a worker to fetch supplies and dispose of products not only is beneficial but also should be encouraged within limits. Another possibility for permitting some movement is to have a sit/stand work station where the worker can alternate between sitting and standing. Standing work is better if there is a “bar rail” or footrest upon which the worker can alternate foot positions.9 Avoid using
For some tasks in auto assembly, painting, or kitchen and laundry work, for example, workers hold an object without movement. Even without an object, the weight of one hand and arm is approximately 4.9% of body weight. The farther from the spine the hand or object, the greater the problem, because torque is a product of weight times moment arm.
Control strategies To address this problem, reduce the torque and its duration. Figure 4e.1 shows how a tipping aid can reduce the strain of holding a drum or container. An angled bar (a “plow”) on a belt conveyor can direct a product on the conveyor toward the side closest to the worker, who need not reach as far for the item and therefore reduces torque on the spine. For standing workers, a conveyor should be about 50 mm below the elbow (by height adjustment or by having short operators stand on platforms) to minimize torque on the arms and back. A balancer (Fig. 4e.2) reduces tool weight.
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Dynamic work Manual handling is quite prevalent in industry. Asfahl2 estimated that for every pound of product, 80-150 pounds of materials are handled and moved. Konz and Johnson9 stated that 25% of all industrial injuries are associated with manual handling—670,000 injuries per year in the United States. Of money spent on industrial injuries, 60% pays for those caused by manual handling, which accounts for 93,000,000 work days lost each year. Dynamic work risks are divided among pushing/pulling, carrying, and lifting/ lowering, the last of which causes most problems.
Pushing and pulling Imrhan7 provided an excellent summary of pushing/pulling. Pushing occurs not only while standing but also while sitting and even kneeling. Height and direction also are important (Fig. 4e.3).
Control strategies Figure 4e.1 Tipping aids permit a drum or carboy to be counterbalanced when pouring. The danger of spills and operator muscle stress is reduced.
A poor interface of the hand and handle is a potential weak link. Although a handle is needed for pulling, pushing may just use a flat surface. Two hands are better than one. The arm and shoulders (rather than the back) tend to be limiting (causing local muscle fatigue) when the activity is repetitive. Workers should avoid pushing or pulling above the shoulders or below the hip. Effective pushing involves leaning toward the load with the rear foot positioned behind the body’s center of mass (Fig. 4e.4), whereas pulling involves leaning away from the load with the rear foot behind the body’s center of mass. Although there should be a high coefficient of friction between the floor and the shoe, the object may have a low coefficient of friction against its supporting surface. Ball transfer sections on conveyors have a kinetic friction of 0.03 to 0.15, for example, so pushing a 50-kg container on balls requires a force of 1.5 to 7.5 kg. Air-film pallets use the same concept of reducing the friction of object against surface. Generally, people push/pull perpendicular to the shoulders. When pushing parallel to the shoulders, the capability is 50-60% of the perpendicular capability. Several recommendations for force limits for pushing and pulling have been published.18,19 In summary, ● Two hands are usually better than one. ● Force capability decreases when it is used more often. ● Initial force capability is higher than sustained capability. ● Pushing capability is higher than pulling capability. ● Pushing should be done at waist level and pulling at thigh level.
Carrying
Figure 4e.2 Balancers reduce tool weight from pounds to ounces. Note that the balancer is suspended from a job crane to minimize horizontal force as the tool is moved about the workplace. The greater tool weight increased torque at the elbow and shoulder, thereby decreasing comfort of the neck and back as well as the arm (Ulin S, Armstrong TJ, Snook SH, Monroe-Keyserling W: Examination of the effect of tool mass and work postures on perceived exertion for a screw driving task. Int J Ind Ergonom 12:105-115, 1993).
Although carrying objects for long distances (those over 10 m) no longer is common in developed countries, workers still carry around work stations. Carrying objects up and down stairs is especially dangerous because the hands are holding the object and thus not free to grasp handrails if there is a slip and because the object may obstruct vision.
Control strategies Long-distance carrying is best when mechanized with lift trucks, conveyors, or carts (Fig. 4e.5). As anyone who has transported a
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Figure 4e.3 Chiming a drum (rotating a tipped drum) requires little effort; with skill, the drum’s momentum can be used to move it onto a pallet. A drum cart is another alternative. A straight push, however, as shown on the right, requires considerable effort.
suitcase through an airport knows, pushing or pulling is better than carrying, so wheels should be used whenever possible. Jib cranes, ball-transfer sections, or manipulators (Fig. 4e.6) can move objects within work stations, as do ramps and elevators between floors.
multiplier, and CM is the coupling multiplier. Konz and Johnson9 explain the calculation procedure in detail, and the disk accompanying the book has a computer program to solve the equation.
Control strategies Lifting and lowering As pointed out above, manual handling creates many problems. Engineers and ergonomists can focus on the job-specific factors with reference to the detailed tables of the manual handling guide.18 For example, Table 4.2 of the guide gives 720 recommended weights for male industrial workers for two-handed symmetric lifting for 8 hours. The table has three box sizes, eight lifting frequencies, six lifting distances, and five population percentiles. The most common approach is that set forth in the National Institute for Occupational Safety and Health (NIOSH) lifting guideline.22 The NIOSH guideline assumes a load of 23 kg but then reduces the 23 through 6 multipliers (all less than 1.0) to arrive at a recommended weight limit (RWL): RWL = LC × HM × VM × DM × FM × AM × CM where LC is the load constant (i.e., 23 kg), HM is the horizontal multiplier, VM is the vertical multiplier, DM is the distance multiplier, FM is the frequency multiplier, AM is the asymmetry
1. Select strong people based on tests: Several studies have shown the significance of the job severity index, the ratio of the task demand to the person’s capability. One approach may therefore be to select workers with large capacities. It is important to consider worker capacity in job-simulated tests, which force the analyst to measure not only this factor but also the task requirements. 2. Bend the knees: Despite a concerted effort to train workers to lift with bent knees and straight backs, the practice has not received universal acceptance. The logic behind the recommendation has been to reduce the moment arm on the lumbosacral disk, thereby reducing mechanical compression. It has been shown, however, that unless the object to be lifted is brought very close to the body, the squat lift can in fact significantly increase mechanical compression on the lumbosacral disk. It has been shown also that the squat lift is associated with significantly higher physiological cost and is more tiring for workers.
Typical posture Recommended posture Figure 4e.4 Posture when pushing makes a difference. Peak intraabdominal pressure was 50% less when pushing with the back (Ridd J: A practical methodology for the investigation of materials handling problems. In T Kvalseth, ed: Ergonomics of work station design. London, 1983, Butterworth-Heinemann).
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A
C B Figure 4e.5 Drum carts reduce stress. (A) A two-wheeled cart; it should have a latch over the top rim during movement. (B) The foot can be used to help tip the drum. Another handle forward of the main handles is useful when tilting and maneuvering the drum to scales and pallets. (C) A four-wheeled cart useful for heavier drums; note that the hand positions are different.
Another disadvantage of the squat lift is that it causes considerable stress on the knees, which are also a frequent site of mechanical disorders. Therefore a universal acceptance of the squat (as opposed to the stoop) lift is neither physiologically nor mechanically sound. It is perhaps for this reason that this method has not been accepted by workers as widely as was initially hoped. Furthermore, the statistics of low back injuries associated with lifting over the past 40 years make clear that a steady increase in incidence has occurred despite many industrial workers’ following the squat method. It is important to assess the job as well as the individual performing it before recommending squat or stoop lifting. Garg et al6 compared the physiologic costs of different methods of lifting. They found that when subjects were allowed to lift any way they wanted, they chose neither pure stoop nor pure squat but combined the features of both in a freestyle lift. This lift was found to be metabolically the least expensive. The recommendation is therefore to use an individualand task-specific method to minimize stress on spine and reduce the chances of injuries.
3. Don’t slip or jerk: Sudden and ballistic movements have a large inertial component. Because of the viscoelastic nature of the human back and the resistance to immediate deformation offered by the fluid portion of the tissue, such inertial forces can exceed the tolerance limits of the tissues.16 In addition, sudden motion may also cause a slip or fall while performing a lift. It is therefore recommended that workers wear shoes with soles having a large contact area and a high coefficient of friction, as should floors, which must not be smooth. Data on a force platform indicate that peak forces and torques during lift are very “spiked,” with the peak force often occurring during initial lowering of the body before the object is even grasped. The accelerations and decelerations during lifting and lowering should be fast enough that the body gets the benefit of the momentum without causing a jerk that may lead to an injury. 4. Avoid twisting: To maintain symmetry of the human body, the spine is provided with a bilaterally symmetric arrangement of muscles and ligaments. Any rotation accentuates the activities in the agonist group of muscles and reduces the
Chapter 4e
5.
6.
7.
8.
Figure 4e.6 Manipulators (balancers with arms) can support tools or can be used to move products around work stations.
contribution of the antagonistic muscles. When manual materials are handled, a twisted posture or when the spine is progressively twisted during a lift, the force production in different muscles is continually varied, accentuating the stress on one group of muscles and ligaments. When most of the load is borne by only 50% of the structures, the stress could easily be doubled, significantly increasing the chances
●
Adaptations
of injury. Twisting while bent over, such as when removing parts from the floor, is risky. A general recommendation is therefore for workers to move their feet instead of twisting their backs. Because workers might not comply as rigorously as desirable, an engineering approach precluding the need to twist is recommended. Such an approach will solve the problem rather than depend on the workers’ knowledge, awareness, alertness, and cooperation. Figure 4e.7 shows how a task can be modified to reduce bending and twisting. Use mechanical aids: The most desirable means of preventing injuries associated with manual materials handling is to eliminate it by using mechanical aids. Instead of moving a power tool around a work station, for example, a balancer (Fig. 4e.2) or manipulator (Fig. 4e.6) can be used. Figure 4e.8 shows a turntable on a scissors lift used to mechanize palletizing; in automation, the operator would be replaced with a palletizer. In some circumstances robots are appropriate. Other machines commonly used to eliminate manual handling are hoists, lift trucks, conveyors (both portable and telescopic), and lever arms. Consider the packaging: For job design, an important concept is to keep the load close to the body, so it is important to keep packages small. Big, bulky, and awkward packaging increases the moment arm of the load on the spine, thereby increasing the compressive load significantly. Bulk may make it more difficult to lift 25 kg of feathers, for example, than 25 kg of iron. Konz and Coetzee11 reported that increasing a box’s volume up to a 30-cm cube did not bother men but strongly bothered women. When determining packaging dimensions, it is therefore important to consider the anthropometry of the work population. Have good coupling: Cardboard boxes with cutout holes provide poor coupling because (1) the hand cannot rotate as the object is lifted from the knee to the waist and (2) the narrow cardboard surface area tends to concentrate the load on a small area of contact with the hands, thereby cutting the circulation and squeezing the muscles. When the packages to be lifted are larger than optimal size, it is particularly important to provide a comfortable handhold to permit a relatively riskfree, orderly, and smooth lifting activity that minimizes the chance of injury. Consider work height and reach: Konz stated, “Drag it, pull it, push it, but don’t lift it.”10 As explained above, if lifting is necessary, it is best done at knuckle height; loads should not be on the floor or above the shoulders. When cartons are loaded from a conveyor, for example, the conveyor height should be adjustable. When they are loaded from a pallet, it should be left on the lift truck forks, the height of which should be periodically adjusted. If the fork lift cannot be tied up, the pallet should be placed on a wheeled lift table.
A summary of all these principles has been provided by Ayoub et al3 in a comprehensive set of guidelines to control and reduce occupational health problems associated with manual materials handling. Their recommendations can be summed up in two statements: (1) eliminate heavy manual materials handling and (2) decrease the stress to the worker. They recommend the use of mechanical aids such as hoists, lift tables, and conveyors and the provision of best work heights that can be varied to suit the operator and achieve an optimum work arrangement.
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Workplace adaptation for the low back region
Figure 4e.7 Work station positioners reduce lifting, bending, and twisting. (A) A scissors lift. (B) A bin on an adjustable-height cart that is useful to create temporary work stations for tasks such as shelf stocking. (C) A self-leveling truck (similar to cafeteria tray dispensers).
Figure 4e.8 Turntables can reduce stress when loading or unloading. The turntable is rotated after a few items are moved. It can be mounted on the floor and a pallet placed upon it. If the turntable surface is rollers, ball casters, or an air table, rotation can be manual. If it is mounted on a scissors table (as shown), horizontal transfer can replace lifting and lowering.
Chapter 4e
A reduction of stress, they suggest, can be achieved by reducing the weight of the object in cases in which it is not possible to split the load between two workers. A reduction in the size and weight of containers is a desirable goal also. The authors recommend changing the type of manual materials handling: lower the load rather than lift, push the load rather than pull, and pull the load rather than carry. They suggest reducing both the horizontal and vertical distance in reaching for an object and transporting it. Avoiding twisting in both standing and seated work is desirable. Modification of an object to make it easier to handle by using handles, balance containers, and reasonable width are all good design criteria. On the worker side, however, it is important also to provide adequate recovery time by reducing the frequency with which a particular task is performed and allowing for job rotation.
7. 8. 9. 10. 11.
12. 13. 14. 15. 16. 17. 18.
REFERENCES 1.
2. 3. 4. 5. 6.
Andersson GBJ: The epidemiology of spinal disorders. In J Frymoyer, Spitzer W, LeBlanc FE, Dupuis, M eds: The adult spine. New York, 1991, Raven Press, pp. 107-146. Asfahl CR: Industrial safety and health management. Englewood Cliffs, NJ, 1984, Prentice Hall. Ayoub MM, Selan J, Jiang B: Manual material handling. In G Salvendy, ed: Handbook of human factors. New York, 1987, Wiley & Sons. Chester M, Rys M, Konz S: Leg swelling, comfort and fatigue when sitting, standing, and sit/standing. Int J Indust Ergon 29:289-296, 2002. Davis PR: The biological basis of physiological ergonomics requirements. Int J Indust Ergon 23:241-245, 1999. Garg A, Sharma D, Chaffin DB, Schmidler JM, et al: Biomechanical stresses as related to motion trajectory of lifting. Hum Factors 25(5):527-539, 1983.
19.
20.
21.
22.
23.
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References
Imrhan S. Push-pull force limits. In W Karwowski, W Marras, eds: The occupational ergonomics handbook. Boca Raton, 1999, CRC Press. Khalil T: Ergonomic issues in LBP: origin and magnitude of the problem. Proceedings of the Human Factors Society, San Francisco, 1991, pp. 820-824. Konz S, Johnson S: Work design: occupational ergonomics, ed 6. Scottsdale, AZ, 2004, Holcomb Hathaway. Konz SA: Work design: industrial ergonomics, ed 4. Scottsdale, AZ, 1995, Publishing Horizons. Konz SA, Coetzee K: Prediction of lifting difficulty from individual and task variables. Proceedings of the Fourth International Congress on Production Research, Tokyo, 1977. Kumar S: A conceptual model of overexertion, safety and hazard. Hum Factors 36:197-209, 1994. Kumar S: Cumulative load as a risk factor for back pain. Spine 15(12):1311-1316, 1990. Kumar S: Functional evaluation of the human back: a research report. 1991. Kumar S, Narayan Y: Spectral parameters of trunk muscles during isometrics axial rotation in neutral posture. J Electromyogr Kinesiol 8:257-267, 1998. Kumar S, Narayan Y, Stein RB, Snijders C: Muscle fatigue in axial rotation of the trunk. Int J Indust Ergon 28:113-125, 2001. Magora A: Investigation of the relation between LBP and occupation. Ind Med 39(12):504-510, 1970. Mital A, Nicholson A, Ayoub MM: A guide to manual material handling. London, 1993, Taylor & Francis Publishers. Snook SH, Ciriello VM: The design of manual handling tasks: revised tables of maximum acceptable weights and forces. Ergonomics 34(9):1197-1213, 1991. Spitzer W, LeBlanc FE, Dupuis, M: Scientific approach to the assessment and management of activity-related spinal disorders. A monograph for clinicians. Report of the Quebec Task Force on Spinal Disorders. Spine 12(Suppl):1-559, 1987. Waddell G, Allan DB, Newton M: Clinical evaluation of disability in back pain. In JW Frymoyer, Spitzer W, LeBlanc FE, Dupuis, M eds: The adult spine. New York, 1991, Raven Press. Waters T, Putz-Anderson V, Garg A: Application manual for the revised NIOSH lifting equation. NIOSH Pub PB94, Rockville, MD, 1994, Department of Health and Human Services. Webster BS, Snook SH: The cost of 1989 workers’ compensation LBP claims. Spine 19(10):1111-1115, 1994.
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Appendix 4e.1 Websites of workstation suppliers
Advance Lifts (work station positioners) www.advancelifts.com American Lifts (scissors lifts) www.americanlifts.com Autoquip (lifting, turning, tilting equipment) www.autoquip.com Bishamon Industries (pallet positioners, lift tables) www.bishamon. com Columbus McKinnon (lift tables) www.cmworks.com Columbus McKinnon (manipulators) www.positech-solutions.com Econolift (lifts/tilters) www.econolift.com Ergonomic Systems (work station/positioners) www. ergonomisystems.com
Glasgow (air tables) www.glasgowproducts.com Knight Industries (balancers, manipulators) www.knight-ind.com Presto Lifts (work station material handling) www.prestolifts.com Rampmaster (work station material handling) www.rampsonline. com Scaglia America (balancers, manipulators) www.scaglia.it Southworth (work positioning) www.southworthproducts.com Tawi USA (vacuum lifting) www.tawi.se Vestil (work positioning) www.vestilmfg.com
CHAPTER
Shoulder and Elbow
5
CHAPTER
5a
Shoulder and Elbow Disorders Marianne Magnusson and Malcolm Pope
This chapter discusses the epidemiology and pathomechanisms of disorders of the shoulder and elbow. Shoulder and elbow disorders were reported as related to certain occupations as long ago as 1713.80 Like other musculoskeletal disorders (MSDs), those of the upper extremity are increasing, as expressed by a more frequent reporting of them as occupational diseases.65 The reason for the increase might be the higher degree of automation resulting from workplace designs improved to reduce heavy workloads like lifting and manual labor. The demands of increasing productivity, however, which in turn imply the simplification of working tasks, has increased the work pace.96
CLASSIFICATION OF DISORDERS Shoulder In the International Classification of Diseases,99 work-related neck-shoulder disorders have been classified into “occupational diseases,” in which there is a direct cause-effect relationship between hazard and disease, and “work-related disease,” in which work environment and the performance of work contribute significantly, but as one of a number of factors, to the causation of a multifactorial disease.98 The concept of occupational cervicobrachial disorder was adopted in 1973.6,61 It is defined as “functional and/or organic disturbances resulting from neuromuscular fatigue to doing jobs in a fixed position or with repetitive movement of the upper extremities.” Waris93 named four categories: the cervical syndrome, the tension neck syndrome, humeral tendinitis, and thoracic outlet syndrome. Introduced in Australia, the term repetition strain injury is defined as “a soft tissue disorder caused by muscle overloading from repetitive use or maintenance of constrained postures” that “occurs among workers performing tasks involving frequent repetitive movements of the limbs or the maintenance of fixed postures for prolonged periods.”12 Cumulative trauma disorder, musculoskeletal injury and disorder, occupational repetitive strain injury, and regional pain syndrome are other terms that describe essentially the same condition.
Elbow Tennis elbow, also called lateral humeral epicondylalgia or lateral elbow syndrome, is a painful condition of the lateral aspect
of the elbow. Cubital tunnel external compression syndrome is caused by compression of the ulnar nerve at certain elbow flexion angles at a subcutaneous location behind the humeral epicondyle (cubital tunnel).
EPIDEMIOLOGY General population In general studies that include large sample populations without special demands for neck and shoulder activity, the 12-month prevalence of neck and shoulder disorders was 15% to 18%.5,94 Disorders of the neck and shoulders are most common among women.7,21,93,94 In a Swedish study, 50% of the women but only 36% of the men reported strain injuries from the neck and shoulders.44 Another study reported a 10 times higher rate of sick leave due to occupational cervicobrachial disorders in women compared with the sick leave in men due to occupational low back pain.51 Perhaps even more than men, women often work in occupations with repetitive and monotonous work tasks, and many studies have reported an increased prevalence of upper limb disorders in repetitive work.32,47,58,78,92 In a large Swedish study of 2537 men and women, 20% of the women and 16% of the men had neck-shoulder problems during the last 12 months,92 the incidence of which increased with age and occupational physical load. Takala et al reported a 1-year prevalence of 18% of women and 16% of men in a Finnish rural population.89 In a random sample of 855 men and women in Iceland, 65% of the women and 43% of the men had neck or shoulder pain during the previous year.79 Neck and shoulder pain has been found to be not only interrelated but also related to low back pain, indicating a susceptibility and a predisposition to develop MSDs.63
Occupational risk groups Epidemiologic studies show, and most researchers agree, that along with personal factors such as age, genetics, and gender, exposure to a combination of physical and psychosocial workplace risk factors is a major contributor to these disorders. Specific physical factors include intense, repeated, or sustained exertions; awkward, sustained, or extreme body postures; insufficient recovery time; vibration; and cold temperatures. Specific examples of workplace psychosocial factors include monotonous work, time pressure, high workload, lack of peer support, and a poor supervisor-employee relationship.34 Musculoskeletal diseases were the major reason for long-term absenteeism in a manufacturing company. Low back pain accounted for 17.7% of all long-term absenteeism (the greatest amount), and neck and shoulder pain caused 15.9%. Back disorders were most common in heavy manufacturing workshops, whereas in the light manufacturing workshops the most dominant diseases related to the neck and shoulder.51 As recorded in a questionnaire and compared with a control group with more varied tasks, females employed in assembly, fish-processing, and ceramics factories, all representing highly repetitive work tasks, had considerably higher prevalences of
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Shoulder and elbow disorders
Table 5a.1 Elbow problems in newspaper workers (% of total)82
12-month prevalence (%) Missed work (%) n
All
Office
Production
8 1 906
6 1 682
12 2 201
complaints and physical examination diagnoses of neck and upper limb disorders.70 Without a specific diagnosis or defined symptoms, neck and shoulder problems have been reported in a large number of studies involving secretaries and office workers,10,41,42,56,91 dentists,55,68 sewing machine operators,86 visual artists and piano players,16,27 and railway station workers.13 The annual prevalences of neck and/or shoulder symptoms for female secretaries and office workers ranged from 45% to 63%, whereas those for male office workers were considerably lower, ranging from 16% to 27%. Table 5a.1 reports the elbow problems found in a study surveying workers in the newspaper industry.82 Musculoskeletal problems in instrumental musicians have a long history.25,26 Lederman and Calabrese52 described an increasing number of reports of musculotendinous overuse. Nerve entrapment syndromes have been reported in musicians by Knishkowsky and Lederman.48 Charness et al17 reported that routine electromyography (EMG) and nerve conduction studies were abnormal in less than half the musician patients studied, attesting to the potential for even mild ulnar neuropathy to produce disabling symptoms.
RISK FACTORS Work-related factors Work-related factors recognized for their association with upper limb disorders include repetitive or forceful exertions, awkward postures, and segmental vibration. Several studies have suggested a relationship between static and/or repetitive load and disorders in the neck and upper extremity.30,44,51,60,95 In their meta-analysis of occupational neck-shoulder disorders, Hagberg and Wegman32 found that jobs with highly repetitive shoulder muscle contractions, static muscle work, and work above shoulder level were associated with the tension neck syndrome. Kuorinka and Forcier49 looked specifically at shoulder tendinitis and stated that the epidemiologic literature is “most convincing” regarding work relatedness, showing an increased risk especially from overhead and repetitive work. Several studies have supported these associations4,16,27,72,86; the mechanical load on the shoulders was obvious, and working tasks involving continuous arm movements always generate a static load component.1,72,85,97 Repetitive work should therefore not be considered independent of posture. Association between repetition and shoulder tendinitis has been reported in three studies,23,71,73 in all of which some or all of the results showed
associations with a combined exposure to repetition and awkward posture. The principal muscle to carry this load is the trapezius. The relative load as a percentage of maximum voluntary contraction (MVC) on the upper trapezius has been shown to increase linearly with the relative torque in the glenohumeral joint.29 There are large differences, however, among muscles and between flexion and abduction. A given shoulder torque during flexion produces smaller amplitudes of both the intramuscular pressure and the EMG than for the same torque during abduction.38 With a shoulder abduction of 30 degrees, the intramuscular pressure in the supraspinatus muscle by far exceeds the level at which the blood flow is significantly impeded. The supraspinatus is thus extremely vulnerable in work situations requiring arm elevation. High shoulder muscle force requirements can cause increased muscle contraction, which may lead to an increase in both muscle fatigue and tendon tension and may possibly impair microcirculation as well. Sjøgaard et al86 found that muscular fatigue would occur at EMG levels as low as 5% of MVC if sustained for 1 hour. Other studies have demonstrated that when the period of muscle contraction is extended to more than an hour, the endurance limit of force may be as low as 8% MVC.40 Workers performing repetitive work with the hands and wrists while maintaining static upper arm elevation may experience fatigue even at low load levels. Jonsson et al40 reported that many constrained work situations are characterized by static load levels near or exceeding 5% MVC even when there is a fairly low mean muscular load. Ohlsson et al71 reported an odds ratio of 3.03 (95% confidence interval, 2.5-7.2) for supraspinatus, infraspinatus, or bicipital tendinitis for work in the fish industry, representing repetitive work and poor posture. Compared with that of a referent population, the odds ratio for assembly work, which requires repetitive arm movements with static shoulder load, was 4.2 (95% confidence interval, 1.35-13.2). Kurppa et al,50 Silverstein et al,85 and others reported that highly repetitive tasks can cause pain and disability in the upper extremity. In many jobs, upper extremity tasks require repetitive contractions of those muscles over long periods of time at low contraction intensities and short contraction-relaxation cycles. Silverstein et al85 created a prevention index to rank industries by averaging the ranks of their number of claims and their claims incidence rate with a focus on nontraumatic soft tissue MSDs. Although the incidence rates for some disorders are decreasing, the overall rate is not decreasing as fast as that for all other claims. In some cases, the rate is stable (sciatica, rotator cuff syndrome) or increasing (epicondylitis). The industries with the highest risk are characterized by heavy manual handling and repetitive work. Edwards22 proposed that fatigue and lack of recovery are the elements that can cause injury to the elbow. In simulations of upper extremity work measuring recovery of blood flow, EMG fatigue index, and subjective ratings, Byström and Kilbom15 concluded that a mean contraction intensity of higher than 17-21% MVC was not acceptable. Using the same techniques, Byström and FransonHall14 suggested in a later article that continuous handgrip contractions higher than 10% MVC are to be avoided. These recommendations are conservative, and many industrial jobs exceed the safety limits.
Chapter 5a
Overall, epidemiologic evidence suggests a relationship between repeated or sustained shoulder postures with more than 60 degrees of flexion or abduction and shoulder MSDs, including both tendinitis and nonspecific pain. The evidence for increased risk of MSDs due to specific postures is strongest with a combination of exposures to several physical factors such as force and repetitive work. An example would be holding a tool while working overhead. Insufficient evidence exists to make an association between shoulder tendinitis and exposure to segmental vibration. Stenlund et al88 found such an association, but work with vibration exposure also placed a large static load on shoulder muscles so that the effects of forceful exertions could not be separated from it. Because they are multifactorial in origin, shoulder MSDs are and may be associated with both occupational and nonoccupational factors whose relative contributions may be specific to particular disorders. The confounders for nonspecific shoulder pain, for example, may differ from those for shoulder tendinitis. (Two of the most important confounders or effect modifiers for shoulder tendinitis are sport activities and age.) Excessive contractions or fatigue can lead to tennis elbow, one of the most common occupational elbow problems.19 This is characterized by intense pain of the lateral aspect of the elbow exacerbated by grip and more use. Coonrad18 reported that the main problem is repetition, but it is multifactorial in origin. Allander3 reported a prevalence of one third in 15,000 subjects. In studies at certain occupational clinics, Dimberg20 found that 64% of all diagnosed cases were related to work. Cyriax19 reported that only 8% of cases actually involved tennis. In a review, however, Maylack67 reported that 50% of competitive tennis players suffer from at least one episode of lateral epicondylitis. Another elbow problem is cubital tunnel external compression syndrome. As the ulnar nerve travels from the brachial plexus to the hand, it is vulnerable to compression at certain elbow flexion angles at a subcutaneous location behind the humeral epicondyle (cubital tunnel). A common occupational risk reported in drivers occurs where the elbow is rested on a hard surface for a long period of time.2 Mansukhani and D’Souza66 reported unilateral ulnar neuropathy in diamond workers that was restricted to the arm holding the eyeglass for inspecting the diamonds.
Individual factors Not all workers performing similar and risky work tasks develop MSDs, due to the obvious influence of individual factors on the exposure-effect relationship. The individual factors most frequently studied or controlled for are sex and age. Some studies have shown that age affects the prevalence of MSDs,36,47,54,91,94 whereas others have shown no such influence.11 Muscle strength and endurance influence the risk of neck and upper limb disorders. With higher muscle strength, the muscle is obviously less loaded than in the case of lower strength for the same force exertion. Women in general have lower strength than men, in particular in the upper extremities, and older people are weaker than younger ones.69 Some studies, however, have shown that compared with men, women have longer muscle endurance
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Pathomechanisms
in proportion to their muscle strength,10,84 but this has not been proven for all muscle groups. Although women may have more neck-shoulder disorders than men because of fatigue and poor strength, it is more likely because women predominate in jobs involving a high degree of repetitiveness and prolonged static postures of the neck and shoulders. Poor muscle strength and low endurance have been shown in patients with neck-shoulder pain. Strength was affected in acute patients,9,51 whereas endurance was impaired in chronic patients as well.31,86,87 Other studies, however, failed to show a relationship between neck and shoulder symptoms and strength and endurance.46 Indeed, the contrary was shown in a prospective study; subjects with high muscle strength in shoulder elevation seemed to be at a higher risk.40,45 A longitudinal study of motor assembly workers showed that low isometric strength of shoulder muscles was a risk factor for neck and shoulder pain.43 Hägg et al33 could not show significant relations between either EMG signs of fatigue during work or isometric strength with the development of muscular disorders during a 2-year follow-up. A few studies found certain personality traits to predispose to MSDs. Characterized by competitiveness, impatience, and a feeling of time urgency, the “type A” personality has been found to be associated with low back pain36,37,94 and with neck-shoulder pain.24,33,83
Social factors Along with recognition of the importance of the physical load to MSDs, there is a growing awareness of their association with psychosocial factors and work environment.59,64 In a longitudinal study, job satisfaction and relations with coworkers and supervisors were the strongest predictors for developing industrial back pain.7,8 Monotony, stress, low job satisfaction, lack of control, and low skill requirements characterized a typical light assembly job where young males reported a high rate of back pain.57,62 In a study of occupational drivers, the group that had the highest incidence of both back pain and neck-shoulder pain reported the highest stress level and lowest job satisfaction.63 The same study found a strong relationship between back pain and neck-shoulder pain also, indicating that individuals who are predisposed will develop any or several MSDs. Tola et al91 reported that moderate or poor job satisfaction and physical loading factors were significant risk factors for neck and shoulder pain. Bergenudd et al7 found that women with a history of shoulder pain were less satisfied with their jobs than women who did not experience pain. Among possible psychologic stresses at work, the combination of high work demand and low control in particular seems to play an important role in the development of musculoskeletal complaints.36,37
PATHOMECHANISMS Workload The common causative factor in MSDs is mechanical stress on musculoskeletal tissues. Normally, the tissues adapt to mechanical stress; that is, tissues strengthen with increased stress and
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Shoulder and elbow disorders
weaken with less.90 When the stress exceeds the limit of adaption, pathologic changes may occur in the tissue. The risk of developing symptoms may also increase, however, when the physical stress is very low.99 Hagberg and coworkers31,32 suggested three possible pathomechanisms for muscle pain as a result of physical load: mechanical failure, local ischemia, and energy metabolism disturbances. Mechanical failure of the muscles is typically the cause of the muscle soreness that occurs 24 to 48 hours after heavy physical exertion. The pain is due to ruptures of the z-disks and outflow of metabolites from the muscle fibers, which directly or through edema activate pain receptors. Local ischemia produces an accumulation of metabolites within the muscle that is typically a result of static or repeated muscular contraction or repeated muscular injuries. Energy metabolism disturbances occur when the energy demands exceed the production. Because of the prolonged replenishment of intracellular glycogen stores, the resulting development of muscle pain may be delayed up to 46 hours. Edwards22 proposed another model for pathologic changes in the muscle after occupational injury, suggesting that occupational muscle pain might result from a conflict between motor control of the postural muscular activity and that needed for movement or exertion. Some studies have been conducted to provoke pain or discomfort in the shoulder-neck region. Hagberg29 studied the immediate and long-term effect of continuous repetitions of shoulder flexions with and without weights for 1 hour or until exhaustion. He found that all subjects had pain localized to the descending part of the trapezius muscle directly after the experiments. In 14 of 18 experiments, the subjects had pain 24 hours later, and after 48 hours, tenderness occurred in the trapezius muscle and the rotator cuff insertions. Harms-Ringdahl and Ekholm35 studied the effect of prolonged extreme flexion of the neck and found that pain was experienced after 15 minutes and increased with time. Interestingly enough, the pain disappeared within 15 minutes, but in 9 of 10 subjects it recurred the same evening or the following morning and lasted for up to 4 days. Lee and Waikar53 found a correlation between EMG root-mean-square values and discomfort ratings in subjects simulating microscope work for 4 hours.
Muscular fatigue Muscular fatigue is related to the force of the active muscle; that is, fatigue develops faster with higher relative muscle force. Some muscle groups are more prone to fatigue than the neck and trunk extensor muscles.28,77,81 Limits to muscular load for constrained work with a duration of 1 hour or more were proposed by Jonsson39: static muscular load should not exceed 2-5% of MVC, mean load level should be limited to 10-14% of MVC, and peak loads should occur within 50-70% of MVC.
Entrapment Radial tunnel syndrome, also known as resistant tennis elbow, is seen in workers who must perform multiple repetitive motions, especially wrist extensions with or without force. The mechanism behind the condition is the entrapment of the radial nerve involving its sensory branch.
PREVENTION According to Hagberg and Wegman,32 the occupationally related etiologic fraction of neck and upper extremity injuries is high, and therefore a relatively large number could be prevented. Some studies have proved that intervention in working conditions can be successful,76 and rehabilitation of neck and upper limb disorders often fails when not combined with such improvements.23,75 Only a few studies have been able to describe an exposure-effect relationship. For successful prevention, future studies of the quantification of physical exposure and the importance of psychosocial factors are needed.
REFERENCES 1.
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Luopajärvi T, Kuorinka I, Virolainen M, Holmberg M: Prevalence of tenosynovitis and other injuries of the upper extremities in repetitive work. Scand J Work Environ Health Suppl 3:48-55, 1979. MacDonald LA, Karasek RA, Punnett L, Scharf T: Covariation between workplace physical and psychosocial stressors: evidence and implications for occupational health research and prevention. Ergonomics 44(7):696-718, 2001. Maeda K: Occupational cervicobrachial disorder and its causative factors. J Hum Ergol 6:193-202, 1977. Maeda K, Horiguchi S, Hosokawa M: History of the studies on occupational cervicobrachial disorder in Japan and remaining problems. J Hum Ergol 11:17-29, 1982. Magnusson M, Granqvist M, Jonson R, Lindell V, Lundberg U, Wallin L, Hansson T: The loads on the lumbar spine during work at an assembly line in a car factory. The risks for fatigue injuries. Spine 15(8):774-779, 1990. Magnusson M, Wilder DG, Pope MH, Hansson T: Investigation of the long-term exposure to whole body vibration: a 2-country study. Vienna Award for Phys Med 1992. Eur J Phys Med Rehab 3:28-34, 1993. Malker B, Blomgren UB: Occupational diseases 1985. Sweden, Stockholm, 1989, National Board of Occupational Safety and Health, and Statistics [In Swedish]. Malker HSR, Hedlin M, Malker BK, Weiner JA: Occupational musculoskeletal disorders. Identification of risk by ISA statistics. Arbete Och Hälsa 29:1-122, 1990 [In Swedish]. Mansukhani KA, D’Souza C: Ulnar neuropathy at the elbow in diamond sorters. Indian J Med Res (B) 94:433-436, 1991. Maylack FH: Epidemiology of tennis, squash, and racquetball injuries. Clin Sports Med 7:233-243, 1988. Milerad E, Ekenvall L: Symptoms of the neck and upper extremities in dentists. Scand J Work Environ Health 16:129-134, 1990. Murray MP, Gore DR, Gardner GM, Mollinger LA: Shoulder motion and muscle strength of normal men and women in two age groups. Clin Orthop 192:268-273, 1985. Ohlsson K: Neck and upper limb disorders in female workers performing repetitive industrial tasks. Thesis. Lund, Sweden, 1995. Ohlsson K, Attewell R, Paisson B, et al: Repetitive industrial work and neck and upper limb disorders in females. Am J Ind Med 27(5):731-747, 1995. Ohlsson K, Attewell R, Skerfving S: Self-reported symptoms in the neck and upper limbs of female assembly workers. Impact of length of employment, work pace, and selection. Scand J Work Environ Health 15:75-80, 1989. Ohlsson K, Hansson GA, Balogh I, et al: Disorders of the neck and upper limbs in women in the fish processing industry. Occup Environ Med 51:826-832, 1994. Onishi N, Nomura H, Sakai K, Yamamoto T, Hirayama K, Itani, T: Shoulder muscle tenderness and physical features of female industrial workers. J Hum Ergol 5:87-102, 1976. Parenmark G, Alffram PE, Malmkvist AK: The significance of work tasks for rehabilitation outcome after carpal tunnel surgery. J Occup Rehab 2:89-94, 1992. Parenmark G, Malmkvist AK, Örtengren R: Ergonomic moves in an engineering industry: effects on sick leave frequency, labour turnover and productivity. Int J Ind Erg 11:1-10, 1993. Petrofsky JS, Phillips CA: The strength-endurance relationship in skeletal muscle: its application to helmet design. Aviat Space Environ Med 53:365-369, 1982. Punnett L, Robins JM, Wegman DW, Keyserling M: Soft tissue disorders in the upper limbs of female garment workers. Scand J Work Environ Health 11:417-425, 1985. Rafnsson V, Steingrimsdottir OA, Olfsson MH, Sveinsdottir T: Muskuloskeletala besv’r bland islänningar. Nord Med 104:104-107, 1989. Ramazzini B: De morbis artificum, ed 2. Translated by WC Wright. New York, 1713, Hafner Publishing Co. Rohmert W, Wangenheim M, Mainzer J, Zipp P, Lesser W: A study stressing the need for a static postural force model for work analysis. Ergonomics 29:1235-1249, 1986. Rosencrance JC, Cook TM, Zimmermann CL: Active surveillance for the control of cumulative trauma disorders: working modes in the newspaper industry. JOSPT 19(5):267-276, 1994. Salminen JJ, Pentti J, Wickström G: Tenderness and pain in neck and shoulders in relation to type A behaviour. Scand J Rheumatol 20:344-350, 1991. Sato H, Ohashi J: Sex differences in static muscular endurance. J Hum Ergol 18:53-60, 1989. Silverstein B, Viikari-Juntura E, Kalat J: Use of a prevention index to identify industries at high risk for work-related musculoskeletal disorders of the neck, back, and upper extremity in Washington state, 1990-1998. Am J Ind Med 41(3):149-169, 2002. Sjøgaard G, Ekner D, Schibye B, et al: Shoulder-neck problems in sewers. An epidemiologic and work physiologic investigation. Copenhagen, 1987, Arbetsmiljøfondet [In Danish]. Sjøgaard G, Simonsen EB, Jensen BR, Christiansen JU, Pedersen SK: Physical workload and musculoskeletal disorders in sewing machine-operators. In AS Adams, RR Hall, BJ McPhee, MS Oxenburgh, eds: Ergonomics International 88. Proceedings in the tenth congress of the International Ergonomics Association. Sydney, 1988, Ergonomics Society of Australia, pp. 384-386.
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Biomechanics of the Shoulder and Elbow Complex
is implicated in a significant proportion of shoulder pathology, limitation of motion at the AC joint leads to minimal alterations in normal shoulder function.53 Like the SC joint, the AC joint possesses an intraarticular meniscus that enhances the contact area between its two incongruent articular surfaces. The AC joint is stabilized by two sets of ligaments: the AC ligaments are primarily condensations of the AC joint capsule, whereas the coracoclavicular ligaments include the more medial conoid and laterally based trapezoid ligaments.
David I. Pedowitz, David P. Beason, and Louis J. Soslowsky
Scapulothoracic Articulation Not a true joint, the scapulotho-
CHAPTER
5b
During physical activity, the forces acting on the shoulder and elbow have been estimated to be upward of several times body weight.1 Many workplace activities are known to involve heavy manual labor and chronic repetitive motion. Accordingly, the resultant forces and associated pain perceived at the shoulder and elbow can be greater at work due to the stress on the upper extremity when larger loads are applied.25,51 Also of importance are work tasks involving postures nearing or exceeding the normal range of joint motion, stationary postures over extended periods of time, highly repetitive motions, and excessive loading. A fundamental appreciation for the anatomy and biomechanics of the shoulder and elbow complexes serves as an excellent foundation for better understanding these injuries.
THE SHOULDER Anatomic considerations Because the shoulder is the primary conduit through which forces travel from the hand and elbow to the axial skeleton, a thorough understanding of the anatomy is paramount when considering its function and relation to patients’ symptoms. The shoulder complex is essentially composed of three bones, the clavicle, the scapula, and the proximal humerus, which participate in four principal articulations (Fig. 5b.1). Through these joints, the shoulder is acted on by nearly 30 different muscles that either affect the shoulder itself or connect the upper extremity to the spine and the chest wall. The following anatomic descriptions are meant to introduce the critical concepts of shoulder form and function.
Articulations Sternoclavicular Joint The most medial articulation in the shoulder complex, the sternoclavicular (SC) joint is comprised of the medial clavicle and the proximal part of the sternum, the manubrium. This joint serves as a strut connecting the axial skeleton to the upper extremity. The congruity of the articulation is enhanced by an intraarticular disk, which also confers some stability and cushioning for the two bony surfaces. The joint has some limited motion in nearly all directions that is stabilized by surrounding tough ligamentous structures.
Acromioclavicular Joint Similarly to the SC joint, the acromioclavicular (AC) joint is a conduit for forces from the distal upper extremity to the central axis of the body. Although the acromion
racic articulation represents the sliding and rotation between the bony thorax and the scapula. The scapula lies flat on the chest wall and is enveloped by muscle. The complex interaction between the scapular and thoracic muscles affords stability and additional rotation for the scapula on the posterior thorax. This in turn changes the orientation of the glenoid surface and significantly contributes to shoulder range of motion and function. Because the scapulothoracic articulation is not a true joint, it has no discrete ligamentous attachments.
Glenohumeral Joint Often likened to a sideways golf ball on a tee, the glenohumeral articulation allows more range of motion than that of any other major joint in the body. The joint itself is composed of the head of the humerus laterally, which articulates with the glenoid of the scapula medially. The glenoid is shaped like a pear, being broader distally and narrow proximally. It is covered in cartilage that is thin at the center and thickens more peripherally. Along the outer edge of the glenoid is a rim of thick fibrous soft tissue, the glenoid labrum, which deepens the articular surface and also acts as the origin for the long head of biceps (LHB) tendon and the glenohumeral ligaments. The articular surface of the humerus extends medially from the anatomic neck to form approximately one third of an irregularly shaped sphere. Unlike the more static midline structures on the chest wall that lie in the standard anteroposterior plane, the shoulder lies in the scapular plane. Viewed from above, the scapula is anteverted 30 degrees to lie flat on the curved posterior chest wall. This placement is balanced by a 30-degree retroversion of the humeral head. The joint capsule of the shoulder is a thin redundant sleeve of fibrous tissue that extends from the glenoid neck to the anatomic neck and variable areas of the proximal shaft of the humerus. The primary ligamentous structures at the glenohumeral joint are the coracohumeral and the three glenohumeral ligaments (Fig. 5b.2). The coracohumeral ligament (CHL) arises from the coracoid process and attaches to the greater and lesser tuberosities of the humerus. The glenohumeral ligaments are essentially condensations of capsule extending from the rim of the anterior articular surface of the glenoid to the head of the humerus. They provide significant stability to the joint and appear as discrete structures when viewed arthroscopically. The superior glenohumeral ligament extends from the tubercle of the glenoid anterior to the LHB tendon origin and inserts at the proximal tip of the lesser tuberosity. The middle glenohumeral ligament spans the distance between the anterior superior labrum and supraglenoid tubercle to the lesser tuberosity, where it blends with the subscapularis tendon. The strongest and most important of the glenohumeral ligaments, the inferior glenohumeral ligament
Chapter 5b
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Biomechanics of the shoulder and elbow complex
Coracoid process
Figure 5b.1 Bones of the shoulder region, anterior (A) and posterior (B) views.
Clavicle (cut)
Acromion Supraglenoid tubercle Anatomical neck Greater tubercle
Neck
Lesser tubercle
Subscapular fossa
Surgical Neck Infragneloid tubercule
Intertubercylar groove
Deltoid tuberosity
Glenoid cavity of scapula Head of Humerus Scapula Humerus
Condyles
{
Medial Lateral
Radial fossa Lateral epicondyle Capitulum
Trochlea
Coronoid fossa
A
Medial epicondyle Clavicle (cut) Coracoid process Acromion
Supraspinatus fossa Greater tubercle Spine
Head of humerus
Neck
Anatomical neck Surgical neck
Infraspinatus fossa
Infraglenoid tubercle Deltoid tuberosity Scapula Humerus
Olecranon fossa
Lateral epicondyle Trochlea Groove for ulnar nerve
B
Medial epicondyle
Chapter 5b
Anterior view
●
The shoulder
Clavicle
Acromion
Trapezoid ligament
Coracoacromial ligament
Conoid ligament
Supraspinatus tendon (cut)
Coracoclavicular ligament
Coracohumeral ligament Greater tubercle and Lesser tubercle of humerus
Coracoid process
Transverse ligament of humerus Subscapularis tendon Biceps brachii tendon (long Head) Capsular ligaments Figure 5b.2
Capsular and ligamentous structures of the shoulder, anterior view.
(IGHL), arises from most of the anterior glenoid labrum and inserts on the inferior margin of the humeral articular surface, around the anatomic neck of the humerus. Another important structure at the glenohumeral articulation is the coracoacromial arch, the osseoligamentous roof of the shoulder region formed by the coracoid process, the coracoacromial ligament, and the acromion of the scapula. Beneath the coracoacromial arch is the subacromial space, the rotator cuff, the LHB tendon, and the head of the humerus. In varying degrees of shoulder pathology, the undersurface of the acromion or Table 5b.1
leading edge of the coracoacromial ligament can impinge against the rotator cuff and LHB tendons.
Muscles The largest and most appreciable muscle in the shoulder region is the deltoid, which defines the thick rounded contour of the healthy shoulder. The muscle consists of three major sections—anterior, middle, and posterior—that are variably active in different aspects of shoulder motion. Overall, the deltoid is active in all forms of elevation.13 Table 5b.1 describes the muscles of the shoulder.
Muscles of the shoulder
Muscle
Origin
Insertion
Innervation
Action
Deltoid
Lateral one third of clavicle, acromion, and spine of scapula
Deltoid tuberosity of humerus
Axillary n. (C5-C6)
Biceps
Tuberosity of the radius and forearm via bicipital aponeurosis
Musculocutaneous n. (C5-C6)
Subscapularis
Short head: coracoid process of scapula Long head: supraglenoid tubercle of scapula Subscapular fossa of scapula
Shoulder flexion, extension, abduction, some internal/ external rotation Forearm flexion, supination of flexed forearm
Lesser tuberosity of humerus
Supraspinatus Infraspinatus Teres minor Teres major
Supraspinous fossa of scapula Infraspinous fossa of scapula Superior border of lateral scapula Inferior border of lateral scapula
Upper and lower subscapular nn. (C5-C7) Suprascapular n. (C4-C6) Suprascapular n. (C5-C6) Axillary n. (C5-C6) Lower subscapular n. (C6-C7)
Trapezius
Spinous processes of C7-T12 vertebrae
Latissimus dorsi
Spinous processes of T7-T12 vertebrae and iliac crest Lateral surface of ribs 1-8
Serratus anterior
n., nerve; nn., nerves.
Greater tuberosity of humerus Greater tuberosity of humerus Greater tuberosity of humerus Medial lip of intertubercular groove of humerus Lateral one third of clavicle, acromion, and spine of scapula Floor of intertubercular groove of humerus Anteromedial border of the scapula
Spinal accessory n. (CN-XI)
Thoracodorsal n. (C6-C8) Long thoracic n. (C5-C7)
Internally rotates and adducts humerus Abducts humerus Externally rotates humerus Externally rotates humerus Adducts and internally rotates humerus Elevates, retracts, and rotates scapula Extends, adducts, and internally rotates humerus Protracts and rotates scapula medially
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Biomechanics of the shoulder and elbow complex
The rotator cuff is a series of coalesced tendons from four muscles. Moving over the head of the humerus from anterior to posterior, these muscles include the subscapularis, supraspinatus, infraspinatus, and teres minor, which work in concert to stabilize and afford discrete motion of the shoulder. These muscles originate from the scapula and form a condensed tendinous sleeve around the anterior, superior, and posterior aspects of the humeral head. The most anterior muscle, the subscapularis, fans out from the anterior scapula over to the lesser tuberosity of the humerus. When contracted, it acts as an internal rotator of the humerus. At the most superior portion of the cuff is the supraspinatus, the rotator cuff muscle most often implicated in shoulder pathology. In its course to its insertion, it travels beneath the coracoacromial arch, forming the floor of the subacromial space. In this space between the acromion and the supraspinatus tendon is the soft subacromial bursa. The relationship between the supraspinatus and the acromion is important to appreciate, especially when considering conditions like impingement syndrome, where the subacromial space may be appreciably decreased in size, leading to pathology. When contracted, this muscle is a shoulder abductor in the plane of the scapula.6 Moving posteriorly on the cuff, the infraspinatus muscle functions to depress the humeral head and externally rotate the humerus. The final and most posterior rotator cuff muscle, the teres minor, is an external rotator of the humerus. Although thought of primarily as an elbow muscle, the biceps has a role in shoulder stability and pathology also. The biceps is unique in that it is one of the body’s few muscles that originate within a joint. Because of this intraarticular labral origin, the LHB is implicated in a great deal of labral pathology. Although functioning primarily as an elbow flexor and supinator of the forearm, the biceps is believed to play a role in the shoulder as a humeral head depressor and as a significant stabilizer to inferior subluxation.33,60 A number of other parascapular muscles act around the shoulder joint but do not necessarily contribute directly to glenohumeral range of motion or stability. The three largest of these are the trapezius, serratus anterior, and latissimus dorsi muscles. The bulky trapezius muscle mainly functions as a scapular retractor. By doing so, it rotates the inferior angle of the scapula laterally, shrugs the shoulders, and clamps the scapula to the chest wall. Sometimes known as the “boxer’s muscle,” the serratus anterior primarily protracts and medially rotates the scapula, drawing it closer to the posterior chest wall. The serratus anterior is active in all motions of the humerus but more so in flexion. The latissimus dorsi is an enormous back muscle that internally rotates and adducts the humerus and extends the shoulder.
Biomechanics of the glenohumeral joint Kinematics This concise discussion of biomechanics focuses on the primary source of motion at the shoulder, the glenohumeral joint. It should be noted however, that the AC, SC, and scapulothoracic articulations do also have roles, albeit less so, in the overall mechanics of the upper extremity.
Glenohumeral kinematics describes the motion of the humeral head in the glenoid cavity without consideration of forces contributed by surrounding musculature. This description can be for either two-dimensional planar motion or three-dimensional spatial motion.49 Planar motion of the glenohumeral joint can be divided into three modes of articulation: sliding, spinning, and rolling41 (Fig. 5b.3). In sliding, the contact point is constant on the translating humeral head but is always changing on the stationary glenoid cavity. The center of rotation is the center of curvature of the glenoid. During spinning, the contact point is always changing on the rotating humeral head but is constant on the stationary glenoid cavity. The center of rotation for spinning is the center of curvature of the humeral head. In rolling, the point of contact is always changing on both the humeral head and the glenoid cavity, with the center of rotation being the contact point itself. Any two of these three divisions can be combined to describe the planar motion of the glenohumeral joint.41 Spatial motion can best be explained in terms of degrees of freedom. In general, an unconstrained rigid body has six degrees of freedom—three translations and three rotations about the orthogonal x-, y-, and z-axes (Fig. 5b.4). In its normal range of motion, the glenohumeral joint is capable of three rotations about three orthogonal coordinate axes and thus has three degrees of freedom. In terms of joint motion, these three rotations are defined as flexion/extension, abduction/adduction, and internal/external rotation. These motions are constrained by soft tissues, ligaments, articulations, and muscles. In flexion/extension, the humerus can generally be moved in the sagittal plane through a range of about 170 degrees.41 Abduction/adduction can be achieved over a range of 180 degrees41 in the coronal plane. The range of motion for internal/external rotation totals approximately 150 degrees.41 Many overhead motions are achieved through combinations of flexion/extension and abduction/ adduction, with additional aid from the scapulothoracic articulation at motion extremes. This type of overhead motion has been reported as a source of numerous shoulder injuries, including those suffered during occupational tasks.22
Constraint The bony architecture of the shoulder affords this joint an exceptional range of motion. It is achieved, however, only with an obligatory reduction in its biomechanical stability. In compensation, both static and dynamic stabilizers help orchestrate a balance between mobility and stability. When viewing plain radiographs, the glenohumeral joint appears to function like a sphere articulating on a flat glenoid surface. Historically, it was therefore assumed that the osseous geometry of the joint surfaces provided little if any inherent stability to the shoulder. Cadaveric studies, however, have determined that the articular geometry of the shoulder does play a substantial role in stabilization. Using gross measurements and magnetic resonance imaging, investigators have documented that the radius of curvature of the average glenoid is about 2 mm greater than that of the corresponding humeral head.28 Using stereophotogrammetry, another center reported similar findings and determined that the mating humeral head and glenoid articular surfaces were in fact congruent.58 When the articular cartilage surfaces were analyzed, furthermore, it was
Chapter 5b
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The shoulder
Figure 5b.3 Planar glenohumeral articulation. Included are spinning, rolling, and sliding motions. These motions may occur either in isolation or in combination. (From Zuckerman JD, Matsen FA: Biomechanics of the shoulder. In M Nordin, VH Frankel, eds: Biomechanics of the musculoskeletal system. Philadelphia, 1989, Lea & Febiger.)
z
3 6 2 y 5 1
4
x Figure 5b.4 Orthogonal coordinate axes, illustrating six degrees of freedom—three translations (1-3) and three rotations (4-6).
observed that the actual articulating surfaces conformed more than previously thought.58 Enlarging the articulating area is thought to add to stability by decreasing the potential for humeral head translation and by increasing what Fukuda and colleagues17 referred to as the “constraining wall height” of the joint. Using this technique57 and Fugi Prescale film,69 contact areas within the glenohumeral joint have been documented also, ranging from approximately 0.75 cm2 with the arm at the side and 5 cm2 at 90 degrees of abduction. Additionally, contact pressure within the joint was found to decrease with increasing abduction to 90 degrees.69 The remaining static stabilizers of the shoulder joint include the glenoid labrum, the joint capsule, and the glenohumeral and coracohumeral ligaments. These coordinate to resist joint translation primarily by preventing displacement through their presence and secondarily by imparting increased joint contact forces resisting the displacement.24 The first of these structures, the glenoid labrum, is a meniscus-like thickening of fibrous tissue that is triangular in cross-section and surrounds the rim
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Shoulder Anatomy and Biomechanics
A
Figure 5b.5 The glenoid labrum. The labrum’s role can be thought of as extending the surface area of the socket, much as adding to the bank of a road deepens a curve. (From Flatow E: Shoulder anatomy and biomechanics. In M Post, L Bigliani, E Flatow, R Pollock, eds: The shoulder: operative technique. Philadelphia, 1998, Lippincott, Williams & Wilkins.)
B
of the glenoid cavity (Fig. 5b.5). Previously thought to be composed of fibrocartilage, the labrum is mostly dense fibrous tissue with few elastic fibers.43 Often conceptualized as a bumper that prevents the humeral head from excursion out of the glenoid, its role in enhancing the stability of the glenohumeral joint has been questioned, as some investigators have found that it offers little in overall shoulder stability.43,63 As a whole, however, the labrum does play some role in shoulder constraint, but its contribution is likely complementary.41 The joint capsule of the shoulder is a relatively thin sheet of fibrous tissue. Depending on the position of the shoulder, the capsule imparts a variable contribution to glenohumeral joint stability. In general, anterior shoulder structures are taut when the arm is externally rotated. Superior, inferior, and posterior structures are accordingly tightened when the arm is adducted, abducted, and internally rotated, respectively. The most obvious and important portions of the shoulder capsule that confer stability are sometimes referred to as the capsule-ligament complex. This complex consists of superior, middle, and inferior portions that along with the CHL define the ligamentous structures providing constraint to the shoulder joint41 (Fig. 5b.6). In general, the capsular structures participate in mechanically stabilizing the joint at the extremes of motion, though they may also have roles in proprioception. Because it extends from the coracoid process to the lesser tuberosity, the CHL is thought to participate in suspending the humerus in the glenoid when the arm is at the side. Its role in stability, however, remains controversial.60 The superior glenohumeral ligament is a fibrous structure that becomes tight when the arm is adducted at the side. As it tightens, it acts primarily as an inferior stabilizer and likely functions along with the CHL and the rotator cuff to prevent inferior translation of the humeral head on the glenoid.48,68 Often well developed, the
middle glenohumeral ligament has been demonstrated to be a significant constraint to anterior displacement of the humerus.14,43 Along with the anterior capsule, the middle glenohumeral ligament becomes taut when the arm is abducted and externally rotated. The IGHL is the ligament thought to be responsible for most of the shoulder’s static stability. Its geometry has classically been described as having three distinct components—a superior
Supraspinatus Long head of triceps Anterior View Posterior View SGHL
Intraspinatus
MGHL Subscapularis
Teres minor Posterior axillary pouch of IGHL Long head of triceps
Superior band of IGHL Anterior axillary pouch of IGHL Capsule
Figure 5b.6 The glenohumeral ligaments. The glenohumeral ligaments are thickenings in the capsule of the shoulder and function as passive check reins, particularly at the extremes of motion.
Chapter 5b
band and anterior and posterior axillary pouches.65 The geometry and mechanical properties of these distinct areas of the IGHL suit it well for its role as the primary static anterior stabilizer of the glenohumeral joint.8 Slack and redundant with the arm adducted, the IGHL is the primary static restraint to anteroinferior subluxation, particularly in abduction and external rotation, a position associated with increased anterior instability.9 In this position the more anterior structures become taut, whereas in internal rotation the posterior aspect of the IGHL is tense. The dynamic stabilizers of the shoulder joint include the rotator cuff, biceps, and deltoid muscles. Directly they act as a bulky barrier with inherent passive muscle tension that resists translation of the humeral head, and they play an important role in stability by providing compressive forces on the humerus into the glenoid socket. Indirectly, the dynamic stabilizers exert their effect by moving the joint into positions that tighten the capsular-ligamentous complex,41 thus engaging these stabilizing structures. As described in the section on anatomy, the rotator cuff is a series of four muscles that coalesce to form a tendinous arc of tissue around the glenohumeral joint. In addition to affording the shoulder with discrete motions, these muscles also provide stability. Anteriorly, the subscapularis muscle forms a musculotendinous curtain from the scapula to the lesser tuberosity. In doing so, it is thought to be the most important dynamic anterior stabilizer.15 This stability is greatest in external rotation and from 0 to 45 degrees of abduction.36,65 At 90 degrees of abduction, the IGHL seems to play the most important role.65 Of all the rotator cuff muscles, the subscapularis provides the most resistance to posterior subluxation when the arm is in forward flexion.10 Superiorly, the supraspinatus muscle has been reported to be an important restraint to inferior translation of the humerus. This action has been observed in cadaveric specimens where the supraspinatus was found to be an inferior stabilizer more effective than any other cuff muscle.60 Investigators demonstrated that moving posteriorly on the cuff, the infraspinatus, the teres minor, and occasionally the supraspinatus function together with the subscapularis to impart notable posterior stabilization.10,46 A complete analysis of the relative contributions of the rotator cuff muscles to glenohumeral joint stability is beyond the scope of this text. It is notable, however, that these muscles do not simply exist and function in isolation. Rather, they have been demonstrated to function in concert, with both anterior and posterior force coupling that yields enhanced joint stability.54 The contribution of the biceps muscle to overall glenohumeral stability is also important. As the LHB tendon courses over the curved head of the humerus, it acts like a cable wrapping around a pulley. When the biceps is activated, it compresses the humeral head into the glenoid.4 Additionally, the biceps has been suggested to be as important as the rotator cuff to glenohumeral stability.29 Because of its size (20% of overall shoulder muscle mass), the deltoid’s contribution to shoulder stability is thought to be noteworthy but remains undefined.7
Kinetics In contrast to kinematics, glenohumeral kinetics is the study of joint motion with respect to the forces responsible for it. The muscles and ligaments of the rotator cuff carry appreciable loads
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161
in day-to-day activities and in strenuous work tasks such as heavy lifting, abduction, and overhead use. The loading that occurs in the glenohumeral joint during normal motion has been reported to be as high as 0.89 times body weight at 90 degrees of abduction, and it is increased appreciably when weight is held.50 Most of the strength and gross motion at the joint is facilitated by the massive deltoid muscle, the three primary sections of which function differently depending on the direction of a force and the arm position when a load is applied. In general, the more anterior portion is important in forward elevation, whereas the posterior portion plays a significant role in posteriorly directed motion such as extension. The middle fibers of the deltoid make relative contributions to both of these movements but are involved mostly in shoulder abduction strength, to which the deltoid contributes over 60%.13 Although debated, the relative contribution of the supraspinatus to overall abduction of the shoulder has more recently been shown to be responsible for between 19% and 33% of the total abduction force generated at the shoulder.30 Its length-tension curve demonstrates maximum force at about 30 degrees of elevation.5 In selective nerve block studies, the infraspinatus and teres minor muscles have been found responsible for as much as 60% and 45% of the external rotation force that can be generated at the shoulder, respectively.13 The subscapularis muscle is the only primary internal rotator of the shoulder and as such is responsible for most of the force in that movement.
Mechanical properties of articular cartilage and ligaments When considering shoulder biomechanics, it is important to understand the mechanical behavior of the soft tissues (namely ligaments and cartilage) associated with the glenohumeral joint, the subject of various experimental techniques (Table 5b.2). Tests of the mechanical properties of glenohumeral articular cartilage have included both indentation44 and tensile testing.70 On average, the aggregate modulus for glenohumeral joint articular cartilage ranges from roughly 0.5 to 0.9 MPa.44 Compressive and shear properties of articular cartilage are important because of the nature of their role in dynamic articulating surfaces. Partly because ligaments are anisotropic, in that they have different properties in the longitudinal and transverse directions, and partly because their primary function is joint stabilization typically through tensile loading, the most common method of
Table 5b.2 Mechanical properties of some key glenohumeral ligaments
Ligament
Failure load (N)
Superior 101.911 glenohumeral Inferior — glenohumeral Coracohumeral 359.811
Stiffness (N/mm)
Ultimate stress (MPa)
Elastic modulus (MPa)
17.411
—
—
—
5.2, 5.5, 5.6* 38.7, 30.3, 41.9* — —
36.711
*Values are for superior, anterior, and posterior regions, respectively.8
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Biomechanics of the shoulder and elbow complex
Linear region
Yield/failure
Stress
Toe region
●
Strain Figure 5b.7 Typical tensile test of a ligament, showing the toe, linear, and yield/failure regions.
obtaining mechanical properties is the quasistatic tensile test. However, more sophisticated methods have enabled precise two-dimensional analysis of the glenohumeral joint. In situ strain fields in the anteroinferior shoulder capsule have been quantified in this way using stereoradiogrammetry, showing that strains are generally higher on the glenoid side of the capsule than on the humeral side.35,37 All biologic soft tissues demonstrate both nonlinear and viscoelastic mechanical behavior under loading. The nonlinearity is characterized initially by a relatively large increase in elongation with respect to load (Fig. 5b.7). In tensile testing, this “toe” region represents the straightening and aligning of collagen fibers in the longitudinal axis, that is, the direction of loading. This is followed by a linear region, over which the mechanical properties such as stiffness are typically evaluated. The ensuing region of nonlinear yield culminates with the failure of the specimen. In addition to behaving nonlinearly, soft tissues are also considered viscoelastic due to the rate dependence of their mechanical properties. When loaded rapidly, a ligament tends to be stiffer than when loaded at a lower rate. IGHL regions have been shown to have up to 62% increased modulus when loaded an order of magnitude more rapidly.44 A phenomenon associated with soft tissue viscoelasticity is the hysteresis effect. When a ligament is cyclically loaded and returned to its resting state, the load-deformation response shifts until equilibrium is eventually reached after 10-20 cycles.38 For this reason, biomechanical testing should begin with a period of preconditioning in which the specimen is cyclically loaded within its normal physiologic range. Although biomechanical studies demonstrated that soft tissue properties change as a function of age38 and epidemiology indicates that shoulder and upper limb disorders tend to arise over time,34 age has not shown a consistently strong association with shoulder tendonitis in the workplace environment. This is due partly to older workers often leaving their jobs because of the injury, resulting in “survivor bias.”23
addressed by testing them. Recently, animal models have gathered significant interest and use to address questions about the biomechanics of the shoulder and its injuries. The most fundamental issue that must be addressed when selecting any animal model is its biofidelity with respect to the body region of interest. For the shoulder, several animal models have been used in studying tendon and rotator cuff injury and repair. New Zealand white rabbits, for example, have been used to study muscle healing characteristics after supraspinatus tendon reattachment.39,66 Other works have investigated rotator cuff repair both in vitro and in vivo using infraspinatus tendons of sheep.18,19 Soslowsky et al59 set out to identify an effective animal model for studying rotator cuff injuries by examining anatomic characteristics of the shoulder in several different species. In an analysis involving 34 criteria applied to 37 animals, the rat emerged as the only model to satisfy all criteria while still being practical for experimental research. The most distinguishing characteristic that makes the anatomy of the rat shoulder comparable with that of a human is the position of the acromion and its associated enclosed arch in relation to the supraspinatus tendon.59 SpragueDawley rats have since been used effectively in numerous investigations into the roles of overuse and extrinsic factors in rotator cuff injuries. In the laboratory setting, overuse activity has produced a reproducible injury in the rat shoulder comparable with that seen clinically in the rotator cuff.61 Injuries stemming from overuse in combination with extrinsic compression have resulted in relatively high maximum stresses and elastic moduli when compared with each of the two factors alone, indicating that rotator cuff tendinosis is not typically attributable to a single factor.62
Prevention of disability through ergonomics Three of the most prominent risk factors to emerge from studies of workplace ergonomics are static or extreme posture,25,51 cyclical occupational motions,16,21 and external loading.16,47 The risk of shoulder disorder has been reported to be two to three times higher in occupations requiring abduction or flexion beyond 90 degrees for at least 10% of the time performing the task.51 This combination of awkward shoulder posture and long time periods has been identified as a key risk factor for disorders.56 The occurrence of shoulder tendinitis has been found to be two to three times higher in workers with highly repetitive or cyclical work tasks involving the upper limbs.16 External hand loads in combination with humeral abduction have been linked to increased rotator cuff muscle pressure, which can have detrimental effects on the shoulder.47 Conversely, when an occupation does not require appreciable loading, the risk of shoulder tendinitis is lower.16 With sufficient effort focused on these issues in the workplace through improved ergonomic conditions, resulting shoulder disorders may be appreciably reduced.
THE ELBOW Anatomic considerations
Animal models Although cadavers have proven beneficial in experimental biomechanics research, certain important questions cannot be
Complex in its articular geometry, the elbow is an important link in the lever arm chain of the upper extremity that facilitates a
Chapter 5b
Condyle
{
●
The elbow
Medial Lateral
Lateral supracondylar crest
Humerus Medial epicondyle Capitulum
Humerus Medial supracondylar crest Coronoid fossa
Radial fossa Lateral epicondyle
Tuberosity
Medial epicondyle Capitulum Head Neck Tuberosity Radius
A
Trochlea Head Neck
Radius
Trochlea Coronoid process
Ulna
Radial notch of ulna
Tuberosity Coronoid process
Tuberosity Ulna
B
Olecranun
Trochlear notch
Ulnar collateral ligament Annular ligament
C Figure 5b.8 Bones of the elbow, anterior (A) and medial (B) views. The orientation of the three components of the medial collateral ligament include the anterior, posterior, and transverse bundles.
broad range of motion, the absence of which causes significant functional impairment. A working knowledge of the elbow’s anatomy is thus important in any effort to understand the biomechanics at this articulation. The elbow is a trochleoginglymoid joint composed of three bones; the distal humerus and the proximal ulna and radius (Fig. 5b.8). The three articulations at the elbow are the ulnohumeral, radiohumeral, and radioulnar joints.
Articulations Ulnohumeral Joint As the metaphyseal bone of the distal humerus flares out distally, it forms two supracondylar regions that end in medial and lateral epicondyles. These epicondyles flank two odd-shaped asymmetric condyles. The condyles compose the distal articular surface of the humerus: the trochlea medially and the capitellum laterally. The ulnohumeral joint is essentially a hinge governed by the intimate matching geometry of the trochlea and proximal ulna. The most constrained portion of the elbow joint, this articulation allows only flexion and extension. On the humeral side, the trochlea resembles a spool of thread with broad ends (of which the medial is larger) that converge into a narrow trochlear groove. In the frontal plane the trochlea has approximately 6 degrees of valgus tilt that helps dictate the carrying angle of the normal elbow. There are two
depressions on the distal humerus that participate in the ulnohumeral joint as well: the coronoid and olecranon fossae. As the joint goes through flexion and extension, the olecranon and coronoid fossae accommodate their similarly named processes on the proximal ulna. The proximal ulna is composed of two arced processes—the olecranon and coronoid—separated from each other anteriorly by the greater and lesser sigmoid notches. A lateral indentation in the lesser sigmoid notch, the radial notch, provides articulation with the proximal radius. Viewed laterally, the proximal ulna resembles a claw that tightly grasps the trochlea of the distal humerus. The olecranon is a large posterior bony process that provides the posterior articulation for the ulnohumeral joint, prevents posterior displacement of the humerus, and serves as the site of attachment for the triceps tendon. Anteriorly, the coronoid provides the anterior articular surface of the joint, prevents anterior translation of the humerus, and serves as the site for the distal insertion of the brachialis muscle. Although strong transverse and oblique fibers do exist, the capsule of the elbow is generally weak and reinforced primarily by strong ligaments medially and laterally that stabilize the joint against varus and valgus forces (Fig. 5b.8b). On the medial side of the elbow, the medial collateral ligament (MCL) (often referred to as the ulnar collateral ligament) has a transverse
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Biomechanics of the shoulder and elbow complex
ligament and an anterior and posterior bundle. Laterally, the radial collateral ligament complex is composed of the annular ligament, radial collateral ligament proper, and lateral ulnar collateral ligament (LUCL). The annular ligament is a strong ring of tissue that loops around the radial head to hold it against the proximal ulna at the proximal radioulnar joint. The radial collateral ligament extends from the lateral epicondyle to the annular ligament and is taut throughout most of the normal range of motion at the elbow. Invariably present, the LUCL extends from the lateral epicondyle to the supinator crest on the proximal ulna.
Radiohumeral Joint The medial condyle of the distal humerus, the capitellum (l. little head), is spherical and covered by articular cartilage. At the radiocapitellar joint it articulates with the cylindrical head of the radius. The radiocapitellar joint allows flexionextension and pronation-supination and also undergoes varus and valgus moments. As the forearm rotates into either pronation or supination, the radial head spins underneath the capitellum.
Radioulnar Joint The radial head is bound to the ulna by the annular ligament and, due to its location, acts as a primary restraint to valgus force. The proximal radioulnar joint allows pronation and supination. Like the radiohumeral and ulnohumeral joints, this joint is enveloped in the elbow capsule.
Muscles The muscles acting on the elbow play defined roles in facilitating its motion. In general, muscles crossing the elbow on the anterior surface of the cubital fossa are elbow flexors, whereas those located posteriorly function to extend the elbow. As described in the shoulder section above, the biceps muscle crosses both the shoulder and the elbow joints. Its function at the elbow is to flex the extended elbow and supinate the flexed forearm, as in tightening a screw with the right hand. Like the biceps, the brachioradialis and brachialis muscles flex the elbow. Posteriorly on the elbow is the triceps brachii muscle, its primary extensor. Composed of a medial lateral and long head, the muscle extends the entire length of the posterior brachium to insert as a thick Table 5b.3
tendon on the olecranon process of the ulna. Adjacent to the triceps insertion is a small triangularly shaped muscle called the anconeus that is minimally involved in forearm extension. The epicondyles of the distal humerus provide the origin for a number of forearm muscles that act mostly on the wrist. Table 5b.3 describes the muscles of the arm.
Biomechanics of the elbow Kinematics In terms of spatial motion, the elbow is considered to have two degrees of freedom, flexion/extension and supination/pronation. Flexion/extension is essentially a hinge-like motion that occurs at the ulnohumeral joint. This motion defines the carrying angle, that formed by the ulna and the humerus. The rotational axis for flexion/extension is formed by the trochlea and capitellum. The normal range of motion in flexion, from 0 to 150 degrees, is restricted by bony impingement of the radial head and fossa, impact between the coronoid process and fossa, and muscular tension from the triceps.2 Extension is limited by the impingement of the olecranon process on the olecranon fossa and tension of the anterior and medial ligaments and flexor muscles.31 For supination/pronation, the axis of rotation passes through the distal ulna and the center of the radial head.2 The elbow is normally capable of approximately 75 degrees of pronation and 85 degrees of supination, or 160 degrees of total motion, limited primarily by muscles and secondarily by ligaments.2
Constraint In addition to the aforementioned stability afforded by the unique topography of the distal humerus and proximal ulna, additional constraint is provided by the elbow capsule and the periarticular ligaments.3,45 At the elbow, the medial and lateral ligamentous complexes provide most of the additional stability to the bony configuration. On the medial side of the elbow is the MCL. Cadaveric studies have determined that the anterior band of the MCL is the most important section of the ligament because it is the primary stabilizer against a valgus force.42
Muscles of the arm
Muscle
Origin
Insertion
Innervation
Action
Biceps brachii Brachialis
Short head: coracoid process of scapula Long head: supraglenoid tubercle of scapula Distal one half of anterior humerus Tip of coracoid process
Triceps brachii
Long head: infraglenoid tubercle Lateral head: posterior surface of humerus superior to spiral groove Medial head: posterior surface of humerus inferior to spiral groove Lateral epicondyle of humerus
Musculocutaneous n. (C5-C6) Musculocutaneous n. (C5-C6) Musculocutaneous n. (C5-C7) Radial n. (C6-C8)
Forearm flexion, supination of flexed forearm Forearm flexion
Coracobrachialis
Tuberosity of the radius and forearm via bicipital aponeurosis Coronoid process and tuberosity of ulna Middle third of medial surface of humerus Proximal olecranon process
Lateral surface of olecranon
Radial n. (C7-C8, T1)
Assists triceps in forearm extension
Anconeus
n., nerve.
Flexes and adducts humerus Extends forearm
Chapter 5b
Clinically, this becomes particularly relevant when the radial head (a secondary valgus stabilizer) is no longer functioning (e.g., due to fracture). The lateral collateral ligamentous complex functions mostly as a varus stabilizer of the elbow. The major component of the radial collateral ligament complex contributing stability to varus and rotatory stability of the elbow is the LUCL.2 Overall, the LUCL specifically is responsible for most of the lateral stabilization.2 In addition to holding the radius in the proximal radioulnar joint, the annular ligament also provides some stability against varus and valgus stress.55
Kinetics Contact in the elbow is typically described with respect to the ulnohumeral joint. The three most common methods of contact measurement in the elbow are silicone casting, cartilage staining, and Fugi Prescale film. Having evaluated all three techniques, Stormont et al64 identified silicone casting as the optimal method for studying elbow contact. In a study using a wax casting technique,20 contact was reported to be concentrated on the medial part of the lower trochlear notch with the elbow in full extension. At 90 degrees of flexion, the contact appeared predominantly as a band extending from the lower medial to upper lateral trochlear notch. At full flexion, the band of contact area increased, and contact between the radial head and capitulum became more pronounced.20 It was noted in a different study that with increased external load, contact area increased and its location became increasingly lateral.64 Although experimentally difficult on curved articulations, the use of Fugi Prescale film provides measurements of contact pressure as well as area. Like the shoulder, the mechanical behavior of elbow ligaments is nonlinear and viscoelastic, although there is substantially less information available. Properties for the medial and radial collateral ligamentous complexes, however, have been reported.52 The radial collateral ligament is reported to have a mean ultimate stress of 15.9 MPa and elastic modulus of 54.3 MPa. The MCL has been found to be stronger and less elastic, with ultimate stresses of 20.7 and 19.2 MPa and elastic moduli of 117.8 and 96.8 MPa for the anterior and posterior bundles, respectively. In the workplace, flexion/extension is typically involved in lifting tasks, whereas supination/pronation in combination with force exertion has been cited as a risk factor for medial and lateral epicondylitis in tasks involving repeated twisting motions.21 As with the shoulder, it has been shown that workers in high-repetition jobs are two to three times more likely to develop conditions such as elbow tendinitis than those performing low-repetition tasks.34
NOVEL DEVELOPMENTS AND FUTURE DIRECTIONS An important area that is gaining momentum in orthopedic biomechanics is in the field of tissue engineering, which strives to combine biologic and mechanical elements. Specifically, the concept of functional tissue engineering mandates consideration of mechanical properties and functional capabilities when dealing with tissues that are structurally vital.12 In particular, functional
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References
tissue engineering approaches are making significant strides toward improving the healing response of injured tissues such as the rotator cuff or in creating replacement structures such as for ligaments and joints. Investigators have begun using resorbable tissue scaffolds in the hope of regenerating new tendon. Using materials like porcine small intestine submucosa, human dermis, and woven starch fabrics, some centers have documented encouraging results in engineering new tissue growth. Advances in these areas will likely yield significant benefit to the patient population in the near future. The use of in vivo techniques and measurements in lieu of cadaveric investigations is another developing trend. In vivo measurements of loading and motion in both normal and abnormal states will further our understanding of the mechanics of the shoulder and elbow joints. Noninvasive techniques have begun to play a more important role in enhancing our understanding of upper extremity biomechanics. Together with three-dimensional reconstructed computer-aided tomograms, some investigators have used in vivo fluoroscopic imaging of the shoulder and elbow to gain exciting new insight into their kinematics. Using these techniques, they have gained a more comprehensive appreciation for the loading, contact area, and dynamic motion at these articulations. This information has helped in the development of better total joint arthroplasties. Ongoing work is making use also of magnetic resonance imaging to measure tendon strain fields in the shoulder. Another area that has seen recent development and is likely poised for significant advancement is in the use of computer models of the shoulder complex. Based on original work by both Högfors et al26,27 and van der Helm,67 efforts to combine finite element and three-dimensional modeling have yielded new methodologies for investigating the shoulder. Using a six-degreeof-freedom electromagnetic tracking device, investigators have obtained complete kinematic descriptions of shoulder motion.40 Additionally, with these three-dimensional models, investigators have been able to estimate muscle attachment sites and reliably apply them to geometric bone models.32 As the horizon for new advances in orthopedic bioengineering broadens, we hope to continue to find even more efficacious applications toward the prevention and treatment of injury and disability at the shoulder and elbow.
REFERENCES 1. An KN, Chao EYS, Kaufman KR: Analysis of muscle and joint loads. In VC Mow, WC Hayes, eds: Basic orthopaedic biomechanics, ed 2. Philadelphia, 1997, Lippincott-Raven, pp. 1-35. 2. An KN, Morrey BF: Biomechanics of the elbow. In BF Morrey, ed: The elbow and its disorders, ed 3. Philadelphia, 2000, WB Saunders, pp. 43-60. 3. An KN, Morrey BF, Chao EYS: The effect of partial removal of proximal ulna on elbow constraint. Clin Orthop Relat Res 209:270-279, 1986. 4. Andrews JR, Carson WG Jr, McLeod WD: Glenoid labrum tears related to the long head of the biceps. Am J Sports Med 13:337, 1985. 5. Atwater AE: Biomechanics of overarm throwing movements and of throwing injuries. Exerc Sport Sci Rev 7:43-85, 1979. 6. Basmajian JV, Bazant FJ: Factors preventing downward dislocation of the adducted shoulder joint. An electromyographic and morphological study. Am J Orthop 41A: 1182-1186, 1959. 7. Bassett RW, Browne AO, Morrey BF, An KN: Glenohumeral muscle force and moment mechanics in a position of shoulder instability. J Biomech 23:405-415, 1990. 8. Bigliani L, Kelkar R, Flatow E, Pollock R, Mow V: Glenohumeral stability: biomechanical properties of passive and active stabilizers. Clin Orthop Relat Res 330:13-30, 1996.
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Bigliani LU, et al: Tensile properties of the inferior glenohumeral ligament. J Orthop Res 10:187-197, 1992. Blasier RB, Soslowsky LJ, Malicky DM, Palmer ML: Posterior glenohumeral subluxation: active and passive stabilization in a biomechanical model. J Bone Joint Surg 79(3):433-440, 1997. Boardman ND, Debski RE, Warner JJ, Taskiran E, Maddox L: Tensile properties of the superior glenohumeral and coracohumeral ligaments. J Shoulder Elbow Surg 5: 249-254, 1996. Butler DL, Goldstein SA, Guilak F: Functional tissue engineering: the role of biomechanics. J Biomech Eng 122:570-575, 2000. Colachis SC, Strohm BR, Brechner VL: Effects of axillary nerve block on muscle force in the upper extremity. Arch Phys Med Rehabil 50(11):645-647, 1969. DePalma AF, Callery G, Bennett GA: Variational anatomy and degenerative lesions of the shoulder bone. AAOS Instruct Course Lect 16:255, 1949. DePalma AF, Coker AJ, Probhaker M: The role of the subscapularis in recurrent anterior dislocation of the shoulder. Clin Orthop Relat Res 54:35-49, 1969. Frost P, Bonde JP, Mikkelson S, Andersen JH, Fallentin N, Kaergaard A, Thomsen JF: Risk of shoulder tendinitis in relation to shoulder loads in monotonous repetitive work. Am J Indust Med 41:11-18, 2002. Fukuda K, Chen CM, Cofield RH, Chao EYS: Biomechanical analysis of stability and fixation strength of total shoulder prostheses. Orthopedics 11:141-149, 1988. Gerber C, Schneeberger AG, Beck M, Schlegel U: Mechanical strength of repairs of the rotator cuff. J Bone Joint Surg 76-B(3):371-380, 1994. Gerber C, Schneeberger AG, Perren SM, Nyffeler R: Experimental rotator cuff repair. J Bone Joint Surg 81-A(9):1281-1290, 1999. Goel VK, Singh D, Bijlani V: Contact areas in human elbow joints. J Biomech Eng 104(3):169-175, 1982. Grieco A: Application of the concise exposure index (OCRA) to tasks involving repetitive movements of the upper limbs in a variety of manufacturing industries: preliminary validations. Ergonomics 41(9):1347-1356, 1998. Grieco A, Molteni G, De Vito G, Sias N: Epidemiology of musculoskeletal disorders due to biomechanical overload. Ergonomics 41(9):1235-1260, 1998. Hales TR, Bernard BP: Epidemiology of work-related musculoskeletal disorders. Orthop Clin North Am 27(4):679-709, 1996. Harryman DT, Sidles JA, Clark JM: Translation of the humeral head on the glenoid with passive glenohumeral motion. J Bone Joint Surg 72(9):1334-1343, 1990. Herberts P, Kadefors R, Högfors C, Sigholm G: Shoulder pain and heavy manual labor Clin Orthop Relat Res (198):166-178, 1984. Högfors C, Peterson B, Sigholm G, Herberts P: Biomechanical model of the human shoulder. II. Shoulder rhythm. J Biomech 24(8):699-709, 1991. Högfors C, Sigholm G, Herberts P: Biomechanical model of the human shoulder. I. Elements. J Biomech 20(2):157-166, 1987. Iannotti JP, Gabriel JP, Schneck SL, Evans BG, Misra S: The normal glenohumeral relationships. An anatomical study of one hundred and forty shoulders. J Bone Joint Surg 74A(4):491-500, 1992. Itoi E, Newman SR, Ruechle DK, Morrey BF, An KN, et al: Dynamic anterior stabilisers of the shoulder with the arm in abduction. J Bone Joint Surg 76b(5):834-6, 1994. Itoi E, Minagawa H, Sato T, Sato K, Tabata S: Isokinetic strength of the shoulder with tears of the supraspinatus tendon. J Bone Joint Surg 79b(1):77-82, 1997. Kapandji IA: The physiology of the joints. Volume 1: Upper limb, ed 2. Edinburgh, 1982, Churchill Livingstone. Kaptein BL, van der Helm FCT: Estimating muscle attachment contours by transforming geometrical bone models. J Biomech 37:263-273, 2004. Kumar VP, Satku K, Balasubramaniam P: The role of the long head of biceps brachii in the stabilization of the head of the humerus. Clin Orthop Relat Res 244:172-175, 1989. Latko WA, Armstrong TJ, Franzblau A, Ulin SS, Werner RA, Albers JW: Cross-sectional study of the relationship between repetitive work and the prevalence of upper limb musculoskeletal disorders. Am J Indust Med 36:248-259, 1999. Malicky DM, Kuhn JE, Frisancho JC, Lindholm SR, Raz JA, Soslowsky LJ: Neer Award 2001. Nonrecoverable strain fields of the anteroinferior glenohumeral capsule under subluxation. J Shoulder Elbow Surg 11(6):529-540, 2002. Malicky DM, Soslowsky LJ, Blasier RB, Shyr Y: Anterior glenohumeral stabilization factors: progressive effects in a biomechanical model. J Orthop Res 14(2):282-288, 1996. Malicky DM, Soslowsky LJ, Kuhn JE, Bey MJ, Mouro CM, Raz JA, Liu CA: Total strain fields of the antero-inferior shoulder capsule under subluxation: a stereoradiogrammetric study. J Biomech Eng 123(5):425-431, 2001. Martin RB, Burr DB, Sharkey NA: Mechanical properties of ligament and tendon. In RB Martin, DB Burr, NA Sharkey, eds: Skeletal tissue mechanics. New York, 1998, Springer, pp. 309-348. Matsumoto F, Uhthoff HK, Trudel G, Loehr JF: Delayed tendon reattachment does not reverse atrophy and fat accumulation of the supraspinatus—an experimental study in rabbits. J Orthop Res 20:357-363, 2002. Meskers CGM, Vermeulen HM, de Goot JH, van der Helm FCT, Rozing PM: 3D shoulder position measurements using a six-degree-of-freedom electromagnetic tracking device. Clin Biomech 13:280-292, 1998.
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Morrey BF, Itoi E, An KN: Biomechanics of the shoulder. In CA Rockwood, FA Matsen, eds: The shoulder, ed 2. Philadelphia, 1998, Saunders, pp. 233-276. Morrey BF, Tanaka S, An KN: Valgus stability of the elbow. A definition of primary and secondary constraints. Clin Orthop Relat Res 265:187-195, 1991. Moseley HE, Overgaard B: The anterior capsular mechanism in recurrent anterior dislocation of the shoulder. J Bone Joint Surg 44B:913, 1962. Mow VC, et al: Material properties of the inferior glenohumeral ligament and the glenohumeral articular cartilage. In FA Matsen, FH Fu, RJ Hawkins, eds: The shoulder: a balance of mobility and stability. Rosemont, IL, 1993, American Academy of Orthopaedic Surgeons, pp. 29-67. O’Driscoll SW, Horii E, Morrey BF, Carmichael S: Anatomy of the ulnar part of the lateral collateral ligament of the elbow. Clin Anat 5:296, 1992. Ovesen J, Nielsen S: Posterior instability of the shoulder. Acta Orthop Scand 57(5):436-439, 1986. Palmerud G, Forsman M, Sporrong H, Herberts P, Kadefors R: Intramuscular pressure of the infra- and supraspinatus muscles in relation to hand load and arm posture. Eur J Appl Physiol 83:223-230, 2000. Patel PR, et al: Anatomy and biomechanics of the coracohumeral and superior glenohumeral ligaments. Trans Orthop Res Soc 21:702, 1996. Pope MH, Wilder DG: Biomechanics of the shoulder. In M Nordin, GBJ Andersson, MH Pope, eds: Musculoskeletal disorders in the workplace. St. Louis, 1997, Mosby-Year Book, pp. 352-358. Poppen NK, Walker PS: Forces at the glenohumeral joint in abduction. Clin Orthop Relat Res 135:165-170, 1978. Punnett L, Fine LJ, Keyserling WM, Herrin GD, Chaffin DB, et al: Shoulder disorders and postural stress in automobile assembly work. Scand J Work Environ Health 26(4):283-291, 2000. Regan WD, Korinek BS, Morrey BF, An KN: Biomechanical study of ligaments around the elbow joint. Clin Orthop Relat Res 271:170-179, 1991. Rockwood CA Jr, Green DP, eds: Fractures in adults, 2nd ed. Philadelphia, 1984, JB Lippincott. Saha AK: Dynamic stability of the glenohumeral joint. Acta Orthop Scand 42(6):491-505, 1971. Søjbjerg JO, Ovensen J, Gundorf CE: The stability of the elbow following excision of the radial head and transection of the annular ligament. An experimental study. Arch Orthop Trauma Surg 106(4):248-250, 1987. Sommerich CM, McGlothlin JD, Marras WS: Occupational risk factors associated with soft tissue disorders of the shoulder: a review of recent investigations in the literature. Ergonomics 36(6):697-717, 1993. Soslowsky L J, Flatow EL, Bigliani LU, Pawluk RJ, Ateshian GA, Mow VC: Quantitation of in situ contact areas at the glenohumeral joint: a biomechanical study. J Orthop Res 10:524-534, 1992. Soslowsky L J, Flatow EL, Bigliani LU, Mow VC: Articular geometry of the glenohumeral joint. Clin Orthop Relat Res 285:181-189, 1992. Soslowsky L J, Carpenter JE, De Bano CM, Banerji I, Moalli MR: Development and use of an animal model for investigations on rotator cuff disease. J Shoulder Elbow Surg 5(5):383-392, 1996. Soslowsky LJ, Malicky DM, Blasier RB: Active and passive factors in inferior glenohumeral stabilization: a biomechanical model. J Shoulder Elbow Surg 6(4):371-379, 1997. Soslowsky LJ, Thomopoulos S, Ton S, Flanagan CL, Keefer CC, Mastaw J, Carpenter JE: Neer Award 1999. Overuse activity injures the supraspinatus tendon in an animal model: a histologic and biomechanical study. J Shoulder Elbow Surg 9(2):79-84, 2000. Soslowsky L J, Thomopoulos S, Esmail A, Flanagan CL, Iannotti JP, Williamson JD, Carpenter JE: Rotator cuff tendinosis in an animal model: role of extrinsic and overuse factors. Ann Biomed Eng 30(8):1057-1063, 2002. Speer KP, et al: Biomechanical evaluation of a simulated Bankart lesion. J Bone Joint Surg 76A:1819-1826, 1994. Stormont TJ, An KN, Morrey BF, Chao EY: Elbow joint contact study: comparison of techniques. J Biomech 5:329-336, 1985. Turkel SJ, Panio MW, Marshall JL, Girgis FG: Stabilizing mechanisms preventing anterior dislocation of the glenohumeral joint. J Bone Joint Surg 63A:1208-1217, 1981. Uhthoff HK, Matsumoto F, Trudel G, Himori K: Early reattachment does not reverse atrophy and fat accumulation of the supraspinatus—an experimental study in rabbits. J Orthop Res 21:386-392, 2003. van der Helm FCT: A finite element musculoskeletal model of the shoulder mechanism. J Biomech 27(5):551-569, 1994. Warner JJ, Deng XH, Warren RF, Trozilli PA: Static capsuloligamentous restraints to superior-inferior translation of the glenohumeral joint. Am J Sports Med 20(6): 675-685, 1992. Warner JP, Bowen MK, Deng XH, Hannafin JA, Arnoczky SP, Warren RF: Articular contact patterns of the normal glenohumeral joint. J Shoulder Elbow Surg 7(4): 381-388, 1998. Woo SLY, Akeson WH, Jemmott GF: Measurements of nonhomogeneous, directional mechanical properties of articular cartilage in tension. J Biomech 9(12):785-791, 1976.
CHAPTER
5c
Evaluation of the Shoulder and Elbow Derek Plausinis and Joseph D. Zuckerman
Coordinated movement of the shoulder and elbow is essential to position the hand in space. Symptoms related to the shoulder and elbow are often vague and clinically difficult to diagnose. Numerous associated musculoskeletal disorders such as tendinitis and nerve entrapment syndromes have been found to be related to repetitive and forceful use of the upper extremity in a wide variety of occupations.4 Because symptoms may overlap, it is important to distinguish referred pain from the cervical spine or adjacent joints from that arising locally. Sound knowledge of local anatomy and appreciation of the salient features of the history and physical examination are crucial to the formulation of an accurate diagnosis, treatment regimen, and plan for prevention, especially with regard to work-related injuries.
THE SHOULDER History Complaints related to the upper extremity must be approached in an organized methodical manner, with care taken to not focus too quickly on a specific complaint so as to avoid missing a more generalized or related condition. At the initial assessment, identification of personal and work-related risk factors is essential. The patient’s age, hand dominance, occupation, and chief complaint should begin every history because these are the major contributors to the establishment of an accurate diagnosis. Age and nature of the complaint can be very directive in identifying the underlying shoulder disorder. A 40-year-old carpenter’s complaint of pain in the overhead position, for example, indicates to the physician to evaluate further the possibility of impingement and rotator cuff pathology, as opposed to a 20-year-old gymnast’s complaint that the shoulder “slips out” in the abducted and externally rotated position, which suggests ligamentous instability. Symptoms of pain, instability, and loss of motion account for most complaints about the shoulder. Noting maneuvers that provoke pain, presence of night pain, radiation of symptoms, and neck and opposite shoulder pain can aid in differentiating between referred pain and local pathology. Bilateral shoulder pain that is worsened by hyperextension or rotation of the neck but not by glenohumeral motion is due most often to cervical spine pathology as opposed to an intrinsic shoulder disorder. The physician must also ask about the presence of any extremity weakness, radiating pain, or paraesthesia. The distribution of neurologic symptoms assists in differentiating cervical radiculopathy from myelopathy or brachial neuritis.
When occupational activity-related pain is the chief complaint, the usual questions as to the location, timing, and character of the pain need to be supplemented by a detailed work history. Exploration into the exact nature of the task and how often it is performed is necessary to further elucidate occupational risk factors that can predispose to or aggravate the current condition. How often and how quickly the task is carried out should be noted. Repetitive work, especially when combined with high force demands, has been associated with shoulder tendinitis.4 Other work-related risk factors include high force, awkward joint posture, direct pressure, vibration, and repetitive overhead activities.21 A history with documentation of prior claims, time off work, and litigation in process constitutes valuable information because secondary gain can play a significant role in the prognosis. Just as important as the task itself is the mechanical and psychologic environment in which it is performed. In addition to the degree of stress involved, the presence of a draft, the need to work at a height, the positioning of equipment/tools, and the use of gloves may all play a role in the multifactorial etiology of repetitive strain disorders. Consideration of how the present condition affects recreation and activities of daily living also assists in determining the severity of the problem. Localized pain that is intense enough to disrupt sleep and cause limitation of simple overhead activities is most commonly due to rotator cuff pathology. Infection, arthritis, and frozen shoulder syndrome, however, can less frequently be manifested in a similar manner. Pain on carrying heavy packages at the side or when pushing a revolving door open may be more indicative of instability of the glenohumeral joint. Patients should be questioned with respect to previous injuries and any preexisting conditions that may have predisposed them to the current problem. If an acute injury is reported, details of its mechanism and the position of the extremity at the time force was applied should be ascertained. In the case of a fall, the height, the type of surface onto which the patient fell, and the body part that struck first should be recorded. Feelings of subluxation or crepitus at the time of injury with an inability to continue working secondary to immediate pain attest to the severity. In addition, symptoms of numbness or paraesthesia may accompany episodes of instability. The mechanism of anterior shoulder dislocation is usually the result of forced abduction and external rotation of the shoulder, whereas direct trauma is more likely to cause contusions or fractures. A fall onto or direct blow to the top of the shoulder often results in varying degrees of acromioclavicular injury, whereas falls onto the outstretched hand can easily result in proximal humeral fractures. For any injury or joint disorder, treatments undertaken to date must be ascertained. These include previous physician consults, medications, physiotherapy, splints, or joint injections. In the shoulder, multiple steroid injections in the subacromial space may lead to rotator cuff degeneration and tearing.26 Finally, a careful past medical history and functional assessment must be obtained. Multiple joint pains may suggest rheumatologic disease or referred pain.
Physical examination Even with the most thorough history, the physician may or may not have a clear sense of the underlying problem. A systematic
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Table 5c.1 Summary approach to shoulder physical examination Cervical spine examination Neurovascular assessment Shoulder examination Inspection Palpation Active and passive range of motion Special tests Impingement Hawkins test Neer’s test Painful arc Rotator cuff muscles Supraspinatus Infraspinatus and teres minor Subscapularis Biceps tendon Check for rupture Speed’s test Yergason’s test Stability tests Anterior Posterior Inferior and generalized laxity AC joint assessment Local tenderness Cross-body adduction Injection tests AC joint Subacromial space Glenohumeral joint
Figure 5c.1 Severe axillary nerve palsy manifested as deltoid atrophy, squaring off of the shoulder, and inferior subluxation of the humeral head.
rotator cuff tears, this may be related also to supraspinatus nerve entrapment neuropathy or C5 nerve root pathology. Prominence of the clavicle may suggest clavicle fracture or malunion as well as acromioclavicular joint dislocations (Fig. 5c.3). Swelling is unusual but may be seen in cases of subacromial bursitis or extravasation of synovial fluid in massive rotator cuff tears. Posterior dimpling or a “sulcus” may suggest anterior shoulder dislocation.
AC, acromioclavicular. Note: see text for detailed description of examination maneuvers.
meticulous approach to the physical examination is therefore required to avoid missing subtle findings and arriving at a diagnosis that is inaccurate or incomplete. A summary of the key elements of the shoulder physical examination is provided in Table 5c.1. Note that evaluation of all potential shoulder problems must include a thorough examination of the cervical spine. Inspection occurs with the patient sitting or standing and appropriately gowned to expose the shoulder entirely. The shoulder should be examined for signs of asymmetry caused by muscle wasting, soft tissue swelling, or bone or articular incongruities and a comparison made with the unaffected side. Muscle spasm involving the trapezius or paracervical muscles may cause asymmetry and may be related to cervical root pathology,8 whereas muscle fatigue may affect shoulder posture and kinematics.9 Deltoid atrophy may be associated with general disuse of the shoulder or related to axillary nerve pathology; best noted from an anterior vantage point, it is characterized by squaring off of the involved shoulder (Fig. 5c.1). Atrophy of the supraspinatus or infraspinatus muscles is best visualized from behind (Fig. 5c.2). Most commonly seen in association with
Figure 5c.2 Supraspinatus and infraspinatus atrophy noted from behind; the atrophy was secondary to a long-standing rotator cuff tear.
Chapter 5c
Figure 5c.3 Acromioclavicular separation with complete loss of articulation of the joint surfaces and prominence of the distal end of the clavicle.
The next step in a comprehensive examination of the shoulder is palpation of the bony and soft tissue elements. Tenderness or crepitus about the clavicle suggests fracture or nonunion, particularly if consistent with details of the history. Acromioclavicular joint tenderness is found in cases of arthritis and may be seen in those whose occupations require carrying heavy loads on their shoulders like lumber or postal bags21 or in the presence of instability secondary to traumatic ligamentous disruption. Tenderness on palpation over various anatomic landmarks can provide important clues leading to a diagnosis: Tenderness of the anterior of the acromion may be a subtle indicator of rotator cuff impingement; tenderness about the greater tuberosity may be seen in cases of rotator cuff tears, supraspinatus tendinitis, or fracture; tenderness over the bicipital groove, which is found between the greater and lesser tuberosities, is suggestive of bicipital tendinitis; and tenderness over the posterior joint line beneath the posterior of the acromion may represent glenohumeral arthritis. Anterior joint or capsular tenderness is more representative of soft tissue injury after anterior shoulder dislocation or subluxation.8 A nonspecific indicator of inflammation, local warmth is seen in conditions such as inflammatory arthritides or infection. Anesthesia or hypoesthesia in the dermatome overlying the middle deltoid suggests injury to the axillary nerve from traction, compression, or demyelination. Both active and passive joint motion must be assessed. It is important to understand the two basic components of shoulder elevation: glenohumeral and scapulothoracic. In the first 30 degrees of elevation in the scapular plane, motion occurs mostly at the glenohumeral joint. As the arm is elevated further, more scapulothoracic motion occurs with an equal contribution of glenohumeral and scapulothoracic movement in the last 60 degrees of elevation. In elevation there is a 2:1 ratio of glenohumeral to scapulothoracic motion overall.12 To assess the relative contributions of each, the scapula should be stabilized by holding the inferior scapular angle. Adhesions or rotator cuff derangement likely alters the normal fluid pattern of glenohumeral motion, and a greater proportion of the arc of motion becomes scapulothoracic.
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The American Shoulder and Elbow Surgeons has recommended that four planes of shoulder motion be assessed in all patients: total forward elevation, external rotation with the elbow at the side, external rotation with the arm abducted 90 degrees, and internal rotation behind the back.22 Active and passive motion for both shoulders should be recorded. Abduction and internal rotation are best examined with the patient sitting upright on the examination table. Forward elevation and external rotation can most accurately be examined with the patient both upright and supine to ensure that compensatory movements of the spine are eliminated. A limited active arc of motion may have a musculotendinous or neurologic etiology, or it may be related to pain. Limited passive motion suggests a mechanical block as in adhesive capsulitis, malunion of fractures, loose bodies, or glenohumeral arthritis. When assessing forward elevation, the practitioner should view the patient from a lateral position and reference the angle of the arm with the posterior thorax. External rotation, both active and passive, is best assessed with the arm at the side and the elbow flexed 90 degrees (Fig. 5c.4). A deficiency in active external rotation generally indicates neurologic or rotator cuff derangement, whereas one in both active and passive external rotation may be seen in adhesive capsulitis or in patients with mechanical blocks such as locked posterior dislocations. Testing external rotation with the arm abducted 90 degrees may be helpful, particularly in patients performing repetitive overhead activities such as throwing or welding. In this position, symptoms suggestive of capsulolabral deficiencies, greater tuberosity pathology, and instability may be elicited. Internal rotation is generally tested with the patient sitting upright. The patient is asked to reach around the back while internally rotating (and slightly extending) the shoulder so as to record the level reached by the outstretched thumb. This is commonly documented as the buttock, sacrum, iliac crest, and exact lumbar or thoracic spinous process reached. Generally, active and passive range of motion in this plane is similar, with limitations again suggestive of subacromial pathology such as rotator cuff derangement or a frozen shoulder.
Figure 5c.4 External rotation of the glenohumeral joint is assessed with the patient supine to prevent torso rotation. The elbow is flexed to 90 degrees with the arm at the side.
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Table 5c.2
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Evaluation of the shoulder and elbow
Muscle grading
Muscle gradations
Description
5 (normal) 4 (good) 3 (fair) 2 (poor) 1 (trace) 0 (absent)
Complete ROM against gravity with full resistance Complete ROM against gravity with some resistance Complete ROM against gravity Complete ROM with gravity eliminated Evidence of muscle contraction; no joint motion No contractility
ROM, range of motion.
Muscle strength testing is essential to assess the competence of the musculotendinous complexes about the shoulder and to identify possible peripheral or central neuropathology such as peripheral compressive neuropathy or cervical stenosis. In this regard, a thorough understanding of the structure of the brachial plexus and innervation patterns more peripherally is critical. Clearly, a suggestion of cervical pathology stimulates a more thorough neurologic examination. Muscle strength should be recorded using the universal system of grading on a scale from 0 to 5, with the opposite and presumably normal limb used as the control for comparison (Table 5c.2). It is important to realize that in the presence of pain, the accuracy of motor strength recording may be called into question. The primary motor functions—forward flexion, abduction, and external and internal rotation—are tested by resisting the particular plane of motion. Forward flexion is primarily the role of the anterior head of the deltoid muscle (axillary nerve, C5-C6) with secondary flexors, including the biceps and coracobrachialis muscles (musculocutaneous nerve, C5-C7), and the clavicular portion of the pectoralis major muscle (lateral pectoral nerve, C5-C6). Abduction tests the strength of both the middle third of the deltoid muscle (axillary nerve, C5-C6) and the supraspinatus muscle (suprascapular nerve, C5). Finally, the presence of scapular winging should be noted, indicating dysfunction of the serratus anterior (long thoracic nerve, C5-C7) or the trapezius (spinal accessory nerve). Scapular winging may be demonstrated by inspecting from behind while asking the patient to push against a wall. For assessing the rotator cuff, the key clinical features are muscle strength and pain. Whereas weakness alone may suggest a compressive neuropathy, that accompanied by pain suggests rotator cuff pathology. Before formal cuff muscle testing, the presence of any muscular atrophy is first noted (Fig. 5c.1). The greater tuberosity is palpated for tenderness or defect at the site of insertion of the supraspinatus, and the shoulder is passively flexed and extended while palpating for subacromial crepitus. The strength of the supraspinatus muscle may be isolated by elevating the arm 90 degrees, maximally pronating the forearm with the thumb down, and applying a downward force on the patient’s arm.24 The supraspinatus is affected in most rotator cuff tears, and when extension into the infraspinatus tendon occurs, external rotation may be weak or painful. External rotation strength with the elbow at the side assesses principally the infraspinatus muscle (suprascapular nerve, C5-C6) and teres minor muscle (axillary nerve, C5-C6). Large rotator
Figure 5c.5 To test for teres minor involvement in rotator cuff disorders, support the patient’s arm at 90 degrees of elevation in the scapular plane and ask the patient to externally rotate against resistance. The inability to externally rotate the arm indicates a positive “horn blower’s” sign.
cuff tears often produce a discrepancy between active and passive motion. The “dropping sign” is demonstrated by grasping the forearm with the elbow flexed and held at the side and passively externally rotating the shoulder 45 degrees. The patient is asked to resist a force in external rotation as the forearm is released. If the patient is unable to hold the arm in this position and the forearm drops to a neutral position, then the “dropping sign” is positive for infraspinatus weakness.9 Further extension of a rotator cuff tear into the teres minor can be suggested by external rotation weakness in abduction. This is tested by supporting the patient’s arm at 90 degrees of elevation in the scapular plane and then asking the patient to externally rotate against resistance (Fig. 5c.5). If the patient cannot externally rotate, then a “hornblower’s” sign is present,27 indicating extension of a tear into the teres minor. This sign can be functionally illustrated by asking the patient to bring the hand to the mouth; patients with infraspinatus and teres minor cuff weakness will abduct the arm to accommodate for inability to externally rotate. The subscapularis cannot be isolated by testing internal rotation strength with the arm at the side but rather requires the “lift-off ” test,6 which involves asking the patient to place his or her hand behind the back at the lumbosacral junction and then lift the hand off. Inability to perform a lift-off suggests subscapularis rupture; many patients with shoulder stiffness, however, are unable to perform this maneuver. The examiner must pay attention to the elbow during the lift-off test, because patients with subscapularis deficiency may give the false impression of being able to lift off by extending the elbow. When patients have limited internal rotation and the ability to perform the lift-off test is compromised, the subscapularis may be tested with the “belly press,”5 which involves asking the patient to place his or her hand on the abdomen and then bring his or her elbow forward to the level of the hand. Patients with subscapularis insufficiency will keep their elbow at the side with the wrist flexed and will be unable to effectively bring the elbow forward.
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Figure 5c.6 Positive impingement sign as described by Neer with forced forward elevation of the arm, causing the supraspinatus to impinge on the undersurface of the acromion.
Several provocative tests can be used to elucidate subacromial impingement, of which two have been classically used. The Neer “impingement sign” consists of forced forward elevation of the arm.13 Pain is elicited as the inflamed supraspinatus tendon impinges against the inferior border of the acromion anterior (Fig. 5c.6). If local anesthetic is administered to the subacromial space, pain in impingement syndrome is eliminated, which then confirms a positive impingement test.13 The impingement sign becomes much less reliable, however, when there is a limitation of passive forward elevation. In the Hawkins impingement test, the arm is forward-flexed 90 degrees and then forcibly internally rotated. Pain is evoked as the inflamed supraspinatus tendon is impinged against the coracoacromial ligament. In addition to these impingement tests, patients with impingement often demonstrate a “painful arc.” As the arm is abducted in the coronal plane, pain occurs between 60 and 100 degrees and is usually maximal at 90 degrees. Patients may be observed to rotate the humerus externally in the abducted position to minimize impingement of the greater tuberosity under the acromion. Assessment of the acromioclavicular joint begins with examination for local tenderness and swelling. A provocative maneuver for acromioclavicular joint pathology, cross-body adduction, can be elicited by passively elevating the arm to 90 degrees and adducting the arm and forearm across the chest. Pain near the acromioclavicular joint with cross-body adduction indicates acromioclavicular joint pathology,3 whereas that in the posterior shoulder usually results from posterior capsular tightness. In patients with documented or suspected glenohumeral instability, anterior instability is the most common clinical presentation. The simplest clinical maneuver, the “apprehension test,” is performed with the patient in the supine position with the arm abducted 90 degrees. The shoulder is externally rotated as the patient’s facial expression is noted. A patient’s apprehension or sense of impending shoulder subluxation or dislocation indicates a positive test. The “relocation” test can then be performed with the shoulder at the point of apprehension.
Figure 5c.7 Anterior instability is tested by placing the shoulder in 90 degrees of abduction and external rotation while attempting to level the humeral head out anteriorly with gentle posterior pressure. Apprehension and pain are indicative of positive responses.
A posteriorly directed force is applied to the proximal humerus, and in cases of instability pain or apprehension is relieved, indicating a positive “relocation” test.25 A similar but more provocative test for anterior instability is to abduct and externally rotate the shoulder in the upright position. When an anteriorly directed force is applied to the posterior proximal humerus, the patient with anterior instability becomes apprehensive or experiences pain in the shoulder (Fig. 5c.7). Although less common, posterior instability may be seen after a traumatic event or in association with a history of seizure disorder or alcohol abuse. A “posterior apprehension test” may be performed by flexing and internally rotating the shoulder and noting if the patient experiences a sense of instability. To further assess posterior laxity, an axial load can be applied to the elbow with the shoulder flexed 90 degrees and in neutral rotation. This maneuver subluxes the humeral head posteriorly. The examiner then abducts the arm and palpates for the sudden reduction of the subluxed shoulder.8 Anterior and posterior capsular laxity may be examined further by assessing the amount of glenohumeral translation. This may
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be difficult to produce on examination without the benefit of anesthesia but should be assessed in all patients. Humeral head translations may be tested with the patient sitting upright or lying supine while the scapula is stabilized with one hand and the humeral head grasped with the other. Anterior and posterior translatory loads are applied to evaluate anterior and posterior instability, respectively. The humeral head normally translates posteriorly up to 50% of the width of the glenoid, but the shoulder does not appreciably translate anteriorly. It is important to compare these findings with those in the opposite shoulder because some degree of laxity may be expected even in normal shoulders. Patients with inferior instability may have their symptoms reproduced by applying longitudinal downward traction on the arm. When the deltoid muscle is relaxed, an inferior “sulcus sign” is usually present in affected patients (Fig. 5c.8). Patients with inferior instability commonly also have anterior and posterior instability, in which case the term multidirectional instability is used. This condition is usually associated with generalized hyperlaxity as evidenced by hyperextension of the elbows and knees or the ability for the patient to bring the thumb passively to touch the ipsilateral forearm.
The long head of the biceps is first assessed by examining for continuity of the tendon. The patient is asked to resist gentle flexion of the elbow, and the upper arm is inspected. An abrupt change in contour of the biceps muscle proximally that is asymmetric with the contralateral side, referred to as a “Popeye” muscle, indicates rupture of the long head of the biceps. With an intact biceps tendon, tenderness in the bicipital groove is a common finding in bicipital tendinitis. As the humerus is externally rotated, the anterior pain of bicipital tendonitis typically moves more laterally with the externally rotated bicipital groove. Common provocative maneuvers for long head of biceps pain include Yergason’s test and Speed’s test. Yergason’s test consists of actively supinating the forearm against examiner resistance with the elbow flexed 90 degrees. Speed’s test involves forward elevation of the arm against resistance with the elbow extended and the forearm supinated. If positive, both tests elicit pain in the region of the bicipital groove. It should be noted that this diagnosis is often a component of the impingement syndrome, and controversy exists as to whether it exists as an isolated entity. In addition to the detailed neurologic examination outlined earlier, a careful vascular examination should be performed to rule out vascular compression in the neck as the source of claudicant shoulder pain, the so-called thoracic outlet syndrome. Distal pulses should routinely be palpated. Several tests have a time-honored role in the diagnosis of vascular insufficiency, perhaps the most commonly used of which is Adson’s maneuver or one of its several modifications. The examiner palpates the radial pulse and abducts the ipsilateral arm 90 degrees while extending and externally rotating the shoulder with the patient turning the head to the opposite side. A diminishing peripheral pulse signifies proximal compression and indicates a positive test. It is critical to identify the source of vascular compression, including an accessory rib, Pancoast’s tumor, fibrous bands, or clavicular malunion, so that proper steps in management may be taken.
Diagnostic testing
Figure 5c.8 Inferior ligamentous laxity exhibited by an inferiorly subluxed humeral head with downward traction on the humerus with the arm at the side.
The practitioner generally establishes the diagnosis after a thorough history and comprehensive physical examination. Most imaging tests are performed to confirm the physician’s clinical impression, but inevitably in some cases the diagnosis remains unclear and further investigation is warranted. The mainstay of imaging remains the standard radiograph. In general, all patients with complaints referable to the shoulder should receive a routine series of at least three radiographs as initial screening. This consists of anteroposterior (AP), scapular lateral, and axillary radiographs of the shoulder with the beam centered over the glenohumeral joint. When shooting these radiographs it is important to follow meticulous guidelines and to keep in mind that the plane of the scapula is rotated anteriorly approximately 35 to 40 degrees (Fig. 5c.9). A true AP radiograph in the scapular plane is taken with the posterior aspect of the affected shoulder against the cassette and the opposite shoulder rotated anteriorly approximately 40 degrees. The AP radiograph in internal rotation shows the greater tuberosity en face, external rotation shows it in profile, and both show
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Technique for obtaining scapular anteroposterior (A), lateral (B), and axillary (C) views of a trauma series required on all patients.
different aspects of the humeral head. In these views the distance between the humeral head and the acromion process should be assessed. In cases of massive rotator cuff tears, the normal interspace, averaging 10 mm, may diminish as the humeral head migrates cephalad, and a break in the inferior calcar line may be seen (Fig. 5c.10).7 Also considered routine in trauma situations is the scapular lateral view, in which the scapula is seen tangentially. This is an anterior oblique projection taken with the patient rotating the involved shoulder 60 degrees toward the central beam.7 Its value lies in identifying shoulder dislocations and fractures of the humeral head or neck or scapula. In the axillary view, the patient is positioned supine with the arm abducted. A horizontal x-ray beam is directed in toward the axilla. This projection visualizes the relationship between the humeral head, glenoid, coracoid, and acromion (Fig. 5c.11). It is a
key projection for identifying shoulder dislocations and any associated anterior glenoid avulsion fractures (bony Bankart lesion) or posterior impression fractures of the humeral head (Hill-Sachs lesion) (Fig. 5c.12). The relative position of the anterior aspect of the acromion with respect to the clavicle should be assessed, particularly in cases of impingement syndrome. Anterior projection of the acromion beyond the anterior limits of the clavicle has been shown to predispose to rotator cuff problems.28 The “outlet view” represents a lateral projection into the subacromial space. It is an ideal projection for assessing the slope of the acromion, which has been shown to have an impact on the development of impingement syndrome (Fig. 5c.13). It is taken with the patient standing and the affected shoulder rotated 60 degrees toward an x-ray beam angled 10 to 15 degrees caudad.7
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Figure 5c.12 Locked posterior dislocation with a humeral head impression fracture. Figure 5c.10 In the presence of massive rotator cuff tears, a highriding humeral head is noted with decreased acromiohumeral distance and a break in the inferior calcar margin.
A specialized AP radiograph angled 15 degrees cephalad is a valuable tool for imaging the distal and middle aspects of the clavicle and acromioclavicular joint. As such, this projection is used to assess clavicle fractures, acromioclavicular joint sprains, arthritis, or spurring (a source of rotator cuff impingement), or distal clavicle osteolysis (common in weight lifters). Magnetic resonance imaging (MRI) has become the imaging modality of choice in most centers for identifying most soft
tissue pathology about the shoulder. Multiaxial images and the development of newer MRI protocols have enabled more accurate assessments of shoulder pathology. For rotator cuff pathology and impingement syndrome, MRI can identify rotator cuff tendinosis and partial and full thickness tears (Fig. 5c.14).1 An estimate of rotator cuff tear size can be made, and the presence of fatty degeneration of the rotator cuff muscles can be identified. In cases of impingement, MRI can also identify potential sources of cuff impingement such as an osteophyte
C
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Figure 5c.11 Axillary view of the shoulder, crucial for determining the position of the humeral head in relation to the glenoid. The labeled structures are the humeral head (H), glenoid (G), coracoid (C), acromion (A), and acromioclavicular joint (AC).
Figure 5c.13 Supraspinatus outlet view with a large subacromial spur, causing impingement.
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AC A RT
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Figure 5c.15 Arthrogram documenting a full-thickness rotator cuff tear with dye extravasation into the subacromial space and laterally to the greater tuberosity.
Figure 5c.14 Magnetic resonance image of the right shoulder revealing a full-thickness rotator cuff tear (RT) with a retracted supraspinatus tendon (SS) underneath the acromion (A) and acromioclavicular joint (AC). The greater tuberosity (GT) is also shown.
from the undersurface of the acromioclavicular joint, acromioclavicular joint hypertrophy, or a downward-beaking acromion that may be associated with a subacromial spur. In cases of instability when the diagnosis is unclear, MRI can be used to detect capsular injury or redundancy as well as labral tears. Although infrequent, in cases of violent traumatic anterior shoulder dislocations, the subscapularis tendon may be torn either directly off its insertion on the lesser tuberosity or in its mid-substance. In the latter case, MRI potentially shows retraction at the site of the tear, or in chronic cases calcific deposits may be seen in the substance of the subscapularis muscle or tendon. The tendon of the long head of the biceps can be imaged on axial cuts as it sits in the bicipital groove. Absence of the tendon in this landmark would imply rupture and subsequent retraction (which should be obvious on clinical examination) or subluxation, as may be seen in a congenitally shallow bicipital groove or after trauma. Bicipital tendinitis is often a more proximal phenomenon and is difficult to image by MRI. Finally, MRI has a role in the diagnosis of osteonecrosis of the humeral head and should be considered in certain high-risk conditions such as sickle cell disease, steroid use, or alcohol abuse or in deep sea divers in the setting of shoulder pain even without radiographic findings. Historically regarded as unreliable, ultrasonography has played an increasing role in rotator cuff diagnoses in recent years. With newer equipment and experienced ultrasonographers, sensitivities and specificities of 94% or greater for the detection of fullthickness tears and 93% or greater for partial-thickness tears have been reported.23 Although it has a lower cost than MRI and is a noninvasive test, the availability of accurate rotator cuff assessment is limited by the availability of an experienced musculoskeletal ultrasonographer.
Although it has largely been replaced by MRI and ultrasound, arthrography continues to have a role in the diagnosis of shoulder disorders. It entails injection of either contrast alone or contrast followed by the injection of room air into the glenohumeral joint. Various x-ray views are then taken to assess different shoulder components. The technique has a time-honored role in the diagnosis of complete rotator cuff tears (Fig. 5c.15). The arthrogram may be used also to visualize the long head of the biceps tendon, thereby diagnosing rupture, tenosynovitis, or subluxation. Computed tomography (CT) is used primarily to assess bony pathology further when details are unclear from plain radiographs, as may be seen in cases of recurrent instability with glenoid or humeral head defects. Lidocaine injection tests serve a vital role with regard to problems of the shoulder in that they can be valuable diagnostic tools when the precise diagnosis is in question. For instance, at times it may be difficult to localize the source of symptoms to the acromioclavicular joint, the subacromial space, or the glenohumeral joint. In these situations, selective lidocaine injection can be of obvious benefit. The subacromial space is the most frequently injected region. Amelioration of symptoms points to rotator cuff tendinitis or tear as the culprit; conversely, if symptoms persist, the source of pain is elsewhere, although the subacromial space may be responsible at least in part. Various techniques for injection have been described; nevertheless, it is always important to follow strict sterile technique to minimize the risk of infection. The subacromial space can be injected from a lateral approach with relative ease (Fig. 5c.16). Downward traction may be applied to the arm to help widen the interval between the humeral head and the acromion. Also a frequent source of pain, the acromioclavicular joint is easily palpated between the distal clavicle and the acromion, with a needle directed from its superior aspect. Often, pathology in this joint is associated with impingement of the rotator cuff, and selective injection here may help clarify the severity of the referred pain.
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Figure 5c.16 Subacromial lidocaine injection test via a lateral approach is extremely valuable in the diagnosis of impingement.
Technetium bone scanning has a limited role in the evaluation of problems related to the shoulder. However, it may be of use in the evaluation of adhesive capsulitis or in ruling out occult infection, tumor, or avascularity in the presence of persistent symptomatology. Electromyographic and other nerve conduction studies have a definite role in distinguishing central from peripheral neuropathy and in investigating the possibility of a neural basis of muscle wasting or weakness when intrinsic myotendinous pathology is ruled out. In suggestive cases, shoulder evaluation may include laboratory studies, particularly routine blood tests such as a complete blood count, erythrocyte sedimentation rate, C-reactive protein, rheumatoid factor, antinuclear antibody, and blood chemistry analysis, to exclude inflammatory arthritides or infection. Additionally, adhesive capsulitis is more likely in diabetic patients, hence the importance of assessing serum glucose levels. If joint sepsis or crystal diseases are suspected, the glenohumeral joint can be aspirated and fluid sent for Gram stain, culture, cell count, and microscopy for crystals.
THE ELBOW History The approach to the history for the patient with an occupational elbow disorder follows an outline similar to that for a shoulder disorder. The general content for history of present illness and occupational history are as outlined previously. Specific complaints arising from elbow pathology with clinical examples are provided below. Symptoms related to the elbow usually involve pain or stiffness. Whereas pain is a common complaint with advanced elbow arthritis, the early phases of degenerative joint disease in the elbow usually present with loss of motion as the primary concern. After any trauma to the elbow, stiffness is also a common complaint, particularly with a history of prolonged
Figure 5c.17 olecranon.
Lateral view demonstrating a spur off the tip of the
immobilization after injury. Elbow stiffness may or may not be associated with pain, and it is important to delineate whether the patient’s primary concern and source of functional impairment is pain or stiffness. Degenerative joint disease ultimately results in activity-related pain, usually first occurring near full extension. Osteoarthritis may present also with a history of episodic sharp pain in the elbow and intermittent loss of motion or locking. These mechanical symptoms commonly arise also after a traumatic event to the elbow and suggest the presence of loose bodies that usually require surgical removal. Patients may notice swelling about the elbow joint. A joint effusion or synovitis is present with some diffuse swelling about the elbow and is often more apparent clinically in the posterolateral aspect. In contrast, olecranon bursitis may present with a recurrent mass directly over the olecranon. Bone spurs off the olecranon (Fig. 5c.17) have been associated with olecranon bursitis (Fig. 5c.18), and the patient may have noticed the development of a more prominent olecranon. Olecranon bursitis may be sterile or septic, and the patient should be questioned as to a history of fever, erythema, previous attempts at aspiration, and drainage. Unlike the shoulder, recurrent instability is an uncommon problem in the elbow. Stiffness is the usual problem after elbow dislocation. When present, instability may present as recurrent episodes of dislocation or more commonly as a sense of elbow subluxation and pain. In cases of recurrent instability after elbow trauma, symptoms are most likely to occur from lateral ligament deficiency and are provoked by activities where a valgus stress is applied to the elbow with the forearm in supination. The valgus instability from medial collateral ligament laxity is typically seen in throwing athletes and very uncommonly as a result of workplace injury.
Chapter 5c
Figure 5c.18 Classic appearance of olecranon bursitis. Note the prominent fluid-filled bursa over the olecranon (compared with a normal elbow in Fig. 5c.19).
Tendinopathy about the elbow is a common problem, usually presenting as medial or lateral epicondylitis. Patients typically complain of pain in the region of the flexor or extensor origin that is aggravated with repetitive active wrist movement. Chronic tendinitis of the distal biceps tendon is uncommon; however, ruptures may occur after resisted activity, typically in the dominant arms of men in their forties. Entrapment neuropathies about the elbow must be considered also as a possible source of elbow pain and may present with weakness or sensory changes in the hand and wrist as well. Lying posterior to the medial epicondyle, the ulnar nerve is prone to compression and irritation with activities requiring recurrent elbow flexion or from direct compression over the nerve. In cases of cubital tunnel syndrome (ulnar nerve entrapment at the elbow), patients typically complain of sensory changes in the ring and small fingers. The ulnar nerve lies close to the ulnohumeral joint and in cases of arthritis can be prone to irritation from osteophytes and loose bodies.17 Median and radial nerve compression at the elbow level may occur also, although less frequently than ulnar nerve entrapment. Patients typically present with elbow pain, and neurologic symptoms are less common.19,20 When considering the diagnosis of peripheral nerve entrapment, the distribution of symptoms and the exacerbating features are critical to help determine whether the symptoms are truly originating at the elbow level or whether referred pain from the shoulder or a cervical radiculopathy may be the underlying cause.
The elbow
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Inspection of the elbow is first undertaken to look for any signs of inflammation or previous injury. To identify subtle findings, comparison with the unaffected side is helpful. An elbow effusion may be clinically apparent by a fullness in the posterolateral aspect, whereas olecranon bursitis presents with a local mass over the olecranon (Fig. 5c.18). With the elbow in full extension and the forearm in supination, the alignment of the ulna compared with humerus (carrying angle) is estimated. Despite considerable variation among individuals, normal values for the carrying angle are approximately 10 degrees for men and 13 degrees for women.19 Childhood injuries to the elbow commonly result in alteration of the carrying angle into either valgus or varus malalignment. Although excess valgus alignment may lead to ulnar nerve irritation,17 varus malalignment, also termed a gunstock deformity, is usually not associated with any functional deficits. Palpation of the elbow relies first on establishing the appropriate surface anatomy. On the lateral aspect, three important bony landmarks appear: lateral epicondyle, radial head, and tip of the olecranon (Fig. 5c.19). The radial head is a bony prominence just distal and slightly inferior to the lateral epicondyle. The location of the radial head is confirmed by rotating the forearm with the elbow held at 90 degrees of flexion; the rotation of the radial head on the stationary capitellum is palpable. At the center of these three bony landmarks (Fig. 5c.19), fullness indicates synovitis or effusion and represents also a safe location for elbow joint aspiration or injection. The radiocapitellar joint may be palpated between the radial head and the lateral epicondyles. While palpating over this region, passive forearm rotation and passive flexion and extension allow for an assessment of any crepitus or soft tissue snapping from the radiocapitellar joint. On the medial side of the elbow, the medial epicondyle and the olecranon may be identified. In the groove posterior to the medial epicondyle lies the ulnar nerve, which may be gently palpated. Medial to the ulnar nerve is the medial aspect of the ulnohumeral joint. Placing the examining index finger and thumb on either side of the ulna just distal to the olecranon while the elbow is gently flexed and extended allows for the assessment of ulnohumeral joint crepitus and tenderness.
Physical examination As in the case of shoulder examination, a thorough elbow examination begins with an evaluation of the cervical spine. Shoulder and wrist examination must be performed also to rule out a referred etiology for the current complaint. In addition, the complete upper extremity examination will reveal any other disabilities from joints above or below the elbow that may contribute to the patient’s functional deficit.
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Figure 5c.19 Lateral side of elbow illustrating the palpable bony landmarks: lateral epicondyles (E), radial head (R), and olecranon (O).
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Tendons about the elbow are then systematically palpated. Each tendon should be palpated for continuity on active contraction of the corresponding muscle group. The presence of local tenderness, pain with resisted activity, and pain with passive stretch of a tendon suggests tendinopathy. For example, the common extensor origin is just distal to the lateral epicondyle. Local tenderness, pain with resisted active wrist extension, and pain with passive wrist flexion all suggest a diagnosis of lateral epicondylitis (tennis elbow). Similarly, pain over the common flexor-pronator origin just distal to the medial epicondyle along with pain with resisted active wrist flexion and passive wrist extension suggest medial epicondylitis (golfer’s elbow). After examining the common flexor and extensor origins, the triceps tendon is examined. The triceps tendon inserts into the olecranon, and palpation may reveal a prominent traction spur (Fig. 5c.17). The distal biceps tendon can then be identified in the middle of the antecubital fossa just lateral to the brachial artery. The biceps assists in elbow flexion and is also the primary muscle responsible for forearm supination. A ruptured distal biceps tendon (reverse Popeye sign) can be identified by having the patient perform resisted supination with the elbow in a flexed position and noting a lack of palpable tendon in the cubital fossa. Another symptom is a prominent bulge of the distal aspect of the biceps muscle. The elbow is then taken through both active and passive movements so that range of motion can be documented. Any crepitus from the ulnohumeral or radiocapitellar joints is noted. In addition to flexion and extension, forearm rotation must also be documented. Limitation of motion or pain on forearm rotation mandates a detailed wrist examination to rule out any pathology at the distal radioulnar joint. Normal elbow range of motion is from full extension (0 degrees) to 145 degrees of flexion. Normal forearm rotation is from 75 degrees of pronation to 85 degrees of supination.2 For a patient to perform most activities of daily living, range of motion from 30 degrees to 130 degrees of flexion and forearm rotation from 50 degrees of pronation to 50 degrees of supination (i.e., 100 degrees of flexion-extension and a 100-degree arc of forearm rotation) is necessary.11 Stability testing of the elbow can be challenging, but in the setting of occupational disorders elbow instability is an infrequent finding. One of the challenges of instability testing is that valgus and varus stability tests require rotationally stabilizing the humerus. From full extension to 20 degrees of flexion the collateral ligaments cannot be isolated, because bony contributions to stability are provided by the seating of the olecranon in the olecranon fossa. Medial collateral ligament laxity has been shown to be greatest with the elbow in 20 degrees of flexion and the forearm pronated.16 To test the medial collateral ligament, the elbow is held flexed approximately 20 to 30 degrees with the forearm pronated and the arm maximally externally rotated as a valgus stress is applied. The presence of medial-sided pain and palpable medial joint line opening are signs of medial collateral pathology. Another test to stress the medial collateral ligaments is the “milking sign” performed by fully flexing the patient’s elbow and grasping the thumb to apply a valgus stress to the elbow. The test is positive if medial elbow pain is elicited. Varus stability is tested also with the elbow at 20 to 30 degrees of flexion but instead requires maximum internal rotation of the arm. The examiner can then stand behind the patient to apply
the varus stress and examine the lateral joint line. Recurrent instability occurs very infrequently after elbow dislocations, and the specific tests for the lateral ligament complex are well described.14 These tests are rarely important, however, in the setting of occupational elbow disorders. At elbow level the ulnar, radial, and median nerves may all be compressed. A detailed assessment of ulnar, radial, and median motor and sensory function, including inspection of the hand and forearm for muscle atrophy or fasciculations, should be performed. The ulnar nerve is palpated behind the medial epicondyle and once identified, the elbow can be brought from a position of extension to flexion to determine whether the ulnar nerve subluxes or dislocates anteriorly during flexion. Gently tapping over the nerve may produce paresthesia radiating into the small finger and ulnar half of the ring finger (Tinel’s sign at the cubital tunnel), indicating nerve irritation. A further sign of ulnar nerve compression at the elbow is to hold the joint in a flexed position for 1 minute and observe for the development of paresthesias or numbness in the ring and small fingers.17 Less commonly, the median and radial nerves may be compressed at elbow level.19,20 The median nerve runs adjacent to the brachial artery in the antecubital fossa and may be sensitive to pressure in the antecubital space or over the proximal portion of the pronator teres.20 Gentle tapping over the course of the median nerve may produce Tinel’s sign at the point of irritation. Compression in the antecubital space (at the lacertus fibrosis) is tested by actively supinating the forearm against resistance with the elbow flexed beyond 120 degrees. For evaluating median nerve compression at the pronator teres, resisted pronation is performed with the elbow in extension. Compression of the median nerve may occur also as it travels under the flexor digitorum superficialis as can be determined with resisted flexion of the long finger.20 For radial nerve entrapment, Tinel’s sign along its course may likewise be elicited. Perhaps the most important point of examining for radial nerve entrapment is the location of the pain. Pain emanating from radial compression is often associated with tenderness approximately 4 to 5 cm distal to the lateral epicondyle, whereas the pain of lateral epicondylitis is present adjacent to the lateral epicondyle.15
Diagnostic testing Routine diagnostic studies for elbow disorders begin with plain radiographs. A standard elbow series consists of an AP (Fig. 5c.20), a lateral (Fig. 5c.17), and an oblique film.18 With a history of trauma, it is particularly important to confirm that the radial head is in joint as evidenced by its lining up with the capitellum on all views. At the same time, any radial head deformity should be noted, as well as signs of radiocapitellar degenerative changes. A radial head view can be requested also if the radial head cannot be adequately assessed (Fig. 5c.21). The ulnohumeral joint can then be studied on the radiographs. In cases of degenerative joint disease, osteophyte formation medially or laterally off the ulnohumeral joint is a common finding on the AP view, and the lateral view may demonstrate osteophytes off the coronoid or tip of the olecranon. In cases where pathology about the olecranon is suspected or if loose bodies are a possibility, an
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Figure 5c.22 Axial view of elbow showing the olecranon (O), trochlea of the distal humerus (T), medial epicondyle (ME), and lateral epicondyle (LE).
Figure 5c.20
Standard anteroposterior radiograph of the elbow.
Figure 5c.21
Radial head view.
axial view of the flexed elbow can be helpful (Fig. 5c.22). For cases of suspected medial and lateral instability, stress views demonstrate abnormal joint widening. When in doubt, comparison views of the unaffected side can be obtained. A complete interpretation of standard radiographs should also include an assessment of soft tissue shadows for signs of swelling or effusion. Seen with cases of elbow effusion, a radiolucent area posterior to the olecranon fossa represents visualization of the posterior fat pad. Anteriorly, it is normal to see a thin concave radiolucent fat pad; however, a convex fat pad known as a “sail sign” indicates an elbow effusion. CT is often helpful in the setting of trauma to identify osseous loose bodies (Fig. 5c.23) or for cases where the osseous anatomy is unclear on standard radiographs.10 Offering the benefit of soft tissue assessment, MRI is ideal for evaluating cases of suspected cartilaginous loose bodies, assessment of tendons when the clinical examination is unclear, assessment of collateral ligaments, or evaluation of soft tissue masses.10,18 It is helpful also in cases of peripheral nerve compression by suspected soft tissue masses such as cysts within the cubital tunnel or synovitis extending into the radial tunnel. Proliferative synovial disorders presenting as an isolated synovitis of unknown etiology are also well suited to MRI evaluation. Although less commonly used in elbow disorders, ultrasound is useful to evaluate fluid collections around the joint and to assess the continuity of superficial muscle tendon units such as the triceps and biceps when the clinical examination is uncertain. It has been used also to investigate for intraarticular loose bodies10; however, because ultrasound requires an experienced ultrasonographer, it is less commonly used than CT or MRI in that setting. Electrodiagnostics can be particularly useful in the patient with neurologic symptoms or signs. Electromyography and nerve conduction studies are particularly useful to determine the presence, location, and extent of peripheral nerve compression
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should be carried out in suspected cases of infection or for isolated effusions of unknown etiology.
REFERENCES 1.
Figure 5c.23 Computed tomography showing a bony loose body in the olecranon fossa.
or to identify a brachial plexus lesion or cervical radiculopathy. Electrodiagnostic studies for cubital tunnel syndrome and posterior interosseous nerve compression syndrome often demonstrate electrophysiologic abnormalities and are helpful to confirm the diagnosis.15,17 In contrast, electrodiagnostic studies in cases of radial tunnel syndrome and pronator syndrome are usually normal.19,20 Diagnostic blocks about the elbow are much less common than for assessment of shoulder disorders but may on occasion be useful. Local anesthetic injection into the radial tunnel distal to the lateral epicondyles may help to distinguish cases of radial tunnel syndrome from lateral epicondylitis.15 Similarly, a local anesthetic block may be used at a potential site of median nerve compression at the elbow to determine whether it is responsible for the patient’s pain.20 Although less commonly used for elbow disorders, technetium bone scanning may be useful to identify biologically active areas of bone in cases of occult infection, tumor, or early degenerative disease. When considering a diagnosis of inflammatory disease or infection, routine blood tests such as a complete blood count, erythrocyte sedimentation rate, C-reactive protein, rheumatoid factor, and antinuclear antibodies may be useful. Joint aspiration
Bencardino JT, Garcia AI, Palmer WE: Magnetic resonance imaging of the shoulder: rotator cuff. Top Magn Reson Imag 14(1):51-67, 2003. 2. Boone DC, Azen SP: Normal range of motion of joints in male subjects. J Bone Joint Surg 61A:756-759, 1979. 3. Chen AL, Rokito AS, Zuckerman JD: The role of the acromioclavicular joint in impingement syndrome. Clin Sports Med 22:343-357, 2003. 4. Frost P, Bonde JP, Mikkelsen S, et al: Risk of shoulder tendinitis in relation to shoulder loads in monotonous repetitive work. Am J Indust Med 41(1):11-18, 2002. 5. Gerber C, Hersche O, Farron A: Isolated rupture of the subscapularis tendon. J Bone Joint Surg 78A:1015-1023, 1996. 6. Gerber C, Krushell RJ: Isolated rupture of the subscapularis tendon: clinical features in 16 cases. J Bone Joint Surg 73B:389-394, 1991. 7. Gold RH, Bassett LW: Disorders of the shoulder: plain radiographic diagnosis. In LL Seeger, ed: Diagnostic imaging of the shoulder. Baltimore, 1992, Williams & Wilkins. 8. Hawkins RJ, Bokor DJ: Clinical evaluation of shoulder problems. In CA Rockwood Jr, FA Matsen, eds: The shoulder, ed 2. Philadelphia, 1998, WB Saunders. 9. McQuade KJ, Dawson J, Smidt GL: Scapulothoracic muscle fatigue associated with alterations in scapulohumeral rhythm kinematics during maximum resistive shoulder elevation. J Orthop Sports Phys Ther 28(2):74-80, 1998. 10. Miller TT: Imaging of elbow disorders. Orthop Clin North Am 30(1):21-36, 1999. 11. Morrey BF, Askew LJ, An KN, Chao EY: A biomechanical study of normal functional elbow motion. J Bone Joint Surg 63A:872-877, 1981. 12. Morrey BF, Itoi E, An K: Biomechanics of the shoulder. In CA Rockwood Jr, FA Matsen, eds: The shoulder, ed 2. Philadelphia, 1998, WB Saunders. 13. Neer CS II: Impingement lesions. Clin Orthop Relat Res 173:70-77, 1983. 14. O’Driscoll SW: Classification and evaluation of recurrent instability of the elbow. Clin Orthop Relat Res 370:34-43, 2000. 15. Plate AM, Green SM: Compressive radial neuropathies. Instruct Course Lect 49:295-304, 2000. 16. Pomianowski S, O’Driscoll SW, Neale PG, Park MJ, Morrey BF, An KN: The effect of forearm rotation on laxity and stability of the elbow. Clin Biomech 16:401-407, 2001. 17. Posner MA: Compressive ulnar neuropathies at the elbow. I. Etiology and diagnosis. J Am Acad Orthop Surg 6(5):282-288, 1998. 18. Potter HG. Imaging of posttraumatic and soft tissue dysfunction of the elbow. Clin Orthop Relat Res 370:9-18, 2000. 19. Regan WD, Morrey BF: Physical examination of the elbow. In BF Morrey, ed: The elbow and its disorders. Philadelphia, 2000, WB Saunders. 20. Rehak DC: Pronator syndrome. Clin Sports Med 20(3):531-540, 2001. 21. Rempel DM, Harrison RJ, Barnhart S: Work-related cumulative trauma disorders of the upper extremity. JAMA 267:838-842, 1992. 22. Richards RR, Bigliani LU, Gartsman GM, Iannotti JP, Zuckerman JD: A standardized method for the assessment of shoulder function. J Shoulder Elbow Surg 3:347-352, 1994. 23. Teefey SA, Middleton WD, Yamaguchi K: Shoulder sonography: state of the art. Radiol Clin North Am 37:767-785, 1999. 24. Tennent TD, Beach WR, Meyers JF: A review of the special tests associated with shoulder examination. Part I. The rotator cuff tests. Am J Sports Med 31(1): 154-160, 2003. 25. Tennent TD, Beach WR, Meyers JF: A review of the special tests associated with shoulder examination. Part II. Laxity, instability, and superior labral anterior and posterior (SLAP) lesions. Am J Sports Med 31(2):301-307, 2003. 26. Tillander B, Franzen LE, Karlsson MH, Norlin R: Effect of steroid injections on the rotator cuff: an experimental study in rats. J Shoulder Elbow Surg 8(3):271-274, 1999. 27. Walch G, Boulahia A, Calderone A, Robinson AHN: The “dropping” and “hornblower’s” signs in evaluation of rotator cuff tears. J Bone Joint Surg 80B(4):624, 1998. 28. Zuckerman JD, Kummer FJ, Cuomo F, Simon J, Rosenblum S: The influence of coracoacromial arch anatomy on rotator cuff tears. J Shoulder Elbow Surg 1:4-12, 1992.
CHAPTER
5d
Treatment of Shoulder Disorders Anthony M. Buoncristiani, Paul H. Marks, and Freddie H. Fu
Disorders of the shoulder girdle are very common and can limit participation in vocational, recreational, and professional activities. Developing an approach to the management of shoulder disorders relies on appropriate history taking, physical examination, and imaging. This chapter outlines the treatment of most common shoulder problems, including rotator cuff pathology; instability; fracture and dislocations of the sternoclavicular joint, clavicle, acromioclavicular joint, and proximal end of the humerus; frozen shoulder; and degenerative joint disease.
ROTATOR CUFF DISEASE IN THE SHOULDER In an older patient who complains of shoulder pain, the diagnosis of rotator cuff disease must be considered. This entity is very common and important. In 1934, Codman’s classic publication32 summarized 25 years of observations on the musculotendinous cuff and its components. Coleman also discussed ruptures of the supraspinatus tendon and performed the first repair of the cuff in 1909. Although there have been recent advances in diagnosis and imaging of the rotator cuff, current views and treatments are quite similar to concepts proposed 50 years ago.
Anatomy and function The components or musculotendinous units of the rotator cuff are known to function as dynamic stabilizers for the glenohumeral joint. Electromyographic and biomechanical studies have demonstrated the role of the rotator cuff in providing support of the capsule and preventing excessive anterior and posterior movement. Studies have suggested that the rotator cuff contributes between one third and one half of the power of the shoulder in abduction and at least 80% of the power in external rotation.30 The rotator cuff, which consists of the subscapularis, supraspinatus, infraspinatus, and teres minor, functions to approximate the humeral head to the glenoid cavity. The supraspinatus assists the deltoid in abduction, whereas the subscapularis, infraspinatus, and teres minor serve to depress the humeral head during elevation of the arm. Depression of the humeral head during elevation of the arm helps to avoid impingement. The infraspinatus and teres minor function to externally rotate the arm. These muscle actions may also reduce the strain on the inferior glenohumeral ligament with the arm abducted and essentially rotated.28 In this position, they serve to pull the humeral head posteriorly. The subscapularis internally rotates the arm. It serves
as an effective restraint to external rotation and anterior translation of the humeral head with the arm at the side of the body; however, it is ineffective in doing so with the arm abducted to 90 degrees.147 At 90 degrees of abduction, the subscapularis lies above the equator of the humeral head and cannot reinforce the anterior aspect of the shoulder. The vascular anatomy of the cuff tendons has been reported by many authors. Most have concluded that the supraspinatus has a “critical zone” that is prone to calcium deposits and potential rupture.103 Rathbun and MacNab122 found that filling of the cuff vessels was dependent on the position of the arm at the time of injection. They documented poor filling of the supraspinatus tendon near its attachment to the greater tuberosity and suggested that tendon failure may be caused by “constant pressure from the head of the humerus which tends to wring out blood supply to the tendon when the arm is held in the resting position of adduction and neutral rotation.”122 The long head of the biceps may be considered a part of the rotator cuff. It attaches to the supraglenoid tubercle of the scapula. This structure is positioned to function as a humeral head depressor. It also guides the humeral head as it is elevated.141 The concomitant tears that occur in the rotator cuff and biceps tendon attest to the close functional relationship between these two structures. Neer stated that “impingement of the rotator cuff beneath the coracoacromial arch has been recognized as one of the causes of chronic disability of the shoulder.” Anatomically, this problem occurs during elevation of the arm anterior to the scapular plane. He attributed pathologic changes of the rotator cuff to mechanical impingement and believed that most rotator cuff tears were due to attritional tears from a narrow supraspinatus outlet.24,106 Additionally, Neer discussed associated alterations on the undersurface of the anterior third of the acromion, the coracoacromial ligament, and in time the acromioclavicular joint. He described three different stages of impingement. Stage I usually occurs in patients less than 25 years old. Pathology is characterized by edema and hemorrhage. The clinical course is reversible and conservative treatment is suggested. Stage II is seen in the 25-year-old to 40-year-old age group. Pathology includes fibrosis and tendinitis. These patients have activity-related pain, and treatment may be surgical if there is no response to rehabilitation. Stage III disease typically occurs in patients greater than 40 years old. Pathology in this group includes acromioclavicular spurs and full-thickness cuff tears. These patients have progressive disability and are often candidates for acromioplasty and repair. Bigliani et al17 reported on a morphologic study in which the variation in shape of the acromion was correlated with tears of the rotator cuff. They described three types of acromion. Type I has a flat profile, type II has a smooth curve, and type III has an angular curve or “hook type” of acromion. The latter type was noted to be present in higher frequency with complete tears of the rotator cuff. Neer108 suggested an important role of the rotator cuff in maintaining a so-called watertight joint space and allowing continuation of the normal synovial fluid mechanics that maintain cartilage nutrition and may prevent secondary osteoarthritis. The scapulothoracic joint must also be considered when rotator cuff problems are managed. The scapula sits on the posteriorlateral aspect of the thorax. It is angled approximately 30 degrees anterior to the frontal plane. As a result of this, abduction of the
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arm relative to the scapula occurs 30 to 40 degrees anterior to the frontal plane. Abduction of the arm in the scapular plane places the rotator cuff muscles in their most efficient position and reduces tension on the joint capsule. The scapula is approximated to the thorax by the scapulothoracic muscles. These include the upper, middle, and lower trapezius, serratus anterior, rhomboideus major and minor, levator scapulae, pectoralis minor, and subclavius. These muscles must function to position and stabilize the scapula during movement of the arm. Inman et al70 described scapulohumeral rhythm as the coordinated motion between the scapula and humerus that occurs when the arm is elevated through its full range. During the first 30 degrees of elevation of the arm, motion primarily occurs at the glenohumeral joint and the scapula is said to be setting. Elevation of the arm beyond this occurs in a 2:1 ratio of glenohumeral to scapulothoracic motion. The total arc of elevation is a result of approximately 120 degrees of motion of the glenohumeral joint and 60 degrees of motion of the scapulothoracic joint. Motion of the scapulothoracic joint occurs as a result of elevation and rotation at the sternoclavicular and acromioclavicular joints. Normal scapulohumeral rhythm is important for normal function of the shoulder girdle; it allows for maintenance of the length-tension relationship of the rotator cuff muscles, which allows them to function efficiently throughout the full arc of motion. Additionally, proper movement of the scapula positions the glenoid under the humeral head to enhance glenohumeral stability. Poor motion and positioning of the scapula have been linked to impingement and rotator cuff problems.
Classification of injury Cuff tendon failure can be classified by various criteria. These include partial- or full-thickness tears, acute or chronic injury, and traumatic or degenerative etiology. The cuff pathology is almost always near the tendon insertion. It nearly always occurs in the supraspinatus component of the rotator cuff, because this is the area that is subject to mechanical impingement against the coracoacromial arch. A full-thickness tear extends from the bursal side through to the humeral aspect of the cuff. A partial tear may involve the bursal or the humeral side of the tendon. Acute tears occur suddenly and are found in only a relatively small portion of patients with rotator cuff pathology. Chronic tears are more common and are usually insidious in onset. It should be noted that the size of the complete tear can also be used to describe the pathology. A “massive tear” is the term used by Cofield33 to describe a defect more than 5 cm in diameter. The incidence of full-thickness rotator cuff tears has been documented in various cadaver studies as being between 5% and 26.5%.111,157 The incidence of cuff pathology has also been documented in clinical subjects. Age has been found to correlate with incidence.102 Moseley102 found that the incidence rose dramatically with the age of the patient. Traumatic cuff tears have also been found in patients with anterior-inferior dislocations. Arthrographically documented tears were seen in 30% in the fourth decade and 60% in the sixth decade.119 The role of secondary impingement and eccentric overload has been recognized in the pathogenesis of rotator cuff injuries in
throwing athletes.71 It is hypothesized that in throwing athletes, weakness and fatigue of the rotator cuff results in overload of the passive restraints. This results in laxity and subluxation of the glenohumeral joint and leads to secondary impingement. Additionally, the rotator cuff muscles are eccentrically overloaded as they attempt to stabilize the head of the humerus in the glenoid cavity. Repetitive eccentric overloading of the rotator cuff results in inflammation and injury to the rotator cuff tendons.
Clinical presentation History Most patients with rotator cuff pathology are over 40 years of age. Fifty percent of patients recall a traumatic incident that initiated the symptoms. They usually do not describe a major injury. One can usually elicit a history of recurrent “bursitis” and/or “tendonitis”; these episodes often resolve with rest or other conservative measures. With time, there is increasing shoulder discomfort. This is noted with forward elevation and external rotation of the arm against resistance. Patients may have complaints of nocturnal discomfort, particularly when sleeping on the affected side. Patients may describe crepitation with movement.
Physical examination The physical findings may be related to the underlying pathology. Crepitation would relate to the lack of smooth surfaces in the subacromial space. Weakness of flexion, abduction, and external rotation relates to loss of the tendonous attachment to bone. Upward riding of the humeral head on deltoid contraction results from a loss of the depressor action of the rotator cuff, and this further exacerbates impingement and cuff degeneration. Partial tears of the rotator cuff may cause pain with motion, crepitation, and stiffness. A complete tear may reveal a palpable defect of the cuff. As previously noted, associated tendonitis of the biceps may be present, and this should be documented. The patient should be examined for impingement signs. Specifically, this includes full-forward flexion with pain at terminal motion, otherwise known as the Neer impingement sign. Pain may also be elicited with the Hawkins test, a provocative test that elicits pain from impingement by bringing the arm into forward flexion, adduction, and internal rotation, thus driving the supraspinatus insertion into the coracoacromial arch and creating pain. The acromioclavicular joint can be stressed with cross-chest adduction. Stability of the biceps tendon should be elicited. Bicipital pathology tests include those of Speed and Yergason. Speed’s test reproduces pain with resisted forward elevation of the humerus against an extended elbow. The pain is localized to the bicipital groove area. Yergason’s test reproduces pain over the bicipital groove with resisted supination of the forearm with a flexed elbow. Muscle strength testing about the shoulder is part of the neurologic examination and should be documented.
Differential diagnosis When assessing a patient with a suspected tear of the rotator cuff, one should consider other underlying pathologies in the differential diagnosis. These include cuff tendonitis, bursitis, frozen shoulder, cervical spondylosis, suprascapular neuropathy,
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snapping scapula, acromioclavicular or glenohumeral arthritis, and glenohumeral instability.
Methods of treatment Despite rotator cuff pathology, not all patients are symptomatic, so aggressive treatment is not indicated in an asymptomatic shoulder. In a symptomatic shoulder, the goals of treatment are elimination of pain, restoration of function, and prevention of recurrence or progression.
Nonoperative treatment Nonoperative modalities of treatment include physical therapy, rest, elimination of aggravating activities, and administration of antiinflammatory medications and steroid injections. In one study, 44% of the patients with arthrogram-proven rotator cuff tears were shown to respond to nonoperative treatment.143 Successful nonoperative management of impingement and rotator cuff injuries requires an understanding of the anatomy and biomechanics of the shoulder girdle and an appreciation of the underlying etiology. Treatment is based on the patient’s signs and symptoms at examination. Progression should be based on the response to treatment. General goals for the rehabilitation of an individual with rotator cuff pathology are listed in the box on this page. Patients with acute signs and symptoms complain of constant pain at rest that is referred distally over the deltoid insertion, and they generally exhibit decreased motion with pain before resistance with passive testing. During this phase, the focus of treatment is on pain control. This includes the use of relative rest to avoid those activities that aggravate the symptoms. Additionally, the patient is encouraged to position the arm in abduction in the scapular plane. This reduces pain and prevents “wringing out” of the rotator cuff as described earlier. Pain-relieving modalities are used and may include ice, moist heat, and transcutaneous electrical nerve stimulation. Gentle mobilization and range-of-motion exercises are performed to prevent loss of motion and development of a stiff shoulder. Patients in the subacute phase have intermittent pain that is more localized to the shoulder. The pain may be aggravated by repeated movements. Motion may be limited and resisted testing may be weak and painful. During this period, treatment continues to consist of relative rest, and modalities can be used to decrease pain and promote healing. The intensity of exercise can be progressed. The focus is on restoration of the normal motion necessary for function of the individual. Full range of motion
Goals of rotator cuff treatment Control pain Restore motion Improve rotator cuff function Strengthen scapular muscles Correct posture Resume function Prevent recurrence
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must be restored, with particular emphasis on restoration of external rotation. External rotation is necessary so that the greater tuberosity can clear the acromion as the arm is elevated overhead. Joint mobilization techniques should be used if glenohumeral mobility is decreased. Often, the posterior capsule is tight and requires stretching. Stretching exercises can also be used to increase motion. Joint mobilization should be avoided for patients with hypermobility. For these patients, the focus of treatment should be on the development of dynamic stabilization. This requires strengthening of the rotator cuff and proprioceptive exercises to retrain the muscles to dynamically stabilize the glenohumeral joint. Finally, strengthening of the axioscapular muscles (serratus anterior, trapezius) is important to establish normal scapulothoracic motion and decrease the role of scapulothoracic dyskinesia in impingement biomechanics. Strengthening exercises begin with isometrics with the shoulder positioned in 30 to 45 degrees of abduction in the scapular plane. Active and light progressive resisted exercises are initiated as tolerated. These should specifically strengthen the rotator cuff muscles. Several studies have demonstrated maximum electromyographic activity in the rotator cuff muscles with a variety of exercises.18,146 The supraspinatus may be strengthened by performing abduction in the scapular plane with the arm internally rotated, but caution must be taken to avoid further impingement with this exercise. Additionally, the supraspinatus may be strengthened by performing prone horizontal abduction with the arm abducted to 100 degrees in the frontal plane and maximally externally rotated. The infraspinatus may be strengthened by performing prone horizontal abduction with the arm abducted to 90 degrees in the frontal plane and externally rotated. The teres minor may be strengthened by prone external rotation with the arm abducted to 90 degrees. The subscapularis may be strengthened by performing internal rotation with the arm at the side. Both eccentric and concentric phases of the rotator cuff exercises are emphasized. Adding excessive resistance to these exercises should be avoided because it will only result in substitution by larger muscles of the shoulder complex. These exercises must be performed precisely without substitution to develop specific muscles of the rotator. Internal and external rotation with the arm at the side of the body will not fully develop the rotator cuff. Strengthening exercises for the scapular muscles should also be included. Particular emphasis should be placed on strengthening the middle and lower trapezius as well as the serratus anterior. Successful treatment of rotator cuff injuries is dependent on an understanding of the underlying anatomy and biomechanics, as well as an appreciation of the underlying etiology. Treatment must be appropriate for the patient’s stage of inflammation. Knowledge of the functional demands placed on the shoulder is also necessary. Signs of overly aggressive treatment must be recognized and include increased pain greater than 2 hours after treatment and/or regression of motion or strength. If the patient’s symptoms do not improve after 3 to 6 months, further investigation with imaging modalities as discussed before is indicated. Some would suggest that nonoperative treatment should continue, but only about 50% of such patients respond.
Operative treatment Samilson and Binder135 outlined the following indications for operative repair: (1) a patient “physiologically” younger than
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60 years, (2) a clinically or arthrographically demonstrable fullthickness cuff tear, (3) failure of the patient to improve with nonoperative management for a period not less than 6 weeks, (4) a need to use the involved shoulder in overhead activities in the patient’s vocation or avocation, (5) full passive range of motion, (6) a patient’s willingness to exchange decreased pain and increased external rotator strength for some loss of active abduction, and (7) the ability and willingness of the patient to cooperate. Currently, anterior acromioplasty with limited detachment of the deltoid appears to be the most direct, least harmful, and most effective procedure for persistent rotator cuff tendonitis. Ellman43 documented an 88% satisfactory result rate in patients who have chronic impingement treated by arthroscopic acromioplasty. Simple debridement of partially torn rotator cuffs has allowed an 85% rate of return to activity in a group of patients treated by Andrews et al.7 Although acromioplasties are still routinely performed in conjunction with rotator cuff repairs, recently Matsen and coworkers91 published their results on 96 patients who underwent mini-open rotator cuff repair without acromioplasty. Significant improvement in self-assessed shoulder comfort and in each of the 12 shoulder functions was observed. Burkhart26 published results of arthroscopic treatment of massive rotator cuff tears. He treated 10 patients with painful, massive, complete tears involving primarily the supraspinatus with arthroscopic acromioplasty and rotator cuff debridement. All patients except one had normal preoperative motion and strength. These patients maintained adequate mechanics of the glenohumeral joint during abduction because there is a balance of two important force couples.120 The first force couple is in the coronal plane and consists of the rotator cuff and deltoid such that the rotator cuff maintains a fixed fulcrum for rotation of the deltoid during abduction. The second force couple acts in the transverse plane and consists of a balance between the anterior and posterior portions of the rotator cuff that allows the humeral head to maintain centering during rotation of the glenohumeral joint. This study showed that normal shoulder function is possible with massive unrepaired rotator cuff pathology. Similar results were seen with Motycka et al104 with their cohort of 64 patients with large rotator cuffs tears followed for a mean period of 5 years. As arthroscopic techniques improve, more surgeons are treating rotator cuff pathology arthroscopically. Several articles have been published demonstrating equal results comparing all arthroscopic versus mini-open rotator cuff repair.25,137,148 However, for most cuff tears that come to operative management, an open approach is still used. The extent of the rotator cuff tear is ascertained at the time of surgery, and the torn edges of the rotator cuff are identified. The following sequence has been suggested for closure: (1) resection of the bursal scar, (2) identification of the tear, (3) assessment of tissue mobility, (4) mobilization of the rotator cuff, and (5) planning for closure, either side to side or in most cases to a trough in bone.81 Concomitant acromioplasty is performed in these patients. Long-term results of this technique were reported by Bigliani et al.16 In patients with an average follow-up of 7 years, 85% had satisfactory results with adequate pain relief and 92% could raise the arm above the horizontal plane. Many techniques have been described for massive tears that cannot be treated as just outlined. These options include accepting the defect, moving local tissue into the deficient area, and inserting a free graft of local or distant tissue, that is, either an allograft,
xenograft, or prosthetic material.34 Latissimus dorsi transfer for the treatment of massive tears of the rotator cuff has been described by Gerber et al.53,55 In cases with good subscapularis function but irreparable defects in the external rotator tendons, restoration of approximately 80% of normal shoulder function was obtained. In fact, in a cohort of patients with massive rotator cuff tears, Harryman et al59 reported patient satisfaction regarding comfort and function despite greater than 50% demonstrating recurrent tears determined by ultrasonography.
Postoperative care Postoperative care after surgery on the rotator cuff is dependent on the status of the deltoid, the size of the repair (i.e., small versus massive), the ability to mobilize tissue, and the safe range of motion achieved at surgery. Therefore, postoperative care must be individualized to the patient and the procedure rather than everyone being treated with a standardized protocol. Immediate postoperative care after rotator cuff surgery should protect the healing structures, control pain, and restore range of motion. For small tears, the arm is generally immobilized at the side for 4 to 6 weeks with a deltoid-splitting technique. Painrelieving modalities can be used to improve comfort. Passive range-of-motion exercises are begun immediately postoperatively and performed several times per day in the range prescribed by the surgeon. Once sufficient healing has occurred (i.e., at 4 to 6 weeks), active assisted and active range-of-motion exercises can be initiated. Strengthening exercises using isometrics can also be initiated at this time. Postoperative management after the repair of massive tears in which the deltoid was detached includes immobilization for up to 6 weeks. Generally, an abduction pillow is used to reduce tension on the postoperative repair. Modalities are used to control pain as necessary. Passive range of motion is performed for the first 6 weeks. The safe range of motion achieved at surgery must be communicated by the physician to the therapist. Active assisted and active range-of-motion exercises are delayed for 6 weeks to ensure adequate tissue healing. Isometric strengthening exercises are usually delayed until 12 weeks after surgery. Once sufficient time for healing has passed, the patient is gradually progressed through the rehabilitation program. Initial emphasis is on restoring the motion necessary for normal function of the shoulder complex. Attention is directed at reestablishing normal scapulohumeral rhythm. Additionally, strengthening exercises focus on developing the rotator cuff and scapular muscles. Functional activities are incorporated to allow gradual resumption of function. The patient must be willing to accept some limitation in level of function. In patients who complain of shoulder pain, pathology of the rotator cuff is important to consider because of the large spectrum of disease from impingement to complete and massive tears of the rotator cuff. Many patients may respond to nonoperative therapy, although slightly fewer than 50% may fall into this group. After careful history taking and physical examination, most patients can initiate a course of nonoperative management. In those patients who do not respond, imaging of the cuff is the next appropriate step in the algorithm. In patients with simple tendinitis or impingement, conservative management is continued. If symptoms persist, acromioplasty, either open or with endoscopic techniques, can be considered. Patients with complete disruption
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or full-thickness disruption may be candidates for other operative approaches as outlined earlier. The most direct and simple repair technique is often the most appropriate: progression from direct tendon repair, to repair of bone, to transposition of local tissue, to grafting. Postoperative support should vary according to need. Physiotherapy after surgery is a vital part of the treatment protocol.
SHOULDER INSTABILITY A rational approach to surgical management of instability should be based on an understanding of the definition of successful repair and an appreciation of the reasons for failure. Successful surgery is traditionally defined as elimination of recurrence of instability. According to this definition, up to a 97% rate of excellent results has been reported with a large variety of procedures.* Both operative and nonoperative treatment must be based on an appreciation of the spectrum of glenohumeral instability. A classification system for shoulder instability should include the following factors: frequency of occurrence, etiology, direction of instability, and degree of instability. One can distinguish between traumatic recurrent instability and atraumatic recurrent instability. The former occurs as a result of a single episode of macrotrauma, is usually unilateral, is less responsive to a rehabilitation program, and has the Bankart lesion as the most common primary pathology. The latter may occur as the result of repetitive microtrauma (e.g., swimming or throwing), may be bilateral, is responsive to a therapy program, and has excessive capsular laxity as the most common primary lesion. Voluntary instability is found in a subset of individuals with a traumatic instability. These patients can be further subdivided into two groups. Group I patients with voluntary instability have an arm position-dependent instability that is usually posterior but may be anterior. These patients usually respond to rehabilitation and do not have an underlying psychiatric disturbance. If they remain refractory to conservative treatment, they may be well managed by surgery. Group II patients have the ability to selectively contract muscles to create a dislocation. Some of these individuals have an underlying psychiatric disturbance and use their instability as a trick to control their environment.131 These individuals are not candidates for surgical treatment and are better managed by psychiatric counseling and conservative rehabilitation. There is a spectrum of glenohumeral instability in which subluxation and dislocation represent degrees of injury to the capsulolabral structures. Dislocation is defined as complete separation of the articular surfaces, and subluxation represents increased humeral head translation within the glenoid to a degree beyond normal tissue laxity. Because the parameters of normal glenohumeral translation have not yet been fully defined,136 clinical subluxation is defined as detectable glenohumeral translation with accompanying symptoms. The increased use of arthroscopy has led to the characterization of an additional group within this spectrum of instability. This group appears to be throwing athletes in whom symptomatic labral tears or attrition develops secondary to increased glenohumeral translation without clinical subluxation.4,6,9
*References 1, 2, 6, 14, 21, 22, 29, 41, 47, 72, 84-88, 90, 97, 101, 109, 112, 124, 130, 139,144.
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Appreciation of the direction of instability is critical to selection of a successful approach to treatment. Traditionally, 95% of all instability has been observed to be simple anterior instability; however, there has been increasing recognition of significant posterior instability in athletes who are loose-jointed individuals.8,52 Posterior instability is usually subluxation inasmuch as dislocation occurs only with rarer traumatic episodes.52 Since Neer and Foster’s article on multidirectional instability (MDI), there has been an increasing awareness of both atraumatic and traumatic capsular laxity occurring in more than one direction. The main direction of instability is usually anterior, although inferior instability appears to be the hallmark of this diagnosis.5,37,49,109,112 Traditional procedures that treat anterior capsular laxity by Bankart repair or capsular plication do not adequately manage the associated components of inferior and/or posterior instability. In the worst scenario, these procedures can actually lead to instability in the opposite direction. Failure of the operative approach may occur at any point in the course of treatment and may be due to either physician or patient error or a combination of the two. For a successful outcome, the diagnosis, surgical procedure, and rehabilitation must be individualized and appropriate in each case. A correct diagnosis is critical in categorizing the instability and recommending the appropriate form of treatment. For example, a misdiagnosis of impingement or failure to recognize a concomitant rotator cuff tear in a patient over the age of 50 may lead to failure despite a technically adequate anterior stabilization procedure. Additionally, a Bankart procedure that ignores the inferior component of capsular laxity in a patient with MDI will fail. Assuming a correct diagnosis, a variety of technical pitfalls is encountered with each type of stabilization procedure. Appropriate anterior capsular tension must be restored, and procedures that over-tighten the anterior capsule or subscapularis tendon may result in serious functional limitation of external rotation. In some cases this may lead to osteoarthritis or exacerbation of posterior instability in patients with unrecognized MDI.63,159 Knowledge of the regional anatomy or an inadequate exposure predisposes to an inadequate repair and possible neurovascular injury.125 Assuming the correct diagnosis and correct procedure, the failure of patient compliance or inappropriate rehabilitation may result in limited range of motion or recurrence of instability. To avoid complications of treatment, it is critical to be both sensitive and specific in the initial diagnostic assessment of the individual’s shoulder complaints. Both the degree and direction of any instability must be accurately determined, and any associated fractures, neurovascular injury, or concomitant rotator cuff pathology must be identified.
Impingement syndrome Impingement syndrome may occur either as an isolated entity or in combination with instability.62,156 Hawkins and Hawkins63 identified several patients whose untreated impingement syndrome was the cause of their ongoing pain after anterior shoulder stabilization. This should not be confused with the common finding in patients with anterior instability of pain located posteriorly in combination with clinical findings consistent with impingement
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syndrome.64,150 This impingement pain is likely a secondary phenomenon related to repetitive traction and compression of the rotator cuff during subluxation or to overwork of the rotator cuff muscles in an attempt to maintain the humeral head centered in the glenoid in the setting of capsular insufficiency. Jobe et al72,134 described this overlap in the literature, and Altchek et al6 observed a 20% incidence of impingement symptoms in individuals with surgically confirmed anterior-inferior MDI. In most cases it is possible to correctly diagnose impingement syndrome from the history and examination; however, if this evaluation is inconclusive, examination under anesthesia and arthroscopic inspection assist in clarification of the diagnosis. Anterior shoulder instability in a patient older than 40 years of age is a unique situation that deserves special consideration if complications and failure of treatment are to be avoided. The association of concomitant anterior shoulder dislocation and rotator cuff tear has been reported by numerous orthopedic surgeons.† This concomitant injury may be missed if one is not attentive. Moreover, there is an increased risk for adhesive capsulitis in this older group of patients if early range of motion is not begun after reduction of a dislocation. The incidence of an associated rotator cuff tear in this group has been reported to be as high as 70% to 90%.62,94,95 Most recently, Neviaser et al113 and Hawkins et al62 increased our understanding of this problem. Anterior dislocation in an older individual may result in disruption of a rotator cuff that has undergone age-related attrition. The anterior capsulolabral structures are spared.62,123 McLaughlin92 and subsequently Craig38 termed this the posterior mechanism of anterior shoulder instability. In older patients with persistent external rotation and abduction weakness after the reduction of an anterior dislocation, physicians should avoid the trap of assuming an axillary nerve injury as the etiology.38,113 The overall incidence of clinically significant axillary nerve injury in this setting has been reported to be in the range of 9% to 18%.19,126 Neviaser et al113 observed an incidence of 7.8% for axillary nerve injury in association with rotator cuff tear after anterior dislocation. A suprascapular nerve injury is rare in the setting of anterior dislocation.38 In general, older patients have a lower rate of recurrence of instability after an initial episode of anterior instability.132 This is particularly true if there is an associated fracture of the greater tuberosity that reduces the range of motion of the joint and muscle strength.95,126 In older patients with an unrecognized rotator cuff tear, pain and weakness appear to be more common problems than recurrent instability.62,113 In a separate group of older patients, recurrent anterior shoulder instability develops as the result of an excessively redundant anterior capsule and no rotator cuff tear.77 These individuals typically demonstrate the stigmata of generalized ligamentous laxity, including thumb to forearm; hyperextension of the elbow, knee, and metacarpal joints; a history of easy bruising, hernias, and scar spreading; and excessive skin laxity. These features should be documented during the examination. An approach to treating older individuals (>45 years) after an initial shoulder dislocation is based on classifying such patients into three groups:
†References
32, 65, 93-95, 113, 142.
Group I: If after reduction no significant weakness of external rotation or abduction is found, immobilization should be continued no longer than 7 to 10 days. A gentle range-ofmotion program should begin and progressive supervised therapy should follow. Failure to move the shoulder early in these patients can result in marked limitation of motion. Group II: Patients with persistent pain and external rotation and abduction weakness likely have an associated rotator cuff tear. Early arthrography and electromyography should be performed to confirm this fact and to rule out any associated axillary nerve injury. Conservative treatment in this setting usually results in a poor outcome.63 Early repair of the rotator cuff generally yields good results, and surgery performed after a delay in diagnosis may be fraught with difficulty because the cuff tissues may become extensively scarred and difficult to mobilize.62,113 If the patient does have an associated axillary nerve injury, we would still perform an early repair of the cuff, although final function will likely be determined by return of axillary nerve function. Group III: Recurrent instability in older patients may be due to either a rotator cuff tear or excessive capsular laxity.62,77,113 Labral lesions may occur but are less common in this group. Examination usually reveals those patients with generalized ligamentous laxity, but an arthrogram is essential to clarify the status of the rotator cuff. It is prudent to know the pathology before surgery is attempted because most cuff pathology is best treated through an anterior superior approach with an acromioplasty, whereas anterior capsulolabral pathology is managed through a deltopectoral interval approach. It should be noted that Neviaser et al113 observed a significant subscapularis tear in all cases of recurrent instability. Fracture of the greater tuberosity, the second most common associated fracture after the Hill-Sachs lesion, occurs in about 10% of all anterior dislocations.92 In most cases this fracture reduces anatomically with reduction of the glenohumeral joint and recurrence of shoulder instability is actually less than if no fracture were present.92 Displacement of the greater tuberosity fragment more than 1 cm may result in residual impingement and blocked external rotation. In these cases, surgical reduction and fixation may be necessary. A glenoid rim fracture may occur with anterior dislocation and continued displacement of the anterior glenoid articular surface of greater than 25% to 35% results in recurrent instability.11,80,129 Computed tomography demonstrates this clearly, and surgical reduction and fixation may be necessary if residual displacement is greater than 2 mm. The axillary nerve is the most commonly injured neurovascular structure, with the reported incidence ranging from 5% to 33% in first-time dislocators.19,130 Both a motor and sensory examination should be performed before and after any reduction maneuver because complete motor paralysis may occur without any detectable hypoesthesia. Any residual neurologic deficit persisting longer than 3 to 4 weeks should be evaluated by electromyography.19 Most patients spontaneously recover over a 6-week period inasmuch as most of these injuries are neuropraxic in nature. The axillary artery is occasionally damaged with anterior dislocation because it is relatively fixed as it passes beneath the pectoralis minor and over the subscapularis.39,73,92,126 This is particularly the case in older individuals, in whom atherosclerosis
Chapter 5d
may render the vessels less compliant to displacement. Clinical findings include severe pain, expanding hematoma, and diminished peripheral pulses; an arteriogram should be performed urgently in such cases because timely repair is crucial to a successful outcome. Failure to recognize the voluntary aspect of a patient’s instability may result in the failure of any procedure for recurrent instability. Rowe et al131 described a typical patient in this group as an adolescent with an underlying psychiatric problem, without any prior history of significant trauma, who can voluntarily dislocate his shoulder and who has essentially normal radiographic findings. As already noted, group I patients are typically emotionally stable individuals with positional instability.52 Group I patients represent a subset of atraumatic voluntary instability, and if they fail to respond to conservative management, an operative procedure that reduces the excessive capsular laxity is a reasonable alternative. It is crucial to sort out this group from those in group II, who have a muscular-control type of voluntary instability that may be used as a trick to control the environment. These individuals are managed by psychiatric counseling and rotator cuff strengthening exercises. The spectrum of MDI includes those individuals with excessive ligamentous laxity (atraumatic type), those with instability resulting from repetitive overhead activities with extremes of motion (microtrauma type), and those with instability after violent trauma (macrotrauma type).6,140 Recognition of MDI is critical because traditional stabilization procedures such as the Bankart or Bristow operations fail to adequately address the inferior component of instability.‡ Moreover, too tight an anterior repair in this setting may actually aggravate the posterior component of MDI.64,159 The diagnosis of MDI is based on the history and the classic finding of a significant “sulcus sign” in addition to anteriorposterior laxity demonstrated with a load-and-shift maneuver. Furthermore, 50% of these individuals usually have stigmata of generalized ligamentous laxity. Up to 50% to 70% of these individuals respond well to a rehabilitation program aimed at rotator cuff strengthening if it is coordinated with activity modification. This is in contrast to young individuals with posttraumatic, unidirectional, anterior recurrent instability, who often require surgery.27 Missed unreduced anterior dislocation may occur in elderly patients, individuals with substance abuse, individuals with seizure disorders, and unconscious polytraumatic patients.60,133 Unlike missed posterior dislocations that go unrecognized because of a failure to perform an adequate radiograph, missed anterior dislocations are usually due to a failure to perform an initial or follow-up radiograph.60 The chronicity of the dislocation must be established. If an anterior dislocation is less than 6 weeks old and no concomitant osteoporosis or history of steroid use is present, an attempt at mild gentle closed reduction may be made under general anesthesia.60 In cases with chronic unreduced dislocations older than 6 weeks, open reduction and stabilization are recommended. In these cases, an axillary radiograph confirms the diagnosis; however, computed tomography gives valuable information about the status of the humeral head and glenoid. It is helpful to have this information before surgery because
‡References
6, 49, 54, 90, 109, 112, 121, 126, 127, 140.
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significant bone loss of the anterior glenoid or posterolateral humeral head may necessitate supplemental bone grafting. In older individuals, an arthrogram may also be appropriate to rule out an associated cuff injury. An anterior surgical approach through the deltopectoral interval is recommended. If necessary for exposure, the superior 1 cm of the pectoralis major insertion may be detached. The anterior 1 cm of the conjoined tendon insertion at the level of the coracoid process can be divided. The subscapularis is usually contracted and fibrotic along with the capsule and rotator cuff, and the axillary nerve may be stretched tightly across the anterior glenohumeral joint. This must be kept in mind during release of these tight anterior structures. After release of the subscapularis and capsule, it is often necessary to remove granulation tissue within the joint before the humeral head is reduced. After reduction and repair of the capsule, early motion is preferred rather than spica immobilization advocated by some surgeons.60 Management of glenoid bone deficiency and large Hill-Sachs lesions is discussed later. In cases in which the dislocation is older than 1 year or when the Hill-Sachs lesion is larger than 50% of the articular surface, the humeral head may no longer be viable and a hemiarthroplasty may be the best alternative treatment. In these cases, placement of the prosthesis at an angle greater than the normal retroversion of 30 degrees (50 to 60 degrees) helps prevent the recurrence of anterior instability. Although most procedures have a success rate in excess of 95% in providing stability to the shoulder, no single surgical technique is perfect. In general, procedures that do not address specific pathology should not be used in the primary surgery setting. An individualized approach to each situation is recommended, because a variety of pathologic lesions may be present in different patients. The optimum technique, as defined by Cofield et al,35 would be one with the following characteristics: low recurrence rate, low complication rate, low reoperation rate, low rate of osteoarthritis (uses no hardware), no limitation of motion, anatomic treatment of pathology, and no technical difficulty. Because no one procedure satisfies all these criteria, we present specific pitfalls and their management for a variety of common anterior stabilization techniques.
Examination under anesthesia and diagnostic arthroscopy It is essential to confirm both the direction and the degree of instability by examination under anesthesia before any surgical procedure. This aids in the decision of which operative approach and procedure to use. One should perform a drawer test on the shoulder to assess the amount of anterior, posterior, and inferior translation of the humeral head in the glenoid. Anterior and posterior translation is assessed with the shoulder at 90 degrees’ abduction and neutral rotation and is graded on a scale of +1 to +3 (+1 is movement of the humeral head to the rim but not over it, +2 represents humeral head dislocation over the glenoid rim with spontaneous reduction when pressure is released, and +3 is frank dislocation of the humeral head that does not reduce spontaneously).6 One should not be surprised to find increased
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posterior translation along with anterior translation when a patient with suspected anterior instability is examined because injury to the ligaments on both sides of the joint may occur with an anterior dislocation.115,136 Inferior instability is assessed by the presence of a “sulcus sign.” This test is performed with downward traction on the adducted arm, and the degree of acromiohumeral interval separation is noted.150 The “sulcus sign” is graded on a scale of +1 to +3 (+1 is 0 to 1 cm, +2 is 1 to 2 cm, +3 is greater than 2 cm).6 Arthroscopic inspection may occasionally be useful in these patients, although office examination, history, and an examination under anesthesia usually confirm the diagnosis. Most labral lesions below the equator of the glenoid are associated with a deficient inferior glenohumeral labrum.
Surgical procedures for instability The classic Bankart procedure13,118 and its modifications72,130,144 anatomically repair a detached glenoid labrum together with the inferior and middle glenohumeral ligaments. Several variations in handling of the subscapularis deserve mention. Thomas and Matsen144 described a technique first proposed by Ellison. The subscapularis and capsule are both divided laterally, with medial retraction allowing repair of the Bankart lesion with the joint in an inside-out fashion. This approach is useful in revision cases in which extensive scarring is found medially at the glenoid. Jobe and Glousman72 recommended longitudinal division of the subscapularis muscle with preservation of its lateral insertion on the lesser tuberosity. This approach is designed to minimize scarring and shortening of the muscle in a throwing athlete. Several potential problems with this approach include limited inferior exposure in cases in which a capsular shift might be necessary and the potential for injury to the axillary nerve and brachial plexus if longitudinal splitting is carried too far medially. To repair the Bankart lesion once the sutures are well placed through the bony anterior glenoid rim, the lateral capsule is repaired to the rim. A potential error here is to not address any concomitant capsular laxity. The standard Bankart procedure handles capsular laxity by placing the sutures more laterally through the lateral capsular flap. The T-plasty repair pulls the inferior portion of the capsule superiorly before placement of the sutures through the capsule. The inferior capsular shift procedure as originally described by Neer and Foster112 is designed to treat excessive capsular laxity occurring with MDI. It has been used successfully and involves detachment of the capsule laterally along its humeral attachment with a superior-lateral shift of the inferior flap and then an inferior-lateral shift of the superior flap.40,49 Repair of an associated Bankart lesion is performed first, and failure to address this lesion has been associated with failure of the procedure.87 Inferior detachment of the capsule laterally along the humeral neck probably involves less risk to the axillary nerve than does a medial paraglenoid capsulotomy incision; however, there is still significant risk with inferior dissection, and Neer109 observed three cases of axillary nerve neuropraxia early in his experience. To avoid this potential complication, the inferior flap should be developed by placing stay sutures in the capsule and pulling superiorly while
applying progressive external rotation. An elevator is placed inferiorly and used to remove any muscle from the capsule before its division. If the axillary nerve cannot be palpated and its exact location is not precisely known, it should be visualized before division of the inferior capsule. A T-plasty procedure can be performed to manage capsular laxity and concomitant labral detachment simultaneously.6 The basic goal of the T-plasty is to restore proper tension in the inferior glenohumeral ligament by advancing this structure superiorly and medially. At completion of the capsular repair, external rotation with the arm at the side should be in the range of 35 to 45 degrees without undue tension on the repair. The Bristow procedure and its modifications basically involve fixation of the coracoid process and attached conjoined tendon to the scapular neck through a split in the subscapularis tendon.§ The procedure theoretically functions by provision of an anterior bone block, formation of a dynamic musculotendinous sling, and partial tenodesis of the inferior third of the subscapularis tendon. It does not directly address pathologic lesions such as labral detachment or capsular laxity. Although the Bristow procedure has a success rate comparable with that of other procedures, it is generally accepted to be a poor alternative for stabilization in athletes involved in overhead sports, because it may limit external rotation.14,66,85,86 The orthopedic literature has documented a high incidence of complications with this procedure.10,12,46,159 The major risk with the Bristow procedure is injury to the musculocutaneous nerve.12,15,48,125,159 This complication is usually due to inadequate knowledge of variations in regional anatomy or poor surgical technique.125 Significant variations in anatomy of the conjoined tendon and musculocutaneous nerve may be encountered.48,125 The musculocutaneous nerve, in most cases, enters the coracobrachialis muscle at a distance of 5 or more cm distal to the coracoid process; however, in 5% of cases it may also be as close as 2.5 cm from the tip of the coracoid.12,48,125 If the nerve is observed to enter the muscle at 2.5 cm or closer to the coracoid process, the Bristow procedure should not be performed. Finally, staple fixation may impinge or rupture the biceps tendon with improper placement. The Putti-Platt procedure treats anterior instability by shortening the subscapularis in a “vest-over-pants” technique to limit external rotation.22,68,84,116 The subscapularis is detached 2.5 mm medial to its insertion, and the capsule and subscapularis are then sutured to the glenoid rim with the arm in internal rotation. The main complication of this procedure is loss of function from excessive limitation of external rotation, and in the extreme case this may result in secondary glenohumeral arthritis caused by excessive constraining forces on the articular surfaces.61 Instability may also result if the patient has unrecognized MDI.63 In the duToit capsulorrhaphy procedure, a staple is used to effect a Bankart-type repair, and complications stem from problems with staple fixation and placement.20,42,139 Injury to the articular surface and loosening of the staple have been reported.160 Metal devices are mentioned here for their historical role in the development of arthroscopic Bankart repairs.
§References
138, 145.
2, 3, 10, 14, 21, 29, 30, 41, 47, 57, 66, 67, 69, 82, 85, 86, 89, 96, 114,
Chapter 5d
The enthusiasm for arthroscopic stabilization of anterior shoulder instability is based on the assumption that limited disruption of the anterior soft tissues results in a better functional outcome. This is particularly relevant to young throwing athletes who require full external rotation and power. Although short-term studies with 2- to 3-year follow-up are encouraging, long-term data supporting this assumption are not available.44,76 However, three recent meta-analyses comparing arthroscopic versus open repair for traumatic anterior shoulder instability both concluded that open repair has a more favorable outcome with respect to recurrence and return to activity.36,50,98 Because arthroscopic management of instability has been in evolution over the recent years, the conclusions drawn from the meta-analyses may be biased toward success of open repair. The technique, which was originally popularized by Johnson,74 uses a dual-pronged staple and attempts to reproduce the duToit capsular staple-Bankart repair arthroscopically.4,42,150 Since then, modified techniques have included the use of a removable rivet,154 modified staple capsulorrhaphy,56 cannulated screw and ligament washers,158 and suture Bankart repair.4,31,99,100 The ideal patient is an individual with posttraumatic, recurrent, anterior, unidirectional instability with labral detachment below the level of the equator of the glenoid. Patients with MDI are not candidates for this procedure. Routine examination of patients under anesthesia is performed before the procedure. Individuals with a significant sulcus sign that does not lessen with external rotation and adduction are treated with a rotator interval closure. One can use a suture technique in which absorbable sutures are placed through the inferior glenohumeral ligament and a Bankart repair is achieved through transscapular drill holes.4,31,99,100 Drill holes are placed above the equator on the anterior scapular neck to allow restoration of tension in the inferior glenohumeral ligament as it is pulled superiorly and medially with the repair. More recently, the use of a biodegradable cannulated tack to avoid problems associated with hardware or drilling across the scapula has been discussed.149 No matter what form of fixation is used, it is essential to adequately prepare the anterior scapular neck to ensure a bleeding bony bed for the repair. When a motorized burr is used, care should be taken not to slip over the glenoid rim and injure the articular surface. Injury to the suprascapular nerve is a theoretical risk with pin placement through the scapula. Excessive lateral penetration of the pins should be avoided.100 In conclusion, many pitfalls and complications are potentially encountered in surgery for shoulder instability. The shoulder surgeon must have an organized approach to diagnosis and treatment. If surgery is contemplated, the procedure must be tailored to the individual patient and must deal with the underlying pathology.
FRACTURES AND DISLOCATIONS ABOUT THE SHOULDER Fractures and dislocations about the shoulder are very common injuries. These injuries are best classified by anatomic location for the purpose of discussion. Shoulder girdle injuries are located at the sternoclavicular joint, clavicle, acromioclavicular joint,
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Fractures and dislocations about the shoulder
proximal end of the humerus, and scapula. An associated neurovascular injury may or may not be present.
Sternoclavicular joint Most often, sternoclavicular dislocations do not cause any significant functional disability.24 An anterior dislocation is usually asymptomatic and does not require any treatment. Posttraumatic ankylosis of the sternoclavicular joint can cause pain and disability. Compression of the mediastinal structures can occur with posterior dislocations of the sternoclavicular joint. In general, anterior injuries can be treated conservatively and posterior injuries may require some intervention. Surgical management of chronic sternoclavicular dislocations may include soft tissue reconstruction, arthrodesis, resection of the medial aspect of the clavicle, and resection combined with costoclavicular ligament reconstruction.
Clavicle Clavicular fractures account for greater than 60% of shoulder girdle fractures. The middle third of the clavicle is involved in 82% and the distal third in 15%.128 Nonunion of the clavicle is relatively uncommon and reported in 1.8% of those patients treated nonoperatively.128 If a nonunion does occur, most often it is minimally symptomatic. One study has determined that atrophic nonunions are less likely to become symptomatic than are hypertrophic nonunions.155 In a study by Johnson and Collins,73 26 clavicular nonunions treated nonoperatively resulted in 23 excellent results, 2 good results, and 1 poor result. Rowe128 noted spontaneous uniting of apparent nonunions as long as 5 months from the time of injury. Only patients with significantly symptomatic nonunions and malunions should be offered reconstructive surgery. Malunion of the middle third of the clavicle, if symptomatic, can be managed with osteotomy and bone grafting. This is supplemented with internal fixation. Nonunions can be managed by excision of the pseudoarthrosis, reduction, bone grafting, and internal fixation with promising results.75,110 Distal clavicular nonunions, which can result after type II distal clavicle fractures, have been treated by excision of the distal fragment and/or open reduction and internal fixation. The results of excision cannot be recommended.73 Neer107 documented some success with transacromial wire fixation. The fixation is removed after union has occurred. However, cases of migratory hardware have made pin or wire fixation less appealing.
Acromioclavicular joint Of shoulder girdle dislocations, 9% involve the acromioclavicular joint. Fifty percent are complete grade III or higher dislocations with disruption of the conoid and trapezoid components of the coracoclavicular ligaments.128 Most acute acromioclavicular injuries can be treated nonoperatively: application of ice over the first 24 hours, possibly a sling for comfort, and resumption of activity at approximately 1 week if tolerated. Posterior displacement of the clavicle is
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uncommon and may require surgery to reduce the clavicle. It may be wedged into the angle between the acromion and the spine of the scapula. One may attempt a closed reduction by displacing the shoulder posteriorly to widen the distance between the acromion and sternum. Treatment of injuries that involve complete separation of the acromion and clavicle is controversial. Some have attempted closed reduction with pressure by tape or a splint, but significant problems with the skin have been noted when these techniques are used. Surgery for acute grade III lesions has included many techniques105: direct acromioclavicular joint stabilization with ligament repair; clavicle stabilization by attachment to the coracoid, as with a Bosworth screw, wire, Dacron tape,58 silk sutures, or absorbable suture; and resection of the outer end of the clavicle and coracoclavicular ligament stabilization with the coracoacromial ligament.151 Most patients with chronic acromioclavicular subluxations or dislocations are asymptomatic or minimally symptomatic and respond well to nonoperative management. Occasionally, acromioclavicular subluxations become symptomatic.105 Degenerative joint disease or osteolysis of the distal end of the clavicle may develop. These problems can be assessed with an acromioclavicular view on plain radiographs and by injection with local anesthetic to confirm the diagnosis with pain relief.
Proximal humerus fracture dislocations The classification of proximal humeral fractures is based on the absence or displacement of each of four major segments: the humeral head, the greater and lesser tuberosities, and the humeral shaft. The Neer classification is most commonly used and considers the segment displaced if there is greater than 45 degrees of angulation or 1 cm of displacement. It should be noted that all patients with a suspected fracture of the proximal end of the humerus require a shoulder trauma series of radiographs. This includes anteroposterior, lateral, and axillary views. The treating physician must exclude concomitant dislocation of the humeral head. A complete vascular and neurologic examination must be performed and documented. Treatment considerations include the patient’s age, functional demands, dominance, expectations, anticipated compliance, degree of segment displacement, and bone quality. Most of these fractures can be managed with protective immobilization and early range of motion. This is, of course, based on the aforementioned factors and includes fracture stability. In a prospective randomized study of proximal humerus fractures (minimally displaced), Kristiansen et al79 compared 1 and 3 weeks of immobilization before starting physical therapy. Shorter immobilization resulted in better functional results during the first 3 months. After 6 months, the results in both groups were essentially the same. Fractures that are more significantly displaced require reduction. This can be accomplished by closed means or with open reduction and internal fixation. Occasionally, prosthetic replacement is preferred. Available internal fixation includes tension band wires, screws, percutaneous pins, plates and screws, and intramedullary nailing. There is a trend toward open reduction and internal fixation as newer types of locking plates become more commonly implemented.45 This restores anatomy and provides fracture stability. The risk of avascular necrosis increases with
fracture comminution and displacement, but conversion to hemiarthroplasty is always a possibility after attempted fracture fixation. Two-part lesser tuberosity fractures are often associated with posterior glenohumeral dislocation. Smaller fragments can be treated nonoperatively: Larger fragments may require open reduction and internal fixation. Two-part greater tuberosity fractures may include a tear of the rotator cuff. This requires open reduction and internal fixation with either a tension band wire or screw and repair of the rotator cuff tear. Two-part fractures of the anatomic neck are uncommon and carry a significant risk of osteonecrosis. Flatow et al48 published a series of 12 two-part greater tuberosity fractures that were treated surgically by open reduction and internal fixation with a heavy nonabsorbable suture and careful repair of the rotator cuff. All fractures healed, and early range of motion resulted in good or excellent results in all patients. Two-part surgical neck fractures can be either impacted or completely displaced and unstable. Options for treatment include closed reduction, with or without percutaneous pinning, or open reduction and internal fixation. Kowalkowski and Wallace78 published a series of 22 displaced fractures treated with closed percutaneous Kirshner wire stabilization of the surgical neck. Significant problems in obtaining adequate reduction and migration of the smooth pins were encountered. Unsatisfactory results were more common in the older age group (greater than 50 years old). In three-part fractures, closed reduction is often difficult to maintain, and therefore open reduction is required. Tensionband wiring can often be used because it incorporates the rotator cuff in the repair. If the fracture is severely comminuted or the bone osteoporotic, a hemiarthroplasty can be considered, especially in elderly patients. In young patients with a four-part proximal humerus fracture, an attempt at open reduction and internal fixation is considered despite the high risk of osteonecrosis. If reconstruction is not possible or the patient is elderly and has poor bone stock, a hemiarthroplasty is preferred. As discussed earlier, it is important to eliminate the presence of concomitant dislocation of the humeral head. Isolated dislocations without fracture can be seen. Many posterior dislocations of the humeral head are missed and recur chronically. These patients most often complain of decreased range of motion. They may or may not complain of pain. Articular impression fractures can often best be imaged with computed tomography. In general, closed reduction can be considered if the injury is less than 6 weeks old; after 6 weeks, open reduction is required. Treatment of the articular impression defect is based on the percentage of head involvement. If the defect is less than 20%, it is generally stable after a period of immobilization. If the defect is between 20% and 40%, a transfer procedure into the defect may be required, as well as possibly a subscapularis transfer for posterior dislocations or infraspinatus transfer for anterior dislocations. A hemiarthroplasty may be used if the defect is greater than 40% of the head or if significant degenerative changes are present.
FROZEN SHOULDER Frozen shoulder—also termed adhesive capsulitis—has many underlying causes. It can be seen in association with other shoulder
Chapter 5d
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References
pathologies, for example, posttraumatic, postsurgical, and rotator cuff pathology. It is also associated with other disease entities, including insulin-dependent diabetes mellitus, parkinsonism, cardiovascular disease, and thyroid disease. Most patients have an insidious onset of pain and stiffness. Most patients demonstrate a gradual decrease in pain and return of motion over time. There may be improvement for up to 24 months. Treatment consists of gentle physical therapy, antiinflammatory medication, and occasional use of cortisone injections intraarticularly and subacromially. If the patient does not respond after an extended trial of therapy, consideration may be given to manipulation under anesthesia. More recently, arthroscopic release and debridement have been proposed.153 Open surgical release is rarely indicated and may in fact worsen the problem. Ozaki et al,117 however, reported on 17 patients treated surgically for recalcitrant adhesive capsulitis. These patients showed significant contracture of the coracohumeral ligament and rotator interval. Resection of these structures relieved pain and restored motion.
excellent pain relief with total-shoulder arthroplasty.51,152 Reverse-type prostheses are reserved for the elderly person with severely debilitating cuff tear arthropathy or loss of the coracoacromial arch. However, early reports are fraught with a high complication rate, and its implementation is still being defined.83
DEGENERATIVE JOINT DISEASE OF THE SHOULDER
REFERENCES
CONCLUSION In attempting to treat the myriad of shoulder problems, the orthopedist must first make an accurate diagnosis. The goals of treatment include controlling symptoms, improving function, and preventing recurrence, if possible. A systematic approach to management includes appropriate conservative modalities and surgical intervention, if necessary. Future concerns must address cost-effectiveness, standards of care, and outcome research.
1.
Degenerative joint disease of the shoulder can occur secondary to a number of different underlying pathologic conditions. The glenohumeral joint requires prosthetic replacement less often than other major joints. Osteoarthritis of the glenohumeral joint is uncommon, and patients with rheumatoid arthritis can most often be managed nonoperatively with regard to the shoulder. Degenerative joint disease may develop after fracture of the proximal humerus and subsequently require treatment. In rare cases, proximal humerus fractures may necessitate prosthetic replacement. Any of the aforementioned pathologic entities may be an indication for shoulder replacement. It is, however, most useful for diseases in which the proximal humeral subchondral bone has become distorted and the articular surface destroyed resulting in painful decreased motion. All patients should pursue a nonoperative course of management initially. Should symptoms persist or progress symptomatically, surgical intervention can be contemplated. Although shoulder prosthetic systems have improved, the patient may be a candidate for arthrodesis. This can be considered in a younger active patient with degenerative arthritis, joint sepsis, or loss of deltoid and rotator cuff function or as a salvage procedure after failed total-joint arthroplasty. The humeral component is designed to preserve metaphyseal bone stock and provide adequate fixation. The glenoid component is often not required, particularly if the rotator cuff is intact or repairable. Hemiarthroplasty is usually considered in younger patients with osteoarthritis, posttraumatic conditions without glenoid loss, rotator cuff pathology, or osteonecrosis. In many patients with more extensive osteoarthritis and rheumatoid arthritis involvement, glenoid resurfacing has improved pain relief. The glenoid most commonly is cemented into position. In younger patients with good bone stock, consideration is given to uncemented glenoid fixation with bone ingrowth. Results of survivorship analysis predicted a 27% failure rate.23 Other studies reported
2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.
15.
16. 17. 18. 19. 20. 21. 22.
Aamouth GM, O’Phelan EH: Recurrent anterior dislocation of the shoulder: a review of 40 athletes treated by subscapularis transfer (modified Magnusson-Stack procedure). Am J Sports Med 5:188-190, 1977. Akermak C, et al: Results of the Bristow repair: sports participation after surgery. In I Bayley, L Kessel, eds: Shoulder surgery. Berlin, 1982, Springer-Verlag, pp. 92-94. Allman F, et al: Symposium on sports injuries to the shoulder. Contemp Surg 7(3):70-109, 1975. Altchek DW, Skyhar MJ, Warren RF: Shoulder arthroscopy for shoulder instability. Instr Course Lect 36:187-198, 1989. Altchek DW, Warren RF, Skyhar MJ, Ortiz G: T-plasty anterior repair for anterior and inferior instability of the shoulder. J Bone Joint Surg 73A:105-111, 1991. Altchek DW, Warren RF, Wickiewicz TL: Arthroscopic labral debridement. A three year follow-up study. Am J Sports Med 20:702-706, 1992. Andrews JR, Broussard TS, Carson WG: Arthroscopy of the shoulder in management of partial tears of the rotator cuff: a preliminary report. Arthroscopy 1(2):117-122, 1985. Andrews JR, Carson WG: The arthroscopic treatment of glenoid labrum tears in the throwing athlete. Orthop Trans 8:44, 1984. Andrews JR, Carson WG Jr, Mcleod WD: Glenoid labrum tears related to the long head of the biceps. Am J Sports Med 13:337-341, 1985. Artz T, Huffer JM: A major complication of the modified Bristow procedure for recurrent dislocation of the shoulder. J Bone Joint Surg 54A:1293-1296, 1972. Aston JW, Gregory CF: Dislocation of the shoulder with significant fracture of the glenoid. J Bone Joint Surg 55A:1531-1533, 1973. Bach BR, OBrien SS, Warren RF, Leighton M: An unusual neurological complication of the Bristow procedure: a case report. J Bone Joint Surg 70A:458-460, 1988. Bankart ASB: The pathology and treatment of recurrent dislocation of the shoulder joint. Br J Surg 26:23-29, 1938. Barry TP, Lombardo SJ, Kerlan RK, Jobe FW, Carter VS, Shields CL, Yocum LA, Tibone JE: The coracoid transfer for recurrent anterior instability of the shoulder in the adolescent. J Bone Joint Surg 67A:383-386, 1985. Bigliani LU, McCann PD, Dalsey RM: An anatomic study of the suprascapular nerve. Presented at the annual meeting of the American Shoulder and Elbow Surgeons, Las Vegas, February 12, 1989. Bigliani LU, Cordasco FA, McIlveen SJ, Musso ES: Operative repair of massive rotator cuff tears: long term results. J Shoulder Elbow Surg 1(3):120-130, 1992. Bigliani LU, Morrison DS, April EW: The morphology of the acromion and its relationship to rotator cuff tears. Orthop Trans 10:216, 1986. Blackburn TA, et al: EMG analysis of posterior rotator cuff exercises. J Natl Athl Train Assoc 25:40-45, 1990. Blom S, Dahlback L: Nerve injuries in dislocation of the shoulder joint and fractures of the neck of the humerus. Acta Chir Scand 136:461-466, 1970. Boyd HB, Hunt HL: Recurrent dislocation of the shoulder. The staple capsulorrhaphy. J Bone Joint Surg 47A:1514-1520, 1965. Braley WG, Tullos HS: A modification of the Bristow procedure for recurrent dislocation of the shoulder. Am J Sports Med 13(2):81-86, 1985. Brav EA: An evaluation of the Putti-Platt reconstruction procedure for recurrent dislocation of the shoulder. J Bone Joint Surg 37A:731-741, 1955.
191
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192
23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41.
42. 43. 44.
45.
46.
47. 48. 49. 50.
51.
52. 53. 54.
55. 56. 57.
●
Treatment of shoulder disorders
Brenner BC, Ferlic DC, Clayton ML, Dennis DL: Survivorship of unconstrained total shoulder arthroplasty. J Bone Joint Surg 71A:1289-1296, 1989. Brown JE: Sternoclavicular dislocation. Am J Orthop 3:134, 1961. Buess E, Steuber KU, Waibl B: Open versus arthroscopic rotator cuff repair: a comparative view of 96 cases. Arthroscopy 21(5):597-604, 2005. Burkhart SS: Arthroscopic treatment of massive rotator cuff tears. Clin Orthop 267:45-56, 1991. Burkhead WZ, Rockwoood CA Jr: Treatment of instability of the shoulder with an exercise program. J Bone Joint Surg 74A:890-896, 1992. Cain PR, Mutschler TA, Fu FH, Lee SK: Anterior stability of the glenohumeral joint: a dynamic model. Am J Sport Med 15:144-148, 1987. Cameron JC, Hall M, Courtney BC: The Bristow procedure for recurrent anterior dislocation of the shoulder. J Bone Joint Surg 67B:327, 1985. Carol EJ, Falke LM, Kortmann JHJPM: Bristow-Latarjet the repair for recurrent anterior shoulder instability: an eight year study. Neth J Surg 37(4):109-111, 1985. Caspary RB: Arthroscopic reconstruction for anterior shoulder instability. Techn Orthop 3(1):59-66, 1988. Codman EA: The shoulder: rupture of the supraspinatus tendon and other lesions about the subacromial bursa. Brooklyn, NY, 1934, G Miller & Co, Medical Publishers. Cofield RH: Rotator cuff disease of the shoulder. J Bone Joint Surg 67A(6):974-979, 1985. Cofield RH: Subscapular muscle transposition for repair of chronic rotator cuff tears. Surg Gynecol Obstet 154:667, 1982. Cofield RH, Kavanaugh BF, Frassica FJ: Anterior shoulder instability. Instr Course Lect 34:210-227, 1985. Cole BJ, Warner JJ: Arthroscopic versus open Bankart repair for traumatic anterior shoulder instability. Clin Sports Med 19(1):19-48, 2000. Cooper RA, Brems JJ: The inferior capsular shift for multidirectional instability of the shoulder. J Bone Joint Surg 74A:1516-1521, 1992. Craig EV: The posterior mechanism of acute anterior shoulder dislocations. Clin Orthop 190:212-216, 1984. Curr JF: Rupture of the axillary artery complication dislocation of the shoulder. J Bone Joint Surg 52B:313-317, 1970. Detrisac DA, Johnson LL: Arthroscopic shoulder anatomy: pathologic and surgical implications. Thorofare, NJ, 1986, Slack. deWaal D, Melefijt J, Ooms AJ, van Rens TJ: A comparison of the results of the Bristow-Latarjet procedure and the Bankart/Putti-Platt operation for recurrent anterior dislocation of the shoulder. Acta Orthop Belg 51:831-842, 1985. DuToit GT, Roux D: Recurrent dislocation of the shoulder. A 24 year study of the Johannesburg stapling operation. J Bone Joint Surg 38A:1-12, 1956. Ellman H: Arthroscopic subacromial decompression: analysis of one-to-three year results. Arthroscopy 3(3):173-181, 1987. Fabbriciani C, Milano G, Demontis A, Fadda S, Ziranu F, Mulas PD: Arthroscopic versus open treatment of Bankart lesion of the shoulder: a prospective randomized study. JBJS Am 86A(11):2574, 2004. Fankhauser F, Boldin C, Schippinger G, Haunschmid C, Szyszkowitz R: A new locking plate for unstable fractures of the proximal humerus. Clin Orthop Relat Res 430:176-181, 2005. Fee JJ, McAvoy JM, Dainko EA: Pseudoaneurysm of the axillary artery following a modified Bristow operation: report of a case and review. J Cardovasc Surg 19:65-68, 1978. Ferlic DC, DiGiovine NM: A long-term retrospective study of the modified Bristow procedure. Am J Sports Med 16:469-474, 1988. Flatow EL, Bigliani LU, April EW: An anatomic study of the musculocutaneous nerve and its relationship to the coracoid process. Clin Orthop 244:166-171, 1989. Foster CR: Multidirectional instability of the shoulder in the athlete. Clin Sports Med 2(2):355-367, 1983. Freedman KB, Smith AP, Romeo AA, Cole BJ, Bach BR Jr: Open Bankart repair versus arthroscopic repair with transglenoid sutures or bioabsorbable tacks for recurrent anterior instability of the shoulder: a meta-analysis. AJSM Epub 32(6):1520-1527, 2004. Friedman RJ, Thornhill TS, Thomas WH, Sledge CB: Non-constrained total shoulder replacement in patients who have rheumatoid arthritis and class-IV fractures. J Bone Joint Surg 71A:494-498, 1989. Fronek J, Warren RF, Bowen M: Posterior subluxation of the glenohumeral joint. J Bone Joint Surg 71A:205-216, 1989. Gerber C: Latissimus dorsi transfer for treatment of irreparable tear of the rotator cuff. Clin Orthop 275:152-160, 1992. Gerber C, Ganz R: Clinical assessment of instability of the shoulder: with special reference to anterior and posterior drawer tests. J Bone Joint Surg 66B:551-556, 1984. Gerber C, Vinh TS, Hertel R, Hess CW: Latissimus dorsi transfer for the treatment of massive tears of the rotator cuff. Clin Orthop 232:51-61, 1988. Gross MR: Arthroscopic shoulder capsulorrhaphy: does it work? Am J Sports Med 17:495-500, 1989. Halley DK, Olix ML: A review of the Bristow operation of recurrent anterior shoulder dislocation in athletes. Clin Orthop 106:175-179, 1975.
58. 59.
60. 61. 62. 63. 64. 65. 66. 67.
68.
69.
70. 71. 72. 73. 74.
75. 76. 77. 78. 79.
80. 81. 82. 83. 84.
85. 86.
87. 88. 89. 90. 91. 92.
Harrison WE Jr, Sisler J: Reconstruction of the AC joint using a synthetic fascial graft. J Bone Joint Surg 56A:1313, 1974. Harryman DT, Mack LA, Wang KY, Jackins SE, Richardson ML, Matsen FA: Repairs of the rotator cuff. Correlation of functional results with integrity of the cuff. JBJS Am 73A(7):982-989, 1991. Hawkins RJ: Unrecognized dislocation of the shoulder. Instr Course Lect 34:258-263, 1985. Hawkins RJ, Angelo RC: Glenohumeral osteoarthrosis. A late complication of the Putti-Platt repair. J Bone Joint Surg 72A:1193-1197, 1990. Hawkins RJ, Bell RH, Hawkins RH, Koppert GJ: Anterior dislocation of the shoulder in the older patient. Clin Orthop 206:192-195, 1986. Hawkins RH, Hawkins RJ: Failed anterior reconstruction for shoulder instability. J Bone Joint Surg 67B:709-714, 1985. Hawkins RJ, Kennedy VC: Impingement syndrome in athletes. Am J Sports Med 6:151-158, 1981. Hawkins RJ, Koppert G: The natural history following anterior dislocation of the shoulder in the older patient. J Bone Joint Surg 64B:255, 1982. Helfet AJ: Coracoid transplantation for recurring dislocation of the shoulder. J Bone Joint Surg 40B:198-202, 1958. Hovelius L, Akepmark, Albrektsson B, Berg E, Korner L, Lundberg B: Bristow-Latarjet procedure for recurrent anterior shoulder subluxation and dislocation. Am J Sports Med 9:283-287, 1981. Hoveluis L, Gavle JJ, Frein LH: Recurrent anterior dislocation of the shoulder: results after Bankart and Putti-Platt operation. J Bone Joint Surg 61A:566-569, 1979. Hovelius L, Korner L, Lundberg B, Akermark C, Herberts P, Wredmark T, Berg E: The coracoid transfer for recurrent anterior dislocation about the shoulder. J Bone Joint Surg 65A:926-934, 1983. Inman VT, Saunders JB, Abbott LC: Observations on the function of the shoulder joint. J Bone Joint Surg 26:1-30, 1944. Irrgang JJ, Whitney SL, Harner CD: Nonoperative treatment of rotator cuff injuries in throwing athletes. J Sport Rehab 1:197-222, 1992. Jobe FW, Glousman RE: Anterior capsulolabral reconstruction. In JE Tibone, ed: Techniques in orthopedics. Frederick, MD, 1989, Aspen Publications, pp. 29-35. Johnson EW Sr, Collins HR: Nonunion of the clavicle. Arch Surg 87:963, 1963. Johnson LL: Arthroscopic management for shoulder instability: stapling. Presented at the annual meeting of the Arthroscopic Association of North America, Atlanta, February 1988. Jupiter J, Leffert RD: Non-union of the clavicle. Associated complications and surgical management. J Bone Joint Surg 69A(5):753-760, 1987. Kim SH, Ha KI, Kim SH: Bankart repair in traumatic anterior shoulder instability: open versus arthroscopic technique. Arthroscopy 18(7):755-763, 2002. Kinnet JG, Warren RF, Jacobs B: Recurrent dislocation of the shoulder after age fifty. Clin Orthop 149:164-168, 1980. Kowalkowski A, Wallace WA: Close percutaneous K-wire stabilization for displaced fractures of the surgical neck of the humerus. Injury 2:209-212, 1990. Kristiansen B, Angermann P, Larsen TK: Functional results following fractures of the proximal humerus: a controlled clinical study comparing two periods of immobilization. Arch Orthop Trauma Surg 108:339-341, 1989. Kummel BM: Fractures of the glenoid causing chronic dislocation of the shoulder. Clin Orthop 69:189, 1970. Kunkel SS, Hawkins RJ: Rotator-cuff repair utilizing a trough in bone. Techn Orthop 3(4):51-57, 1989. Latarjet M: A propos du traitment des luxations recidivantes de s’epaule. Lyon Clin 49:994-997, 1954. Laudicina L, D’Ambrosia R: Management of irreparable rotator cuff tears and glenohumeral arthritis. Orthopedics 28(4):382-388, 2005. Leach RE, Corbett M, Schepsis A, Stockel J: Results of a modified Putti-Platt operation for recurrent shoulder dislocation and subluxation. Clin Orthop 164:20-25, 1982. Lombardo SJ: The modifed Bristow-Laterjet procedure. Techn Orthop 3(4):12-22, 1989. Lombardo SJ, Kerlan RK, Jobe FW, Carter VS, Blazina ME, Shields CL: The modified Bristow procedure for recurrent dislocation of the shoulder. J Bone Joint Surg 58A:256-261, 1976. Loomer R, Fraser J: A modified Bankart procedure for recurrent anterior-inferior shoulder instability. A preliminary report. Am J Sports Med 17:374-379, 1989. Mackenzie DB: The treatment of recurrent anterior shoulder dislocation by the modified Bristow-Laterjet procedure. S Afr Sports Med J 65:325-330, 1984. Mackenzie DB: The Bristow-Helfet operation for anterior recurrent dislocation of the shoulder. J Bone Joint Surg 62B:273-274, 1980. Matsen FA III, Zuckerman JD: Anterior glenohumeral instability. Clin Sports Med 2(2):319-338, 1983. McCallister WV, Parsons IM, Titelman RM, Matsen FA: Open rotator cuff repair without acromioplasty. JBJS Am 87A(6):1278-1283, 2005. McLaughlin HL: Dislocation of the shoulder with tuberosity fracture. Surg Clin North Am 43:1615, 1963.
Chapter 5d
93. McLaughlin HL: Injuries about the shoulder and arm. In HC McLaughlin, ed: Trauma. Philadelphia, 1959, WB Saunders, pp. 233-296. 94. McLaughlin HL, Cavallaro WV: Primary anterior dislocation of the shoulder. Am J Surg 80:615-620, 1950. 95. McLaughlin HL, MacLellan DI: Recurrent anterior dislocation of the shoulder. A comparative study. J Trauma 2:191-201, 1967. 96. Mead NC: Bristow procedure. Letter presented at the Spectator Society, July 9, 1964. 97. Miller LS, Donahue JR, Good RP, Staerk AJ: The Magnuson-Stack procedure for recurrent glenohumeral dislocation. Am J Sports Med 12:133-137, 1984. 98. Mohtadi NG, Bitar IJ, Sasyniuk TM, Hollinshead RM, Harper WP: Arthroscopic versus open repair for traumatic anterior shoulder instability: a meta-analysis. Arthroscopy 21(6):652-658, 2005. 99. Morgan CD: Arthroscopic Bankart suture repair—2 to 5 year results. Presented at the annual meeting of the American Shoulder and Elbow Surgeons, Las Vegas, February 12, 1989. 100. Morgan CD, Bodenstab AB: Arthroscopic Bankart suture repair: technique and early results. Arthroscopy 3(2):111-122, 1987. 101. Morrey BF, Janes JM: Recurrent anterior dislocation of the shoulder: long-term follow-up of the Putti-Platt and Bankart procedure. J Bone Joint Surg 58A:252-257, 1976. 102. Moseley HF: Ruptures of the rotator cuff. Springfield, IL, 1952, Charles C Thomas. 103. Moseley HF, Goldie I: The arterial pattern of the rotator cuff of the shoulder. J Bone Joint Surg 45B(4):780-789, 1963. 104. Motycka T, Lahner A, Landsiedl F: Comparison of debridement versus suture in large rotator cuff tears: long-term study of 64 shoulders. Arch Orthop Trauma Surg Epub 124(10):654-658, 2004. 105. Mumford EB: Acromioclavicular diagnosis-a new operative treatment. J Bone Joint Surg 23:799-802, 1941. 106. Neer CS: Anterior acromioplasty for the chronic impingement syndrome in the shoulder. J Bone Joint Surg 54A(1):41-50, 1972. 107. Neer CS: Fractures of the distal third of the clavicle. Clin Orthop 53:43, 1960. 108. Neer CS: Impingement lesions. Clin Orthop 173:70-77, 1983. 109. Neer CS: Involuntary inferior and multidirectional instability of the shoulder: etiology, recognition, and treatment. Instr Course Lect 34:232-238, 1985. 110. Neer CS: Non-union of the clavicle. JAMA 172:1006-1011, 1960. 111. Neer CS, Craig EV, Fukuda H: Cuff-tear arthropathy. J Bone Joint Surg 65A:1232-1244, 1983. 112. Neer CS, Foster CR: Inferior capsular shift for involuntary inferior and multidirectional instability of the shoulder. J Bone Joint Surg 62A:897-908, 1980. 113. Neviaser RJ, Neviaser TJ, Neviaser JS: Concurrent rupture of rotator cuff and anterior dislocation of the shoulder in the older patient. J Bone Joint Surg 70A:1308-1311, 1988. 114. Nielson AB, Nielson K: The modified Bristow procedure for recurrent anterior dislocation of the shoulder. Results and complications. Acta Orthop Scand 53:229-232, 1982. 115. Norris T: Diagnostic techniques for shoulder instability. Instr Course Lect 34:239-257, 1985. 116. Osmond-Clark H: Habitual dislocation of the shoulder: the Putti-Platt operation. J Bone Joint Surg 30B:19-25, 1948. 117. Ozaki J, Nakagawa Y, Sakarai G, Tamai S: Recalcitrant chronic adhesive capsulitis of the shoulder. Role of contracture of the coracohumeral ligament and rotator interval in pathogenesis and treatment. J Bone Joint Surg 71A:1511-1515, 1989. 118. Perthes: Uber operation bei habitueller Schulterluxation. Deutsche Zeitschr Chir 85:199-277, 1906. 119. Pettersson G: Rupture of the tendon aponeurosis of the shoulder joint in anterior inferior dislocation. Acta Chir Scand 77(Suppl):1-184, 1942. 120. Poppen NK, Walker PS: Forces at the glenohumeral joint in abduction. Clin Orthop 135:165-170, 1978. 121. Protzman RR: Anterior instability of the shoulder. J Bone Joint Surg 62A:909-918, 1980. 122. Rathbun JB, MacNab I: The microvascular pattern of the rotator cuff. J Bone Joint Surg 52B:540-553, 1970. 123. Reeves B: Experiments on tensile strength of the anterior capsular structures of the shoulder in man. J Bone Joint Surg 50B:858-865, 1968. 124. Regan WD, Webster-Bogaert S, Hawkins RJ, Fowler PJ: Comparative functional analysis of the Bristow, Magnusson-Stack, and Putti-Platt procedures for recurrent dislocation of the shoulder. Am J Sports Med 17:42-48, 1989. 125. Richard RR, Hudson AR, Bertoia JT, Urbaniak JR, Waddell JP: Injury to the brachial plexus during Putti-Platt and Bristow procedure. A report of eight cases. Am J Sports Med 5:374-380, 1987. 126. Rookwood CA: Subluxation and dislocation about the shoulder. In CA Rockwood, DP Green, eds: Fractures in adults. Philadelphia, 1984, JB Lippincott, pp. 722-860. 127. Rockwood CA Jr: Subluxation of the shoulder: the classification, diagnosis and treatment. Orthrop Trans 4:306, 1979.
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References
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CHAPTER
5e
Workplace Adaptation for Shoulder Disorders Thomas J. Armstrong
This chapter is concerned with workplace adaptations for preventing work disability due to shoulder, neck, and elbow impairments. Disability occurs when work demands exceed worker capacities (Fig. 5e.1).3,9 Development of workplace adaptations requires information about both worker and job demands, which can then be compared to determine whether new or additional adaptations are required. Although population work capacity data can often be determined from published data and models, individual data must be obtained from a qualified health care provider. The health care provider plays an important role also in determining how successful intervention has been and whether additional job modifications are required. Development of workplace adaptations requires the affected worker, the health care provider, and the employer to work closely together. Although the concept of disability is straightforward, its determination of disability and the development of adaptations are more complex due to the multiple physical, behavioral, and social variables involved. It is possible unwittingly to declare a worker disabled who is not or to declare one able who is not. It may be found, for example, that a worker is disabled because of a shoulder impairment that restricts his or her reach capacity, but that worker might have learned to adapt the workplace by rearranging equipment or standing up to reach distant objects. Similarly, it may be found that a worker is able to reach all the necessary work objects but is disabled by inability to do the job for 8, 10, or 12 hours per day.
EXPOSURE-RESPONSE RELATIONSHIP It is necessary to understand in general and specific terms the relationship between work factors and conditions that affect fatigue and risk of musculoskeletal disorders (MSDs). This relationship is referred to as the exposure-response relationship.4,34,35 Figure 5e.2 shows a hypothetical exposure-response relationship with exposure on the horizontal axis and response on the vertical axis. A number of metrics have been proposed and used for describing exposure; some of these are described later in this section. Response is typically expressed as the prevalence of symptoms or conditions at a given time or as an incidence rate of cases over time. Exposure-response relationships typically exhibit a sigmoid relationship as exposure increases from low to high. The prevalence and incidence of MSDs at low exposures are referred to as the background level and may be due to personal or other nonwork factors. The prevalence and incidence may also vary from one sign, symptom, condition, and measurement method to another. Figure 5e.2 illustrates two examples: curve a shows a low background level and a high sensitivity to work factors and curve b shows a high background level and a low sensitivity to work factors. In the future, we will have sufficient data to specify job designs for given populations that will produce an acceptable level of risk. Until then, the exposure-response relationship still provides important insights for job designers. Exposure-response relationships are based on a series of biomechanical and physiologic mechanisms.4,34,35 Work activity entails exertion of the body to overcome the weight, resistance, and inertia of work objects. These forces produce moments about joints that must be counteracted by muscles. The position of the body and the external forces are exposure variables and the moment about the shoulder is a response variable. At a second level, the joint moments can be regarded an exposure variable, whereas the muscle force acts as a response variable. At a third level, muscle forces can be regarded as exposure variables and perceived exertion, discomfort, and fatigue as short-term
Modify job
Treat worker Yes
Determine job demands
Response
Disability
b
Evaluate worker Demands > capacities
a
Exposure No Successful adaptation Figure 5e.1 Basic process for accommodation of work populations or individual workers.
Figure 5e.2 General exposure-response relationship shows an increasing prevalence or incidence of pain, fatigue, or other musculoskeletal disorders with increasing frequency and duration of force and posture. Curve a illustrates a low background level and a high sensitivity to a given factor and curve b illustrates a high background level and low sensitivity to a given factor.
196
Chapter 5e
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Workplace adaptation for shoulder disorders
response variables. Chronic tissue injuries and corresponding symptoms can be regarded as long-term responses. These biomechanics and physiology relationships are supported by experimental, psychophysical, and epidemiologic studies.4,34,35
Law, when a worker reaches for an object, the muscles in the shoulder and elbow must produce sufficient moment forces of gravity on the arm, forearm, and hand (Fig. 5e.3). A work object in the hand requires additional muscle force. The load moment on the shoulder, Ms, can be calculated based on the size of the body parts and their weight13,36:
Biomechanics An important example of the exposure-response relationship is found in the shoulder, the examination of which provides useful tools for developing workplace adaptations. By Newton’s Third
Ms = cosθ1x1w1 + (cosθ1l1 + cosθ2x2)w2 + (cosθ1l1 + cosθ2l2 + cosθ3x3)(w3 + wobject) where l1, l2, l3 are lengths of the arm, forearm, and hand; θ1, θ2, θ3 are angles of the arm, forearm, and hand with respect to
Mtot W3 W1
W1
X1
X2
I1
A
Wobject
X3
I2
I3
q3 q1
q2
B Figure 5e.3 (A) The moment produced about the shoulder is equal to the sum of the moments produced by the arm, forearm, and hand. In addition, the weight of a work object such as a part or tool contributes to the shoulder moment. (B) The angles of the arm, forearm, and hand with respect to the horizontal are shown.
Chapter 5e
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Exposure-response relationship
Table 5e.1a Average body link sizes as fractions of total stature16
Table 5e.1c Body segment weights as percentages of total body mass15,29
Link
Link
Stature Floor-ankle Floor-knee Floor-hip Floor-shoulder Floor-elbow Floor-wrist Floor-hand Floor-buttocks Floor-eye Center-shoulder Shoulder-elbow Elbow-wrist Wrist-hand
Fraction 1.000 0.039 0.285 0.530 0.818 0.630 0.485 0.377 0.480 0.936 0.129 0.188 0.145 0.108
the horizontal; x1, x2, x3 are the moment arms between the proximal joint and the center of gravity of the arm, forearm, hand, and work object; and w1, wf2, w3, wobject correspond to the weights of the arm, forearm, hand, and work object. The moment arms can be measured for a given individual or estimated from height of a given population percentile using the relative link lengths shown in Table 5e.1a16 and the link center of gravity locations shown in Table 5e.1b.15,29 Weights of each segment can be estimated for a given individual or population percentile weight using the relative segment weight data shown in Table 5e.1c. Height and weight data for the U.S. adult population are shown in Table 5e.2. The calculated shoulder and elbow moments for persons with average female and male stature and weight performing a horizontal reach at elbow height and at shoulder height are shown in Figure 5e.4. Figure 5e.4, b, d, f, and h, shows how the moment about the shoulder due to the weight of the arm, forearm, and hand increases with the horizontal reach distance. Added to the weight of the arm, forearm, and hand, the moment of the weight of a held object such as a tool or part would equal the distance between the shoulder and hand times the weight. Holding a 10 N (2 pound) tool in the hand at a distance of 0.6 m, for example, would add 6 Nm to the 10 Nm of the arm and forearm. This simple biomechanical analysis can be applied to many work tasks. Figure 5e.4, for example, shows a 7-Nm shoulder load in the shoulder of an average female holding her hands over a keyboard at a distance of 0.5 m, with the moment proportionally
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Relative body mass
Head Arm Forearm Hand
6.9% 2.7% 1.6% 0.6%
higher for a worker with greater body weight. The biomechanical analysis provides both a qualitative and quantitative rationale for job design.
Important limitations Deliberately simplified for demonstration purposes, this analysis of shoulder stress generally underestimates the actual loads. Increased loads result from inertial forces associated with acceleration and deceleration of the body and work object. Additional loads may result also from antagonistic muscle forces. Although some antagonistic muscle contractions are inevitable, others may result from psychologic stresses,7 the contributions of which, although real, are difficult to quantify and beyond the scope of this discussion.
Other biomechanical considerations In addition to the effect on muscle workload, increasing shoulder angles produce pressure on internal and surrounding soft tissues.22 In fact, although the required muscle loads actually decrease as the arm torso arm angle exceeds 90 degrees, pressure on soft tissues continues to increase. Epidemiologic studies show that elevated elbow postures are associated with elevated incidences of chronic shoulder pain and impairment.6
Other body parts Similar analyses can be performed for other parts of the body, such as the neck.23 Bending the neck or torso forward to reach or see work objects such as documents, controls, or equipment produces load moments on the neck that must be counteracted by internal muscle forces. Extreme rotation of the forearms in combination with forceful exertions of the hands produces stress on the attachments of the finger flexor and extensor muscles. As a general rule, jobs should be designed so that workers do not have to perform sustained or repeated exertions at or near range of motion limits. Ideally, the elbows should be near the sides of the body, the forearms should not be rotated to one extreme or the other, and the head should be held upright. At the other extreme, the work pace should enable workers to periodically stretch and change positions. Even the best posture eventually becomes uncomfortable if it is maintained too long.
Table 5e.1b Body segment distance from proximal joint center of gravity15 Link Arm Forearm Hand
Center of gravity 43.6% 43.0% 50.6%
Localized fatigue Acceptable work design standards for preventing MSDs that may afflict the elbow, neck, and shoulder have not been established, but recommendations may be made for preventing localized fatigue. An important problem in its own right, localized
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Table 5e.2 Statures (m) and body masses (kg*) for males and females ages 18 and over from the National Center for Health Statistics11 Female
Stature Weight
Male
Average
5%
50%
95%
Average
5%
50%
95%
1.618 69.2
1.504 48.0
1.618 65.6
1.73 102.5
1.755 82.1
1.636 59.7
1.755 80.0
1.880 110.8
*1 N = kg × 9.8 m/s2.
fatigue may be a harbinger or precursor of more serious MSDs.34,35 According to the above exposure-response relationship, localized fatigue responses include concentrations of metabolic substrates, metabolites, and ions. These changes may result in altered electromyograms, reduced motor control, reduced strength, and, perhaps most importantly, pain. Exposures are expressed as percentages of maximum voluntary contraction (% MVC), exertion frequency, and duty cycle. The % MVCs are computed as the ratio of the required muscle force to that possible for a given task, individual, or population or as the ratio of job demands to worker capacities, as shown in Figure 5e.1. Recommended acceptable exposure limits for continuous work previously ranged from 0 to 15% MVC; those for intermittent work range from 17% to 21% MVC. Bystrom and Fransson-Hall10 recommended an upper limit of 10% MVC for continuous static work and 17% MVC for intermittent work. The above biomechanical analysis of the shoulder loads during reaching and lifting can be used to estimate relative muscle workload for a given task, but first it is necessary to consider worker capacity.
Worker capacity Acceptable workloads vary from group to group and person to person, and design commonly accommodates the general population or a specific individual. In the former case, work capacity data are typically taken as a lower percentile of the general population. It is all too common to design for a 5th percentile, a practice that seems to be reinforced by reference books showing the 5th percentile, average, and 90th percentile population data. The problem is that 5 people out of 100 may be disqualified or experience significant difficulty or injury doing the job. Design for an individual requires a function evaluation that specifies strength limits for that person. The designer should work closely with the evaluator during and after design implementation to make sure that the job can be performed without risk of injury or reinjury. For discussion purposes, data from Winters and Kleweno,40 shown in Figure 5e.5, indicate that female strength is about half that of male strength and that male strength is sensitive to shoulder posture. The average female strength of approximately 30 Nm is significantly less for an elderly or injured worker. Reaching results not only in increased load moments on the shoulder (Fig. 5e.4) but also in decreasing strength (Fig. 5e.5). Vertical reaching also reduces strength. Figure 5e.6 shows a job in which a female of average stature, proportions, and weight gets 10 N parts at a rate of 20 per minute from a rack at a distance of 0.625 m at shoulder height
and places the parts on a moving tray at a distance of 0.32 m. Because the trays are moving, the worker cannot rest her forearms while waiting for them to come into position. The shoulder moments due to the weight of the body and load are calculated in Table 5e.3 and are plotted in Figure 5e.6B. (Loads between successive positions are approximated as straight lines.) It can be seen that the moments increase due to the weight of the arms during the reach. The moment then increases as the part is lifted and then decreases as it is moved into position to wait for the tray to come into position. Finally, the load force decreases to zero as the load is released, but the shoulders must continue to support the weight of the body. The average total shoulder moment can be calculated as a time-weighted average: Ms =
( ∑ t i Mi ) ∑ ti
where Ms is the average shoulder moment, ti is the duration of the ith work element, and Mi is the average total moment produced during the ith element. For this sample task the average moment is calculated as = [0.67 × (4.5 + 9.8)/2 + 0.13 × 9.8 + 0.79 × (16.05 + 7.71)/2 + 2.00 × 7.71 + 0.36 × 7.71 + 0.07 × (7.71 + 4.5)/2]/4.0 = 8.4 Nm This analysis provides important insights into the factors that should be considered in evaluating and designing work stations. It is important to know the locations of controls and those where materials, parts, and tools are stored and used as well as the forces required to obtain, hold, and use work objects. The list of work elements and their durations33 are likewise all significant factors affecting the load on the shoulder and other parts of the body. As described earlier, loads on the body are frequently normalized as a fraction of maximum strength or percent of maximum voluntary contraction, % MVC, which is used commonly as a metric of physical workload and predictor of localized fatigue. Calculation of relative workload requires information about both the absolute load and the corresponding work strength. Strength varies among workers, joints and their relative positions, hands, ages, and occupational groups and may be affected by fatigue, injuries, and diseases. The analyst may select a value from the literature that corresponds to the population of interest or use data provided by a functional evaluation of a specific worker of interest. Based on an average strength of 30 Nm, the average relative workload for the worker described in Figure 5e.5 and Table 5e.3 would be 28% MVC. Joint loads can be estimated also from surface electromyography (EMG), which can be regarded as a response variable
–0.40 –0.20 0.00 – 0.05 – 0.10 – 0.15 – 0.20 – 0.25 – 0.30 – 0.35
0.00
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0.40
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Moment (Nm)
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0
14 12 10 8 6 4 2 0 –2 –4 –6
Shoulder moment (Nm) Shoulder angle (°)
– 20 – 40 – 60 – 80 –100 –120 –140 –160
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B
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14 Shoulder moment (Nm) Shoulder angle (°)
12
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C
0.00
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Moment (Nm)
10
– 20 – 40
8
– 60
6
– 80
4
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–2
–140 –160
–4 0.0
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Female 0 –10 – 20 – 30 – 40 – 50 – 60 –70 – 80 – 90 –100
14 Shoulder moment (Nm) Shoulder angle (°)
0.00 0.00 – 0.05 – 0.10 – 0.15 – 0.20 – 0.25 – 0.30 – 0.35
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12 10 8 6 4 2 0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Distance (meters)
E
F
Male
Male 0 –10 – 20 – 30 – 40 – 50 – 60 –70 – 80 – 90 –100
14 Shoulder moment (Nm) Shoulder angle (°)
0.00 0.00 – 0.05 – 0.10 – 0.15 – 0.20 – 0.25 – 0.30 – 0.35
0.20
0.40
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0.80
Moment (Nm)
12 10 8 6 4 2 0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Distance (meters)
G
Female
H
Female
Figure 5e.4 Calculated shoulder and elbow moments due to the weight of the arm, forearm, and hand for an average male and female performing a horizontal reach at elbow (A-D) and at shoulder (E-H) heights for females (C, D, G, H) and males (A, B, E, F).
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ANALYSIS OF JOB TASK DEMANDS
100
As stated at the beginning of this chapter and shown by the above discussion, information about task demands is necessary for disability evaluation and work adaptation design. Collecting job and worker information requires a systematic approach in two steps.
80
MS (N-m)
Males 60
Job task demands The first step documents what, where, when, and how the job is performed and includes the process, equipment, procedures, and environment.
40
20
Job documentation
Females
0 0
30
60
90
120
Figure 5e.5 Shoulder strength for four healthy young females and four healthy young males versus shoulder angle with elbows straight (triangles) and flexed 90 degrees (circles).
to external load.23,26,31 Generally, EMG methods are used to verify hypotheses developed using biomechanical analyses and psychophysical studies. Electrodes are attached over one or more of the muscles associated with the joint motion of interest and connected to appropriate preamplifiers, amplifiers, data loggers, and computers. The test can be normalized with respect to a maximum exertion or some other reference signal and provide a continuous real-time indication of muscle load. Further discussion of EMG methods is beyond the scope of this chapter.
A thorough documentation of the job helps to ensure a systematic analysis of all relevant factors and enables the analyst to identify those that contribute to stressful postures. Finding that the job involves exposures to extreme shoulder postures, for example, is insufficient without information explaining what actions like reaching for a part or operating a control produce those postures. This information enables the analyst to recommend possible interventions to reduce that stress. Evaluation of particular stresses, such as part weight and location, can be used to calculate the load moment on the shoulder.
Observations Documentation procedures may need to be adapted to the type of jobs being studied. In many settings, particularly manufacturing, the work is by design standardized to control work quality and production, but subtle differences from worker to worker may depend on their sizes, methods, and skill levels. A short worker, for example, may have to reach up and over, whereas a tall worker may have to reach down and under. One may choose
Shoulder (Nm)
20 Total (Nm) Load (Nm) Body (Nm)
15 10
Average
5 0 0
A
1
2 Time (s)
3
4
B
Figure 5e.6 (A) A worker reaching 0.625 m forward to get 10 N (2 pounds) parts from trays 0.320 m in front of her on a moving tray and a rate of 20 per minute. (B) The moment due to the weight of the body and work object are shown. Average total moment (body plus work object) is 8.4 Nm for the work cycle.
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Table 5e.3
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Analysis of Job Task Demands
201
Work elements, locations, and loads for a repetitive hand transfer task
Work element
Elapsed time
Hand location
Load weight
Moment load
Moment body
Total
Reach Grasp Move Wait Position Release
0.67 0.13 0.79 2.00 0.36 0.07
32.1→62.5 62.5 62.5→32.1 32.1 32.1 32.1
0 0 10 N 10 N 10 N 0
0 0 6.25→3.21 3.21 3.21 0
4.5→9.8 9.8 9.8→4.5 4.5 4.5 4.5
4.5→9.8 9.8 16.05→7.71 7.71 7.71 4.5
to walk around a pallet of parts, whereas another reaches across. Although one worker may be able to complete work promptly and take brief rest periods, another may have trouble keeping up and have no rest. How workers perform their jobs may change over time. In some cases, jobs contain multiple tasks, as though each was two or more jobs. The documentation should include identification of each task, its frequency, and its duration. Frequencies and duration may vary from day to day, so it is necessary to either observe the job over time as previously described or to ask the worker or supervisor to estimate the variation. An increasing trend to rotate workers among jobs occurs in many cases to maintain production schedules by cross-training them to deal efficiently with absenteeism and schedule changes. In other cases it is done to reduce exposure to highly demanding jobs. Generally, the analyst performs at least a cursory analysis of all the jobs the worker performs, particularly if he or she has had a musculoskeletal injury. It is common to manufacture different product models or even products on the same production line. In some cases the worker may have to hurry to perform all the required assembly operations without rest, whereas at other times they may be able to work quickly and rest frequently. Some jobs, such as maintenance, repair, and office work, have yet to achieve a high level of standardization and instead typically entail two or more tasks that may be performed at irregular intervals for variable periods. These multitask jobs may require considerably more time than a standardized singletask job. For the above reasons, observations should be repeated for several workers over time to assess job variations for those being studied. While interviewing workers, the analyst should anticipate this variability. Differences from one worker and one work station to the next often provide insights into how the job can be improved. The documentation can be performed from available job descriptions, time studies, workplace inspections and measurements, equipment specifications, and interviews with workers and supervisors. To facilitate cooperation of both the worker and employer, it is important that the job analysis minimizes disruption of work activities. Because the goal is to obtain information about how the job is performed under normal work conditions, minimal disruptions will help keep the worker from being distracted by the analyst. Available information may include job descriptions from the personnel department, standard work method descriptions, and
time analyses from industrial engineering or previous ergonomic assessments. Job descriptions from the personnel department tend to focus on skill requirements rather than on force and posture patterns. Work method and time descriptions can be quite useful because they usually describe the methods and time allocations. Combined with information about work objects and work stations often make it possible to predict loads and postures as described above. Because the job may have changed since the standard was developed, work method and time descriptions should always be verified with observations or interviews. Although in some cases an ergonomic job analysis has previously been performed, at present such analyses are not standardized. Unless the analyst has first-hand knowledge of the job and the methods used to analyze it, each job should be inspected to verify that all necessary information was included or that it has not changed.
Video recordings Still and video images have become integral parts of job analyses. Readily available low-cost digital and video cameras can now be used to collect images and transfer them into computers where they can be viewed and edited. Freeware, such as Apple Computers QuickTime™, can be used to play back digital films frame by frame, the most useful of which can be captured and pasted into report documents. A few simple steps will greatly improve the quality of the video data: (1) obtain permission from the worker and the employer, preferably in writing; (2) record several representative work cycles, both to allow the worker to get used to the camera and to observe variations; (3) take pictures from several angles (the view of one hand may be blocked by the body or other obstructions); and (4) use a tripod to improve video steadiness most efficiently and least expensively. Video cameras often can be set up and left to run unattended, even with intermittent pauses at specified intervals.24 If video recordings are not possible, the analyst may elect to make periodic tours of the workplace to observe and record personally. Intermittent observations of worker activities are referred to as “work sampling”; statistical procedures have been described for estimating confidence limits for the frequency that a task occurs.17,33 To get a confidence limit of a few percent, typically hundreds of samples are required, which may be beyond the scope of most studies. Statistical calculations are based on the assumption that the observations are randomized. Although generally there is sufficient variation in the work process to allow fixed interval sampling, the analyst should make sure that
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observations are not synchronized from any workplace activities that could bias the results.
Measurements of the work station and equipment Physical measurements of the work station often can be made before or after the shift or while the worker is on break. The employer may have engineering drawings that enable the analyst to determine key dimensions such as the height of the work surface and the location of parts, assemblies, and controls; otherwise, it will be necessary to determine these dimensions using a tape measure. In either case it is necessary to establish reference lines or planes for these measurements. The ideal reference plane for vertical measurements for a vertical worker, for example, is the floor. The ideal horizontal reference plane is a vertical plane that passes through the barrier separating the worker from the work object. For a seated worker, this is the front of the desk, whereas for a standing worker reaching into a bin of parts it is the edge of the bin. The reference plane for horizontal measurements should correspond to a barrier that restricts movement from side to side. For a worker seated in a fixed location, this may correspond to the sagittal plane of the body; if the worker is standing and free to step side to side, then measurements to either side may not be of critical importance, unless the worker is required to reach two objects with opposite hands at the same time.
Table 5e.4 Basic job documentation information can be obtained from existing job descriptions, interviews, observations, and physical measurements For the job Formal job title (in company documentation) Informal job title (among workers and supervisors at the work site) ● Work objectives (one or more reasons that the job exists) ● Job tasks (all worker duties that share a common purpose; tasks may or may not be separated in time and space) For each job task ● ●
● ● ● ●
● ●
Objective Tools and equipment (ID, size, weight) Materials and parts (ID, size, weight) Methods (step-by-step description in necessary detail of what the worker does to perform the task) Work station (sketched or described with key dimensions) Environment (location and conditions of job)
The second part of the analysis assesses the physical job stresses. As mentioned at the beginning of this chapter, exposure-response entails a cascading series of relationships.4 Job demands may be characterized as a force and posture profile, as a load moment profile for a joint such as the shoulder, as the muscle activity (measured in an EMG), or as a symptom such as localized discomfort.
same time or push and pull quickly, creating an inertial factor. Direct weight and breakaway force measurement may be a starting point, but often second- or third-level methods such as EMG or perceived exertions are also necessary. Joint angles between two adjacent body segments can be measured using goniometers, including manual devices that require the worker to stop while they are positioned over joints and electrical devices that can be attached to a data logger or computer for continuous posture recordings. Gerr et al20 described the use of manual goniometers for determining major body angles in computer users. Joint angles can also be estimated from direct observations of workers or indirect observations of photographs and movies. Observations are subject to observer and parallax errors.30 Parallax errors can be minimized by aligning the viewer with the axis of joint rotation. Often this is not possible; however, an experienced job analyst can often do an adequate job of mentally compensating for parallax errors. It is helpful to observe or record images from several views. Joint moments can be calculated from loads and body positions. Recall that moments are related to both the magnitude of the force and the distance between the force and the center of joint rotation. In some cases, it may be possible to stop the worker and measure distances using a tape measure. Sometimes distances can be estimated from dimensions of the work place. In other cases, they may be estimated from pictures. In some cases, the forces correspond to the weight of an object lifted; in others, they correspond to the force to hold or move one object against another. Then it is necessary to simulate the workers’ actions with a force gauge.
Measurement of posture and force
Surface EMG
Postures and forces can sometimes be measured directly using force gauges and goniometers. In the example shown in Figure 5e.6, the major forces are due to the weight of the work object and that of the upper limb. However, many cases are not this simple: The worker may lift, push, and pull, for example, at the
Surface EMG, in which electrodes are placed on the skin over the muscles of interest, is used most commonly for exposure and fatigue assessment. Electrodes are connected to preamplifiers, amplifiers, and some kind of recording device. The signals may be recorded by a portable memory device that the worker
Interviews Worker and supervisor interviews are important sources of information, the quality of which can be greatly improved with a few rules32: (1) explain the purpose of the interview, (2) list the key points to be covered, (3) avoid leading questions, (4) clarify by summarizing back to the interviewee, (5) do not let the interview wander into irrelevant areas, (6) protect the interviewee’s confidentiality, and (7) take careful notes or use an audio recording device. Interviews may be performed with one or more workers at a time. Questionnaires also can be used to obtain information from workers and supervisors, but development of a valid questionnaire to obtain desired information about a given job can be a major undertaking in its own right. Table 5e.4 is intended as a template for a job documentation data collection form that the user can modify to suit specific needs.
Physical job stresses
Chapter 5e
wears or by a digital computer. The worker may be tethered to the computer by wires or connected via radio transmitter. Because EMG values may change very quickly, it is necessary to record signals over several representative cycles at high frequencies. The volumes of data generally dictate the use of a computer and appropriate software for analysis. Jonsson26 and Mathiassen and Winkel31 described procedures summarizing force patterns using EMG data that indicate rest/recovery time versus work time. The investigator must be familiar with human anatomy and with the operation (including calibration) of the equipment to obtain meaningful results. An important quality of EMG is that it provides information about a specific body part under real work conditions by a real worker; a limitation is that an EMG provides information about only a very small part of the body. In some cases additional channels can be used to monitor multiple muscle groups simultaneously, but this may be too cumbersome and disruptive in many work situations. Some EMG measurements can be performed on a subject simulating some part of or the entire job in a laboratory. Although an important tool, EMG is an advanced technique for use after observations and simulations have documented the job and identified the specific muscle groups. A number of commercial EMG systems are now available and easy to find on the Internet; the user is cautioned, however, to understand clearly where and how the test will be used and to have adequate technical support.
Psychophysical responses Joint loads can be assessed also using perceived exertion,8,23 which is affected by localized fatigue. Most commonly it is measured using a Borg scale of relative perceived exertion (Fig. 5e.7B), but it may be assessed using visual analog scales also shown in Figure 5e.7C. On average both work equally well, but some prefer the Borg scale while others prefer the visual analog scale.39 One of the important and useful features of perceived exertion
2
0 1
6
10
3
7
11 12 13
4 5
8 9
14
15
16
17
A
Very uncomfortable work
0 0.5 1 2 3 4 5 6 7 8 9 10
Nothing at all Very, very easy Very easy Easy Moderately hard Somewhat hard Hard Very hard Very, very hard
B
Very comfortable work
C Figure 5e.7 Local discomfort patterns can be mapped by asking the worker to indicate areas on a body part map as shown in A. Localized and overall discomfort and effort can be quantified using the modified Borg scale shown in B or a visual analog scale shown in C.
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Analysis of Job Task Demands
is that it can be measured simultaneously for different parts of the body.14 Regional body discomfort patterns can be compared with workload patterns and with underlying impairments. Saldana et al37 described the use of a computer program to evaluate discomfort patterns in rural letter carriers. Readily applicable to other types of work, this method is particularly well suited for studying office workers who regularly use a computer. Studies by Ulin et al39 showed that perceived exertion associated with the use of a pneumatic hand tool increases with work distance from the body and with increasing elevation above the shoulder and decreasing elevation below the elbow. Krawczyk et al27 showed similar results for the hand transfer tasks. With repeated or sustained exertions, the worker may begin to experience discomfort. With exertions performed over longer periods such as days, weeks, or years, the worker may experience chronic symptoms. The Nordic Health Questionnaire provides a standardized instrument for collecting work symptom data.28 Saldana et al37 demonstrated how a computer could be used to collect worker symptom data and how these data correspond with work patterns. Symptom data are easy to collect and require minimum equipment; the data may be highly variable from one worker to the next, however, and care is required to avoid bias.
Event-based versus time-based observations The analysis may be “event based” with observations recorded only when an event of interest occurs, such as when a worker reaches for or uses a work object. Joint loads are plotted as a function of time in Figure 5e.6, but because the times correspond with the worker’s reaching for parts, it is an event-based analysis. The definition of events is arbitrary: They may correspond to specific work elements as shown in Figure 5e.6, with only selected work elements, or with the use of certain tools. The example shown in Figure 5e.6 is an event-based analysis in which the events are work elements and straight-line extrapolations are used between successive events. The selection of events is determined by the job documentation and the goals of the analysis. The analysis may also be “time based” in that the forces and postures are observed continuously or at specific time intervals. The corresponding events are then examined to identify the work factors that cause the extreme force or posture. Forces and postures may be estimated from observations, measured directly using force gauges and goniometers, or predicted by biomechanical models and insights. The work sampling method described above is a time-based analysis of activities, but it could be combined with force and posture measurements.
Prediction of posture and forces Figure 5e.4 shows how link data can be used to estimate postures and forces of males and females of given percentiles at selected locations. In many cases, the analyst may mentally extrapolate based on observations and experience. When a tall worker is seen reaching overhead for a part, for example, it becomes obvious that a short worker or one with limited mobility will be even more challenged to perform the same task. The analyst may want to report not only what was observed, but what might be observed for another worker. The moments about the shoulder and elbow can be computed using the methods described above if additional quantification is desired. These values can be used to predict and compare
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worker endurance at the observed versus modified work stations. Many third-party biomechanical models available for purchase or for download as shareware or freeware can be used to facilitate analysis of loads on the entire body or on selected body parts. One commercially available product is the University of Michigan Three-Dimensional Static Strength Prediction Program.13 This program enables the user to enter information about the location and direction of the load, at which the model calculates moments and populations for percentiles at each major joint. The user also can directly enter body part sizes and positions for a given problem.
WORKPLACE ADAPTATION The preceding discussion indicates that workplace adaptations entail reducing load moments by rearranging work objects and eliminating stressful postures, reducing forces themselves, or reducing the time that forces must be exerted. Such adaptations include rearrangement of work space layout and use of lighter tools or materials, mechanical assistance, and/or body supports.
Placement of work objects Ideally, work objects such as materials, parts, tools, assemblies, controls, and data input devices should be placed as close to the worker as possible at or near elbow height. Aforementioned studies by Ulin et al39 found that some workers prefer to use tools slightly above elbow height, which may provide better visibility, whereas others prefer them slightly below, which may enable them to lean into the task at hand. Similarly, Sauter et al38 and Grandjean et al21 showed that most keyboard users prefer positioning conventional keyboards at or near elbow heights, but some prefer it slightly higher or lower. Personal preferences vary significantly from person to person. As shown in Table 5e.2, worker size varies significantly between and within gender groups. Individual preferences also vary among workers of the same size and for the same worker over the course of the day; even the best position eventually becomes uncomfortable. Because one-size work station will not fit everyone, it is very important for each worker to be able to adjust the work station to his or her own preference. Achieving this flexibility begins with designing equipment in ways that make such adjustments easy and convenient. If a mechanic must come to raise or lower a keyboard, the adjustment probably will not occur as often as needed. Workers must be trained and encouraged to adjust their work stations, with periodic inspections to make sure that they are doing so. A worker’s failure to adjust a work station upon inspection may not mean a discipline problem but rather a lack of training or time, an adjustment for temporary stretch break, or equipment that is difficult or unsuitable to adjust. It is important to discuss these issues with the worker. Although it is usually desirable to locate work objects close to the worker, it is not always possible. In many cases the job may entail work on large equipment, parts from multiple sources, or use of several tools and controls. Work station design begins with a thorough knowledge of the work objective, tools, materials, and methods as well as worker size and strength, as shown in
Tables 5e.1a, 5e.2, and 5e.4. Together this information can be used to map worker reach capabilities or envelopes and to calculate load moments, as shown in Table 5e.3.
Anthropometric considerations Figure 5e.8 shows maximum reach envelopes for 5th percentile female and 95th percentile male statures on horizontal work surfaces. In one case the arm is outstretched at shoulder height, and in the second case the shoulder is constrained to -60 degrees (Re. horizontal). There is nothing sacred about the 5th and 95th percentiles; universal designs that accommodate all possible users are preferable. As a practical matter the selection of design benchmarks is based on costs and benefits, although the cost of potential litigation can favor inclusion of more users in an analysis and design. In either case, it is still necessary to have information about the size of the potential work population or a specific individual to be accommodated. It is also possible to estimate the effective work area subject to desired posture constraints. The effective work area for the small female shown in Figure 5e.8d, for example, is approximately 0.48 m2. Based on a straight hand, this calculation disregards any intrusion of the body into the work space. As a practical matter, the area should be reduced a minimum of 8% for a relatively lean body. The reach distance and area would be further reduced if the worker must hold an object like a mouse or a power tool. Reducing the reach distance by one-half hand length to allow for gripping would reduce the effective work area by 24% from 0.48 to 0.36 m2. Adjusting for the incursion of the body into the work area further reduces the work area to 0.32 m2. Of course the worker can reach farther, but it would be at the expense of increased shoulder and/or back flexion. Although reasonable for short periods, such increased flexion may be unsatisfactory for prolonged or sustained work. Objects that are used continuously or frequently should have first priority for this space. For a data entry job, for example, these would be the keyboard, mouse, and source documents. Objects used less frequently such as a telephone, the computer CPU, or stored reference documents may be placed at the outer limits of the reach envelope. A typical keyboard requires 0.1 m2 of space, a mouse another 0.1 m space, and a standard 8.5 × 11-inch document another 0.6 m2, totaling 0.26 m2 of the available 0.32 m. The areas required for the keyboard, mouse, and documents, however, are not contiguous, and workers generally position them in a way that conforms with their body positions. As a result the 0.32 m2 will be more than used up. The required space can sometimes be reduced by selecting alternative equipment. A track ball or touch pad, for example, would reduce the mouse area to less than 0.01 m2. Unless the worker uses the numeric keypad, a shorter keyboard might be substituted. By holding a document on an incline, a stand or holder can reduce its footprint. With the many choices of computer input devices and work stations that are now available, the feasibility of these adaptations of course depends on job demands and individual capacities. Additional anthropometric guidelines for design of computer work stations have been published by the Human Factors and Ergonomics Society.25
Chapter 5e
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Figure 5e.8 Reach envelopes computed according to National Health Survey Data of stature and relative link length data reported by Drillis and Continni.16 (A and B) Side views of someone with 5% female stature and average body proportions with an arm outstretched at shoulder height and the shoulder constrained to −60 degrees (Re. horizontal). Restricting shoulder flexion to −60 degrees reduces reach distance by 21% from 0.66 to 0.52 m and elbow height from 1.23 to 0.99 m. (C and D) Top views of the elbow height reach envelopes for the 5 percentile females with and without shoulder constraints. (E and F) Top views of the elbow height reach envelopes for the 95 percentile males with and without shoulder constraint. For the large male, restricting shoulder flexion reduces reach distance by 22% from 0.83 to 0.65 m and reduces elbow height from 1.54 to 1.23 m.
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The above calculations were based on standard percentiles. Similar calculations can be performed based on link length estimates for an individual by using the link length fractions reported by Drillis and Contini16 and displayed in Table 5e.1a or those reported by Dempster15 and others.13,29 Minimizing the reach distance helps to minimize the load on the shoulder. Work that requires continuous visual feedback may result in prolonged neck flexion, however, requiring a tradeoff between loads on the shoulder and neck. The solution depends on the task. Most experienced keyboard users, for example, can work without watching their hands; however, documents laid flat on the work surface require the worker to look down. In many cases this problem can be solved with a document holder. It is not uncommon, particularly in medical billing, for the source documents to contain many pages that are bound together and may require a custom holder. In some cases, like fine assembly and dental work, it is necessary to bring the work in line with the eyes, often by providing arm and body supports. The traditional assembly line presents some special design challenges because it is often in continuous motion and difficult to make work stations individually adjustable (Fig. 5e.9a). Also, the worker often must reach over a structure along the sides of assembly line. Space is required not only for the line itself, but also for parts containers and tools. Parts may be stacked in front of, beside, or behind the worker, whereas tools may be suspended overhead or mounted or laid along the side of the line. There have been many improvements in manufacturing methods over the last 30 years that help to address these issues. Lean manufacturing discourages large inventories of parts that fill up the work space and increase reach requirements (Fig. 5e.9b). There is increasing emphasis on kitting of parts so that only those needed for a specific assembly are delivered to the work
site at the time required. In addition to reducing inventory costs, these methods also reduce reaching.
Tool weight control Loads can also be reduced by decreasing the weight of work objects by using lighter tools, for example. Armstrong et al2 found that workers consistently rated hand tools weighing more than 18 N as “too heavy.” The weight of a work object may otherwise be an asset; for example, the weight of a power tool for driving threaded fasteners or for sanding or buffing may reduce the force required. Of course, this is true only with horizontal surfaces, when the worker is driving threaded fasteners down or sanding or polishing the top, as opposed to underneath, where tool weight would be a liability. Tools that work well in one situation may not work well in another. Adaptation development requires a thorough job analysis.
Mechanical assists A mechanical assist can be defined as any mechanical device that helps to reduce the task demands on the worker. In this context we are concerned with devices that reduce the load moments about the elbow, shoulder, and neck. A mechanical assist may range from a complex robotic device capable of supporting high forces with low-force guidance to a simple work surface that relieves the worker of the need to support an object in use. Some examples of mechanical assists include the following: Lifts raise or lower materials to reduce bending and reaching and support work objects while they are in use.
A
B Figure 5e.9 (A) A traditional continuously moving assembly line. Parts are stored in front, beside, and behind the worker. (B) A modern “lean” line in which the parts for each operation are supplied in kits that follow the assembly on the line. The line stops until the work is complete.
Chapter 5e
Turntables rotate materials and work objects to reduce reaching. Tool balancers support tools against gravity. Articulating arms may be neutrally balanced to support tools and resist reaction forces and may be powered to provide increased lifting capability for heavy objects. Carts may be used to support work objects while in use and to transport them from one work station to another. Mounting fixtures and brackets hold tools in convenient locations/ orientations when not in use. Work fixtures and jigs hold work objects, reduce loads otherwise required to hold or use them, and free one or both hands for performing useful work. Work benches support the weight of work objects and should be adjustable to accommodate various heights of users and tasks. Tools and power tools ranging from a simple pry bar to a complex poster tool combined with an articulating arm reduce the strength required to perform tasks. Although mechanical assists can greatly reduce physical loads and task demands, failure to design, select, and install them properly can result in stressful postures and increased workloads. Assists must also be easily adjustable to suit each worker and task. Additional details of these devices are beyond the scope of this chapter but are readily available on the Internet.
Worker fitness and weight National health survey data show that the level of obesity in our society is growing rapidly.12 Although fitness and weight training are the concerns of health care providers, job designers need to understand their effects on work capacities and ability to meet job demands (Fig. 5e.1). Workers with low fitness levels exert less force for a given amount of time. Load moments on the shoulder of heavy people tend to be higher than those for a person with a low body weight because their arms are heavier (Table 5e.1c). Large body masses encroach on the work space close to the body, which is the ideal location for many work objects. A large body mass also may require a worker to reach farther and to produce greater shoulder moments than a small body mass. The treating physician or therapist should be consulted regarding how the work space should be adapted for a worker with a very large body mass.
Body supports Body supports such as arm rests are widely used to counteract gravity forces on the body.1,5,18,19 In the absences of arm rests, workers often use the edge of the work bench, desk, or keyboard or the work object itself, padded with pillows, foam pads, packing materials, and duct tape. Although improvised arm rests may look crude, they are often more effective than those provided with a chair or by the employer because their position is just right for specific workers and tasks. Although chair arm rests may be fine when the arms are relaxed at the sides, they may not be close when the work task is performed, or worse they may actually obstruct a worker’s arm motions. It is increasingly common, however, to find chair arm rests with vertical and lateral adjustability. Arm rests in motor vehicles are frequently
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adjustable, folding down to support the arm for highway driving and up and out of the way for city driving. Forearm rests can also be mounted on articulating arms that adjust vertically and move freely in a horizontal plane. Articulating forearm rests are well suited for keyboard- and mouse-intensive jobs and for some bench assembly work. Forearm rests may be fashioned also from slings suspended from balancers overhead that enable the worker to move in three dimensions while reducing loads on the shoulder. As with balancers used for power tools, placement and force adjustments for each worker and task are very important.
Evaluation of adaptations It is important that workplace adaptations be evaluated to ascertain their effectiveness. A well-intended adaptation may increase rather than reduce work demands because it was ill-conceived or improperly installed or adjusted. As a minimum, evaluations should include inspection of the job. A more formal assessment may require time- and event-based analyses of work postures and forces. Worker feedback in the form of perceived exertion from one or more users also may be used to evaluate the intervention. As a practical matter, there is very seldom sufficient control or statistical power to show a significant reduction in chronic soft tissue complaints and impairments, but most employers continue to monitor health records for possible changes.
SUMMARY Resulting from job demands that exceed an individual’s work capabilities, disability can be controlled by reducing these demands through workplace adaptations or by increasing workers’ capabilities through medical treatment and physical therapy. Determining disability and designing adaptations require understanding of the exposure-response relationship, which provides a framework for work factors, external workloads, internal tissue loads, pain, fatigue, and MSDs. Many examples of mechanical assists and body supports can be found by searching the Internet. Population and individual anthropometric data can be used to specify workplace layouts, equipment, tools, and procedures that help to reduce job demands and disability. Workplace adaptations should be evaluated to verify that they have achieved their intended effect.
REFERENCES 1. Aaras A, Fostervold KI, Ro O, Thoresen M, Larsen S: Postural load during VDU work: a comparison between various work postures. Ergonomics 40(11):1255-1268, 1997. 2. Armstrong T, Punnett L, Ketner P: Subjective worker assessments of hand tools used in automobile assembly. Am Ind Hyg Assoc J 50:639, 1989. 3. Armstrong TJ, Buckle P, Fine LJ, et al: A conceptual model for work-related neck and upper-limb musculoskeletal disorders. Scand J Work Environ Health 19(2):73-84, 1993. 4. Armstrong TJ, Franzblau A, Haig A, et al: Developing ergonomic solutions for prevention of musculoskeletal disorder disability. Assist Technol 13(2):78-87, 2001. 5. Attebrant M, Winkel J, Mathiassen SE, Kjellberg A: Shoulder-arm muscle load and performance during control operation in forestry machines: effects of changing to a new arm rest, lever and boom control system. Appl Ergon 28(2):85-97, 1997.
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18. 19.
20. 21. 22.
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Bernard B, ed: Musculoskeletal disorders and workplace factors: a critical review of epidemiologic evidence for work-related musculoskeletal disorders of the neck, upper extremity, and low back. Cincinnati Department of Health, Education, and Welfare, Public Health Service, 1977, Centers for Disease Control, National Institute for Occupational Safety and Health. Bongers PM, deWinter CR, Kompier MA, et al: Psychosocial factors at work and musculoskeletal disease. Scand J Work Environ Health 19(5):297-312, 1993. Borg GA: Psychophysical bases of perceived exertion. Med Sci Sports Exerc 14(5):337-381, 1982. Brandt E, Pope A, eds: Enabling America: assessing the role of rehabilitation science and engineering. Washington, DC, 1997, National Academy of Press. Bystrom S, Fransson-Hall C: Acceptability of intermittent handgrip contractions based on physiological response. Hum Fact 36(1):158-171, 1994. Centers for Disease Control: Anthropometric reference data, United States, 1988-1994. National Center for Health Statistics, 2003. Centers for Disease Control and Prevention: Physical activity and good nutrition: essential elements to prevent chronic diseases and obesity 2004. Atlanta, 2004, Centers for Disease Control and Prevention. Chaffin DB, Andersson GBJ, Martin BJ, et al: Occupational biomechanics. New York, 1999, Wiley-Interscience Publication. Corlett EN, Bishop RP: A technique for assessing postural discomfort. Ergonomics 19(2):175-182, 1976. Dempster WT: Space requirements of the seated operator. Geometrical, kinematic and mechanical aspects of the body with special reference to the limbs. WrightPatterson Air Force Base, OH, 1955, Wright Air Development Center. Drillis R, Contini R: Body segment parameters. New York, 1966, New York Office of Vocational Rehabilitation. Drury CG: Methods for direct observation of performance. In JR Wilson, EN Corlett, eds: Evaluation of human work: a practical ergonomics methodology. Bristol, PA, 1995, Taylor & Francis, pp. 45-68. Feng Y, Grooten W, Wretenberg P, Arborelius UP: Effects of arm support on shoulder and arm muscle activity during sedentary work. Ergonomics 40(8):834-848, 1997. Feng Y, Grooten W, Wretenberg P, Arborelius UP: Effects of arm suspension in simulated assembly line work: muscular activity and posture angles. Appl Ergon 30(3):247-253, 1999. Gerr F, Marcus M, Ortiz D, White B, Jones W, Cohen S, et al: Computer users’ postures and associations with workstation characteristics. Aihaj 61(2):223-230, 2000. Grandjean E, Hunting W, Nishiyama K, Piderman M: Studies on an adjustable video screen work station. Soz Praventivmed 27(5):249-250, 1982. Hagberg M: Occupational musculoskeletal stress and disorders of the neck and shoulder: a review of possible pathophysiology. Int Arch Occup Environ Health 53(3):269-278, 1984.
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Harms-Ringdahl K: On assessment of shoulder exercise and load-elicited pain in the cervical spine. Biomechanical analysis of load—EMG—methodological studies of pain provoked by extreme position, Scand J Rehabil Med Suppl 14:1-40, 1986. Homan M, Armstrong T: Evaluation of three methodologies for assessing work activity during computer use. Am Indust Hyg Assoc J 64(1):48-55, 2003. Human Factors and Ergonomics Society: Draft standard for trial use human factors engineering of computer workstations, BSR/HFES 100. Santa Monica, 2002, Human Factors and Ergonomics Society. Jonsson B: The static load component in muscle work. Eur J Appl Physiol Occup Physiol 57(3):305-310, 1988. Krawczyk S, Armstrong TJ, Snook SH: Preferred weights for hand transfer task for an eight hour workday. Sweden, 1992, Intl. Scien. Conf. on Prevention of Work Related Musculoskeletal Disorders. PREMUS, Sweden, May 12-14, 1992. Kuorinka I, Jonsson B, Kilbom A, et al: Standardized Nordic health questionnaires for the analysis of musculoskeletal symptoms. Appl Ergon 18(3):233-237, 1987. LeVeau BF, Williams M: Williams & Lissner’s biomechanics of human motion. Philadelphia, 1992, W.B. Saunders. Lowe BD: Accuracy and validity of observational estimates of shoulder and elbow posture. Appl Ergon 35(2):159-171, 2004. Mathiassen SE, Winkel J: Quantifying variation in physical load using exposure-vs-time data. Ergonomics 34(12):1455-1468, 1991. McCormick E, ed: Task analysis: handbook of industrial engineering. New York, 1982, John Wiley & Sons. Niebel BW, Freivalds A: Methods, standards, and work design. Boston, 1998, WCB/McGraw-Hill. NRC: Work-related musculoskeletal disorders: a review of the evidence. Washington, DC, 1999, National Academy Press. NRC and IOM: Musculoskeletal disorders and the workplace: low back and upper extremities. Washington, DC, 2001, National Academy Press. Ozkaya N, Nordin M: Fundamentals of biomechanics: equilibrium, motion, and deformation. New York, 1999, Springer-Verlag. Saldana N, Herrin GD, Armstrong TJ, Franzblau A: A computerized method for assessment of musculoskeletal discomfort in the workforce: a tool for surveillance. Ergonomics 37(6):1097-1112, 1994. Sauter SL, Schleifer LM, Knutson SJ: Work posture, workstation design, and musculoskeletal discomfort in a VDT data entry task. Hum Fact 33(2):151-167, 1991. Ulin SS, Ways CM, Armstrong TJ, Snook SH: Perceived exertion and discomfort versus work height with a pistol-shaped screwdriver. Am Ind Hyg Assoc J 51(11):588-594, 1990. Winters JM, Kleweno DG: Effect of initial upper-limb alignment on muscle contributions to isometric strength curves. J Biomech 26(2):143-153, 1993.
CHAPTER
Wrist and Hand
6
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6a
Epidemiology of Wrist and Hand Disorders David Rempel and Laura Punnett
This chapter summarizes the findings of epidemiologic studies that address workplace and individual factors associated with hand and wrist musculoskeletal disorders (MSDs). From an epidemiologic point of view, this topic is challenging because although many specific hand and wrist disorders such as carpal tunnel syndrome (CTS) and hand-arm vibration syndrome are recognized, no criteria for case definitions are universally accepted. More data are available for CTS than for other hand and wrist disorders because of its relatively well-defined pathology and available diagnostic methods such as nerve conduction velocity testing.79 These disorders are not new; epidemics and clinical case series of work-related hand and wrist tendinitis were reported throughout the 1800s and early 1900s.17,92 As summarized by a review by a National Academy of Sciences panel,65 many crosssectional studies and more recent prospective studies consistently identify certain key risk factors at the same time that they point to the multifactorial nature of work-related hand and wrist disorders. The etiology of these disorders includes both biomechanical and work organizational factors, along with reporting and clinical progression that are likely affected by the worker’s perception of the work environment and by medical management. A conceptual model of this complicated relationship, adapted from Armstrong et al4 and presented in Figure 6a.1, is based on epidemiologic studies and pathophysiologic mechanisms clarified in laboratory studies. Health care providers can apply this information and limit workplace exposures to risk factors both to reduce the overall incidence of hand, wrist, and other musculoskeletal disorders (primary prevention) and to prevent loss of function in patients (secondary and tertiary prevention) in whom such disorders have occurred.
FREQUENCY, RATES, AND COSTS National incidence rates of work-related hand and wrist disorders in the United States are not easy to assess because of the difficulty in attributing causation and the sparse data on background incidence and prevalence. Annual incidence rates of all work-related repeated-motion disorders reported by U.S. private employers to the Bureau of Labor Statistics are shown for 1980 to 2000 in Figure 6a.2. Approximately 55% were hand or wrist disorders, a percentage also reported in industrial studies60 and in studies from other countries.46 The dramatic rise after 1983 may be partially explained by early industry under-reporting on the Occupational Safety and Health Administration (OSHA)
200 log, a factor partially rectified in the early 1980s after OSHA levied large fines against some meat processing and automobile manufacturers for under-reporting. A similar calendar trend in work-related hand/forearm problems has been observed in other countries such as Finland,46 Australia,7 and Japan.70 Rates of hand and wrist symptoms and associated disability among working adults were assessed by a 1988 national interview survey of 44,000 randomly selected U.S. adults (National Health Interview Survey).71 Of those who had worked any time in the past 12 months, 22% reported some finger, hand, or wrist discomfort that fit the category “pain, burning, stiffness, numbness, or tingling” for 1 or more days in the past 12 months. Only one fourth were due to an acute injury such as a cut, sprain, or broken bone. Nine percent reported having prolonged hand discomfort, that is, discomfort of 20 or more days during the last 12 months or 7 or more consecutive days that was not due to an acute injury. Of those with prolonged hand discomfort, 6% changed work activities and 5% changed jobs because of the hand discomfort. From the same data set it was estimated that in 1988 alone there were 520,000 cases of work-related hand and wrist disorders (CTS and tendon syndromes) in the United States.89 Administrative records (e.g., workers’ compensation) are frequently used to estimate incidence rates, but the data are extremely problematic to interpret because of varying decision rules that may have no clinical value in defining a “case.” For example, Fine et al26 evaluated multiple records for the same time period at two U.S. automobile plants. Within each facility the magnitude of the incidence rates of hand and arm disorders varied dramatically between data sources: The rates were 10 times higher in the workers’ compensation records than in the OSHA 200 log and 10 times higher in the plant medical records than in the compensation data. Nevertheless, the relative ranking of the departments within each plant was similar, regardless of which data source was used. The incidence of work-related CTS, impact of work disability, and factors predicting disability have been assessed on a large scale in Washington State. A review of 7926 workers’ compensation claims for CTS from 1984 to 1988 yielded an industry-wide
Work-related factors • Work organization • Repetition • Force • Posture Individual factors • Size • Capacity • Behavior • Repair
Internal load (dose) Discomfort Pain Disorder Disability
Figure 6a.1 A possible model of the relationship between exposure to work, worker attributes, and development of chronic musculoskeletal disorders of the hands and wrist. Internal loads and individual capacity result in a reversible cascading series of events ranging from minor mechanical or biologic disturbances to tissue damage and disability. (Modified from Armstrong TJ, Buckle P, Fine LJ, et al: Scand J Work Environ Health 19:73-84, 1993.)
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Figure 6a.2 Incidence rates (per 1000 full-time employees) of repeated-motion disorders for all U.S. private-sector workers from 1980 to 2000. The lower curve is the incidence for industries with primarily office work (finance, insurance, and real estate). Approximately 55% are hand/wrist disorders. (From Bureau of Labor Statistics, 1980-2000.)
incidence rate of CTS claims of 1.74 per 1000 full-time employees.27 Rates up to 20 cases per 1000 full-time employees were observed in shellfish, fish, and other meat-packing industries. Industries with the highest rates of occupational CTS are presented in Figure 6a.3. The ranking of these rates also shows a high correspondence with the occupations in Finland having the highest rates of hand, wrist, and forearm disorders, despite some geographic differences in industry. Disability burden was quantified as “years of productivity lost,” addressing time lost from work for incident compensation claims in 1986.30 Upper extremity strains were the third
highest cause of years of productivity lost, after sprains of the back/neck and lower extremity, representing 1.8 years lost per thousand workers per year. CTS had a lower incidence rate but caused more lost time per case, accounting for 0.5 years lost per 1000 worker-years. Approximately 40% of all the Washington State workers with CTS went on to surgical treatment.1 Of these, the mean duration of lost time was 4 months. The length of time lost from work was not associated with demographic factors (age, gender, wage) or case severity as assessed by clinical staging or nerve conduction values. Most (67%) returned to the same job, 15% found a different job, and 3 years after surgery 18%
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Figure 6a.3 Population age-specific incidence rates of carpal tunnel syndrome for Rochester, Minnesota, from 1961 to 1980 (——) (n = 1016)75 as compared with work-related incidence rates for the Washington State workers’ compensation system from 1984 to 1988 (...) (n = 7926).28
Chapter 6a
had not returned to work. Workers from jobs with elevated rates of CTS or those involving repetitive hand activity were less likely to return to the same job. A return to repetitive or physically demanding work is a predictor of poor long-term outcome after surgery.2,58 Few data are available to assess the long-term financial and functional impact on patients and society, but best estimates by the National Academy of Sciences panel place the average direct cost per workers’ compensation case at over $8000, with total cost estimates for all MSDs as high as $45 to $54 billion per year, around 0.8% of the nation’s gross domestic product.65 A population survey in Connecticut indicated that only about one in five persons with medical treatment for work-related MSDs was reimbursed by compensation and that they had substantial other social and economic costs, ranging from loss of function to decreased job advancement to losing a car or home for financial reasons.62
DISORDER TYPES AND THEIR NATURAL HISTORY Figure 6a.3 lists some hand and wrist disorders identified in occupational epidemiologic studies. Nonspecific hand/wrist pain is the most common problem, followed by tendinitis, ganglion cysts, and CTS.38,53,60,86 In their early stages, these disorders may be manifested by nonspecific symptoms without signs or laboratory findings. It is important to remember that symptoms in the hand may be due to nerve or vascular lesions further up the arm. When measured in high-risk workplaces, rates of nonspecific symptoms, tendinitis, and CTS appeared to track each other; that is, specific disorders usually do not occur in isolation. For example, in a pork processing plant, the rank order of hand and wrist problems as a percentage of all morbidity was nonspecific hand/wrist pain, 39%; CTS, 26%; trigger finger, 23%; trigger thumb, 17%; and de Quervain tenosynovitis, 17%.61 Among packers in a bread factory, whose work involved repetitive and forceful gripping, approximately one half had wrist/hand tenosynovitis (compared with 14% among retail shop assistants).53 The most common disorder of the hand or wrist was thumb tenosynovitis, followed by finger/wrist extensor tenosynovitis. CTS was diagnosed in four packers and in no control subjects. Similar ratios of disorders have been observed in manufacturing workers,6,60,86 food processors,47,53 and computer operators.9,38 For the purposes of this chapter, tendinitis includes hand, wrist, and distal forearm tendinitis or tenosynovitis and trigger finger. Tendinitis occurs at discrete locations, the most common site being the first extensor compartment (de Quervain disease), followed by the five other pulley sites on the extensor side of the hand and three on the flexor side. The diagnosis is based on the history, symptom location, and palpation and provocative maneuvers on physical examination.34 No association of tendinitis with age has been found, but a bimodal curve with seniority has been described; work-related tendinitis was higher among workers with less than 3 years of employment, for example,60 suggesting that performance of unaccustomed tasks is a risk factor and/or that affected workers are less likely to remain in the job. In cross-sectional workplace studies, the prevalence of ganglion cysts, as assessed by physical examination, is 2% to 3%.9,38,60
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Individual Factors
Whether these rates are higher among those performing repetitive hand activity versus those performing tasks with low repetitiveness is unknown. In the absence of universally accepted diagnostic criteria for CTS, some consider just an abnormal nerve conduction study a gold standard.39,45,63 Relying exclusively on nerve conduction studies can lead to very high prevalences, however, such as 28%63 and 19%8 in low-risk working populations. The usual signs of CTS have relatively poor sensitivities and specificities28,39,45; only in the late stages of the disease or in the elderly are weakness and thenar atrophy noticeable features, and in approximately 25% of cases, CTS is accompanied by other disorders of the hand or wrist.72 Although consensus criteria using symptom history and nerve conduction study findings have been proposed,79 the combination of a positive nerve conduction velocity test and symptoms consistent with CTS represents a preferable case definition. Few studies have evaluated how osteoarthritis of the hand and wrist relates to work.35,99 Hadler et al35 assessed the hands of 67 workers at a textile plant in Virginia. Significant differences in finger and wrist-joint range of motion, joint swelling, and radiograph patterns of degenerative joint disease were observed between three different hand-intensive jobs; the observed differences were reported to match the pattern of hand usage. Hand-arm vibration syndrome, or vibration white finger disease, occurs in occupations involving many years of exposure to vibrating hand tools.66 This disorder of the small vessels and nerves in the fingers and hands is manifested as localized blanching at the fingertips with numbness on exposure to cold or vibration. The symptoms are largely self-limited if vibration exposure is eliminated at an early stage,20,31 but with continuing exposure the condition becomes irreversible. Hypothenar hammer syndrome, or occlusion of the superficial palmar branch of the ulnar artery, has been associated in clinical series and case-control studies with habitually using the hand for hammering52,69 and with exposure to vibrating hand tools.44 The mean length of exposure before seeking medical attention was 20 to 30 years. Small case-control studies or clinical series have described factors associated with less common disorders such as gamekeeper’s thumb,14,68 digital neuritis, ulnar neuropathy at the wrist,86 and Kienböck disease.32
INDIVIDUAL FACTORS In general population studies and clinical case series, the average age of patients with CTS is approximately 55 years.10,72,88,100 In contrast, the mean age for “occupational” cases, based on the Washington State workers’ compensation study, is 37.5 years.27 Furthermore, as displayed in Figure 6a.3, the incidence increases with age in the general population but does not appear to do so in the occupational cohort. Only 3% of the variability in median nerve latency in a cross-sectional study of an industrial cohort is explained by age.63 In another prospective study, age was not a predictor for incidence of CTS or for wrist tendonitis in a mixed occupational cohort51 or of tendon-related disorders of the hand and forearm among computer users.34 Similarly, gender appears to play a greater role in populationbased studies of CTS than in industrial studies. In regional
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population studies and clinical series, the incidence of CTS is higher in females than in males by a factor of 2.2:1 to 3.7:1,10,72,88,100 whereas in workplace studies, when employees perform similar hand activities, the ratio is much closer to unity at 1.2:1.27,34,63,86 CTS can be a sequela (usually self-limiting) of pregnancy21; however, the role of other female reproductive factors such as oophorectomy, hysterectomy,11,15,18,77 or the use of oral contraceptives82 is less certain. The overall implications are that when hand activities are taken into account, the differences between working men and women are not particularly prominent, and hormonal influences likely account for relatively little morbidity when ergonomic exposures are high.76 Other individual factors with strong associations to CTS are diabetes mellitus,72,88,100 rheumatoid arthritis,72,88,100 and obesity.18,23,63,94,97 For other factors, including thyroid disorders,38,72 vitamin B6 deficiency,3,22,59 wrist size and shape,5,12,33,43 and general deconditioning,63 the associations are based on single studies or the studies present conflicting results. Nonspecific distal symptoms have also been associated with systemic disease, obesity, smoking, and other nonoccupational factors.51,73,75
WORK-RELATED FACTORS Figure 6a.3 summarizes the characteristics of work that have been associated with elevated rates of hand and wrist symptoms and with specific disorders like CTS and tendinitis. The number of prospective studies has increased substantially in recent years, and the risk factors identified tend to be quite consistent with
those of older cross-sectional studies of the same endpoints.95 Tables 6a.1 and 6a.2 summarize selected studies of wrist and hand tendinitis and CTS that included a control group. Hand/wrist pain and disorders have been associated with repetitive hand and finger motions characterized by a variety of metrics. Prevalences are generally high in manual-intensive occupations such as data-entry work, postal sorting, cleaning, industrial inspection, and packaging.65 In a study relying exclusively on nerve conduction measurements, median nerve slowing occurred at a higher rate among assembly line workers than among administrative control subjects.64 Assembly line workers appeared to have more repetitive tasks than the control group. Similar results were obtained in comparisons of garment workers performing repetitive hand tasks with hospital employees not using computer keyboards77 and in bread packers compared with retail shop attendants.53 A number of other cross-sectional and prospective studies have similarly observed the importance of high hand pace, short cycle time, little variation in tasks, and lack of rest breaks for risk of CTS,8,16,50,80,98 tendinitis,47 and hand pain or combined disorders.25,49 This range of metrics illustrates the varied ways that “repetitive motion” may be operationalized in addition to high velocity or acceleration of the wrist or rate of repetition of postural stress.57 The force applied to a tool or materials during repeated or sustained gripping is also a predictor of the risk for tendinitis, CTS, and other distal extremity disorders. For example, in a study of the textile industry, the risk of hand and wrist tendinitis was 3.9 times higher among packaging and folding workers than among knitting workers, who performed work that was
Table 6a.1 Selected controlled epidemiologic studies evaluating the association between work and wrist, hand, or distal forearm tendinitis* Authors
Exposed population
Control population
Kuorinka et al, 1979 Luopajarvi et al, 197953† Silverstein et al, 198686§||
90 scissors makers 152 bread packaging Industrial 143 low force/high rep 153 high force/low rep 142 high force/high rep Manufacturing 369 packers/folders 562 sewers 296 boarding workers 102 meat cutters 107 sausage makers 118 packers 352 manufacturing workers (high/low rep)
133 shop attendants 133 shop attendants Industrial 136 low force/low rep 136 low force/low rep 136 low force/low rep Manufacturing 352 knitting workers 352 knitting workers 352 knitting workers 141 office workers 197 office workers 197 office workers
McCormack et al, 199060
Kurppa et al, 199147†¶
Latko et al, 199949
*Case criteria are based on history and physical examination. †All exposed and control subjects are female. ‡Significant difference from control. §Adjusted for age, sex, and plant. ||Analysis includes other disorders, although tendinitis was most common. ¶Cohort study with a 31-month follow-up. OR, odds ratio.
Rate in exposed (%)
Rate in control (%)
18 53‡
14 14
3? 4? 20‡
1.5 1.5 1.5
3.3‡ 4.4‡ 6.4‡ 12.5? 16.3‡ 25.3‡ OR = 3.23
0.9 0.9 0.9 0.9 0.7 0.7
Chapter 6a
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Work-Related Factors
Table 6a.2 Selected controlled epidemiologic studies evaluating the association between work and carpal tunnel syndrome* Authors
Exposed population
Control population
Criteria
Silverstein et al, 198787†
Industrial High force/high rep 22 keyboard operators 164 assembly line 115 general plant 23 grinders 106 ski manufacturing repetitive jobs 65 factory workers/65 case controls
Industrial Low force/low rep 147 admin/clerical 147 admin/clerical 147 admin/clerical 147 admin/clerical 67 ski manufacturing nonrepetitive jobs
History and physical examination Electrodiagnostic Electrodiagnostic Electrodiagnostic Electrodiagnostic Electrodiagnosis and signs Symptoms, signs, electrodiagnosis, surgery
Nathan, 198864§||
Barnhart, 19918§ Roquelaure et al, 199780
Rate in exposed (%)
Rate in control (%)
5.1‡
0.6
27 47 38 61‡ 15.4‡
28 28 28 28 3.1
OR = 9.0 (2.4-33.4) for force and OR = 8.8 (1.8-44.4) for repetition
*Diagnoses are based on history and physical examination or nerve conduction study. †Controlled for age, gender, and years on job. ‡Significantly different from control group. §Controlled for age and gender. ||Low participation rate and limited exposure assessment. OR, odds ratio.
much less physically demanding. In a study by Moore and Garg61 at a pork processing plant, in the jobs that involved high grip force or long grip durations such as Wizard knife operator, snipper, feeder, scaler, bagger, packer, hanger, and stuffer, almost every employee was affected. Others observed a similar relationship with work involving sustained or high force grip in grinders,64 meatpackers and butchers,23,47 and other industrial workers.51,92,96 A comprehensive cross-sectional study of the combined factors of repetition and force was conducted among 574 industrial workers by Silverstein et al.86,87 Disorders were assessed by physical examination and history and were primarily tendinitis followed by CTS, Guyon tunnel syndrome, and digital neuritis. Subjects were classified into four exposure groups based on force and repetition. The “high-force” work involved a grip force averaging more than 4 kg of force, whereas “low-force” work involved less than 1 kg of grip force. The “high-repetition” work involved a repetitive task in which either the cycle time was less than 30 seconds (greater than 900 times in a work day) or more than 50% of the cycle time was spent performing the same kind of fundamental hand movements. After adjusting for plant, age, gender, and years on the job, the high-risk groups were compared with the low-risk group. The odds ratio of all hand/wrist disorders for high force alone was 5.2 and that for high repetition alone was 3.3; this increased to 29 for jobs that required both high force and high repetition. The identical analysis of just CTS revealed an odds ratio of 1.8 for force, 2.7 for repetition, and 14 for the combined high-force high-repetition group. Years of exposure to both repetitive wrist movement and “heavy load on the wrist” were strongly associated with CTS.83 Estimates of the CTS cases among workers who perform repetitive or forceful hand activity that can be attributed to work range from 50% to 90%.36,91 Other investigations similarly highlighted the combined effects of repetition, force, postural load, and
other physical stressors.37, 77, 80 The importance of addressing all such exposures simultaneously in workplace interventions is further demonstrated by the effect of multifaceted ergonomic interventions in reducing upper extremity morbidity.13,25,67 Work involving increased wrist deviation from a neutral posture in either the extension/flexion or ulnar/radial direction has been associated with CTS and other hand and wrist problems.40,92,93 de Krom et al18 conducted a case-control study of 156 subjects with CTS versus 473 control subjects randomly sampled from the hospital and population registers in a region of the Netherlands. After adjustment for age and sex, a doseresponse relationship was observed for increasing hours of work with the wrist in extension or flexion. No risk was observed for increasing hours performing a pinch grasp or typing, although methodologic limitations may have obscured such associations. Some studies of computer operators have linked awkward wrist postures to severity of hand symptoms,24 risk of tendinitis or CTS,84 and arm and hand discomfort.19,41,83 In a large population sample, both CTS and distal tendonitis were associated with repetitive occupational bending and twisting of the hands and wrists.89,90 Wrist angles measured by electrogoniometry were strongly linked with wrist disorders in a range of service and manufacturing occupations; forceful exertions and repetitiveness were also risk factors, although they were correlated with each other too strongly to distinguish their effects.55 Prolonged exposure to vibrating hand tools such as chain saws has been linked in prospective studies to hand-arm vibration syndrome.20,31 The risks are primarily vibration acceleration, amplitude, and frequency; hand coupling to tool; hours per day of exposure; and years of exposure. Based on existing studies, however, no clear vibration acceleration/frequency/duration threshold has been found that would protect most workers. Medical surveillance is therefore recommended to identify
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cases early while the disease can still be reversed.66 Nonetheless, both the American National Standards Institute and the International Standards Organization have promulgated guidelines limiting the duration of exposure as a function of acceleration and frequency. The use of vibrating hand tools may also increase the risk of CTS,15,81,85,98 either by direct nerve injury or by indirectly increasing applied grip force through a reflex pathway.78 Prolonged or high-load localized mechanical stress over tendons or nerves from tools or from resting the hand on hard objects has been associated with tendinitis93 and nerve entrapment40,72 in case studies. The average total hours per day that a task is repeated or sustained has been a factor in predicting hand problems.54,56 For example, an increase in hours of computer use has consistently been a predictor of increased symptom prevalence.9,24,26,41,74 In prospective studies of computer users, increasing hours of keyboard and mouse use predicted increased incidence of hand/ wrist pain and tendonitis, especially above 20 hours per week.34,42 In cross-sectional studies, work organizational factors (e.g., work structure, decision control, workload, deadline work, supervision) and psychosocial factors (e.g., job satisfaction, social support, relationship with supervisor) appear to have some influence on hand and wrist symptoms. Work organizational factors represent upstream determinants of both physical motion patterns and subjective psychosocial work experiences. For example, justin-time production systems increase both the work pace48 and the risk of CTS.50 In an automotive manufacturing plant, improved work station design was negatively offset by a change to assembly line production with very short-cycle, monotonous, “robotized” jobs.29 Among banking employees, longitudinal changes in work scheduling and rest break policies were shown to predict changes in medical morbidity.25 Among newspaper reporters and editors, psychosocial factors modified the expected relationship between work station design and hand and wrist symptoms. Symptom intensity increased as keyboard height increased among those with low decision latitude but not among those with high decision latitude.24 In another study of newspaper employees, the risk of hand and wrist symptoms was increased among those with increasing hours of deadline work and less support from the immediate supervisor.9 Among directory assistance operators at a telephone company, high information-processing demands were associated with an elevated rate of hand and wrist disorders.38 On the other hand, in an industrial setting, Silverstein et al86 observed no association with job satisfaction. Because these problems may develop in the workplace after and as a consequence of employees’ symptoms and unsuccessful efforts to obtain job modifications or other accommodation, psychosocial factors are the most difficult to interpret in crosssectional studies. Overlapping measurement approaches may also obscure the relationships among work organization, physical, and psychosocial factors.
SUMMARY Although variability exists between industries, hand and wrist disorders account for many work-related upper extremity MSDs. These disorders are costly to the worker, employer, and workers’
compensation system; however, a full accounting of their financial impact has yet to be done. Hand and wrist problems may present in any number of ways, from the most common presentation of nonspecific hand symptoms to discrete entities such as hand-arm vibration syndrome or de Quervain tenosynovitis. The rates of specific disorders correspond to high symptom rates in a work population. Studies point to a multifactorial relationship between work and these disorders. Some disorders such as tendinitis and CTS are clearly associated with repetitive and forceful hand use, postural stress, and vibration. For other disorders such as ganglion cysts and osteoarthritis, the relationship to work has not been well studied. Symptom severity and disorder rates—or at least their reporting—appear to be influenced by work organizational factors such as decision latitude and cognitive demands. In population-based studies and clinical case series, CTS in particular has been linked to individual factors. However, in workplace studies when workplace exposure is high and quantified, individual factors play a limited role relative to workplace factors.5,15,24,38,41,87
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Epidemiology of wrist and hand disorders
Rothfleisch S, Sherman D: Carpal tunnel syndrome: biomechanical aspects of occupational occurrence and implications regarding surgical management. Orthop Rev 7:107-109, 1978. Sabour M, Fadel H: The carpal tunnel syndrome, a new complication ascribed to the pill. Am J Obstet Gynecol 107:1265-1267, 1971. Sauter SL, Scheifer LM, Knutson SJ: Work posture, work station design, and musculoskeletal discomfort in a VDT entry task. Hum Fact 33:151-167, 1991. Seligman P, Boiano J, Anderson C: Health hazard evaluation of the Minneapolis Police Department. Springfield, VA, 1986, NIOSH HETA 84-417-1745, U.S. Department of Commerce, National Technical Information Service. Seppalainen AM: Nerve conduction in the vibration syndrome. Scand J Work Environ Health 6:82-84, 1970. Silverstein BA, Fine LJ, Armstrong TJ: Hand wrist cumulative trauma disorders in industry. Br J Ind Med 43:779-784, 1986. Silverstein BA, Fine LJ, Armstrong TJ: Occupational factors and carpal tunnel syndrome. Am J Ind Med 11:343-358, 1987. Stevens JC, Sun S, Beard CM, O’Fallon WM, Kurland LT: Carpal tunnel syndrome in Rochester, Minnesota, 1961 to 1980. Neurology 38:134-138, 1988. Tanaka S, Petersen MR, Cameron LL: Prevalence and risk factors of tendinitis and related disorders of the distal upper extremity among U.S. workers: comparison to carpal tunnel syndrome. Am J Ind Med 39:328-335, 2001. Tanaka S, Wild DK, Cameron LL, Fruend E: Association of occupational and nonoccupational risk factors with the prevalence of self-reported carpal tunnel syndrome in a national survey of the working population. Am J Ind Med 35:550-556, 1997.
91. Tanaka S, Wild DK, Seligman PJ, et al: The US prevalence of self-reported carpal tunnel syndrome. Am J Public Health 84:1846-1848, 1994. 92. Thompson A, Plewes L, Shaw E: Peritendinitis crepitans and simple tenosynovitis: a clinical study of 544 cases in industry. Br J Ind Med 8:150-160, 1951. 93. Tichauer E: Some aspects of stress on forearm and hand in industry. J Occup Med 8:63-71, 1966. 94. Vessey MP, Villard-MacInosh L, Yeates D: Epidemiology of carpal tunnel syndrome in women of childbearing age. Finding in a large cohort study. Am J Epidemiol 19:655-659, 1990. 95. Viikari-Juntura E, Silverstein BA: Role of physical load factors in carpal tunnel syndrome. Scand J Work Environ Health 25:163-185, 1999. 96. Welch R: The causes of tenosynovitis in industry. Ind Med 41:16-19, 1972. 97. Werner RA, Albers JW, Franzblau A, Armstrong TJ: The relationship between body mass index and the diagnosis of carpal tunnel syndrome. Muscle Nerve 17: 632-636, 1994. 98. Wieslander G, Norback D, Gothe CJ, Juhlin L: Carpal tunnel syndrome (CTS) and exposure to vibration, repetitive wrist movements, and heavy manual work: a case-referent study. Br J Ind Med 46:43-47, 1989. 99. Williams WV, Cope R, Gaunt WD, et al: Metacarpo-phalangeal arthropathy associated with manual labor (Missouri meta-carpal syndrome). Arthritis Rheum 30:1362-1371, 1987. 100. Yamaguchi D, Liscomb P, Soule E: Carpal tunnel syndrome. Minn Med J 22-23, 1965.
CHAPTER
6b
Biomechanics of the Wrist and Hand Rita M. Patterson and Kai-Nan An
The human hand is a relatively mobile three-dimensional structure capable of conforming to the shape of manipulated objects. The biomechanical structure of the hand can be considered a linkage system of intercalated bony segments balanced by muscle and tendon forces and joint constraints. This chapter reviews some of the unique qualities that affect the biomechanics of the hand and wrist: normal skeletal and soft tissue anatomy, joint constraint and stability, range of joint motion and strength, and more basic biomechanical considerations of muscle-tendon function.
SKELETAL AND LIGAMENTOUS ANATOMY/JOINT CONSTRAINT Joint constraint and stability are provided by the joint articular surfaces, the capsuloligamentous structures, and the musculotendinous units. Primary joint stability is related to balance of the muscle and tendon forces to an externally applied force, with the capsuloligamentous structures appearing to stabilize initially against instantaneous loading and to provide secondary maintenance of joint stability. The collateral ligaments of all the hand joints and the intercarpal ligaments in the wrist are important soft tissues for joint constraint. The locations and orientations of the ligament lines of action determine their characteristics in resisting loads on the joint. For example, the radial collateral ligament and the ulnar collateral ligament are the primary ligaments of the metacarpophalangeal joint. Originating from the radial-dorsal aspect of the metacarpal head with insertion into the radial-volar aspect of the proximal phalanx, the radial collateral ligament is the primary ligament resisting ulnar deviation and pronation of the proximal phalanx at the metacarpophalangeal joint. The ulnar collateral ligament, on the other hand, is the primary constraint in resisting radial deviation and supination of the proximal phalanx. The relative contribution of each of the ligaments in resisting joint displacement has been studied by sequential sectioning or removal of the individual ligaments (Fig. 6b.1). The reduction of the load after removal of each ligamentous structure represents the contribution of that ligament. Anatomic studies performed on the carpal bones and the ligaments of the wrist in particular have identified several morphologic differences associated with degenerative changes and with specific kinematic (motion) patterns. Viegas and colleagues14 identified two different lunate shapes. Type II has a facet that articulates with the hamate and has been associated with increased arthritis in its proximal pole. Type I has no facet.
Most wrist ligaments are considered true intracapsular ligaments and tend to be oriented obliquely, from the periphery of the wrist toward the midline, from a proximal to distal direction. The volar ligaments are well established as the primary stabilizers of the wrist joint. Studies investigated the anatomy and mechanical strength of the dorsal ligaments of the wrist. Together the dorsal intercarpal (DIC), dorsal radiocarpal, and dorsal scapholunate (SL) interosseous ligaments create a lateral “V” that delivers indirect dorsal stability between the scaphoid and the radius while still allowing a threefold change in distance between the radius and the scaphoid dorsal groove. This unique design allows dorsal stability of the scaphoid throughout the range of motion of the wrist that would require changes in the linear dimension of a “dorsal radioscaphoid ligament” far greater than any fixed ligament could accommodate (Fig. 6b.2). The combined mechanical properties of the DIC, dorsal SL interosseous, and dorsal radiocarpal ligaments together function to maintain scaphoid stability and alignment while allowing for carpal mobility.18 Three distinct ligaments around the scaphoid trapezium and trapezoid (STT) joint have also been identified. The STT ligaments extend distally (scaphoid trapezial ligament) and ulnarly (scaphocapitate and scaphotrapezium ligaments) to form a “V.” The plane of the V-shaped STT ligament is essentially parallel to that of the trapezium-trapezoid articulation and corresponding interfacet ridge on the joint surface of the distal pole of the scaphoid. This ridge runs radiodorsal to ulnopalmar, a 45-degree angle from the sagittal plane13 (Fig. 6b.3).
MOTION The fingers and thumb consist of phalanges articulated at the interphalangeal joints. Within the physiologic range of motion, the interphalangeal joints can be considered hinges that allow flexion/extension. In a normal hand, each interphalangeal joint has at least 90 degrees of motion. The proximal phalanx articulates with the metacarpal at the metacarpophalangeal joints, which are usually considered universal joints, allowing not only flexion/extension but also abduction/adduction. Normally, the range of flexion/extension is about 90 degrees and that of abduction/adduction is 20 to 30 degrees. A composite articulation of eight carpal bones, the wrist joint connects the digits of the hand to the radius and ulna of the forearm. The range of wrist motions required to comfortably perform activities of daily living consists of 60 degrees of extension, 54 degrees of flexion, 40 degrees of ulnar deviation, and 17 degrees of radial deviation. Most of the hand placement and range-of-motion tasks can be accomplished with 70% of wrist motion maximum range. This converts to 40 degrees each of wrist flexion, wrist extension, and combined radial/ulnar deviation. Wrist flexion/extension and radial/ulnar deviation has traditionally been modeled as a fixed center of rotation through the proximal aspect of the capitate. However, studies have described the flexion/extension axis of the wrist as moving between the lunate and capitate. During global wrist motion, the radiolunate joint contributes more motion in flexion, whereas the lunocapitate joint contributes more motion in extension.16 Other studies described the kinematics of the lunate and the differences due to lunate type.13,18 The kinematics of type I lunate
Chapter 6b
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Biomechanics of the Wrist and Hand
0.6 Extended MP joint a
a: Intact
b c
Sequential sectioning of b: RCL-P c: RCL-D d: UCL-P e: UCL-D
Torque (N-m)
220
0.4 a b c
0.2 a b c
Pronation 20
a b c
10
10
a
d
d e
20 Supination
a
0.2 a
0.4
Figure 6b.1 Load-displacement curves were obtained by measuring the restraining torques when the metacarpophalangeal joints were displaced in supination and pronation. Curve a represents the torques with the entire capsule-ligament complex intact. Curves b and c represent the torques when the palmar and dorsal portions of the radial collateral ligament, respectively, were sectioned, whereas curves d and e represent those when the palmar and dorsal portions of the ulnar collateral ligament, respectively, were sectioned. The difference in load between each curve for a given displacement indicates the contribution of that particular sectioned element. For example, the difference in load between curves a and b represents the contribution of the palmar portion of the radial collateral ligament. N-m, newton-meter. (From An KN, Cooney WP III: Biomechanics, section II, the hand and wrist. In BF Morrey, ed: Joint replacement arthroplasty. New York, 1991, Churchill Livingstone International, pp. 137-146.)
motion differs from that of type II. The total range of radial/ ulnar translation of type II lunates was greater than that of type I lunates during radial/ulnar deviation. Compared with that of type I lunates, extension of type II lunates occurred later during ulnar deviation, whereas flexion of type II lunates occurred earlier. Describing the kinematics of the STT joint, Moritomo et al13 found that the trapezium and the trapezoid rotate as a unit with respect to the scaphoid during either flexion/extension or radial/ ulnar deviation of the wrist.
STRENGTH The potential strength of various joints in the hand and wrist in normal subjects has been studied with dynamometers. Normal pinch strengths ranged from 3 to 10 kg and grasp strengths from 20 to 40 kg. The wrist position and size of the grasped object have a significant influence on grip strength, which has been studied extensively as a function of wrist joint position. A self-selected wrist position of 35 degrees of extension and 7 degrees of ulnar deviation has been identified as the position in which maximum grip strength can be generated.15 For a given size of an object, grip strength is significantly reduced when the wrist position deviates from this self-selected position.
Forearm position has been shown also to affect key and fingertip pinch strength but not three-jaw chuck pinch strength. The neutral forearm position rendered the highest mean score and the pronated position the lowest mean score for key and fingertip pinch strength. Although these effects were consistent, the statistically significant effects of forearm position were less than 1 pound of force and may not be clinically relevant. However, standardized forearm positioning during pinch strength measurement is still recommended.17 The strength of the wrist joint is in the range of 10 to 20 Nm of flexion, 6 to 10 Nm of extension, 10 to 18 Nm of radial deviation, and 10 to 20 Nm of ulnar deviation.
TENDON EXCURSION The ability to control the movement of an individual digit of the hand depends very much on the anatomic arrangement of the musculotendinous complex. The magnitude of tendon excursion during joint movement for a given task would be important also for assessing possible overuse injury caused by cumulative trauma. For the finger and thumb, the pulley structures on the palmar side of the digits restrain bowstringing of the digital flexor
Chapter 6b
Flexion Tq
Sc
Radius Ulna
Extension Sc
Tq
Radius Ulna
Figure 6b.2 The lateral “V” configuration of the dorsal radiocarpal/ dorsal intercarpal construct allows dorsal stability of the scaphoid along with a threefold change in the distance between the radius and the dorsal groove of the scaphoid between flexion and extension of the wrist (arrows).
c
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Muscle and Joint Forces
during joint flexion. Alteration of such a pulley system in the hand disturbs the relationship between tendon excursion and joint angular displacement, and thus joint function. Parameters have been defined from the curves of tendon excursion and joint motion for comparing tendon-pulley joint interactions under normal and abnormal conditions.9 The range of movement of the joint produced by a given standardized amount of excursion is called the effective range of motion. Absolute tendon excursion is that from full extension to 90 degrees of flexion as measured with the flexor tendon set at its normal length in the neutral position. Division of the pulley would result in bowstringing and adding slack to the tendon system, which would have to be taken up before any joint motion could occur. This amount of tendon slack is termed bowstring laxity. Subtracted from absolute tendon excursion, bowstring laxity defines relative tendon excursion. The biomechanical functions of the musculotendinous complex can be understood in terms of the relationship of tendon excursion to joint angular displacement. The rate of change in tendon excursion as the joint rotates is equal to the moment arm of the associated muscle or tendon for that specific joint motion.4 The moment arm defines not only the effectiveness of the tendon in joint rotation but also its mechanical advantage in resisting external loads. The larger the moment arm, the higher the torque and rotation angle generated for the same amount of muscle force and excursion. A determination of the potential moment arm contributions of muscles can provide insight into the balance of forces at a joint for planning tendon transfers or designing orthotics to help provide mobility or stability while minimizing loss of function. Tendon excursion and joint rotation angles of the wrist, for example, are measured by using an electric potentiometer and an electromagnetic tracking device, respectively.1 The instantaneous moment arms of each tendon are then calculated from the slope of the curve between the tendon excursion and the joint angular displacement. Calculated tendon moment arms are found to be consistent throughout a full range of flexion/extension and radio/ulnar deviation motion; they correspond closely to the anatomic location and orientation of the tendons (Fig. 6b.4).
MUSCLE AND JOINT FORCES a
FCR b
Figure 6b.3 The ligaments around the scaphoid trapezium and trapezoid joint at the palmar aspect of the left wrist. (a) The scaphotrapezial (S-Tm) ligament; (b) the scaphocapitate (S-C) ligament; (c) the capitate-trapezium (C-Tm) ligament. FCR, flexor carpi radialis.
The potential force generated by a muscle depends on its size and architecture. Three anatomic parameters of muscle morphology have been recognized for their importance in defining its biomechanical potential5: (1) muscle fiber length is related to the potential range of physiologic excursion of the tendon and muscle, (2) the physiologic cross-sectional area of a muscle is proportional to its maximum tension potential, and (3) physically, the product of the force and distance is work; therefore, the muscle mass or volume is proportional to its work capacity. In addition, potential force generation is further regulated by the velocity of shortening or lengthening of the muscle and, as is well known, its length at the time of contraction. Usually, an optimum length can be found for generating maximum contractile force. The arrangement of the muscle fiber architecture further influences the characteristics of the muscle contraction.8 It has been demonstrated that parallel muscle fibers produce a
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Biomechanics of the Wrist and Hand
Figure 6b.4 (Left) Tendon excursion and moment arm of the five wrist motor tendons during flexion/extension motion. (A) Tendon excursion. The wrist joint was moved from full flexion to full extension passively. (B) Moment arms calculated from A. The flexors and extensors show the different directions of the moment arm: extensors show the plus, and flexors show the minus. (Right) Tendon excursion and moment arm of the five wrist motor tendons during radial/ulnar deviation. (A) Tendon excursion. The wrist joint was moved from radial deviation (R.D.) to ulnar deviation (U.D.) passively. (B) Moment arms calculated from A. The ulnar side tendons show the plus moment, and the radial side tendons show the minus moment. ERCB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; ECU, extensor carpi ulnaris; FCR, flexor carpi radialis; FCU, flexor carpi ulnaris. (From Horii E, An KN, Linscheid RL: Excursion of prime wrist tendons. J Hand Surg 18(1):83-90, 1993.)
length-tension curve with maintained force throughout a wider range of excursion than do muscles with a shorter fiber pennate structure, which produce sharply peaked curves. The index of muscle architecture, defined as the ratio of muscle fiber length to muscle belly length, has been used to define such characteristics. The orientation or constraint of muscles or tendons crossing a joint determines the characteristics of excursion and the moment arm. In general, the larger the moment arm, the better the mechanical advantage for the same amount of tendon or muscle force. On the other hand, the larger the moment arm, the more tendon excursion expected for the same amount of joint rotation. The excursion of the tendon eventually affects the muscle length of contraction and ultimately determines the potential force generation according to the muscle length-tension characteristics. The size and shape of the object to be grasped determines the joint configuration of the thumb and fingers involved in
grasp function. The corresponding moment arms of both the intrinsic and extrinsic muscles at a particular joint configuration determine the mechanical advantage, tendon excursion, and corresponding muscle length. Therefore, as mentioned earlier, the size and shape of the object are important considerations in determining the power and strength of the grasp. Furthermore, the extrinsic muscles of the fingers and thumb originate from the forearm. Wrist joint motion therefore creates excursion of these tendons and modifies the muscle contraction characteristics because of the length-tension relationship. Thus grasp power and strength are regulated by wrist joint configuration as well. Because of the relatively smaller moment arms or mechanical advantage of the muscles and tendons across the joints as compared with those of externally applied forces at the tip of the digits, the muscle force required to balance grip or pinch functions is much higher. For example, in the tip and pulp pinch
Chapter 6b
function, the forces of the flexor profundus and sublimis are about one to two times the force at the tip of the digits. The associated forces in the intrinsic muscles are in the range of 0.5 to 1.5 times the applied forces.2,3 Accordingly, with such a magnitude of muscle and tendon forces, the compressive and shear forces across the finger joints are quite significant (Fig. 6b.5).
●
Force Through Wrist Carpal Joint
CX2 = 2.7
CX4 = 4.9 A=1 CZ6 = 0.2
FORCE THROUGH WRIST CARPAL JOINT When the hand is used, the wrist joint encounters a tremendous amount of force. The distribution of the forces among the carpal bones has great potential for injury to the associated bone and soft tissue. Cumulative trauma with compression of the lunate, for example, has been thought to result in avascular necrosis of the lunate (Kienböck disease). It has been postulated that excessive and uneven loading is experienced by the lunate between the lunate fossa of the radius and the compressible triangular fibrocartilage of the ulna. The overall force transmitted from the proximal row of carpal bones to the distal radioulnar joint has been examined by numerous investigators. Although the findings have not been in complete agreement and probably depend on the measurement technique, trends of certain important characteristics have been quite consistent. On average, 15% to 20% of axial wrist joint force is transmitted by the distal end of the ulna, and 80% to 85% is transmitted through the radius in the neutral position (Fig. 6b.6A).7
CX6 = 3.9
CY6 = 2.3
Figure 6b.5 Resultant joint forces during tip pinch function of one unit force, that is, A = 1. Forces represent the actions of the proximal segment applied onto the distal segment crossing the joint. CX, joint compressive joint force; CY, joint dorsal shear force; CZ, joint radial shear force. (From An KN, Cooney WP III: Biomechanics, section II: the hand and wrist. In BF Morrey, ed: Joint replacement arthroplasty. New York, 1991, Churchill Livingstone International, pp. 137-146.)
Figure 6b.6 (A) Each arrow represents the cumulative compressive force vector between adjacent bones and between the carpal bones and distal ends of the radius and ulna. These joint compressive forces or pressures within the carpus are calculated by this model when all the joints and ligaments are intact and axial loads are applied along the metacarpals. (B) Predicted displacements of the carpal bones under the loading condition shown in A. Slight ulnar translation is present as a result of a component of force tangential to the radial articular surface. Carpal bone displacement must be considered when the concentration of the force vector across articular surfaces is analyzed. The dotted line represents the unloaded position and the solid line represents the loaded position of the carpus: S, scaphoid; L, lunate; Tq, triquetrum; Tr, trapezium/trapezoid; C, capitate; H, hamate; R, radius; U, ulna. (C) Each arrow represents the calculated tension for the different carpal ligaments under the same loading condition: 1, palmar radiolunate ligament; 2, dorsal radiotriquetral ligament; 3, palmar radiocapitate ligament; 4, palmar capitatotriquetral ligament; 5, dorsal scaphotriquetral ligament; 6, palmar/dorsal hamatocapitate ligaments; 7, flexor retinaculum. (From Horii E, Garcia-Elias M, Bishop AT, Cooney WP, Linscheid RL, Chao EY: J Hand Surg Am 15A(3):393-400, 1990.)
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The effect of joint position and forearm rotation on the percentage of load transmission across the radius and ulna has also been recognized. With the wrist in the neutral position, at the midcarpal joint 30% of the total force was transmitted through the scaphotrapezial joint, 19% through the scaphocapitate joint, 31% through the lunocapitate joint, and 21% through the triquetrohamate joint. With the wrist loaded, the carpal bones translate in the ulnar direction down the inclined slope of the distal end of the radius (Fig. 6b.6B), and tensions in the intercarpal ligaments are observed as well (Fig. 6b.6C). Interaction of the carpal bones is conceptually analogous to a Rubik’s cube in which motion in one segment directly affects the position of another.
POSTTRAUMATIC INJURY Dobyns et al6 introduced the concept of traumatic carpal instabilities, and many reports have described their clinical features, treatments, and long-term consequences. The most common type of carpal instability is the dorsal intercalated segmental instability (DISI). Although many reports describe the anatomy and function of the volar ligaments of the wrists, only recently has the anatomy of the dorsal ligaments been better detailed and their function discussed. Most articles, which describe the pathomechanism of SL instability (SLI), concentrate on the scaphoid instability. However, there has been relatively little information about lunate instability and no clear explanation of the anatomic differences between dynamic and static SLI. Studies suggested that the DIC ligament is important in maintaining the carpal alignment of both the scaphoid and lunate.19 When the DIC and the SL interosseous ligaments were disrupted from the scaphoid but the DIC was still attached to the lunate, the resulting carpal instability demonstrated a flexed posture of the scaphoid and a widened SL gap, but only when the hand was loaded. This was comparable to a clinical dynamic SLI. When the DIC ligament was also disrupted from the lunate, the resulting instability demonstrated a flexed posture of the scaphoid and a widened SL gap in both loaded and unloaded conditions. Furthermore, when the DIC was detached from the lunate, the latter changed position to an extended posture, also in both loaded and unloaded conditions. This was comparable with a clinical static SLI with DISI. There was no apparent effect or further destabilization of the scaphoid or lunate resulting from disruption of the lunotriquetral interosseous ligament. The existence and progression of a dynamic SLI to a static SLI with a DISI deformity resulting from SL dissociation is well accepted in the clinical setting. To date, however, there has not been any detailed anatomic explanation and/or example of what the causes and the differences are between a dynamic SLI and a static SLI with DISI. The anatomic and mechanical integrity of the DIC ligament appears to play a significant role in SL stability and in determining whether the SL dissociation develops a dynamic or a static instability and DISI deformity. It is, of course, uncertain whether or not the progressive stages of instability simulated in these studies reflect actual clinical injury patterns. These results nevertheless propose that the treatment of the SLI should address not only the SL interosseous
With OA
Without OA Radiographic TT inclination
A
B
Figure 6b.7 (A) Radiographic measurements in the scaphoid axial view. Radiographic trapezium-trapezoid (TT) inclination is an angle formed by a line running axially through the 3rd metacarpal and another line running from the dorsal to the palmar articular edges of the proximal trapezium and trapezoid surfaces. (B) TT inclination is associated with increased osteoarthritis (OA).
ligament but also the DIC ligament at both its scaphoid and lunate attachments.10,19 The second most common site of degenerative changes in the wrist is scaphoid trapezium trapezoid degeneration. The etiologic factors in the development of degenerative changes in the STT joint are still unclear; studies have suggested, however, that degenerative changes are associated with scaphotrapezial ligament tears and increased trapezium-trapezoid inclination (the degree of coverage by the facets of the trapezium and trapezoid over the distal pole of the scaphoid) (Fig. 6b.7).12 Fractures of the scaphoid (the most commonly broken carpal bone) are difficult to treat because of its complex threedimensional shape and oblique orientation. Fractures of the proximal pole of the scaphoid have been associated with increased pressure and degenerative changes in the radius under its distal pole. Whether the fracture line passes distal or proximal to the dorsal apex of the ridge of the scaphoid (where the DIC ligament and the dorsal component of the SL interosseous ligament attach) appears to determine the likelihood of subsequent DISI deformity and the pattern of degenerative changes, if the fracture progresses to a scaphoid nonunion.11 In the volar type, the distal fragment displaces volarly with respect to the proximal fragment, and in the dorsal type, the distal fragment displaces dorsally.
SUMMARY Work-related injuries of the hand commonly occur. The nature of hand function places a tremendous amount of tension and repetition on the tendons and intrinsic muscles. Although tension may not be high enough to cause great damage, it can create compressive and frictional forces on the tendons and adjacent tissues around the pulley, bony surface, or other soft tissues. These compressive and friction forces can potentially cause cumulative trauma disorders of the bone and soft tissue.
Chapter 6b
REFERENCES 1. 2. 3.
4. 5. 6. 7.
8. 9. 10.
An KN, Berger RA, Cooney WP: Biomechanics of the wrist. New York, 1991, SpringerVerlag. An KN, Chao EY, Cooney WP, Linscheid RL: Forces in the normal and abnormal hand. J Orthop Res 3:202-211, 1985. An KN, Cooney WP III: Biomechanics. Section II: The hand and wrist. In BF Morrey, ed: Joint replacement arthroplasty. New York, 1991, Churchill Livingstone International, pp. 137-146. An KN, Ueba Y, Chao EY, Cooney WP, Linscheid RL: Tendon excursion and moment arm of index finger muscles. J Biomech 16:419-425, 1983. Chao EYS, An KN, Cooney WP, Linscheid RL: Biomechanics of the hand. A basic research study. Singapore, 1989, World Scientific. Dobyns JH, Linscheid RL, Chao EY, Weber ER, Swanson GE: Traumatic instability of the wrist. In A.A.O.S. 1975. St. Louis, MO, 1975, C.V. Mosby, pp. 182-199. Horii E, Garcia-Elias M, Bishop AT, Cooney WP, Linscheid RL, Chao EY: Effect on force transmission across the carpus in procedures used to treat Kienböck’s disease. J Hand Surg Am 15A(3):393-400, 1990. Kaufman KR, An KN, Chao EYS: Incorporation of muscle architecture into muscle length-tension relationship. J Biomech 22:943-948, 1989. Lin GT, Amadio PC, An KN, Cooney WP: Functional anatomy of the human digital flexor pulley system. J Hand Surg Am 14A:949-956, 1989. Mitsuyasu H, Patterson RM, Shah M, Buford W, Iwamoto Y, Viegas SF: Role of the dorsal intercarpal ligament in dynamic and static scapholunate instability. J Hand Surg 29(2):279-288, 2004.
11.
12.
13.
14. 15.
16.
17.
18.
19.
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References
Moritomo H, Viegas SF, Elder KW, et al: Scaphoid nonunion: a three dimensional analysis of patterns of deformity. J Hand Surg 25A(3):520-528, 2000. Moritomo H, Viegas SF, Nakamura K, Patterson RM: The scaphotrapezio-trapezoidal joint: Part 1. An anatomic and radiographic study. J Hand Surg 25A:899-910, 2000. Nakamura K, Beppu M, Patterson RM, Viegas SF: Motion analysis in two dimensions of radial-ulnar deviation of type I versus type II lunates. J Hand Surg 25A:877-888, 2000. Nakamura K, Patterson RM, Moritomo H, Viegas SF: Type I vs. type II lunates: ligament anatomy and presence of arthrosis. J Hand Surg 26A:428-436, 2001. O’Driscoll SW, Horii E, Ness R, Cahalan TD, Richards RR, An KN: The relationship between wrist position, grasp size, and grip strength. J Hand Surg 17:169-177, 1992. Patterson RM, Nicodemus CL, Viegas SF, Elder KW, Rosenblatt J: High speed, three dimensional kinematic analysis of the normal wrist. J Hand Surg 23A(3):446-453, 1998. Stegink Jansen CW, Simper VK, Stuart HG Jr, Pinkerton HM: Measurement of maximum voluntary pinch strength: effects of forearm position and outcome score. J Hand Ther:16:326-336, 2003. Viegas SF, Patterson RM, Hokanson JA, Davis J: Wrist anatomy: incidence, distribution and correlation of anatomy, tears and arthritis. J Hand Surg 18A:463-475, 1993. Viegas SF, Yamaguchi S, Boyd NL, Patterson RM: The dorsal ligaments of the wrist: anatomy, mechanical properties, and function. J Hand Surg 24A(3):456-458, 1999.
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6c
Functional Evaluation of the Wrist and Hand Jane Bear-Lehman
MULTIDIMENSIONAL ASSESSMENT PROCESS FOR THE WRIST AND HAND A comprehensive multidimensional assessment plan for the wrist and hand requires the selection and use of many different types of evaluation instruments to measure the outcomes of the patient’s health status, impairment level, functional limitations, and disability status. Assessment focuses on the outcome levels for those variables that can change because of time, treatment, or disease.27 Often generic or condition-specific self-report questionnaires are now selected to measure health, function, and disability status from the patient’s perspective, and performancebased instruments known as the tools of our trade still provide data about functional impairment and limitations. Clinical assessment of the wrist and hand is both a quantitative and a qualitative process. Its aim is to help the clinician construct and then monitor the effectiveness of the treatment plan, the progression or the prevention of the disease or injury, and the health status over time. Treatment of a patient who has sustained a musculoskeletal occupational injury of the wrist and hand focuses on helping the patient achieve maximal function of both body and limb and regain independence in ordinary activities of daily living while restoring health status. Occupational musculoskeletal wrist and hand injuries can result from direct or indirect trauma in the workplace. The injury affects the musculoskeletal system, which includes the bone, its joints, and their related structures: muscles, tendons, ligaments, nerves, and arteries. Direct trauma injuries are usually a medical emergency; they have a date, time, and place of injury and may result from a fall in the workplace or adverse physical contact with tools or machinery. Indirect trauma is microtrauma to the muscles, tendons, ligaments, nerves, or arteries that persists and develops over time. The physical performance assessment of a patient with direct or indirect trauma to the wrist and hand focuses specifically on the injured and adjacent body parts as appropriate for the medical and surgical stage of recovery; these results are compared with function of the uninjured limb, if available. Several performance-based instruments that produce quantitative measurements are used in the therapeutic setting to assess the functional impairment level, including range of motion (ROM), muscle performance, edema (limb size), and sensation; functional limitations are assessed using instruments that measure activities of daily living, dexterity, and physical capacity. This chapter reviews the performance-based measures for the wrist
and the hand that are considered tools of the trade, with attention to each instrument’s stage of development and achieved reliability and validity. Although it is assumed that the use of reliable and valid tests increases the statistical probability for making correct clinical decisions and predictions about performance potential, we are cautioned to not rely exclusively on these functional impairment or functional performance quantitative data alone. Qualitative data in terms of behavioral response, such as personal attitude and response to pain, fear, and loss of control, often influence the quantitative wrist and hand functional evaluation results.10 Furthermore, in today’s clinic it is essential to have outcome documentation, including information about the patient’s health status, function, and overall satisfaction level, to understand the different kinds of results.3 The clinical assessment of a patient with a musculoskeletal disorder affecting the wrist and hand follows a biomechanical frame of reference to evaluate the results or outcomes. The problems are identified by gathering and then synthesizing subjective, observational, and objective information about the patient to determine the quality of the result and the level of satisfaction.3 This information is derived from the patient, the clinician’s observation of the patient visually and through touch (palpation), and the outcome measures the patient achieves on administered self-report and performance-based tests. The assessment relies on the patient’s effort and voluntary cooperation with clinical stimuli, inquiries, and directives. To begin the assessment, the clinician gathers a history from the patient’s perspective about the nature and the course of the injury, prior medical and therapeutic attention sought, and success of these interventions. This report from the patient’s perspective is compared for congruity with the written medical history. The clinician poses many questions about life-style adjustment, to document the alterations but more so to appreciate the patient’s ability to recognize, understand, and function within the restrictions imposed by the present physical problem(s). Patients are therefore asked to describe how the impact of the injury has affected their life-styles, namely, the changes in ability to perform ordinary activities of daily living at home, at work, and at leisure.25 The course, location, duration, and type of pain are addressed through standardized questionnaires, such as the McGill Pain Profile or the Visual Analog Scale, to detect painful reaction, patterns about the patient’s pain, and methods to control it.11,30 Outcome self-report instruments are administered to measure health status and function; some of the measures include information about pain level, performance of activities of daily living, and satisfaction level. Generic or condition-specific scales in self-report instruments are selected to help standardize the functional assessments. These tools provide the clinician, the patient, and others with basic functional information that is meaningful and helps serve as a screen at the outset of treatment.3 The SF-36, a widely used generic scale, measures health status in 36 items addressing key elements such as physical function, physical role, bodily pain, general health, social function, and emotional role.40 Many suggest that when assessing a patient with a wrist or hand injury, the highly regarded SF-36, with its impressive reliability and validity, should be combined with a more condition-specific instrument, of which several are available for selection.8 Care in selection increases the quality of
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responsiveness and meaningfulness of the information. Attention should be directed to condition-specific regional self-report tests on function and health status such as the DASH (disabilities of the arm, shoulder, and hand), the Michigan Hand Questionnaire, or the Upper Body Musculoskeletal Assessment for patients who have upper limb injuries.8,15,24 More focused questionnaires are appropriate for specific conditions, such as the Patient-rated Wrist Evaluation Questionnaire for those who have sustained a wrist fracture and the Carpal Tunnel Syndrome Questionnaire for individuals recovering from that syndrome. When matched with the patient who has the targeted diagnosis, these highly specific instruments are more responsive than the DASH or the SF-36.3,27 In the biomechanical component of the clinical hand and wrist assessment, the clinician observes the patient’s posture and attitude of the injured wrist or hand and its adjacent structures to answer the following questions: Is the patient favoring a posture to protect the injured part from environmental contact through upper extremity flexion and adduction? Is there biomechanical alteration in the body to compensate for the poverty of movement or the increase in pain? Is there symmetry in size and shape between the injured and uninjured wrist and hand? Does the body move symmetrically? What are the preferred postures during static positions such as sitting? What are the transition patterns, that is, moving from sitting to standing, and the dynamic patterns of movement such as walking? What is the quality of movement at the injured site and in the adjacent structures? Is there a change in coloration at the injured site; does the coloration vary? Palpation of the skin gives the clinician more information about the skin’s temperature, the presence of nodules, and the tightness of muscle-tendon units. Physical or anatomic measurement is a continuous and ongoing process; it is carefully coordinated and monitored with the stage of healing, the plan for movement during healing, and the trajectory of recovery. Physiologic changes can and do occur quite rapidly during the acute stage.18 Objective measures provide the treating clinician with information about the effectiveness of a given treatment, confirm the need to continue with a given treatment regimen, or signal the need for revision if the progress or response is not as anticipated. The data are used to justify the need for continuation of treatment or the consideration of other therapies.
CLINICAL ASSESSMENT OF THE MUSCULOSKELETAL SYSTEM Physical performance measurements provide the clinician with information on the functional impairments affecting the wrist and the hand. These measurements rely on familiar hand care tools of the trade; some of the tools or instruments, such as goniometers for measuring active or passive range of motion, have remained the same. Others have been further developed to improve the reliability of the measurement: Hydraulic pinch meters have replaced spring gauges, for example. Tools have also been redesigned to improve the quality of measurements, as in the continual instrument development for the measurement of light-touch deep pressure sensory response or two-point discrimination testing. Functional impairment requires the assessment
of the wrist and the hand for actual measures of ROM, edema, muscle performance testing, sensation, and pain, as follows.
Range of motion Since the 1940s, clinicians have been reporting their use of the goniometric system to obtain accurate information about patients’ joint status and movement capacity. Although technically not a standardized assessment tool, the universal goniometer is the most widely selected tool for measuring joint ROM. The American Academy of Orthopaedic Surgeons guide is used as a reference for normative values.4 In terms of reliability, Hamilton and Lachenbruch20 found no difference in the results of determining joint angles with different goniometers. The reliability of readings by the same tester over time has shown a 5-degree error when measuring joints in the wrist or the hand. The method of recording continues to follow the Academy guideline in which minus sign notation is used to show an extension limitation and a plus sign indicates hyperextension. The American Society for the Surgery of the Hand accepted the method of reporting goniometric scores in terms of the total arc of movement at a given joint or a related series of joints. Use of the arc measurement system for the digits is reported as total active movement and as total passive movement for the summation of the angles of the three joints in each digit.14,18 That is, the total active movement or total passive movement represents the summation of the amount of movement available in all three joints, the metacarpophalangeal, proximal interphalangeal, and distal interphalangeal, with full ROM yields a score approximating 260 degrees. This composite measurement does not isolate the individual joint that is creating the deficit, but it is suited for graphic representations of the patient’s performance over time; it is very useful after a tendon or nerve repair. ROM measurements are conducted on the adjacent joints in the acute stage of recovery; deficits in the adjacent joints that were not present before the injury are remediated in therapy. Depending on the nature of the injury and the medical or surgical protocol, measurements may be taken for active or passive ROM at the injury site immediately or may be deferred until the integrity of the joint or the surrounding tissue allows a measurement. ROM assessment of the injured joints depends on the type of protection and stabilization used for healing. If complete rest of the injured region is required, measurements are delayed until movement is permissible. If controlled movement at the injured site is allowed, the clinician measures the type of movement (active or passive) within the range allowed and restricts movement beyond the prescribed arc.
Edema Trauma or surgery is frequently followed by an abnormal accumulation of fluid in the interstitial spaces of tissues, resulting in an increase in limb size. This edematous state limits ROM and, ultimately, function. Measurement of wrist and hand size circumferentially with a tape measure is often done at three locations: proximal to and distal from the edematous part and over the edematous part. To allow for a more valid comparison of
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sequential measurements, anatomic landmarks are used as reference points for placement of the tape measure. Placement and tension of the tape measure or finger gauge affect intertester and intratester reliability. In the past, clinicians have used jewelers’ rings to help reduce the measurement error related to tension on the tape measure. Now clinicians rely on the Gulick tape, which has a unique spring gauge, or the finger circumference gauge for more consistent measurements for repeated measures (Figs. 6c.1 and 6c.2). Because edema may be not localized in a digital segment but more generalized over the hand and arm, a volumeter method is preferred to accurately measure edema changes in the hand and wrist (Fig. 6c.3). The volumeter, based on Archimedes’ principle of water displacement, is used to measure composites of hand mass. Waylett and Seibly41 documented 10-ml test-retest reliability when the manufacturer’s guidelines are followed.23 Normative values for any of these measures are not available; the contralateral side is used as the approximate normal value for that patient. Because hand-size changes may be attributed to factors other than edema, such as normal asymmetry or muscle atrophy in the affected limb from disuse, care must be taken regarding generalization and interpretation of the findings.
Muscle performance testing Muscle testing is used to evaluate the level of nerve injury and nerve regeneration and preoperatively to determine potential donors in tendon transfer surgery. The manual muscle test designed by Lovett and Martin26 is a screening device that relies on the external forces of gravity and resistance to assess muscle strength.
Figure 6c.1 Gulick tape measure has a unique spring gauge to provide consistent measurements. (NC70170-95: Courtesy of North Coast Medical, Inc., Morgan Hill, CA.)
Figure 6c.2 Finger circumference gauge is used for consistent measurement in inches or centimeters. (NC70157-95: Courtesy of North Coast Medical, Inc., Morgan Hill, CA.)
The strength of muscle contractions can be measured clinically by means of spring scales, dynamometers, weights, or manual resistance. Manual resistance is added to voluntary maximal contraction once it has been established that the muscle exertion and the applied resistance will not adversely affect the healing bone, joints, and related structures. There is no agreement regarding whether isometric or isotonic contraction should be used in muscle testing or whether testing scores are best derived from the muscles’ isometric contractibility under load at the end of the range, which is often chosen as the point for applied resistance.22 Few discrepancies are found in
Figure 6c.3 Hand volumeter is used to measure changes in hand size. (NC70310.00: Courtesy of North Coast Medical, Inc., Morgan Hill, CA.)
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manual muscle testing procedures. Hislop et al21 used a gravityeliminated position to test metacarpophalangeal joint extension, whereas Kendall et al22 did not distinguish the effect of gravity in the hand. The scoring methods of Lovett and Martin26 and Brunnstrom and Denner13 continue to be used: 0 (zero), 1 (trace), and 2 (poor) represent test results in the gravity-eliminated posture; 3 (fair) uses the external force of gravity; and 4 (good) and 5 (normal) add the dimension of resistance. Overall, reports of reliability are descriptive. No predictive validity has been established for grip and pinch scores, although many are hypothesized, nor is hand function predictive. Functional hand strength is measured by grip and pinch tests. In the case of a distal forearm, wrist, or hand fracture, measurements are deferred for at least 2 to 4 weeks after the removal of immobilization. Hand strength measurement is the most common standardized assessment using hydraulic dynamometers. Figure 6c.4 shows the use of the Jamar hydraulic dynamometer to measure hand-grip strength. Pinch patterns are measured using the hydraulic pinch meter (Fig. 6c.5). Spring pinch gauges are not recommended because they cannot be calibrated and have yet to prove as reliable or consistent in measuring as
Figure 6c.5 The hydraulic pinch gauge gives accurate and consistent results, and like the Jamar dynamometer it can be calibrated. (NC70141_03: Courtesy of North Coast Medical, Inc., Morgan Hill, CA.)
the hydraulic instruments. If regularly calibrated, the hydraulic hand strength instruments have been shown to be reliable and produce consistent measurements.7,18 Both grip and pinch hand strength instruments allow for readings in kilograms-force and pounds-force. The literature shows a variety of test procedures that can have an impact on interrater and intrarater reliability, as well as on its normative data pool.29 The American Society for the Surgery of the Hand and the American Society of Hand Clinicians accept the seated posture with humeral adduction and neutral humeral rotation, the elbow flexed to 90 degrees, and the forearm and wrist in neutral position as the desired body posture for grip testing.28 Norms have been established for age 5 to adulthood. Healthy adult grip strength values for the five handle positions, when providing full voluntary effort, yield a normal bell-shaped curve.36 The first position, the closest, is the least advantageous because it relies primarily on the ulnar nerve-innervated hand intrinsics, whereas the widest or fifth position relies on the median nerveinnervated long finger flexors. Middle-range handle positions require the intrinsic and extrinsic musculature to work together. A patient without neural or tendon damage who has a flattened curve may be suspected of providing submaximal voluntary effort. The traditional pinch patterns of lateral, palmar (also known as tripod or three-jaw chuck), and tip pinch are reported as the average of three trials for each type of pinch. The normative data tables are described on the basis of age and gender for both grip and pinch. Three test trials are recorded for each grip and pinch pattern tested. The mean (average of the three), the standard deviation, and the coefficient of variation (standard deviation/average) are computed to monitor the consistency or sincerity of effort.32,33,36
Sensation Figure 6c.4 The handheld Jamar dynamometer records grip strength in kilograms-force or pounds-force.
The hand is a complex organ whose function depends on harmony between sensory and motor abilities.16 Sensory testing
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can frequently identify sensorineural changes earlier than traditional motor examination. Studies have shown, for example, that in median nerve entrapment at the carpal canal level, sensory changes precede motor changes. Clinical tests of vibration and Semmes-Weinstein monofilament testing show changes earlier than electromyographic studies because the latter does not show the process of change. Many of the tools used clinically to test sensation are being revised and improved, and because of the changes offered by microsurgery, more patients now have greater potential to achieve sensory results of higher quantity and quality. Sensory testing of a patient with a wrist and hand injury addresses the ability to perceive light touch and deep pressure, to discriminate touch, and to detect vibration. To monitor the progress of a patient’s sensory status, particularly if a neural injury is suspected, it is advisable to use instruments that yield ordinal rather than nominal data. Early methods to test light touch and deep pressure called for the use of a cotton ball or a cotton-tipped applicator. This form of testing yields the results that the patient perceived the touch or is normal, may not have perceived or appreciated the stimulus fully or is impaired, or did not perceive the stimulus at all or is absent. This hierarchy represents an ordinal-level data system ranging from normal to absent response levels; the increment between the values is not known, nor is it equal. Abnormal results need to be monitored during the course of treatment. It is expected that sensitivity over scars and pin tracks is heightened. The deep pressure-to-light touch interval hierarchy for sensation in the hand resulted from the findings of von Frey,39 a surgeon who had a passion for learning about sensation and a love of horses. von Frey discovered that some of his patients could detect only the sensation of thicker horse hairs when applied to their skin surfaces, and as they healed, they could begin to feel finer horse hairs. The horse hairs that were first used are now 20 calibrated nylon monofilaments graded in diameter and individually attached to Plexiglas handles. The amount of force transmitted is related directly to the diameter of each filament, which bends at a specific force controlling the magnitude of the touch-pressure stimulus.9 Weinstein42 developed a smaller more portable version of his original test, the Weinstein Enhanced Sensory Test (WEST), for ease of use in the clinic. Now clinicians use either the WEST or the Touch-Test Sensory Evaluators. The latter are individually calibrated within a 5% standard deviation of the predetermined targeted force. No other commercially available “monofilament type” testing device meets this scrutiny (Fig. 6c.6). The larger set of 20 still provides greater specificity for those patients who require it. To test for discriminatory touch sensation, the static or stationary two-point discrimination instrument continues to be challenged. The original Weber two-point discrimination instrument’s sliding scale allowed for adjustment of the spacing between the two points; however, the adjustment often did not allow the same precision as a tool with fixed points. Some practitioners open up paper clips to approximate distances, which leads to variability in spacing and uneven pressure between points. The two-point discrimination instrument, the Diskcriminator, designed by Dellon et al,17 controls for the precision between points and provides even application when two points are applied, and the
Figure 6c.6 The Touch-Test Sensory evaluators (Semmes-Weinstein monofilaments) are individually calibrated and accurately measure light touch-deep pressure. (NC12757: Courtesy of North Coast Medical, Inc., Morgan Hill, CA.)
Touch-Test Two-Point discriminator provides the opportunity for clinicians to have all points of measure on a single disk (Fig. 6c.7). Studies show that the amount of pressure offered when two points are applied can be very different from that of just one. The ability to perceive vibratory stimuli is clinically valuable when the patient has undergone nerve repair or when nerve compression or a peripheral neuropathy is suspected. The 30-Hz and 256-Hz tuning forks continue to be used to test for vibratory response. Clinical studies have proposed that both the 30-Hz and the 256-Hz tuning forks be used because it is believed
Figure 6c.7 The Touch-Test Two-Point discriminator allows for two-point discrimination testing in one unit. (NC12776A: Courtesy of North Coast Medical, Inc., Morgan Hill, CA.)
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that each elicits the response of an individual sensory neurite receptor. The 30-Hz fork is believed to evoke the response of the Meissner corpuscle and the 256-Hz fork from the Pacinian corpuscle.16 Whether the prong or the stem should be applied to the skin surface is often debated; in either event, the lack of control of amplitude and variability in technique make the reliability of the test inconsistent.7 Furthermore, the patient may hear the sound of the tuning fork before perceiving it on the skin surface, confounding the response. Only ordinal data are gleaned from this form of testing. A vibrometer with a fixed frequency level provides a result measured in microns of motion at 120 c/s (Fig. 6c.8). The data are interval and therefore quantifiable, allowing for specific tabulation of progress. The raw score is a logarithmic function of probe displacement measured in volts that is converted mathematically into microns. Normal expected values of the displacement for skin surface are presented in an anatomic diagram and table format. This instrument requires the use of an electrical outlet and is not as readily portable as other hand assessment tools that fit into a laboratory coat pocket.
Pain Observed during the course of the assessment, pain can be monitored over time in several ways. Pain is measured as part
of the health and function status at the outcome evaluation by the use of the McGill Pain Questionnaire or the Visual Analog Scale,11,30 and it is monitored as treatment progresses. The patient is asked to describe the type, location, and threshold of pain perceived before, during, and after each therapy session. Perception of pain varies from one patient to the next with the same injury as well as for the same patient over time. The clinician must also observe and address signs that may be causing pain, such as a constrictive dressing, cast, or splint or an infection. Pain may and often does occur at the onset of therapy; this form of pain is localized and should subside within 2 hours of the session.
FUNCTIONAL ASSESSMENT OF THE MUSCULOSKELETAL SYSTEM Critical to the assessment process is to appreciate wrist and hand use in terms of functional limitations that result from the injury and to monitor change. Information about functional limitations can be derived from the self-report questionnaires such as the generic SF-36, the condition-specific DASH, or the diagnosis condition-specific Patient-Rated Wrist Evaluation. Performance tests are administered, and the scores are compared with the normative tables, if available. The performance scores can be compared also with the self-report questionnaire findings. Less often, clinicians may consider direct observation performance measures for activities of daily living; however, when this occurs, it is usually to resolve a specific concern or clarify a patient’s self-report.
Information processing
Figure 6c.8 The Bio-Thesiometer Vibrometer measures the threshold of appreciation of vibration. (Courtesy of Bio-Medical Instrument Company, Newbury, OH.)
The patient comes to the medical setting mainly because of pain, fear, and disability.6 A satisfactory result depends not only on the technical skills of the team but also on the team’s ability to communicate, engender confidence, and fully understand and explain the problem to the patient.12 It is necessary for the clinician to look at the process of therapy and the patient’s response to it. The clinician helps the patient by designing a learning environment that emphasizes the salient traits and the characteristics of the problem to be solved or the condition to be learned. One method is to engage the patient in metacognitive experiences, that is, conscious thinking and awareness of feelings that accompany and pertain to the problem-solving task.1 Flavell19 defined metacognitive knowledge as information or beliefs about the course and outcome of the cognitive enterprise in three areas of cognitive awareness: person, task, and strategy. Every patient has a different level of cognitive awareness and a variety of beliefs, feelings, understanding of goals, and strategies for problem solving. In therapy, practice or instructional programs are systematically used with a focus on the process rather than the content.35 Each task is analyzed relative to its repetition, imitation, and substitution. The training is assessed for the patient’s need to have cues or anchors and intermodal training and for the patient’s performance in a novel or new learning situation. How the patient accepts and responds to the information that has been shared is viewed in more than just a physical sense. Fear, pain, or side effects of medications often intervene in the patient’s ability to orientate to the therapy situation and to
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focus attention (alertness); this also affects the patient’s ability to learn. A patient in pain may find one voice instrumental in helping to learn the new way of moving the wrist. A verbal, visual, or kinesthetic voice (cue) from the clinician may be sufficient as the patient learns to move the wrist and hand again. Two voices, visual and verbal, may be needed, or the two voices may bombard the patient’s ability to concentrate if given at the same time because of the high threshold of pain. By observing how the patient learns to move again and how feedback is obtained and used,2 the clinician determines whether the patient is reliant on others for direction and guidance to perform tasks or is selfdirected and self-regulated.35 It is important to know whether the patient can detect an error in movement alone, how the error is corrected, and what kind of reinforcement is required. The clinician also observes the patient’s ability to cope with the injury. After guidance in how to select and terminate activities that correspond to the patient’s stage of healing, the clinician observes how the patient follows such guidelines in performing ordinary daily tasks, in participating in rehabilitation, and in assuming societal and family roles. The patient is observed for the ability to adhere to safety precautions and exhibit selfcontrol in terms of physical limitations and reactions to pain.
Activities of daily living The quantity and the quality of the patient’s performance of activities of daily living are ascertained by interview. Information from the self-report health and functional status can be used or an additional inquiry may be conducted for more specific information as warranted. For problematic deficit areas, the clinician may observe the patient’s actual performance. Early in the healing process, when medical restrictions are in place as to the amount of movement or force allowed at the site of injury or the ability of the injured part to get wet, the patient must be assessed for methods of accommodation in activities of daily living.5 For patients with a wrist or hand injury, this may require an assessment of eating, personal hygiene, dressing, bathing, and communication. Adaptive methods and devices may be indicated temporarily to facilitate one-handed methods, such as using a rocker knife for cutting meat or a button-hook for fastening buttons, or the clinician might suggest purchasing precut or prepared foods. During the course of the rehabilitation program it is important for the clinician to guide the patient as to when and how the injured wrist and hand can be safely reintegrated into the performance of activities of daily living corresponding with the clinical progress. The first reintegration is in the performance of personal activities of daily living. When strengthening is introduced into the clinical program, the clinician needs to consider the patient’s need to perform such instrumental tasks, including those related to meal preparation, household management and shopping, and care of others. For many patients, work during the acute phase of recovery may not be possible due to extensive manual demands on the job, whereas others may not have a work interruption. For those who are working, the clinician identifies the components and demands of the patient’s job by interview and helps the patient assume those tasks that correspond to the achieved clinical status. For those unable to work, the demands essential to the
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patient’s job are delineated to develop the requirements for return to work and the goals for therapy. As treatment progresses, the patient’s performance level is reviewed and compared with the levels needed for safe return to work. The feasibility of meeting the physical demand levels in terms of essentially required dexterity, strength, or physical endurance are determined during the rehabilitation process.
Dexterity Commonly defined as skill and ease in using the hands, dexterity is considered a functional limitation when impaired. To assess manual dexterity or physical functioning efficiently, the examiner must select the standardized test that suits the patient’s abilities and needs. Most have a high index of reliability (greater than 0.75) and show good face and content validity; little has been done on concurrent validity or predictive validity, which is most needed for the clinical decision-making process.6 Predictive validity determines whether the patient, based on the performance on the test, is ready to return to work. Dexterity tests can be classified by their demand for fine to gross motor movement patterns, requirement of one hand or integration of both to perform the task, requirement of a tool for their administration, and length of time the test takes to perform. The Moberg Pick Up test can be classified as a sensory and dexterity test because it brings together the sensate and motor functions. This test is usually performed with unrestricted vision and with vision occluded, and the patient is timed as the familiar objects are scooped, handled, identified, and placed in a designated location. The Nine Hole Peg Test (Fig. 6c.9), the Purdue Pegboard (see Fig. 6c.10), the O’Connor Tweezer Dexterity Test, the O’Connor
Figure 6c.9 The Nine-Hole Peg Test quickly measures fine motor dexterity. (NC34547.d1: Courtesy of North Coast Medical, Inc., Morgan Hill, CA.)
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Figure 6c.10 The Purdue Pegboard Test has four subtests: right hand placement, left hand placement, use of the hands in parallel, and, as shown, integrated use of the two hands on assembly.
Finger Dexterity Test, and the Crawford Small Parts Test are all examples of fine-motor dexterity movement patterns. However, the Nine Hole Peg Test and the Purdue Pegboard Test are short tests that do not provide information about endurance; the Purdue Pegboard Test does require the use of one hand as well as that of both hands in a parallel and in an integrated fashion, as shown in Figures 6c.9 and 6c.10. The O’Connor Tweezer Dexterity Test and the Crawford Small Parts Test both require the use of a small tool to handle and manipulate the test parts. The former requires the use of small tweezers, and testing is completed on the use of one hand at a time for all functions; the latter requires the use of tweezers or a screwdriver in one hand while the alternate hand is assistive. The Minnesota Manual Dexterity Test (Fig. 6c.11) and the Bennett Hand-Tool Dexterity Test assess gross motor function; the former requires the patient to handle the test items directly, whereas the latter requires the use of ordinary mechanic’s tools. Both allow for the direct use of both hands during some of the test components. Many of the Valpar38 Corporation Work Samples (VCWS) are well suited to assess precise finger and hand movements. In particular, the VCWS 1 small tools (mechanical) work sample38 is helpful in assessing the use of small tools in tight or awkward spaces requiring use of the hand(s) without direct visual monitoring. The outcome scores for manual dexterity performance are reported as the amount of time (the speed) that the patient required to perform the task, and the increments of time are compared with normal data based on age, gender, and occupation published in the test manuals. The clinician also reports the preferred prehensile patterns used during the course of the tasks and the control the patient had over performance. Observations of motor control are discussed relative to the patient’s safe use of the injured part, biomechanical alignment of the injured part relative to the body, postural accommodation of the body to the injured part, and quality of task performance. Qualities of concern include the patient’s ability to integrate both the injured hand or wrist and the principles of joint protection spontaneously into the dexterity pattern and the ability of the two hands to work together as a dominant and subdominant pair.
Figure 6c.11 The Minnesota Manual Dexterity Test measures eyehand-finger movement in two subtests: one-handed placement and twohanded turn and placement. (NC70030-96: Courtesy of North Coast Medical, Inc., Morgan Hill, CA.)
The patient is observed for safety relative to the injured part, him or herself, and others.
Physical capacity evaluation Most physicians and clinicians use a physical capacity evaluation to try to answer the question of whether a patient can safely return to work. The capacity to perform work may be directly related to achieved physical performance but is more complex due to the contribution of both philosophic and psychologic issues.34 Many sophisticated instruments are available to assist in the evaluation process, but the level of validity for these instruments is less than is often required. Performance on these systems is interpreted in a variety of ways, including MTM (motiontimes-measurement) standards, U.S. Dictionary of Occupational Titles Worker Qualification Profiles37 or U.S. Department of Labor O*NET.31 The theoretical model that is followed is Parson’s trait factor from the early 1900s in industrial engineering. The procedure is to identify the traits that the patient now has physically, behaviorally, and cognitively; to keep symptoms under control to work safely and effectively; and to match these to environmental factors, including the design of the work station, to determine safe maximum levels of functional work ability in the work force.
SUMMARY Success and satisfaction in rehabilitation of the wrist and the hand is measured by the patient’s ability to use the injured
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part spontaneously in usual, customary, and ordinary activities. Instruments that produce reliable and valid data assist in accountability for the assessment of upper extremity function and restoration of health status. The art of practice requires awareness and documentation not just of the patient’s quantitative wrist and hand dysfunction characteristics, but also of the qualitative ones. To move effectively and efficiently, the patient needs to learn again how to do so in a controlled rhythmic way. Today’s practice requires the clinician to use standardized assessments and report results or outcomes that are meaningful to the clinician, the patients, and all who have access to the information. Using an outcome model allows the clinician to understand what is happening to the patients who are treated.
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14.
Abreu BC: Evaluation and intervention with memory and learning impairments. In C Unsworth, ed: Cognitive and perceptual dysfunction: a clinical reasoning approach to assessment and treatment. Philadelphia, 1999, F. A. Davis, pp. 163-207. Abreu BC, Peloquin S: The quadraphonic approach: a holistic rehabilitation model for brain injury. In N Katz, ed: Cognition and occupation across the life span: Models for intervention in occupational therapy, 2nd ed. Rockville MD, 2005. AM. Occ Therapy Assoc. Amadio PC: Outcome assessment in hand surgery and hand therapy: an update. J Hand Ther 14:63-67, 2001. American Academy of Orthopedic Surgeons: Joint motion: method of measuring and recording. Chicago, 1965, The Academy. Appelby MA, Schkade JK, Gilkeson GE: Timing of ADL education with hand surgery patients. J Hand Ther 5:218-225, 1992. Bear-Lehman J: Factors affecting return to work after hand injury. Am J Occup Ther 37:189-194, 1983. Bear-Lehman J, Abreu BC: Evaluating the hand: issues in reliability and validity. Phys Ther 69:1025-1033, 1989. Beaton DE, Katz JN, Fossel AH, Wright JG, Tarasuk V, Bombardier C: Measuring the whole or the parts? Validity, reliability, and responsiveness of the disabilities of the arm, shoulder, and hand (DASH) outcome measure in different regions of the upper extremity. J Hand Ther 14:128-146, 2001. Bell-Krotoski JA: Sensibility testing with Semmes-Weinstein monofilaments. In J Hunter, E Mackin, A Callahan, eds: Rehabilitation of the hand and upper extremity, ed 5. St. Louis, 2002, Mosby, pp. 194-213. Brand PW: The mind and spirit in hand therapy. J Hand Ther 1:145-147, 1988. Briggs M, Closs JS: A descriptive study of the use of the visual analog scales and verbal rating scales for the assessment of post-operative pain in orthopedic patients. J Pain Sympt Manage 18:438-446, 1999. Brown PW: The role of motivation in patient recovery. Conn Med 42:555-557, 1978. Brunnstrom S, Denner M: Round table on muscle testing. Annual conference of American Physiotherapy Association, Federation of Crippled and Disabled, New York, 1931. Cambridge-Keeling CA: Range-of-motion measurement of the hand. In J Hunter, E Mackin, A Callahan, eds: Rehabilitation of the hand and upper extremity, ed 5. St. Louis, 2002, Mosby, pp 169-182.
26. 27.
28. 29. 30.
31. 32. 33. 34.
35. 36. 37. 38. 39. 40.
41. 42.
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Chung KC, Pillsbury MS, Walters MR, Hayward RA: Reliability and validity testing of the Michigan Hand Outcomes Questionnaire. J Hand Surg 23A:575-587, 1998. Dellon AL: Evaluation of sensibility and re-education of sensation in the hand. Baltimore, 1981, Williams & Wilkins. Dellon AL, Mackinnon SE, Crosby PM: Reliability of two point discrimination measurements. J Hand Surg Am 12A:693-696, 1987. Fess EE: Documentation: essential elements of an upper extremity assessment battery. In J Hunter, E Mackin, A Callahan, eds: Rehabilitation of the hand and upper extremity, ed 5. St. Louis, 2002, Mosby, pp. 263-284. Flavell JH: Metacognition and cognitive monitoring: a new era of cognitive developmental inquiry. Am Psychol 34:906-911, 1979. Hamilton GF, Lachenbruch PA: Reliability of goniometers in assessing finger joint angle. Phys Ther 49:465-469, 1969. Hislop HJ, Montgomery J, Daniels I: Worthingham’s muscle testing techniques of manual examination, ed 7. Philadelphia, 2002, WB Saunders. Kendall FP, McCreary EK, Provance PG: Muscles: testing and function, ed 4. Baltimore, 1993, Williams & Wilkins. King TI: The effect of water temperature on hand volume during volumetric measurement using water displacement method. J Hand Ther 6:202-204, 1993. Kramer JF, Potter P, Harburn KL, Speechly M, Rollman GB, Evans D: An upper body musculoskeletal assessment instrument for patients with work-related musculoskeletal disorders: a pilot study. J Hand Ther 14:115-121, 2001. Law M, Cooper BA, Strong S, Stewart D, Rigby P, Letts L: Theoretical contexts for the practice of occupational therapy. In C Christiansansen, C Baum, eds: Occupational therapy enabling function and well-being, ed 2. Thorofare, NJ, 1997, Slack. Lovett RW, Martin EG: Certain aspects of infantile paralysis and a description of a method of muscle testing. JAMA 6:729-733, 1916. MacDermid JC: Outcome measurement in the upper extremity. In J Hunter, E Mackin, A Callahan, eds: Rehabilitation of the hand and upper extremity, ed 5. St. Louis, 2002, Mosby, pp. 285-296. Mathiowetz V, Kashman N, Volland G, et al: Grip and pinch strength: normative data for adults. Arch Phys Med Rehabil 66:69-74, 1985. Mathiowetz V, Kashmen N, Volland G, Weber K, Downe M, Rogers S: Reliability and validity of hand strength evaluation. J Hand Surg Am 9A:222-226, 1984. Melzack R, Mathiowetz V, Weber K, Volland G, Kashman N: Reliability and Validity of grip and pinch strength evaluations. The McGill pain questionnaire: major properties and scoring methods. Pain 1:265-276, 1975. O*NET on-line. Retrieved from http://online.onetcenter.org Schectman O: The coefficient of variation as a measure of sincerity of effort of grip strength. Part 1. The statistical principle. J Hand Ther 14:180-187, 2001. Schectman O: Using the coefficient of variation to detect sincerity of effort of grip strength: a literature review. J Hand Ther 13:25-32, 2000. Schneider LH: Impairment evaluation. In J Hunter, E Mackin, A Callahan, eds: Rehabilitation of the hand and upper extremity, ed 5. St. Louis, 2002, Mosby, pp. 297-307. Schwartz RK: Therapy as learning. Rockville, MD, 1985, American Occupational Therapy Association. Stokes HM: The seriously injured hand: weakness of grip. J Occup Med 25:683-684, 1983. U.S. Dictionary of Occupational Titles: Worker qualification profiles. Retrieved from www.oalj:dol.gov/libdot.htm Valpar Corporation Catalog. Retrieved from http://www.valparint.com von Frey M: Zur physiologie der juckempfindung. Arch Neurol Physiol 7:142, 1922. Ware JE, Kosinski M, Keller SD: SF-36 physical and mental health summary studies: a user’s manual. Boston, 1994, The Health Institute, The New England Medical Center. Waylett J, Seibly D: A study of the accuracy of a commercially available volumeter. J Hand Ther 4:10-13, 1991. Weinstein S: Fifty years of somatosensory research: from the Semmes-Weinstein monofilaments to the Weinstein enhanced sensory test. J Hand Ther 6:11-22, 1993.
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6d
Wrist and Hand: Treatment Options David M. Kalainov and Mark S. Cohen
Disorders of the wrist and hand are common in the work environment.23 Effective management frequently depends on a multidisciplinary approach with coordinated input from a physician, hand therapist, and nurse case manager. This chapter reviews several wrist and hand conditions that may occur in an occupational setting, including tendinitis, peripheral nerve compression lesions, sprains, fractures, arthritis, ganglia, and complex regional pain syndrome. The underlying pathologies, diagnostic methods, treatment options, and projected outcome for the various conditions are discussed.
TENDINITIS Tendinitis is a general term used interchangeably with tenosynovitis, stenosing tenosynovitis, and tendovaginitis. A thin low-friction envelope that surrounds individual tendons, the tenosynovium, enhances tendon gliding around bony prominences and through retinacular sheaths. Tenosynovitis, which refers to inflammatory changes in this lining, is often associated with a systemic disease process. A more frequently encountered condition, termed stenosing tenosynovitis or tendovaginitis, involves thickening of the tendon and overlying retinacular sheath with only a paucity of tenosynovial inflammation. de Quervain disease and trigger digit are two common examples.
is occasionally palpable as are small ganglia arising from the diseased compartment. The best objective tool in confirming the diagnosis of de Quervain disease is the Finkelstein test. By maximizing the excursion of the tendons through the stenotic first dorsal compartment, this maneuver produces significant discomfort for the patient if the condition is present. Conservative treatment options for de Quervain disease include splinting, corticosteroid injections, nonsteroidal antiinflammatory medication, temporary job modifications, and therapy. Splinting alone may be beneficial for management of acute pain, but symptom recurrence is common. A single corticosteroid injection into the first extensor compartment successfully relieves pain in 60% of cases, whereas two injections may provide relief in up to 80% of cases. Because the soft tissue in this region is thin, however, repeated corticosteroid injections, with infiltration into the subcutaneous tissues, can lead to localized depigmentation, fat necrosis, and subcutaneous atrophy. If conservative measures fail, surgical release of the first extensor tendon compartment may be considered. Surgery involves incision of the retinacular sheath and division of any septae separating the abductor pollicis and extensor pollicis brevis tendons. Vigorous retraction or injury of skin sensory nerves intraoperatively can cause periincisional pain and/or numbness. A therapist may be helpful in the early postoperative period with scar desensitization and strengthening exercises. Release of the first dorsal compartment predictably leads to a satisfactory result in over 90% of cases. Patients are generally able to return to unrestricted employment within 6 to 8 weeks after surgery.
Trigger finger The flexor tendons projecting to each digit enter a retinacular sheath that begins in the distal palm. Thickening of the tendons and sheath at this point may obstruct normal tendon gliding, leading to catching and locking of the digit (Fig. 6d.2).
de Quervain disease The dorsal wrist is comprised of six retinacular compartments encompassing the extensor tendons of the wrist and hand. The first compartment, which contains the abductor pollicis longus and the extensor pollicis brevis tendons, is located directly over the styloid process of the distal radius (Fig. 6d.1). Painful restricted tendon motion through this compartment is referred to as de Quervain disease.19 de Quervain disease is frequently associated with activities involving repetitive flexion and extension of the thumb and ulnar deviation of the wrist. The condition is also associated with direct trauma, rheumatoid arthritis, gout, and diabetes mellitus. A subdivision of the compartment by a septum is thought to predispose some individuals to the development of this condition. A patient with de Quervain disease presents with symptoms of pain, swelling, and tenderness over the radial styloid. Pain can be quite severe, with guarding and limitation of wrist and thumb motion. Crepitation with thumb flexion and extension
Figure 6d.1 Wrist and finger extensor tendons. The first dorsal compartment contains the abductor pollicis longus and extensor pollicis brevis tendons (arrow). Painful restricted tendon motion through this compartment is referred to as de Quervain disease.
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area four fingerbreadths proximal to the radial styloid. Often, palpable and audible crepitus occurs in this region with active wrist motion. Other tendons occasionally involved by inflammation and stenosis include the flexor carpi radialis, the extensor carpi ulnaris, and the extensor pollicis longus. In these cases, nonoperative treatment measures that may include splinting, ice, corticosteroid injection(s), antiinflammatory medications, activity modifications, and therapy are usually successful.
CARPAL TUNNEL SYNDROME
Figure 6d.2 Digital flexor tendon sheath. Thickening of the tendons and sheath proximally may lead to triggering (arrow).
Examination often reveals a tender nodularity in the distal palm that moves with excursion of the tendons.26 Conservative care of a trigger digit entails activity modifications and a corticosteroid injection into the proximal flexor tendon sheath. Single finger involvement, a discreet palpable nodule, and a short duration of symptoms are favorable prognostic indicators. Splinting of the metacarpophalangeal joint for a brief period may be added to the treatment regimen. In individuals whose symptoms are aggravated by the use of small tools, modification of these instruments to distribute forces over a greater area with a lesser requirement for digital flexion may be beneficial. The reported success rates after an injection range from 60% to 84%. If conservative management fails, surgical treatment may be considered. Incision of the proximal portion of the flexor tendon sheath in the palm is curative in over 95% of cases. Most patients are capable of returning to unrestricted work activities within 4 to 8 weeks postoperatively.
The median nerve passes across the wrist through an unyielding fibroosseous canal, termed the carpal tunnel (Fig. 6d.3). Compression of the median nerve within this space is termed carpal tunnel syndrome. The condition occurs due to a mismatch between the volume of the canal and its contents: the median nerve and the nine digital flexor tendons. Carpal tunnel syndrome is associated with diabetes, hypothyroidism, rheumatoid arthritis, and renal failure. Other contributory risk factors include wrist fractures, aging, obesity, female gender, smoking, pregnancy, and alcoholism. In the workplace, carpal tunnel syndrome has been attributed to repetitive forceful use of the wrist and digits, repeated impact on the palm, and operation of vibratory tools. Task-related factors, however, are variable and inconsistent, and the mechanisms by which they may contribute to carpal tunnel syndrome are poorly understood. The diagnosis of carpal tunnel syndrome relies initially on the patient history.8 Symptoms may include tingling and numbness in the thumb and central digits, burning pain, weakness, and clumsiness of the hand, all corresponding to the motor and sensory distributions of the median nerve. Symptoms often appear after prolonged wrist flexion while sleeping and extended periods of wrist extension while driving. Loss of sensation (in the radial four digits) and atrophy of the thenar eminence muscles are symptoms of advanced median nerve compression. Carpal tunnel syndrome is diagnosed primarily through physical examination, including evaluation of thenar muscle
Other tendonopathies Intersection syndrome refers to tenosynovitis of the radial wrist extensor tendons where they cross the first dorsal compartment tendons in the distal forearm. Pain is typically localized to an
Figure 6d.3 Wrist magnetic resonance image, axial view. The carpal tunnel (white arrow) contains the median nerve and the nine flexor tendons. The adjacent ulnar tunnel (black arrow) contains the ulnar nerve and artery.
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Hand-Arm Vibration Syndrome
bulk and strength and performance of sensibility testing. A variety of provocative maneuvers is used to reproduce or accentuate the symptoms. Phalen’s test refers to placing the wrist in a fully flexed posture, whereas Tinel’s test refers to percussion of the median nerve over the wrist. The median nerve compression test involves direct pressure on the median nerve over the carpal canal. An electrodiagnostic study may be obtained to confirm the diagnosis of carpal tunnel syndrome and to quantify the degree of median nerve injury. In the absence of diminished sensation, muscle atrophy, or denervation potentials on electrodiagnostic testing, initial treatment for carpal tunnel syndrome involves splinting the wrist in neutral alignment and injecting corticosteroid into the carpal canal.11 A neutral wrist position relaxes the median nerve and maintains a low pressure in the carpal tunnel. Splinting and injection provide short-term relief of symptoms in over 75% of patients and continued symptomatic relief for 1 year or more in 13% to 40% of patients diagnosed early with mild symptoms. Presence of symptoms for less than 12 months, intermittent numbness, male gender, absence of advanced sensory changes, and normal thenar muscle bulk are good prognostic indicators for success. Activity modifications and use of antivibration gloves are encouraged in manual laborers.16 Associated systemic diseases such as diabetes and hypothyroidism should be recognized and appropriately managed. Ergonomic changes may be considered for general patient comfort and satisfaction. Many recommended measures have not, however, been scientifically proven to prevent or ameliorate symptoms of carpal tunnel syndrome. If patients experience only partial or temporary relief with conservative treatment measures, surgical decompression of the carpal tunnel may be considered. Individuals who report at least temporary relief after an injection are more apt to obtain similar relief from carpal tunnel release surgery.10 Newer techniques such as limited-incision carpal tunnel releases and those performed endoscopically have been developed to decrease palm discomfort and allow for a more rapid return to activities. Compared with a standard open decompression, the endoscopic procedure has been found to shorten the recovery period, but it may be associated with a higher reoperation rate and possibly an increased risk of nerve injury.20 Operative release reliably diminishes tingling in the digits, whereas improvements in numbness and weakness are less predictable. In patients with severe chronic nerve compression, it is not unusual to have permanent low-grade symptoms after uncomplicated carpal tunnel release surgery. Palm sensitivity around the scar, referred to as pillar pain, is fairly common and can be helped by scar desensitization performed by an occupational therapist. Activity restrictions in a manual laborer are typically recommended for a period of 6 to 8 weeks after surgery, with maximum medical improvement anticipated between 3 and 6 months postoperatively. Successful carpal tunnel release surgery usually produces no permanent impairment.
passes the ulnar nerve and artery. Compression of the ulnar nerve at this site can occur from trauma, use of vibrational tools, ulnar artery thrombosis or aneurysm, or presence of a space-occupying lesion such as a ganglion cyst. Symptoms include intrinsic muscle weakness, numbness, and tingling in the ring and small fingers, or a combination of motor and sensory abnormalities. The diagnosis depends on a thorough physical examination and pertinent ancillary studies. The examination should include palpation, percussion, vascular and motor evaluations, and sensory testing. Wrist radiographs are helpful in excluding a hook of hamate fracture in patients with a history of trauma. Magnetic resonance imaging (MRI) or an ultrasound study may be valuable in identifying a ganglion cyst, ulnar artery aneurysm, or arterial thrombosis. An electrodiagnostic study can assist in locating the anatomic site of compression and in determining the severity of the nerve involvement. If a specific etiology for ulnar tunnel syndrome is identified, treatment is directed toward the cause. Examples include excision of a space-occupying lesion, resection of an arterial aneurysm, and repair or resection of a hook of hamate fracture. When no cause is found, conservative treatment measures such as wrist splints, antivibration gloves, activity modifications, and nonsteroidal antiinflammatory medication are instituted. Surgery is considered in these patients only if the diagnosis is certain and nonoperative modalities fail. The procedure involves decompression of the ulnar nerve and artery in the proximal palm. Most patients with ulnar tunnel syndrome without a structural lesion do well with nonoperative management. In patients managed surgically, assistance from an occupational therapist may be beneficial in the early postoperative period. Most patients are able to return to previous employment activities in 6 to 8 weeks, with maximum medical improvement expected from 3 to 6 months postoperatively. An uncommon cause of ulnar tunnel syndrome that deserves special mention is the hypothenar hammer syndrome.6,9 This condition results from repetitive impact to the ulnar aspect of the hand leading to ulnar artery damage and formation of a pseudo-aneurysm and/or clot. Clinical findings include local tenderness and ischemic changes with numbness in the ring and small fingers. A pathologic Allen test with compression of the radial artery and impaired blood flow to the ulnar digits supports the diagnosis. The location of the lesion can be determined with ultrasonography, selective angiography, or MRI angiography. Initial treatment of hypothenar hammer syndrome includes cessation of impact trauma to the hand, elimination of tobacco products, and avoidance of prolonged cold exposure. Arterial thrombosis may be addressed nonoperatively in some individuals with injection of a thrombolytic agent or surgically in others by resecting the damaged vessel segment. Because of the potential for repeated thrombi formation and emboli to the digital arteries, an aneurysm is best managed operatively. Although residual cold intolerance can be expected, the results of surgical treatment are generally good.
ULNAR TUNNEL SYNDROME
HAND-ARM VIBRATION SYNDROME
Neuropraxia of the ulnar nerve at the wrist is referred to as ulnar tunnel syndrome.3 The ulnar tunnel, or loge of Guyon, is a fibroosseous space adjacent to the carpal tunnel through which
Hand-arm vibration syndrome, or vibration white finger, is a complex condition associated with vibration exposure and the use of hand-held vibrating tools.14,18,22 Symptoms include
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white fingers, sensory disturbances, reduced hand dexterity, and diminished grip strength. Additional symptoms may include cold intolerance, wrist and hand pain, and muscle cramps. Vibration exposure has a cumulative effect on both vessels and nerves. The duration of exposure necessary to elicit symptoms, however, has never been clearly defined. The diagnosis of hand-arm vibration syndrome is based on a history of vibration exposure and the presence of symptoms. The Stockholm workshop scales are widely used in assessing the severity of this condition in affected individuals. Electrodiagnostic and vascular flow studies are helpful in excluding other etiologies such as an arterial thrombosis or peripheral nerve compression lesion, although separate conditions may coexist. Prevention of hand-arm vibration syndrome is of paramount importance, with measures including use of well-padded antivibration gloves and frequent breaks from operating vibratory machinery. If symptoms develop, avoidance of the inciting tool(s) is essential. Discontinuation of smoking, oral vasodilators, and limitation of cold exposure may be beneficial in reducing associated digital vasospasms. In early stages, the condition is typically reversible, but in long-standing cases, blanching of the fingers may persist indefinitely despite avoidance of vibration exposure.
include wrist arthrography (Fig. 6d.4), MRI arthrography, and arthroscopy. Initial nonoperative management is indicated for acute and stable scapholunate interval injuries. Individuals with partial ligament tears and no clinical or radiographic evidence of carpal instability can be treated by temporary wrist immobilization. A nonsteroidal antiinflammatory medication and a localized cortisone injection may also be considered. Patients with chronic scapholunate ligament tears and evidence of marked degenerative arthritis can be initially managed similarly. If symptoms persist beyond approximately 4 months, surgical options may be discussed. In patients with acute and unstable scapholunate ligament injuries, early operative intervention is recommended. The decision to intervene surgically, however, depends on additional factors, including patient age, health status and expectations, and anticipated compliance with postoperative care. Because most individuals who sustain an acute scapholunate interval injury are physiologically young and active, direct ligament repair with capsular augmentation is perhaps the best means of managing this injury. However, other surgical procedures
SPRAINS A sprain constitutes an injury to one or more ligamentous structures stabilizing a joint. The complex anatomy of the wrist ligaments includes thickened bands of capsular tissue interconnecting the distal radius to the distal ulna and carpal bones, along with deeper structures such as the scapholunate and lunotriquetral interosseous ligaments linking adjacent carpal bones. The finger metacarpal and interphalangeal joints are stabilized by medial and lateral capsular thickenings termed collateral ligaments and a strong palmar structure designated the volar (palmar) plate.
Scapholunate interval Stability of the scapholunate interval depends on the integrity of the scapholunate interosseous ligament and secondary capsular ligament restraints.31 A history of falling onto the affected hand is often described in association with a scapholunate interval injury, the symptoms of which include dorsoradial wrist pain and a weakened grasp. Occasionally, active wrist flexion against resistance produces a painful snapping sensation. The diagnosis is suspected when pain is elicited with finger pressure over the scapholunate interval. The scaphoid shift test is helpful in excluding other causes of dorsoradial wrist pain, such as a ganglion cyst. A positive shift test is noted if the proximal pole of the scaphoid can be translated over the dorsal rim of the radius under dynamic load. In the initial evaluation, plain radiographs are useful. If an abnormality in carpal bone spacing is detected, comparative views of the contralateral wrist are obtained to distinguish a normal variation in carpal spacing from pathologic carpal alignment. In equivocal cases, fluoroscopic imaging can be helpful. Additional studies that may assist in making the diagnosis
Figure 6d.4 Wrist arthrogram. Radiopaque dye injected into the radiocarpal interval with leakage into the midcarpal and distal radioulnar joints. The appearance is diagnostic for tears of the scapholunate and lunotriquetral ligaments and the triangular fibrocartilage complex (TFCC).
Chapter 6d
have been described for treatment of both acute and chronic scapholunate interval trauma. Depending to a large degree on the specifics of the surgery, the course of rehabilitation and the results of treatment vary.
Lunotriquetral interval Analogous to scapholunate instability, pathologic laxity of the lunotriquetral interval requires injury to both the lunotriquetral interosseous ligament and the secondary capsular restraints.27 The spectrum of pathology ranges from partial ligament tears with retained carpal stability to complete dissociation with carpal collapse. Symptoms may include pain and crepitus with diminished wrist motion, grip weakness, and sensation that the carpus is giving way. To differentiate a lunotriquetral interval injury from other lesions that can cause ulnar-sided wrist symptoms, a careful examination is necessary. Palpation over the lunotriquetral joint predictably elicits pain. A ballottement test, performed by grasping the pisotriquetral unit between the thumb and index finger of one hand and the lunate between the thumb and index finger of the other hand, reproduces symptoms and may demonstrate abnormal joint laxity. Plain radiographs are recommended in the evaluation of ulnar-sided wrist pain. Lunotriquetral instability may not be readily apparent on standard radiographic images, however. An MRI arthrogram can assist in diagnosis and occasionally reveal other lesions contributing to the symptom complex. Initial management is typically nonoperative, involving activity modifications and a 4- to 6-week course of wrist immobilization. A midcarpal corticosteroid injection and short-term use of an antiinflammatory medication may be beneficial also. Most patients with isolated lunotriquetral ligament tears respond well to conservative treatment. Persistent pain localized to the lunotriquetral interval with failure of conservative management is an indication to intervene surgically. The result depends on a variety of factors, including chronicity of the injury, associated carpal arthrosis, and specifics of the operation performed. Surgical options include simple ligament debridement, shortening of the ulna to decompress the lunotriquetral joint, lunotriquetral ligament reconstruction, and lunotriquetral fusion. Poor response to a previous injection and/or immobilization is a strong indicator of a potential surgical failure.
Sprains
in the soft tissues distal to the tip of the ulnar styloid predictably elicits discomfort. Stress testing of the stabilizing function of the TFCC is performed by applying dorsal and palmar pressure to the interval between the distal ulna and the carpus. Wrist radiographs are recommended to assess arthritic changes, carpal instability patterns, and ulnar bone length relative to the radius (ulnar variance). MRI with or without intraarticular contrast may assist in the diagnosis. In most patients, initial treatment of a TFCC injury involves a variable period of wrist immobilization and possibly a cortisone injection into the ulnocarpal joint. Exceptions include the rare traumatic tear with gross instability at the distal radioulnar joint. These cases usually require early operative intervention. In those individuals who fail conservative measures and have significant symptoms, surgical intervention may be indicated. Simple arthroscopic debridement is effective in the management of many traumatic TFCC lesions, especially central tears (Fig. 6d.5). In individuals with positive ulnar variance or lunotriquetral instability, this can be combined with formal ulnar shortening. Open or arthroscopically assisted repairs of a peripheral tear have exhibited results similar to or better than debridement alone. The expected postoperative recovery period depends to a large extent on the details of the operation performed. After discontinuation of splint immobilization, all patients may benefit from a short period of therapy. Maximum medical improvement is expected 3 to 6 months postoperatively.
Triangular fibrocartilage complex The triangular fibrocartilage complex (TFCC) is a soft tissue structure composed of seven contiguous elements that combine to stabilize the distal radioulnar joint and suspend the ulnar carpus.15 Traumatic disruption of the TFCC can lead to ulnarsided wrist pain, instability of the distal radioulnar joint, and articular cartilage degeneration. Patients typically describe pain and a clicking sensation localized to the ulnar aspect of the wrist after known injury or repeated microtrauma. Symptoms are often aggravated by forearm rotation and ulnar deviation of the wrist. Applied pressure
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Figure 6d.5
Wrist arthroscopy.
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Gamekeeper’s thumb Disruption of the ulnar collateral ligament of the thumb metacarpophalangeal joint occurs when a significant valgus stress is applied to the joint,13 often from a fall on the outstretched thumb. The injury may result in metacarpophalangeal joint instability, causing pain with thumb motion and adversely affecting both grip and pinch strength. Two terms commonly used to describe this injury are the gamekeeper’s thumb and the skier’s thumb. The anatomy of the thumb ulnar collateral ligament is analogous to that of the collateral ligaments stabilizing the finger metacarpophalangeal and interphalangeal joints. The thumb ulnar collateral ligament ruptures most often from its distal insertion at the base of the proximal phalanx. Displacement of the ligament can occur such that it comes to lie superficial and proximal to the adductor pollicis muscle, a specific pattern of injury referred to as a Stener lesion (Fig. 6d.6). The diagnosis of a gamekeeper’s injury involves a careful examination of the involved thumb. Plain radiographs should be obtained to assess for an underlying bone injury. Stress radiographs with applied valgus force to the metacarpophalangeal joint can confirm the diagnosis and determine the degree of ligament disruption. Treatment of partial ligament tears involves a 4- to 6-week period of thumb immobilization. A hand-based spica splint or cast incorporating the thumb proximal phalanx usually suffices. A complete ligament tear is an indication for surgical intervention; in these cases a Stener lesion may preclude effective ligament healing with nonoperative treatment. The thumb is commonly immobilized for 4 weeks postoperatively. Unrestricted activities are permitted after 6 weeks in cases treated nonoperatively and after 3 months in patients managed surgically. In thumbs with partial ligament injuries, nonoperative treatment yields a stable and painless thumb with near-normal motion in most cases. In thumbs with a complete ligament
rupture treated early with surgery, more than 90% of patients can expect a good to excellent result.
Fingers The finger metacarpophalangeal and interphalangeal joints may be injured by a variety of different mechanisms, resulting in partial or complete disruption of the collateral ligaments and palmar plate. Although the closely conforming articular surfaces of the proximal and distal interphalangeal joints usually afford residual stability, the metacarpophalangeal joints are less anatomically constrained and may exhibit pathologic laxity with injury to identical periarticular structures. The diagnosis of a finger sprain is relatively straightforward. The involved joint exhibits variable swelling and limited motion with maximum tenderness in the area of soft tissue injury. Gentle stress may elicit visible or palpable joint instability. Assessment and documentation of neurovascular status commonly reveals a digital neuropraxia. Radiographs are valuable in excluding the presence of a fracture, joint subluxation, or joint dislocation. Ultrasound and MRI studies may be considered but are often unnecessary for initial diagnosis. A stable sprain of the finger metacarpophalangeal joint is treated with buddy strapping and immediate motion. Velcro straps or athletic tape is placed around the injured digit and adjacent finger, leaving the interphalangeal joints free for motion exercises. An unstable metacarpophalangeal joint may be managed by buddy strapping and/or immobilization in a handbased splint for 4 to 6 weeks. The decision to intervene surgically depends on several factors, including the presence of an associated avulsion fracture and residual joint instability with splint immobilization. Sprains of the proximal and distal interphalangeal joints are managed by finger extension splinting for a brief period followed by active motion exercises and protective buddy strapping. Progressive static or dynamic extension splinting may be indicated during the course of treatment to address a developing joint contracture. Supervised therapy is often helpful. Most finger sprains can be managed without surgical intervention. Some degree of permanent swelling is expected, and a small flexion contracture may persist. The deformity will unlikely impair hand function or preclude a return to gainful employment.
FRACTURES Distal radius
Figure 6d.6 Torn and displaced ulnar collateral ligament of the thumb metacarpophalangeal joint, termed a Stener lesion (arrow). This pattern of displacement is often responsible for failure of nonoperative management of complete ligament tears.
Distal radius fractures, commonly called Colles’, Barton’s, Smith’s, and Chauffeur’s fractures, account for 14% of all extremity injuries.12,24 Approximately 50% of these injuries involve the articular surface of the distal radius. In healthy and active individuals, restoration of bone and joint alignment is indicated to preserve function and to deter posttraumatic arthrosis. The initial examination should include an assessment for concurrent bone and soft tissue injuries with specific attention to the stability of the distal radioulnar joint. Although vascular compromise occurs rarely, neurologic symptoms are relatively
Chapter 6d
frequent and typically involve the median nerve in the carpal tunnel with paresthesias in the radial four digits. Radiographic evaluation is performed both before and after attempted closed fracture reduction (Fig. 6d.7). Assessment of the intraarticular extent of the injury is crucial. A residual joint incongruity of 2 mm or greater displacement has been associated with posttraumatic arthrosis. Special imaging studies such as computed tomography are useful when the fracture pattern and/or magnitude of displacement is difficult to determine on plain radiographs. Closed stable fractures in acceptable alignment can be treated nonoperatively. Serial radiographs are obtained, and a cast is worn for approximately 6 weeks, followed by the use of a temporary removable splint. Supervised therapy may be helpful early during the course of healing to assist with finger motion and later, after fracture consolidation, to help improve wrist motion and grip strength. Displaced and unstable fractures usually require surgery. Procedural options include the use of percutaneous pins, external fixation, open reduction and internal fixation, or a combination of methods. The results of treatment vary, depending in part on the severity of the initial injury and the extent of articular surface involvement. Although maximum medical improvement is anticipated 6 months after injury or surgery, patients may continue to demonstrate improvements in wrist motion, grip strength, and endurance for well over 1 year.
Scaphoid
Figure 6d.7
Figure 6d.8
Displaced distal radius fracture (arrow).
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Fractures
The scaphoid is the most commonly fractured carpal bone.7 This type of injury typically results from a sudden impact on the palm with the wrist hyperextended, such as occurs with a fall onto the outstretched hand. When the fracture is complete, intrinsic forces may lead to displacement of a scaphoid fracture into a flexed humpback position: The proximal pole extends, whereas the distal pole flexes. Classically, the patient presents with loss of wrist motion, snuff box tenderness, and pain with resisted forearm pronation and supination. Wrist swelling may be present, but this and other signs of local trauma are not always apparent. In many instances the presentation and diagnosis are delayed, with the injury initially attributed to a “sprain.” Although most scaphoid fractures can be detected acutely on good quality plain radiographs (Fig. 6d.8), some do not become apparent for several weeks. Specialized imaging studies, including MRI, scintigraphy, and computed tomography, are occasionally helpful in early diagnosis and subsequent management. Closed treatment is indicated for acute nondisplaced scaphoid fractures. If diagnosed promptly and immobilized for an adequate duration, more than 90% of stable scaphoid injuries heal. Surgical intervention is indicated for acute fractures that are either displaced or unstable and for older fractures that have failed to unite. Instability is defined as displacement greater
Scaphoid waist fracture (arrow).
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than 1 mm in any direction and injuries associated with loss of carpal bone alignment. Relative indications for surgical treatment include a proximal pole fracture and prolonged wrist immobilization that would be unacceptable to the patient for social and/or economic reasons. Intramedullary pins or screws have become the standard of fixation for scaphoid fractures, with union rates comparable with those reported for closed-cast treatment. When screws are used and stability is achieved, early mobilization of the wrist is often permitted. In one study of military personnel, percutaneous screw fixation of nondisplaced scaphoid fractures was shown to result in more rapid radiographic union and return to duty when compared with cast immobilization.5 Maximum medical improvement is expected 4 to 6 months after injury or surgery but is contingent upon fracture healing.
Metacarpals and phalanges Fractures involving the metacarpals and phalanges occur in multiple patterns: transverse, oblique, spiral, and comminuted.4,17 Most of these injuries may be evaluated using standard radiographs. The rotational alignment of the digit is assessed with active finger motion or by generating finger motion through a tenodesis effect with passive wrist flexion and extension. The phalanges should be parallel during extension and point toward the thenar eminence when flexed. Most metacarpal and phalangeal shaft fractures can be treated nonoperatively with protective casting or splinting. Clinical union usually requires 4 to 5 weeks for metacarpal injuries and 3 to 4 weeks for proximal and middle phalanx injuries. A distal phalanx fracture may take longer to unite. Metacarpal fractures are typically immobilized with a forearm-based cast or splint incorporating the metacarpophalangeal joint of the injured finger and one or two adjacent digits. Hand-based immobilization is indicated for proximal and middle phalanx shaft fractures, whereas distal phalanx fractures are treated with a simple finger splint. All cases require close radiographic follow-up to assess for loss of fracture alignment. Operative treatment is indicated for irreducible or unstable fractures and those associated with tendon lacerations. Articular injuries with marked incongruency and/or persistent joint subluxation are also considered for surgical repair. The type of fixation used depends on the fracture pattern, the soft tissue injury, and the judgment and experience of the surgeon. Depending in part on the severity of the fracture and associated soft tissue trauma, the reported results after nonoperative and operative treatment of metacarpal and phalangeal fractures are variable. A successful outcome requires patient compliance with treatment and an appropriately structured rehabilitation program. In most cases maximum medical improvement is anticipated approximately 3 to 4 months from injury or surgery.
affecting the hands symmetrically. The distal interphalangeal joint of the finger is the most commonly involved hand joint, followed by the thumb basilar joint. In contradistinction to systemic arthritic conditions such as rheumatoid arthritis, the finger metacarpophalangeal joints are usually spared. Although several studies have alluded to repetitive activities as having an influence on the development of osteoarthritis in the wrist and hand, a causal relationship between repetitive activities and degenerative joint disease has never been conclusively proven.
Wrist Osteoarthritis of the wrist most often develops secondary to a traumatic event. Intraarticular fractures of the distal radius, malunited scaphoid fractures, scaphoid nonunions, and intercarpal ligamentous injuries all predispose the wrist to degeneration. In many cases, however, a specific cause is never identified. Patients with wrist arthritis report pain, loss of mobility, and weakness in grip. Crepitation during motion or loading activities and swelling over the dorsal carpus are common in advanced disease. Plain radiographs confirm the diagnosis and assist in devising a treatment strategy (Fig. 6d.9). For early degenerative disease of the wrist, conservative measures are frequently successful. These include nonsteroidal
OSTEOARTHRITIS Osteoarthritis is a slowly progressive joint disease of multifactorial etiology.21,29 Cartilage degeneration and osteophyte formation are often seen in association with advancing age, characteristically
Figure 6d.9 Wrist degenerative arthritis developing after a scapholunate interval injury (arrow).
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antiinflammatory medication, wrist immobilization, activity modifications, and corticosteroid injection(s). Significant degenerative arthritic changes predict some degree of permanent functional impairment. Surgery is indicated if symptoms warrant and conservative treatment measures have failed. Procedures include proximal row carpectomy (excision of the three most proximal carpal bones), partial carpal bone fusions, and total wrist arthrodesis. The period of postoperative immobilization depends on the specifics of the operation performed, averaging 6 to 8 weeks for a fusion procedure. Results of surgical treatment are favorable in terms of pain relief. Motion-retaining procedures such as a partial wrist fusion and proximal row carpectomy require a considerable amount of therapy after cast removal. Total wrist fusion is the most reliable in terms of relieving pain and improving grip strength but at the expense of wrist motion. Work restrictions after surgery must be determined on an individual basis, taking into account the specific job requirements. Maximum medical improvement is anticipated 6 months postoperatively.
Thumb basilar joint The basilar joint of the thumb consists of the metacarpal base and trapezium bone.2 Arthritis around the trapezium is the second most common site for degenerative joint disease in the hand (preceded only by the distal interphalangeal joint). More frequent in females than males, the condition has been attributed to laxity of the important stabilizing ligaments of the thumb. Patients with basilar thumb joint arthritis have pain localizing to the base of the thenar muscles. Opening jars and turning door knobs are often difficult tasks to perform comfortably. As the condition advances, pinch and grip strength diminish, and thumb range of motion may decrease as well. Examination reveals a tender and enlarged basilar joint. Axial grinding of the thumb metacarpal exacerbates the pain and may elicit sensations of instability and crepitation. The Finkelstein test is usually negative, helping to distinguish basilar joint arthritis pain from de Quervain disease. The diagnosis is confirmed by plain radiographs (Fig. 6d.10). Initial treatment of basilar joint osteoarthritis includes activity modifications, splint immobilization, nonsteroidal antiinflammatory medication, thenar muscle strengthening exercises, and joint injection(s). If a patient’s symptoms are not satisfactorily relieved by conservative means, surgical intervention may be considered. The most commonly performed operation entails partial or total excision of the diseased trapezium with stabilization of the thumb metacarpal base using local tendon graft. A significant hyperextension deformity of the thumb metacarpophalangeal joint may require a concomitant procedure to stabilize the metacarpophalangeal joint. The postoperative course typically involves a 4- to 6-week period of wrist and thumb immobilization followed by a supervised therapy program. Pain relief from surgery is nearly universal but not always complete, especially in younger and more active individuals. Activity modifications in the workplace may be indicated for an extended period of time after surgery. Thumb motion and
Figure 6d.10
Thumb basilar joint arthritis (arrow).
grip/pinch strength improve slowly. Maximum medical improvement is anticipated after approximately 6 months.
Proximal interphalangeal joint Osteoarthritis of the proximal interphalangeal joint is relatively rare. The condition typically arises after a dislocation or intraarticular fracture. The earliest signs of degenerative arthritis are swelling and morning stiffness. Limited proximal interphalangeal joint motion follows with the development of marginal osteophytes (Bouchard’s nodes). Late joint degeneration leads to an angular deformity and joint instability. Radiographs confirm the diagnosis and reveal the degree of joint deterioration. Conservative treatment measures include nonsteroidal antiinflammatory medication, activity modifications, and short-term splinting. Early in the degenerative process, steroid injections can be helpful in ameliorating pain. If these measures fail and considerable symptoms persist, surgical intervention may be considered. Arthrodesis is the most reliable method of eliminating pain. Fusion of the ulnar digits at the proximal interphalangeal joint level impairs grip strength and finger dexterity to a greater
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degree than it does in the radial digits. Fusion rates vary from 84% to 100%. Implant arthroplasty also provides pain relief with the added benefit of preserving partial joint motion. Joint replacement, however, carries an attendant risk of implant breakage and should be avoided in younger patients and/or manual laborers. Maximum medical improvement is expected 3 to 6 months postoperatively.
Distal interphalangeal joint Idiopathic degeneration of the distal interphalangeal joint commonly involves multiple digits in a symmetric distribution, whereas single finger joint degeneration is more suggestive of previous injury. In most cases, symptoms are mild and functional impairment is negligible. Swelling and stiffness are common symptoms in early degeneration of the distal interphalangeal joint. As the disease progresses, joint enlargement is seen secondary to osteophyte formation (Heberden’s nodes), resulting in limited motion. Late in the disease, angular and rotational deformities occur at the finger tip. Radiographs confirm the diagnosis and demonstrate the severity of joint destruction. In most individuals, conservative care is successful. Treatment measures include nonsteroidal antiinflammatory medication, activity modifications, corticosteroid injection(s), and splinting. Surgery is reserved for symptomatic degenerative disease that does not respond to conservative measures. Distal interphalangeal joint fusion reliably relieves pain, restores stability and strength, and improves the appearance of the digit. Fusion rates vary from 80% to 100%. Maximum medical improvement is expected 2 to 4 months postoperatively.
GANGLIA Ganglia are fluid-filled structures that arise from a joint, tendon, or tendon sheath.28,30 They contain lubricating fluid called mucin that is similar in content to but more viscous than the fluid found in joints and tendon sheaths. Ganglia can emanate from almost any anatomic region, but they are most common at the wrist, the proximal margins of digital flexor tendon sheaths, and the finger distal interphalangeal joints. Cysts communicate with these structures through one or more ducts that account for their intermittent fluctuation in size. The true etiology of a ganglion is unknown, although approximately 10% have been associated with previous trauma.
Carpal ganglia Ganglia of the wrist are seen most frequently dorsally, near the articulation of the scaphoid and lunate bones (Fig. 6d.11). They occur less commonly at the palmar aspect of the wrist, adjacent to the flexor carpi radialis tendon. Cysts may be multiloculated and much larger than clinically apparent, extending far away from their point of origin. Patients with carpal ganglia may complain of activity-related wrist pain and weakness. Guarding with minor loss of wrist
Figure 6d.11 Wrist magnetic resonance image, axial view. Dorsal ganglion attached to the scapholunate interval (arrow).
motion secondary to pain may result. In most cases, however, the cysts yield few or no symptoms and require no specific intervention. For a symptomatic dorsal wrist ganglion, aspiration of the cyst with or without a corticosteroid injection is initially recommended and successful in up to 50% of cases. Aspiration is relatively contraindicated for volar wrist ganglia because of the close proximity of the radial artery. In these cases temporary wrist splinting and use of a nonsteroidal antiinflammatory medication may be helpful. Surgical excision of wrist ganglia is indicated for persistent pain, with reported recurrence rates averaging approximately 5%. The procedure is frequently performed in an open manner, although an arthroscopic technique for excising dorsal ganglia was recently described.25 After ganglion excision, most patients experience continued low-grade discomfort for several weeks. Supervised therapy may be helpful in diminishing pain and in restoring wrist motion and grip strength. Maximum medical improvement is anticipated 2 to 3 months postoperatively.
Retinacular cysts Ganglia arising from the digital flexor tendon sheath are termed volar retinacular ganglia or retinacular cysts. Appearing as a small bump at the base of a digit adjacent to the palmar digital flexion crease, this type of cyst commonly causes discomfort during activities that require gripping or holding objects in the palm. A painful cyst can usually be treated by needle aspiration. Surgery to excise the lesion is considered in recalcitrant cases and when the diagnosis is uncertain. A rapid return to regular work activities is expected.
Mucous cysts Cysts arising from the distal interphalangeal joint, termed mucous cysts, are invariably associated with degenerative arthritic changes in the underlying joint. Because of their location, mucous cysts
Chapter 6d
may disrupt the germinal matrix of the nail bed and lead to longitudinal nail plate grooves and ridges. Aspiration and instillation of a corticosteroid can be attempted, but this treatment is rarely curative. Because the distal interphalangeal joint is immediately deep to the skin surface, aspiration increases the likelihood of septic arthritis. Simple cyst excision carries a recurrence rate of 25% or greater. Excision of the cyst in conjunction with debridement of marginal joint osteophytes, however, is successful in over 95% of cases. Recovery after surgery is relatively rapid, and unrestricted use of the hand should be possible within 6 weeks.
COMPLEX REGIONAL PAIN SYNDROME Complex regional pain syndrome (CRPS) is a neurogenic disorder characterized by pain out of proportion to the level anticipated with the diagnosis, swelling, autonomic dysfunction, and joint stiffness.1,32 In the past, a variety of terms, including reflex sympathetic dystrophy, causalgia, Sudeck’s atrophy, and shoulder-hand syndrome, has been used to describe this condition. Type 1 CRPS develops after a noxious event without identifiable nerve injury, whereas type 2 CRPS occurs in association with a nerve injury. The pathogenesis of CRPS remains poorly understood. Autonomic hyperactivity is implicated in syndrome development, and in many cases psychologic factors seem to play a role. Initially, pain, swelling, restricted motion, and vasomotor changes (hyperhidrosis, erythema, excessive warmth) predominate the symptom complex. After several months, swelling changes from a soft to a hard brawny edema. Eventually, the skin appears shiny and glossy, and stiffness becomes marked with fixed joint contractures. The diagnosis of CRPS is made on clinical examination but may be confirmed by a variety of objective tests. Radiographs frequently reveal diffuse osteopenia secondary to bone demineralization. Three-phase bone scans show characteristic diffuse uptake in the involved areas. Thermography can depict asymmetric temperature when compared with the contralateral limb. Anesthetic blockade at the neck/shoulder level confirms the diagnosis in cases with primary involvement of the sympathetic nervous system. Successful treatment of CRPS depends on prompt diagnosis and early intervention. The appearance and persistence of inordinate pain after injury or surgery is typically the first sign. The possibility of nerve injury should be entertained and any painful stimulus (e.g., cast compression) eliminated. Active range-ofmotion exercises, edema control, interval splinting, and a stressloading program are initiated by an experienced therapist. Pharmacologic treatment measures include corticosteroids, αadrenergic blocking agents, calcium channel blockers, and regional anesthetic injections. To address marked joint contractures late in the disease process, surgical intervention may be indicated. Evidence suggests that the earlier treatment is instituted, the better the chance for a successful result. A significant percentage of patients, however, still complain of pain, cold intolerance, sensory disturbances, swelling, hand weakness, and stiffness years later. Once the chronic stages of CRPS have occurred, results are less favorable, with expected varying degrees of permanent upper extremity impairment.
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References
CONCLUSION Management of an occupational-related disorder of the wrist or hand is contingent upon the recognition of factors related to condition development, a coordinated team approach to care, and the patient’s active participation in recovery. Conservative treatment measures include supervised therapy, splinting, corticosteroid injection, oral pain medication, and activity modifications. Surgical intervention may be indicated for trauma, advanced nerve compression lesions, arterial thrombosis, recalcitrant tendonitis, symptomatic degenerative arthritis, painful ganglia, and various other conditions. The ultimate goals of treatment should include patient satisfaction, symptom resolution, and return to gainful employment.
REFERENCES 1. 2. 3. 4. 5.
6. 7. 8. 9. 10. 11.
12. 13. 14.
15. 16. 17. 18.
19. 20. 21. 22. 23.
Atkins RM: Aspects of current management complex regional pain syndrome. J Bone Joint Surg Br 85(8):1100-1106, 2003. Barron OA, Glickel SZ, Eaton RG: Basal joint arthritis of the thumb. J Am Acad Orthop Surg 8:314-323, 2000. Bednar MS: Ulnar tunnel syndrome. Hand Clin 12(4):657-663, 1996. Blazar PE, Steinberg DR: Fractures of the proximal interphalangeal joint. J Am Acad Orthop Surg 8:383-390, 2000. Bond CD, Shin AY, McBride MT, Dao KD: Percutaneous screw fixation or cast immobilization for nondisplaced scaphoid fractures. J Bone Joint Surg Am 83(4):483-488, 2001. Cooke RA: Hypothenar hammer syndrome: a discrete syndrome to be distinguished from hand-arm vibration syndrome. Occup Med 53(5):320-324, 2003. Cooney WP III: Scaphoid fractures: current treatments and techniques. Instr Course Lect 52:197-208, 2003. D’Arcy CA, McGee S: Clinical diagnosis of carpal tunnel syndrome. JAMA 284(15):1924-1925, 2000. De Monaco D, Fritsche E, Rigoni G, Schlunke S, Von Wartburg U: Hypothenar hammer syndrome: retrospective study of nine cases. J Hand Surg Br 24(6):731-734, 1999. Edgell SE, McCabe SJ, Breidenbach WC, LaJoie AS, Abell TD: Predicting the outcome of carpal tunnel release. J Hand Surg Am 28(2):255-261, 2003. Gerritsen AA, de Krom MC, Struijs MA, Scholten RJ, de Vet HC, Bouter LM: Conservative treatment options for carpal tunnel syndrome: a systematic review of randomized controlled trials. J Neurol 249(3):272-280, 2002. Hanel DP, Jones MD, Trumble TE: Wrist fractures. Orthop Clin North Am 33(1):35-57, 2002. Heyman P: Injuries to the ulnar collateral ligament of the thumb metacarpophalangeal joint. J Am Acad Orthop Surg 5:224-229, 1997. Jetzer T, Haydon P, Reynolds D: Effective intervention with ergonomic, antivibration gloves, and medical surveillance to minimize hand-arm vibration hazards in the workplace. J Occup Environ Med 45(12):1312-1317, 2003. Kalainov DM, Culp RW: Arthroscopic treatment of TFCC tears. Tech Hand Upper Extremity Surg 1(3):175-182, 1997. Kasdan ML, Lewis K: Management of carpal tunnel syndrome in the working population. Hand Clin 18(2):325-330, 2002. Kozin SH, Thoder JJ, Lieberman G: Operative treatment of metacarpal and phalangeal shaft fractures. J Am Acad Orthop Surg 8:111-121, 2000. Kurozawa Y, Nasu Y, Hosoda T, Nose T: Long-term follow-up study on patients with vibration-induced white finger (VWF). J Occup Environ Med 44(12):1203-1206, 2002. Lane LB, Boretz RS, Stuchin SA: Treatments of de Quervain’s disease: role of conservative management. J Hand Surg Br 26:258-260, 2001. Macdermid JC, Richards RS, Roth JH, Ross DC, King GJ: Endoscopic versus open carpal tunnel release: a randomized trial. J Hand Surg Am 28(3):475-480, 2003. Palmieri TJ, Grand FM, Hay EL, Burke C: Treatment of osteoarthritis in the hand and wrist: nonoperative treatment. Hand Clin 3(3):371-383, 1987. Pelmear PL: The clinical assessment of hand-arm vibration syndrome. Occup Med 53(5):337-341, 2003. Piligian G, Herbert R, Hearns M, Dropkin J, Landsbergis P, Cherniack M: Evaluation and management of chronic work-related musculoskeletal disorders of the distal upper extremity. Am J Ind Med 37(1):75-93, 2000.
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24. 25.
26. 27. 28.
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Rettig ME, Raskin KB: Acute fractures of the distal radius. Hand Clin 16(3):405-415, 2000. Rizzo M, Berger RA, Steinmann SP, Bishop AT: Arthroscopic resection in the management of dorsal wrist ganglions: results with a minimum 2-year follow-up period. J Hand Surg Am 29:59-62, 2004. Saldana MJ: Trigger digits: diagnosis and treatment. J Am Acad Orthop Surg 9:246-252, 2001. Shin AY, Battaglia MJ, Bishop AT: Lunotriquetral instability: diagnosis and treatment. J Am Acad Orthop Surg 8:170-179, 2000. Steinberg BD, Kleinman WB: Occult scapholunate ganglion: a cause of dorsal radial wrist pain. J Hand Surg Am 24:225-231, 1999.
29. 30. 31. 32.
Steinberg DR: Management of the arthritic hand. In MW Chapman, ed: Operative orthopaedics, ed 2. Philadelphia, 1993, JB Lippincott. Thornburg LE: Ganglions of the hand and wrist. J Am Acad Orthop Surg 7:231-238, 1999. Walsh JJ, Berger RA, Cooney WP: Current status of scapholunate interosseous ligament injuries. J Am Acad Orthop Surg 10:32-42, 2002. Zyluk A: The sequelae of reflex sympathetic dystrophy. J Hand Surg Br 26(2): 151-154, 2001.
CHAPTER
6e
Biomechanical Aspects of Hand Tools Robert G. Radwin
The mechanical relationships between hands, tools, and tool operation are important for understanding and controlling physical stress of tool operators. Hand exertions needed for many tool operations are affected directly by the selection of specific tools and accessories for the task. Although many of the recommendations in this chapter are based on years of extensive biomechanics research, others arise out of simple mechanical principles and reasonable assumptions about mechanical relationships between tools and their operators. The objective is to illustrate how the characteristics of a particular tool (such as size, shape, output, and accessories) and its manner of use (such as orientation or location relative to the operator) can significantly affect the effort needed for performing specific tasks. Both manual (hand powered) and power (electric, pneumatic, or hydraulic) hand tools require that operators produce forces at varying levels. Manual tools may require exertion of forces to squeeze together tool handles, such as those of pliers and cutting tools. Other manual tools may require twisting, pulling, or pushing. Safe operation of a power tool requires that an operator support it adequately in a particular position and apply the necessary forces while reacting against the force generated by the tool itself. Force demands that exceed an operator’s strength capabilities can cause loss of control and result in an accident or an injury. If improper selection, installation, or use of a power tool requires an operator to make substantially greater exertion than necessary, it may lead to muscle fatigue or a musculoskeletal disorder.1,5,28,39,40 Tools that are selected to minimize hand forces are usually the best ones for the task. The discussion begins with simple manually operated hand tools, including screwdrivers and pliers. An investigation of the means by which different kinds of screw fasteners can affect forces in the hands is followed by a description of how selection and installation of power hand tools can control the static and dynamic hand forces associated with their use. Mathematical and biomechanical calculations are provided to enable interested readers to follow them and to impress other readers less concerned with how objective conclusions can be ascertained through mostly deterministic methods. These principles should be applicable to occupational health professionals in the selection and installation of tools. Designers and engineers should be able to adapt these calculations to new tools and job designs.
of screws and work situations. A screw is tightened usually by grasping the screwdriver handle and simultaneously applying a torque while exerting a push force. The amount of torque, T, needed for tightening a screw depends on the kind of screw and the characteristics of the screw joint such as friction, screw diameter, thread, and clamping load. The push force is often called feed force. Feed force, F, is the axial force applied against the screwdriver shaft that is required to thread the screw and keep the screwdriver blade seated. Numerous taskrelated factors affect feed force, including thread type (whether the screw is self-tapping or threaded), material hardness, thread size, and hole diameter. The choice of a particular size screwdriver can have a great effect on the hand exertion required for a task.
Handle length A question often asked is how does screwdriver length affect hand force? Experience has found that a longer screwdriver handle generally results in less effort.32 This can be explained by considering the motions needed for tightening a screw. When a screw is tightened, torque is transferred to the handle, usually by rotating the forearm in combination with flexion and ulnar deviation of the wrist. The asymmetry of the hand, wrist, and forearm relative to the screwdriver’s radial axis produces eccentric rotation of the handle that causes perturbation of the handle and shaft along a horizontal displacement Δ from the vertical axis (Fig. 6e.1). The magnitude of this displacement depends on the particular action and anthropometry of the wrist.
F
Fx
Δ
Fy
Direction of twist θ
L
Direction of rotation
MANUAL SCREWDRIVERS One of the most commonly used hand tools, the screwdriver, is available in various sizes and forms suitable for different types
Figure 6e.1 Rotation and perturbation of a manual screwdriver when the handle is twisted in the hand.
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This perturbation causes the screwdriver shaft to tilt to a maximum angle, θ, as the screwdriver rotates. If screwdriver handle size, diameter, and shape and shaft diameter remain the same, hand and wrist rotation is unaffected by the shaft length, so the handle perturbation remains constant. Assuming that the handle displaces the same distance Δ from the axis of the fastener shaft (Fig. 6e.1), the maximum angle, θ, that the screwdriver shaft tilts as it is twisted can be described as ⎛ Δ⎞ θ = sin−1 ⎜ ⎟ ⎝ L⎠ Orthogonal feed force components (Fig. 6e.1) can be resolved into Fy = F cosθ, Fx = F sinθ If a screwdriver has a length, L, then the maximum component parallel to the fastener shaft is Fy: ⎡ ⎛ Δ⎞ ⎤ Fy = F cos θ = F cos ⎢ sin−1 ⎜ ⎟ ⎥ ⎝ L⎠⎦ ⎣ Solving for F, F=
Fy ⎡ ⎛ Δ⎞ ⎤ cos ⎢ sin−1 ⎜ ⎟ ⎥ ⎝ L⎠⎦ ⎣
A consequence of this relationship is that if the required axial force component Fy remains constant, F decreases as L increases. Hence, the hand force exerted can be reduced by increasing L and using the longest screwdriver available. For example, if the shaft of a 6-cm screwdriver displaces Δ = 3 cm, the feed force F needed to drive a screw is F=
Fy ⎡ ⎛ 3⎞ ⎤ cos ⎢ sin−1 ⎜ ⎟ ⎥ ⎝ 6⎠ ⎦ ⎣
= 1 . 15 × Fy
Therefore, the maximum feed force can be as much as 15% greater than the axial force needed. If the screwdriver length is increased to 25 cm, the feed force needed to drive a screw would be F=
Fy ⎡ ⎛ 3 ⎞⎤ cos ⎢ sin−1 ⎜ ⎟ ⎥ ⎝ 25 ⎠ ⎦ ⎣
= 1 . 01 × Fy
which decreases the force feed to only as much as 1% more force than is actually needed. Of course, a very long screwdriver may not be practical under all circumstances. Clearance and spatial constraints may limit the size of screwdriver that can be used. Furthermore, a very short screwdriver can facilitate the precision grip needed for light precise work, such as that afforded with a jeweler’s screwdriver. Another way to limit the horizontal perturbation of a screwdriver as it rotates in the hand is by supporting the screwdriver shaft, as might be done when two hands are used. If the screwdriver were held straight by supporting the shaft with the fingers of the free hand, then the tilt angle θ remains close to 0 degrees
~F cos 0 degrees ~ ~ F. This action therefore aids the and Fy~ operator by keeping the axial feed force requirements minimal and unaffected by screwdriver length. When high feed forces are required, screwdriver shafts should be long enough to be pinched or gripped by the other hand as a guide. Using a similar argument, the hand force needed for a nut driver should be mostly independent of the shaft length because the shaft is coupled to the nut, permitting concentric rotation with the handle despite the asymmetries of the hand and forearm.
Handle diameter Another common question is how does a screwdriver handle diameter affect hand force? Several studies investigated the effect of handle diameter on the torque capability of the hand. A study involving volitional torque exerted for different manual screwdrivers, locking pliers, and wrenches found that the resulting torque magnitude was influenced strongly by the kind of tool and the posture assumed.26 From a purely mechanical standpoint, a greater handle diameter should result in more torque at the screwdriver shaft for the same effort, provided that the frictional properties of the handles are similar and the diameter is not too large. The diameter of a screwdriver handle plays a critical role in limiting a user’s torque-generating capability. Large grip forces are often needed for sustaining a grip and for coupling the hand and the tool to prevent the handle from slipping. A simplified relationship between the torque and diameter illustrates the effect of mechanical advantage on torque: T = S G = μ FG G where T is torque, S is the shear grip force, G is the handle radius, μ is the coefficient of friction between the hand and the handle, and FG is grip force.32 If FG remained constant, torque would linearly increase as the handle diameter increased. As is well known, however, grip strength is not constant for all diameters but rather is affected by handle size.4,17,19 If a handle is too large or too small, the strength of the hand is greatly compromised. The relationship between cylindrical handle size and grip strength is summarized in Figure 6e.2.29 Maximum grip force occurs around 6 cm. Consequently, the optimal diameter is one in which a further increase in diameter increases the mechanical advantage while simultaneously decreasing grip force. Research has found that this optimum depends on handle design, friction, gender, and hand size.32 Torque performance diminishes when handle diameters are greater than 5 cm,33 and a diameter of 4 cm is sometimes recommended for screwdrivers.7,8 Sufficient friction must be present between the handle and the hand to provide a secure grip, exert force or torque, and prevent a tool from slipping. Surfaces that do not provide adequate friction require greater grip force that may result in greater effort and even loss of control of the tool. The amount of friction depends on the coefficient of friction between the hand and the material or object grasped. Some materials have greater coefficients of friction and consequently better frictional characteristics than others. No one handle size is practical for all tasks, and certain handles serve some objectives better than others. A panel of ergonomics experts recommends using a small-diameter handle (8-13 mm)
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Grip strength
400
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Screwdriver blades and screw heads
Allowances should be made for all these factors. The three most common threaded fastener heads are slotted, Phillips, and Torx™ (Fig. 6e.3), each of which has different feed force requirements.
Slotted screws 300
200 4
5
6
7
Handle span (cm) Figure 6e.2 Grip strength for a population of 29 subjects (19 university students and 10 factory workers). Error bars represent one standard error of the mean.
for a precision grip and a large-diameter handle (50-60 mm) for a power grip.27 In one study, handles between 31 and 38 mm in diameter were considered optimal for a power grip12; several studies recommend 50 mm as an upper limit diameter.4,33,38
SCREWDRIVER BLADES AND SCREW HEADS Screwdriver feed force can be affected by the particular type of screw fastener head and screw tip needed.6 Self-tapping screws require more feed force than do screws tightened through pretapped holes. Material hardness and friction are also important factors to consider for self-tapping screws. Feed force requirements increase as the torque level increases for cross-recess screws.
Slotted
Phillips head
Torx
The oldest and simplest type of screw head, the slotted screw, has a single slot across the entire diameter of the head. When a screwdriver blade is inserted inside a screw slot and rotated, contact is usually made at the two edges of the blade, as shown in Figure 6e.4. The size of the screwdriver width, w, limited by the radius of the screw head provides a slight mechanical advantage for applying torque against the screw. Wider screw heads and screwdriver blades generally require less torque exertion at the screwdriver shaft. We ignore frictional force by assuming that friction between the screw and screwdriver blade is zero. (Because in this case, friction assists the operator by helping keep the screwdriver blade in the screw slot, zero friction would be the worst-case condition.) If the width of the screwdriver blade is w and the applied torque at the screwdriver shaft is T, then the normal contact force, FC, between the blade and the screw head slot is FC =
T W
Because the blades of slotted screwdrivers are usually tapered to an angle φ to ease insertion of the screwdriver blade and accommodate different size screw slots, the normal contact force FC is not actually perpendicular to the screwdriver shaft but rather acts at an angle perpendicular to the blade edge (Fig. 6e.4). This results in an axial force at each contact point
Fy = FC sin φ =
T sin φ W
Figure 6e.3 Slotted head, Phillips head, and Torx™ head screws.
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Fy
F = 4Fy = 4FC sin φ = 4
Because φ is typically greater for Phillips head screws and w is much smaller, Fy is considerably more than for slotted screwdrivers. The typical taper angle for a Phillips head screw is φ = 40 degrees, so
T
F=4 φ Fc Fc
T T sin( 40 °) = 2 . 57 . W W
which is more than six times the force needed for a slotted screw with an equivalent diameter head.
Torx™ head screws W
Figure 6e.4
T sin φ. W
Static forces acting on a slotted screwdriver blade and shaft.
that acts to push the screwdriver blade out of the slot as torque is applied to the shaft. The hand must react against this force by exerting an equal and opposite axial force Fy that is a component of the feed force. Because there are two contact points, the total axial force is 2Fy. Consequently, the axial force required to keep the blade from coming out of the slot is F = 2Fy = 2
T sin φ. W
The greater the torque T, the greater the axial force needed to keep the screwdriver blade in the slot. If the screwdriver blade taper angle φ is 12 degrees, F=2
T T sin(12 °) = 0 . 42 . W W
If the screwdriver blade angle is not tapered but parallel to the slot, this force is negligible (Fy = 0) because no axial force acts to unseat the blade. Such a screwdriver, however, would be limited to certain size slots and more difficult to insert into them.
Phillips head screws Although slotted screws are simpler, screwdriver blades sometimes slip out of slotted heads and have the potential to damage or scratch the work piece. The Phillips head screw (Fig. 6e.3) gained popularity because it prevented slippage and discouraged vandals from removing screws in public places with a coin or knife edge.31 A Phillips head screwdriver blade contains four wedges acting on the blade. Similarly to the slotted screwdriver, the axial forces acting parallel to the fastener can be described by the equation
Torx™ screws offer the advantages of both slotted screws and Phillips head screws. Because φ = 0 for Torx™ head screws (Fig. 6e.3), no axial force component other than the actual feed force is required to advance the fastener. Because the screwdriver blade cannot be tapered to accommodate different-size screws, Torx™ head screws are not as flexible as slotted or Phillips head screws. The disadvantage of requiring a large assortment of screwdrivers with corresponding blade sizes may be outweighed by the mechanical advantage of Torx™ head screws. Furthermore, they are more difficult to tamper with because Torx™ head screwdrivers are less readily available than slotted and Phillips head screwdrivers and an assortment of sizes are needed. The advantages and disadvantages of slotted, Phillips, and Torx™ head screws are summarized in Table 6e.1.
PLIERS AND CUTTING TOOLS The particular finger or combination of fingers used can affect grip strength.2,37 As the strongest fingers, the thumb, index, and middle fingers should be used for producing the most grip force. The weaker ring and small fingers should be used for stabilizing handles rather than acting as primary force contributors. Sometimes tool operators handle tools in ways that take these differences into account. Table 6e.1 Summary of ergonomic advantages and disadvantages of different screw heads Screw head
Advantages
Disadvantages
Slotted
Very flexible tool—one size fits all
Difficult to keep seated in the slot Can slip and damage work piece Requires more axial feed force
Requires little axial feed force Phillips Torx™
Easy to keep seated in head Flexible tool No axial feed force needed Easy to keep seated in head
Inflexible—must have a specific size for an associated screw head
Chapter 6e
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Power hand tools
Xj
θ Lj
L1 X1
L2 L3 L4
X2 X3 X4
Figure 6e.6
Figure 6e.5 grasped.
Static forces acting on the hand when a pair of pliers is
Offering the mechanical advantage provided from squeezing together two opposing lever arms, pliers are used often for pinching, grasping, and cutting. The common use of pliers involves a grip depicted in Figure 6e.5, where the pliers jaw is held on the radial side of the hand. In many instances, however, this grip does not optimize the mechanical advantage with finger strength and can result in greater exertion than necessary. Swedish researchers observed that some sheet metal workers held metal shear blades on the ulnar side of the hand by using an inverted grip (Fig. 6e.6) rather than that used with conventional shears.10,41 Finger strength data revealed that the inverted grip allowed a greater span between the larger index finger and thumb than between the small finger and the palm, providing a better-suited handle size for more force in each cut.14 The articulation angle from the closed position to the pivot point is defined as θ. The jaw span Xj is related to the grip span Xi as L Xi = X j i Lj where Li is the distance from the fulcrum to the finger i, Lj is the distance from the fulcrum to the jaw tip, and Xi is the grip span available for finger i. Assuming there are no coupling effects between fingers, the resultant force is the sum of all four fingers. Individual-finger
Inverted pliers grip.
normal strengths for the distal phalanx while grasping handles of different sizes are taken from Amis.2 By summing the moments about the pivot point, the total moment is MJ = F1L1 + F2L2 + F3L3 + F4L4 This moment is counteracted by that produced from reaction forces at the jaw. Consequently, the maximum jaw force is Fj =
Mj Lj
Using the dimensions provided in Table 6e.2, the maximum jaw force available increases from 714 to 786 N (10) just by inverting the handle. Because the index and middle fingers have the greatest strength, they are provided with larger moment arms for generating force with the inverted grip, providing additional mechanical advantage. One study observed that the maximum force of one finger depended not only on its grip span but also on those of the other fingers.14
POWER HAND TOOLS One of the best methods of controlling applied hand exertion is to substitute a power hand tool for a manual tool. In fact, many repetitive jobs could not be performed without the use of power tools. Modern power hand tools can operate at high speeds and produce very high forces. Exertions and forces acting against the hand in power tool operation can be reduced by eliminating excess weight, by making the best use of the mechanical advantage, or by
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254
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Biomechanical aspects of hand tools
Table 6e.2 Pliers handle dimensions and associated finger strength for showing the mechanical advantage using an inverted grip Grip
Index
Middle
Ring
Small
Grip span Xi (cm) Grip strength Fi (N) Finger distance Li (cm) Torque (Nm) Jaw force FJ Inverted
6.0 60 7.0 420 165
6.6 63 8.3 523 206
6.4 44 10.2 449 177
5.4 37 11.4 422 166
Grip span Xi (cm) Grip strength Fi (N) Finger distance Li (cm) Torque (Nm) Jaw force FJ
5.4 62 11.4 707 278
6.4 64 10.7 685 270
6.6 43 8.3 357 141
6.0 35 7.0 245 97
Si Gi
Total
Conventional 204 1814 714
LGY
L1Y
204 1994 786 T
providing mechanical aids for holding tools, parts, and materials. Selecting a power hand tool having certain dimensions and shapes can often reduce tool reaction forces and provide mechanical advantages that assist the operator. Increasing friction between the hand and objects grasped can also reduce the forces required for gripping tools. Nut runners and power screwdrivers are widely used for securing screws and threaded fasteners in manufacturing and assembly operations, such as in the automotive, mechanical equipment, and electronics industries. Using electromyography as an index of muscle effort during pneumatic shut-off nutrunner operation, Radwin et al37 observed that electromyographic activity during threaded fastener torque buildup was affected by tool torque output and torque buildup time. Electromyographic activity during torque buildup was more than three times greater than during preparation and shut-off. Oh and Radwin29 observed that the operator initially overcomes the tool reaction force with a concentric muscle exertion. As the force rapidly rises, the tool eventually overcomes the operator, causing the motion in opposition to muscle contraction and resulting in an eccentric muscle exertion. Due to passive properties of the muscle, during an eccentric, or lengthening, contraction the muscle acts like a spring, producing proportionally more force as it lengthens. Because they directly affect handle force in a complex manner, tool geometry, mass, moment of inertia, and center of gravity are important factors in the design and selection of power hand tools. By providing mechanical advantages, the handle length of pistol-grip and right-angle tools and the diameter of in-line tool handles likewise affect hand exertions.11,20,36 Tool load affects grip force,9,16,21,43 fatigue onset,18 task performance,13 and subjective preference by tool operators.3,30,42 In addition to the static forces exerted by an operator when carrying and positioning tools or when a tool is running at a constant state, the impulsive forces and torques produced by rotating spindle power hand tools are dynamic.
Figure 6e.7 operated.
Forces acting in the hand when an in-line nut runner is
Static forces Lin et al22 developed a mechanical model of power hand nutrunner operation for static equilibrium (no movement) conditions. Using hand force, reaction force from the work piece, tool weight, and tool torque, the static force model calculates handle force when carrying tools and when spindle torque is constant. The model uses a Cartesian coordinate system relative to the orientation of the handle grasped using a power grip (Fig. 6e.7A). This coordinate system has the x-axis perpendicular to the axial direction of the handle, the y-axis passed through the long axis of the handle, and the z-axis perpendicular to both. The origin is the end of the bit or socket. Hand forces are described here in relation to these coordinate axes. To simplify the model, we assume that orthogonal forces can be summed along the handle without producing coupling moments, an assumption that allows force to have a single point of application. The variables used in the model are summarized in Table 6e.3 and illustrated in Figure 6e.7. When a tool is in static equilibrium, the sums of all forces (F), moments (M) about the origin, and grip moments generated by the spindle (MG) are zero. Therefore three vector equations can be developed: Σ Fi + Σ Ri + W + FF + Fs = 0
(Σ F = 0)
Σ (Fi + Ri) × Li + W × LG = 0
(Σ M = 0)
Σ Si × Gi + T = 0
(Σ MG = 0)
These vector equations can be written in matrix form: The full model considers forces and moments exerted by both hands (subscripts 1 and 2), but not all these equations are
Chapter 6e
0 0 1 0 0 0 0 0 0 0 0 ⎡ 1 ⎢ 1 0 0 1 0 0 0 0 0 0 0 ⎢ 0 ⎢ 0 0 1 0 0 1 0 0 0 0 0 0 ⎢ L1z −L1y L 2z −L 2 y 0 0 0 0 0 0 0 ⎢ 0 ⎢ −L1z 0 0 0 0 0 0 L 1x − L 2 z L 2x 0 0 ⎢ 0 L 2 y −L 2 x 0 0 0 0 0 0 0 ⎢ L 1y − L 1x ⎢ 0 1x 0 0 G 2x 0 0 0 0 0 0 0 G ⎢ ⎢ 0 0 0 0 0 0 0 G1y 0 0 G2 y 0 ⎢ 0 0 0 0 0 0 0 G1z 0 0 G2z ⎣ 0 ⎡F1x ⎤ ⎢ ⎥ ⎢F1y ⎥ ⎢F1z ⎥ ⎢ ⎥ ⎢F 2 x ⎥ ⎢F 2 y ⎥ ⎢ ⎥ ⎢F 2 z ⎥ ⎢S1x ⎥ ⎢ ⎥ ⎢S1y ⎥ = ⎢ ⎥ ⎢S1z ⎥ ⎢ S2 x ⎥ ⎢ ⎥ ⎢ S2 y ⎥ ⎢ S2 z ⎥ ⎢ ⎥ ⎢Fsx ⎥ ⎢ ⎥ ⎢Fsy ⎥ ⎢⎣Fsz ⎥⎦
Legend of variable notation
Variable*
Description
Fi Si
Handle force acting on hand i Shear force acting in hand i, applied when the handle rotates in the y-axis Reaction force produced by the spindle torque at point i Tool weight Feed force; not applicable when carrying a tool Surface support force; not applicable when carrying a tool Tool torque Location vector of point i Location vector of the center of gravity Grip radius at point i, applied when the handle rotates in the y-axis
Ri W FF Fs T Li LG Gi
0 1 0 0 0 0 0 0 0
Power hand tools
0⎤ ⎥ 0⎥ 1⎥ ⎥ 0⎥ 0⎥ × ⎥ 0⎥ 0 ⎥⎥ 0⎥ ⎥ 0⎦
− W x − R1x − R 2 x − FFx ⎡ ⎤ ⎥ ⎢ − W y − R1y − R 2 y − FFy ⎥ ⎢ ⎥ ⎢ − W z − R1z − R 2 z − FFz ⎥ ⎢ ⎢ L1zR1y − L1yR1z + L 2 zR 2 y − L 2 yR 2 z − LGzW y + LGyW z ⎥ ⎢ L1xR1z − L1zR1x + L 2 xR 2 z − L 2 zR 2 x − LGxW z + LGzW x ⎥ . ⎥ ⎢ ⎢L1yR1x − L1xR1y + L 2 yR 2 x − L 2 xR 2 y − LGyW x + LGxW y ⎥ ⎥ ⎢ −T Tx ⎥ ⎢ ⎥ ⎢ − Ty ⎥ ⎢ − Tz ⎦ ⎣
required for all situations, and in certain cases the equations system may be reduced depending on tool shape and operating conditions. For example, the shear force needed for in-line tools is insignificant for pistol grip tools except when a hand grasps the tool around the spindle. The tool torque and feed force are Table 6e.3
1 0 0 0 0 0 0 0 0
●
*All the variables in bold type are vectors. Subscript i represents a specific hand used in operating the tool. The right hand is annotated using subscript 1 and the left hand is annotated using subscript 2.
assumed always to act in a single axis. When the matrix becomes degenerate or singular, additional assumptions are needed to solve for handle force. Nut runners are commonly configured as pistol grip, right angle, and in-line (Fig. 6e.7). Examples are provided in this article to demonstrate the resulting matrix reduction for these three common tool shapes. A set of more general cases are fully described in Lin et al.22
Pistol-grip power drivers Consider the free-body diagram of the pistol-grip nut runner in Figure 6e.7B, which shows the use of the right hand (subscript 1), and the tool geometry shown in Figure 6e.8A. The spindle stall torque T acts clockwise in the xy-plane. The tool operator must oppose this equal and opposite reaction torque Tz counterclockwise by producing a reaction force R1x along the x-axis that is equal to and opposite of the hand force component F1x. This is not, however, the only force that the tool operator must produce. A force acting along the z-axis F1z provides feed force FFZ and produces an equal and opposite reaction force FSz. The operator must also react against the tool mass to support and position the tool by producing a vertical force component F1y. The tool weight Wy and push force F1z tend to produce a clockwise rotation of the power tool about the spindle in the yz-plane that is countered by this vertical support force.
255
256
Chapter 6e
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Biomechanical aspects of hand tools
y x L1z z LGz Tz FFz F1y
LGy −Tz
L1y Wy F1z
F1x
Figure 6e.8
Static forces during pistol-grip nut runner operation.
In the case of one-handed operation, the right hand (subscript 1) reacts against all tool forces and torques. The vector equations can therefore be reduced to ⎡ 0 0 1 ⎢ 0 1 ⎢ 0 ⎢ 0 0 0 ⎢ ⎢ 0 L1z − L1y ⎢ L 1y 0 0 ⎣
0 1⎤ ⎥ 1 0⎥ 0 1⎥ × ⎥ 0 0⎥ ⎥ 0 0⎦
⎡F1x ⎤ ⎢ ⎥ ⎢F1y ⎥ ⎢F1z ⎥ = ⎢ ⎥ ⎢Fsy ⎥ ⎢Fsz ⎥ ⎣ ⎦
0 ⎤ ⎡ ⎥ ⎢ − W y ⎥ ⎢ ⎢ − FFz ⎥ . ⎥ ⎢ ⎢ − W yLGz ⎥ ⎢ − Tz ⎥ ⎦ ⎣
These equations reveal several relationships between tool parameters and hand force. Torque reaction force R1x = F1x is directly proportional to the reaction torque Tz and inversely proportional to the handle length L1y. The torque reaction force is therefore less for longer tool handles than for shorter handles. The vertical support force F1y is inversely proportional to the tool length L1z and dependent on tool weight, center of gravity location, handle length L1y, and feed force FF = F1z. The equations indicate that less effort is probably needed for supporting a pistol-grip power hand tool when the tool body is long than when it is short. When feed force is large, supporting force decreases when the handle length is short. This is why handles aligned close to the tool spindle axis and with long tool bodies are advantageous for tools such as power hand drills. These drills often require considerable feed force with torque reaction forces relatively less than for a nut runner, so a short handle is favorable. Alternatively, when torque is large and feed force is small, a tool with a long handle is advantageous. When both feed force and torque are significant factors, however, as when drilling large holes or shooting self-tapping screws in hard wood, these parameters must be optimized. The model can be used for comparing resultant hand forces associated with different tools for the same operation and for
selecting the tool requiring the least exertion. Consider the four hypothetical power nut runners shown in Figure 6e.9. All four tools weigh the same (30 N) and have the same torque output with different dimensions and mass distribution. Comparisons between the four tool dimensions are provided in Table 6e.4. Assuming one-handed operation, resultant hand force was predicted by using the model for the four different tools and plotted as a function of torque in Figure 6e.9. Hand force was determined for both low-feed force (1 N) and high-feed force (100 N) conditions when the tools were operated against a vertical surface. When feed force was small, the resultant hand force was affected mostly by the torque reaction force, which increased as torque increased for all four tools. Because the greatest force component in this case was the torque reaction force, tools 3 and 4 resulted in the least resultant hand force because they had the longest handles (Table 6e.4). Tool 3, however, had a considerably greater resultant hand force when feed force was high because the hand was located farthest from the spindle for that tool. This effect was not observed for tool 4, which also had a long handle, because of its greater tool body length. Although tool 4 had the least resultant hand force when both feed force and torque levels were high, tools 1 and 2 had less resultant hand force for high feed force and low torque because these tools permitted the hands to grasp the tool close to the spindle axis. Consequently, the best tool depended on both feed force and the torque requirements for the task. All tools were assumed to weigh the same; had they varied weights, the differences might have been even greater. Additional factors the model can consider include relative tool weight, mass distribution, and tool orientation. This analysis does not take into account the relative strength capabilities of the hand in the three component directions, although use of such a model does not exclude strength comparisons.
Chapter 6e
●
Power hand tools
Tool types
1 Figure 6e.9
2
3
Comparison of resultant hand forces acting on the hand for four equivalent power nut runners plotted against reaction torque.
The reaction force transmitted to the hand for right-angle power drivers is affected also by the magnitude of spindle torque and the tool dimensions. Right-angle nut runner spindle torque can range from less than 0.8 Nm to more than 700 Nm. A tool operator opposes these forces while supporting the tool and maintaining control. This torque is transmitted to the operator as a reaction force and opposed by the great mechanical advantage resulting from the long reaction arm created by the tool handle.37
Right-angle power drivers A right-angle nut runner is functionally nothing more than a pistol-grip nut runner with a very short body and long handle. The model for a right-angle nut runner is shown in Figure 6e.7C. Because right-angle nut runners are usually operated with both hands, two-hand forces are now in the z-axis; F1z is applied at the handle for supporting the tool, and F2z is applied over the tool spindle to help provide feed force. (When these tools are used one handed, the equations for a pistol grip nut runner apply.) Right-angle tools have short spindles perpendicular to the long axes of the handles. Because the handle is usually longer than the spindle, these tools are often held in two hands (Fig. 6e.7C). In this case, the right hand (subscript 1) grasps the tool at the distal end of the tool handle, whereas the left hand (subscript 2) grasps it proximal to the spindle. It is further assumed that equal amounts of force are exerted by both hands to react against tool torque along the long axis of the handle, and hence F1z = F2z. The resulting matrix is
Table 6e.4 Pistol-grip nut runner dimensions, load, and center of gravity location Tool 1 2 3 4
4
Weight (N) 30 30 30 30
L1z (m)
L1y (m)
L1z (m)
0.09 0.40 0.11 0.40
0.06 0.09 0.50 0.50
0.07 0.26 0.07 0.32
0 1 0 ⎤ ⎡ F1x ⎤ ⎡ − W x ⎤ ⎡ 1 ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ − 0 0 1 0 1 ⎥ ⎢ F1z ⎥ ⎢ ⎢ ⎥ × = ⎢ 0 L 1y 0 L 2 y ⎥ ⎢ F 2 x ⎥ ⎢ − T x ⎥ ⎢ ⎥ ⎢ ⎥ ⎢ ⎥ ⎣L1y 0 L 2 y 0 ⎦ ⎣ F 2 z ⎦ ⎣ − W xLGy ⎦ These equations can be used to compare hand forces between a right-angle and a pistol-grip power nut runner used on a horizontal surface (Fig. 6e.10). The right-angle nut runner in this example weighs 20 N, whereas the pistol-grip nut runner weighs 50 N. A graph of torque reaction force plotted against torque shows that the mechanical advantage of the right-angle nut runner for high torque levels is considerable. The other hand, however, exerts greater feed force for the right-angle nut runner than for the pistol-grip nut runner. Because the pistol-grip nut runner weighs more and has its center of gravity closer to the tool spindle, it requires less support force for F1z and F2z than for the right-angle nut runner (Fig. 6e.10). Sometimes handle force can be reduced further through the proper use of accessory handles and torque reaction arms.
In-line power drivers The form factor and associated forces and moments involved in operating an in-line power tool are shown in Figure 6e.7D and dimensions in Figure 6e.8C. Assuming that the right hand (subscript 1) supports the tool, the static handle force matrix is ⎡1 0 ⎤ ⎡F1y ⎤ ⎡ − W y ⎤ ⎢ ⎥×⎢ ⎥=⎢ ⎥ ⎣0 G1x ⎦ ⎣ S1y ⎦ ⎣ − Ty ⎦ The static torque developed at an in-line power hand tool spindle has an equal and opposite reaction torque Ty that must be overcome by tangential shear forces between the hand and the handle. The tangential shear force S1y produces torque about the grip radius G. The shear force S1y is proportional to the compressive hand force FG and the coefficient of friction μ between the hand and the handle, similar to a manual screwdriver except in this case the spindle rather than the hand is producing the torque. In-line power driver operation is therefore limited by the
257
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Chapter 6e
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Biomechanical aspects of hand tools
z x L1y y LGy Lzy
F1x F2z
L1z
LGz F1z Wz −Tz Tz
FRz Figure 6e.10
Static forces for right-angle nut runner operation.
maximum compressive grip force an operator can produce and by the dimensions of the tool. The relationship between the static torque, grip force, and tool diameter is similar to that of manual screwdriver operation: Ty = S1yG = μFG G Push-to-start activated power hand tools free the operator from having to squeeze a trigger or lever, but they can increase force requirements because they require more feed force to start them. A flange at the end of in-line handles helps prevent the hand from slipping during feed force exertion.15
Accessory handles and torque reaction arms Accessory handles assist a pistol-grip power tool operator by providing an additional handle for two-handed operation. A torque reaction bar can sometimes be used to transfer loads back to the work piece. In fact, reaction torque can be completely eliminated from the operator’s hand by use of either a stationary reaction bar adapted to a specific operation so that reaction force can be absorbed by a convenient solid object or a torque-absorbing suspension system. A reaction bar can be installed on in-line, pistol-grip, and angled tools. The advantages of tool-mounted reaction devices are that (1) all reaction forces are removed from the operator; (2) one-hand-operated pistol-grip and in-line reaction bar tools can be used rather than right-angle nut runners, which usually require two hands; (3) reaction bar tools can be less restricting on
the operator’s posture; (4) tool speed and weight are improved over right-angle nut runners in most tool sizes; and (5) use of reaction bars can improve tool performance. The limitations are that (1) torque reaction bars must be custom-made for each operation, (2) several attachments can make tool use difficult, (3) adding weight to the tool makes it more cumbersome to handle, and (4) the intervention is not practical when the accessibility is limited, the manipulation is restricted, or the reaction bar has no surfaces to contact. If a reaction bar is provided, however, a smaller tool handle can be used. When an accessory handle or torque reaction bar is used with a pistol-grip nut runner (Fig. 6e.11), the horizontal hand force F1x is reduced. If a vertical force is applied to a torque reaction bar, as depicted in Figure 6e.12, an additional term is needed for the sum of the moments in the z-axis: T − F1x L1y + FSy LSx = 0 As a result, F1x becomes F1x = − FSy L Sx +
T L1 y
If a torque reaction bar is used and all the torque reaction force acts against a stationary object, then T = −FSy LSx Consequently, F1x = 0
Chapter 6e
●
Power hand tools
259
Tool types
Pistol grip
Right angle
Figure 6e.11
Comparison of hand forces between a right-angle nut runner and a pistol-grip nut runner operated on a horizontal surface.
Tool counterbalancers The force requirements for a job are often related to the weight of the tools being handled. The effort needed for holding an object in the hands is usually associated with its mass,34,35 so that heavier tools generally require greater exertion. There is a tradeoff between the selection of a lightweight tool and the benefit of the added weight for performing operations that require high feed force. A spring counterbalance or air balancer can help reduce the load from heavy tools that are operated frequently. When used to support the tool, the counterbalance produces a force that opposes gravitational force. This is illustrated with a pistol-grip power tool in Figure 6e.13. When the tool is held freely in the hand, there is no torque to react against (T = 0) and consequently no reaction force (F1x = 0). Besides creating a
moment in the yz-plane, the counterbalance force FCy also influences F1y. The moment is counteracted by a coupling moment, C, from the hand, as described in the following equations: F1y + Wy + FCy = 0 F1yL1z + WyLGz + FCyLCz + C = 0 If the counterbalance force FCy is set to counteract the tool weight Wy, then FCy = −WTy Consequently, the y-axis component of the hand force becomes F1y = 0. The location that the counterbalance force acts against the tool can affect operator exertion when holding it. Solving for the coupling moment C, C = FCy(LGz − LCz)
LSx
The equation shows that the coupling moment can be eliminated (C = 0), if
−TZ
LGz = LCz
FSy
F1x
Figure 6e.12 Force and moment arm for a pistol-grip nut runner equipped with a torque reaction bar.
Balancers should therefore be attached to tools at or near their centers of gravity so as to avoid additional effort by the tool operator to counteract the handle moment. Balancers should be installed carefully so that minimal effort is needed when holding and using the tools in the desired work location. Spring counterbalances produce a force that opposes gravitational force so the tool weight is reduced. If installed incorrectly, however, these balancers can actually have the reverse effect of increasing force. Spring tension should be adjusted so that the operator does not have to counter more force than necessary and balancers so that the tool aligns as close to the work area as possible to prevent unnecessary reaching. The counterbalance should not lift the tool when it is released so that the operator must elevate the shoulder to reach it; the tool should remain suspended at the same height at
260
Chapter 6e
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Biomechanical aspects of hand tools
y
FCy
x
LCz L1z
z
LGz
LGy L1y Wy Figure 6e.13 Static forces when handling a pistol-grip power hand tool with a counterbalance. Counterbalance force FCy creates a moment in the yz-plane that is counteracted by a coupling moment C.
which it was released. Also, situations where operators tend to work ahead of or behind the assembly line should be avoided. If a tool is moved horizontally, a trolley and rail system should be installed. Special attention may be required to be sure that the balancer is attached directly above the work.
Dynamic forces Tool torque buildup model There are three elements involved in power nut runner operation using a threaded fastener: the operator, the tool, and the mechanical joint that joins or clamps two objects together, the hardness of which is analogous to the stiffness of a spring. The clamping
Figure 6e.14 Recording of torque buildup profiles for hard (light line) and medium-soft (heavy line) joints. (From Lin JH, Radwin RG, Fronczak FJ, Richard TG: Ergonomics 46(12): 1161-1177, 2003.)
F1y C
force of a threaded fastener is therefore proportional to torque, with a desired clamping force achieved by rotating the fastener to a specific target torque. Levels of joint stiffness range from a hard joint (30 degrees of spindle rotation) to a soft joint (360 degrees of spindle rotation). Examples are illustrated in Figure 6e.14 The spindle torque and angular displacement during torque buildup have a linear relationship such that θt θ( T ) = ( T − T0 ) Tt − T0 where T is tool spindle torque, θ is spindle angular displacement, Tt is the target torque, T0 is the rundown torque, and θt is the target angle.
Chapter 6e
Pneumatic motors have a distinctive speed-torque relationship. The motor does not produce torque at the free running speed, whereas it exerts maximum torque when the motor stalls. The spindle speed can be described using the equation S( T ) = S0 (1 −
T ), T max
where S is spindle speed expressed as a function of torque T, Tmax is the motor maximum torque output, and S0 is free running speed. Because speed S(T) is the derivative of angular displacement θ(T), the unique solution for the differential equation is the torque delivered to the spindle T ( t ) = T max + ( − T max + T0 )e
−
●
Power hand tools
following differential equation results in terms of the tool rotation θ: ( J T + Msh 2 )
d 2θ dθ + csh 2 + ks h 2 θ = T(t) dt dt 2
where T(t) is the tool torque, Ms, cs, and ks are the operator mechanical parameters, JT is the mass moment of inertia of the tool about its spindle, and h is the distance between the hand and the tool spindle.
( Tt − T0 ) S0 t θtT max
The force experienced by the hand can be obtained by dividing the equation for T(t) by the distance of the hand from the rotating spindle.
Handle force model: dynamics Lindqvist25 proposed that a simple mass-spring mechanical system might be sufficient to describe the handle response to impulsive reaction forces encountered in nut runner operation but did not identify specific parameters for these elements. Lin et al23 advanced this model of the human operator; their method identifies these mechanical properties to predict the kinematic and kinetic response of the handle (motion and force) when an impulsive reaction force was encountered in threaded fastener power hand tool operation. A brief description of the model is provided here. The human operator is represented as a dynamic mechanical analog of a single degree-of-freedom mechanical system consisting of a linear spring, a mass, and a viscous damper (Fig. 6e.15). Instead of modeling for individual contributing muscles, the model combines the loading of the muscles and joints into mechanical elements without considering the directions of the loads. The mechanical properties, Ms, ks, and cs, are assumed to be passive and invariant for an individual, a given posture, and a tool orientation. The effective mass Ms represents the total contributions of the standing operator coupled to the tool through the hands. The effective spring stiffness and damping represent the gross effect of the operator acting against the handle, including contributions from the entire body and nonspecific muscle groups. A system identification method using free oscillation measures these mechanical parameters for various work locations for three common tool shapes: pistol grip, right angle, and in-line. This method measures the influence of the operators’ mechanical elements on the system dynamic response (oscillation frequency and damping ratio) of a known mechanical system. The mechanical parameters are then extracted analytically.23 Given the mechanical parameters for an operator, the model estimates the dynamic response (angular displacement and force) when the operator encounters an impulsive reaction force from a power tool. A torsional dynamic equilibrium equation about the tool spindle axis can be written. The
Figure 6e.15 A pistol-grip pneumatic hand tool is illustrated with a normal operator grip. The mechanical parameters can be defined as follows: Ms = the total effective mass of the operator’s arm, hand, and a portion of the upper body lumped at the distance h from the center of rotation of the tool spindle or line of action of the tool torque, T(t). JT = the rotational mass moment of inertia of the tool about the center of mass of the tool. h = location of the center of pressure of the operator’s hand on the tool handle. ks = the effective stiffness of the operator’s arm, hand, and a portion of the upper body. cs = the effective damping of the operator’s arm, hand, and a portion of the upper body. T(t) = the tool torque which is transmitted to the operator in a typical mechanical fastening operation. θ = the rotation of the tool and hand about the tool spindle axis. H = horizontal distance between the floor and the handgrip. V = vertical distance between the ankles and the handgrip. (From Lin JH, Radwin RG, Richard TG: Handle dynamics predictions for selected power hand tool applications. Hum Fact 45(4):645-656, 2003.)
261
262
Chapter 6e
●
Biomechanical aspects of hand tools
This second-order differential equation can be solved numerically using finite difference techniques and a discrete time step variation of the tool torque, T(t). The result will be a description of the time variation of the tool rotation, θ(t),
⎧ ⎪ ⎪ 1 θi + 1 = ⎨ 2 2 ⎪ Msh + J T + cs h 2 ⎪ ( Δt ) 2 Δt ⎩
⎫ ⎪⎡ ⎤ ⎫ ⎪⎧ cs h 2 2( Ms h 2 + J T ) ⎪⎫ ⎪ ⎪⎧ 2( Ms h 2 + J T ) 2⎪ sh ⎬ θi + ⎨ k θ i − 1 + Ti ⎥ , − ⎬ ⎬ ⎢⎨ ( Δt ) 2 ( Δt ) 2 ⎥⎦ ⎪ ⎢⎣ ⎩⎪ ⎭⎪ ⎭⎪ ⎩⎪ 2 Δt ⎪ ⎭
where i is the iteration step, Δt is the time step, and T is the tool torque. With the rotational response of the tool predicted, the motion of the handle can be defined as hθ(t). The force F(t) delivered to the handle can be approximated by csh
situations can be assisted by comparing the mechanical relationships between the task and tool parameters. Other aspects that should be considered but are not covered in this chapter include repetitive use, assumed postures, vibration exposure, and contact stress.
dθ + ks hθ = F(t) dt
Here the handle force F was estimated by solving the above equation. The tool operator mechanical model was also used to estimate tool handle kinematics during torque buildup. The resultant handle displacement and force for using a right-angle tool having buildup times ranging from 35 (hard) to 1000 (soft) ms was calculated and is plotted in Figure 6e.16 for the female with the smallest stiffness and the male with the greatest stiffness.24
CONCLUSIONS AND RECOMMENDATIONS Tool operator exertion can be minimized by considering the forces acting on the tools and the way they are used for a specific task. The selection of alternative hand tools for different work
The following recommendations can be made: 1. When large feed forces are necessary, use the longest manual screwdriver available and provide a screwdriver shaft long enough so that it can be gripped by the other hand as a guide. Nut drivers and socket drivers also help reduce hand forces by providing concentric handle rotation and additional mechanical advantage at the screw head. 2. Large-diameter manual screwdriver handles with high frictional characteristics are recommended; if the handle diameter is too large, however, the mechanical advantage may be counteracted by reduced grip strength. 3. Phillips head screws should be avoided because they require greater axial push force as torque increases. Torx™ head screws provide the least axial reaction force. 4. Pliers and shears can sometimes be used to a greater mechanical advantage by gripping them so that the pivot is on the ulnar rather than the radial side of the hand. 5. Torque reaction force is less for longer pistol-grip and rightangle nut runners than for equivalent tools with shorter handles. 6. When pistol-grip power hand tools that have longer tool bodies are used, less vertical support force is required than for
Figure 6e.16 Model prediction for handle displacement and force when using a right-angle nut runner on a horizontal surface for different torque buildup times. (From Lin JH, Radwin RG, Richard TG: Handle dynamics predictions for selected power hand tool applications. Hum Fact 45(4): 645-656, 2003.)
Chapter 6e
equivalent tools with shorter tool bodies, provided that their mass distribution is similar. 7. All other factors being equivalent, when feed force is large and torque is small, a pistol-grip power tool with a shorter handle should be used. When feed force is small and torque is large, a pistol grip power hand tool with a longer handle is more advantageous. 8. Torque reaction bars help eliminate torque reaction forces, and accessory handles help distribute torque reaction forces among the two hands. 9. A tool counterbalance can help reduce the force needed to support a power hand tool. The optimal location for attaching a balancer is at the tool center of gravity.
17. 18.
19. 20.
21.
22. 23. 24.
25. 26.
REFERENCES
27.
1.
28.
2. 3. 4. 5. 6. 7. 8. 9.
10.
11.
12. 13. 14. 15. 16.
Aghazadeh F, Mital A: Injuries due to hand tools. Appl Ergonom 18(4):273-278, 1987. Amis AA: Variation of finger forces in maximal isometric grasp tests on a range of cylinder diameters. J Biomed Eng 9:313-320, 1987. Armstrong TJ, Punnett L, Ketner P: Subjective worker assessments of hand tools used in automobile assembly. Am Indust Hyg Assoc J 50:639-645, 1989. Ayoub MM, LoPresti PL: The determination of an optimum size cylindrical handle by the use of electromyography. Ergonomics 14(4):509-518, 1971. Cannon LJ, Bernacki EJ, Walter SD: Personal and occupational factors associated with carpal tunnel syndrome. J Occup Med 23:255-258, 1981. Cederqvist T, Lindberg M: Screwdrivers and their use from a Swedish construction industry perspective. Appl Ergonom 24(3):148-157, 1993. Cochran DJ, Riley MW: The effect of handle shape and size on exerted forces. Hum Fact 27:253-265, 1986. Cochran DJ, Riley MW: An evaluation of handle shapes and sizes. Proceedings of the 26th Annual meeting of the Human Factors Society, Seattle, WA, 1982, pp. 408-412. Cook TM, Rosecrance JC, Zimmerman CL: Work-related musculoskeletal disorders in bricklaying: a symptom and job factors survey and guidelines for improvements. Appl Occup Environ Hyg 11:1335-1339, 1996. Dahlman S, et al: Tools and hand function: requirements of the users and the use situation. In Y Quéinnec, F Daniellou, eds: Designing for everyone. London, 1991, Taylor & Francis. Deivanayagam S, Weaver T: Effects of handle length and bolt orientation on torque strength applied during simulated maintenance tasks. In FI Aghazadeh, ed: Trends in ergonomics/human factors V. Amsterdam, 1988, Elsevier Science, pp. 827-833. Drury CG: Handles for manual materials handling. Appl Ergonom 11(1):35-42, 1980. Drury CG, Hibschweiller ML: Size and weight effects on robot teach pendants. In SA Robertson, ed: Contemporary ergonomics. London, 1994, Taylor & Francis, pp. 417-423. Fransson C, Winkel J: Hand strength: the influence of grip span and grip type. Ergonomics 24(7):881-892, 1991. Grant KA, Habes DJ: Effectiveness of a handle flange for reducing manual effort during hand tool use. Int J Ind Ergonom 12:199-207, 1993. Grant KA, Habes DJ, Steward LL: The influence of handle diameter on manual effort in a simulated assembly task. In S Kumar, ed: Advances in industrial ergonomics and safety IV. London, 1992, Taylor & Francis, pp. 797-804.
29. 30.
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37. 38. 39.
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Greenberg L, Chaffin DB: Workers and their tools. Midland, MI, 1977, Pendell. Hallbeck MS, Sheeley GA, Bishu RR: Wrist fatigue in pronation and supination for dynamic flexion and extension: a pilot study. In S Kumar, ed: Trends in ergonomics/human factors I. Amsterdam, 1984, Elsevier, pp. 51-57. Hertzberg T: Some contributions of applied physical anthropology to human engineering. Ann NY Acad Sci 63(4):616-629, 1955. Huston TR, Sanghavi N, Mital A: Human torque exertion capabilities on a fastener device with wrenches and screwdrivers. In A Mital, ed: Trends in ergonomics/human factors I. Amsterdam, 1984, Elsevier, pp. 51-57. Kattel BP, Fernandez JE: Criteria for selection of hand tools in the aircraft manufacturing industry: a review. In MA Hanson, ed: Contemporary ergonomics. London, 1998, Taylor & Francis. Lin JH, Radwin RG, Fronczak FJ, Richard TG: Forces associated with pneumatic power screwdriver operation: statics and dynamics. Ergonomics, 46(12):1161-1177, 2003. Lin JH, Radwin RG, Richard TG: Dynamic biomechanical model of the hand and arm in pistol grip power hand tool usage. Ergonomics 44(3):295-312, 2001. Lin JH, Radwin RG, Richard TG: A single-degree-of-freedom dynamic model predicts the range of human responses to impulsive forces produced by power hand tools. J Biomech 36(12):1845-1852, 2003. Lindqvist B: Torque reaction in angled nutrunners. Appl Ergonom 24:174-180, 1993. Mital A: Effect of body posture and common hand tools on peak torque exertion capabilities. Appl Ergonom 17(2):87-96, 1986. Mital A, Kilbom A: Design selection and use of hand tools to alleviate trauma of the upper extremities. Part I. Guidelines for the practitioner. Int J Ind Ergonom 10:1-5, 1992. Myers JR, Trent RB: Hand tool injuries at work: a surveillance perspective. J Saf Res 19:165-176, 1988. Oh S, Radwin RG: Pistol grip power tool handle and trigger size effects on grip exertions and operator preference. Hum Fact 35(3):551-569, 1993. Örtengren R, Cederqvist T, Lindberg M, Magnusson B: Workload in lower arm and shoulder when using manual and powered screwdrivers at different working heights. Intl J Indust Ergonom 8:225-235, 1991. Petroski H: The evolution of useful things. New York, 1992, Alfred A Knopf. Pheasant S: Body space: anthropometry, ergonomics and design. London, 1988, Taylor & Francis, pp. 227-233. Pheasant S, O’Neill D: Performance in gripping and turning-a study in hand/handle effectiveness. Appl Ergonom 6(4):205-208, 1975. Radwin RG, Armstrong TJ: Assessment of hand vibration exposure on an assembly line. Am Ind Hyg Assoc 46(4):211-219, 1985. Radwin RG, Armstrong TJ, Chaffin DB: Power hand tool vibration effects on grip exertions. Ergonomics 30(5):833-855, 1987. Radwin RG, Oh S, Fronczak FJ: A mechanical model of hand force in power hand tool operation. In Proceedings of the Human Factors and Ergonomics Society, 39th Annual Meeting, San Diego, CA, October 1995, pp. 548-552. Radwin RG, VanBergeijk E, Armstrong TJ: Muscle response to pneumatic hand tool reaction forces. Ergonomics 32(6):655-673, 1989. Replogle JO: Hand torque strength with cylindrical handles. Proceedings of the 27th annual meeting of the Human Factors Society, Norfolk, Virginia, 1983, pp 412-416. Rothfleish S, Sherman D: Carpal tunnel syndrome: biomechanical aspects of occupational occurrence and implications regarding surgical management. Orthop Rev 7:107-109, 1978. Silverstein BA, Fine LJ, Armstrong TJ: Occupational factors and carpal tunnel syndrome. Am J Ind Med 11:343-358, 1987. Swedish National Institute of Occupational Health: Forskning & Praktik. Vol. 2. 1993, The Institute, pp. 14-17 (English edition). Ulin SS, Armstrong TJ, Snook SH, Monroe-Keyserling W: Perceived exertion and discomfort associated with driving screws at various work locations and at different work frequencies. Ergonomics 36:833-846, 1993. Westling G, Johansson RS: Factors influencing the force control during precision grip. Exp Brain Res 53:277-284, 1984.
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CHAPTER
Hip and Knee
7
CHAPTER
7a
Epidemiology of the Lower Extremity
Age, sex, and social life are of importance, along with occupational factors. When compared with the upper extremities, neck, and lower back, diseases and disorders of the lower extremities have less association to work.12 Workers’ compensation claims for disorders of the lower extremities account for fewer than 10% of all musculoskeletal claims in Sweden.
DEFINITIONS
Gunnar B. J. Andersson
Musculoskeletal impairments increase with age. This is true for lower extremity impairments as well. Praemer et al26 concluded, based on 1995 data, that over 5% of the U.S. population had lower extremity or hip impairments. This number is probably slightly higher today as the population has aged. Although the percentile rates were 1.8% among those below age 17, it was 7.7% in individuals 65 years of age and older. Women experience a slightly smaller percentage of lower extremity impairments than men. More than 20 million Americans have osteoarthritis (OA), which makes OA the leading cause of long-term disability in persons older than age 65 years. Nonspecific knee pain is reported by 4.6% of persons older than 18 years, and the corresponding number for hip pain is 3.1% (NHANES III). Specific to the workplace, in 1996 there were about 5.7 million occupational injuries in the United States, of which 6.4% were fractures and 43.6% were sprains and strains. Some 8.6% of fractures and 10.3% of sprains and strains involved the leg (excluding the foot and ankle); 71% of injuries occur from knee causes: overexertion (28%), contact with objects (26.2%), and falls (16.9%). Fractures resulting in work loss often involved the lower extremities (41.8%), but most of those affect the foot and ankle. On the other hand, sprains and strains involved the lower extremity frequently (20%), with the knee being affected in 8.5% of cases (Table 7a.1). In a population-based study of 55 year olds (575 subjects), Bergenudd5 showed that 11% had femoropatellar pain and 10% had knee joint pain. The prevalence was higher in women than in men. In a study correlating knee pain and low IQ measured 40 years earlier, low job satisfaction, obesity, and increased s-glutamyltransferase were found in men, whereas low education level, low income, low life success, and sleeping disturbances were found in women. For the entire group, knee pain and high occupational workload were also correlated. Similar results were found for hip pain. Occupational workload correlated with hip pain in men but not in women. Increased body weight correlated with knee pain in men and hip pain in women. As with many other musculoskeletal conditions, the background for symptoms from the knee and hip is multifactorial.
From an etiologic perspective, occupational musculoskeletal disorders can be viewed as caused, aggravated, or accelerated by work. An occupational injury is defined as any injury that results from a work-related accident or exposure involving a sudden event in the work environment.25 An occupational illness is any abnormal condition or disorder other than that resulting from occupational injury that is caused by exposure to factors associated with employment.25 Cumulative trauma disorders are considered occupational illnesses.
OCCUPATIONAL INJURIES In the United States, injuries to the musculoskeletal system in 1997 had an annual incidence of 7.1 per 100 full-time equivalent workers. Injuries among men are most common between 18 and 44 years of age. Rupture of tendons and muscles is not often caused by occupational loading. The strength of tissues decreases with age, but ruptures are most often seen in sports activities and as a result of rather high-loading injuries.
OCCUPATIONAL ILLNESS Joints are made for loading and movement. The cartilage of the joints is well designed to withstand compression, translation, and shear forces. Deleterious types of loading are loads in extreme positions (nutcracker effect) and axial impact loads particularly at high speed.23 Low-frequency vibrational loading may be deleterious to the joints and the joint cartilage but is often attenuated by the time it reaches the knee and hip. High-frequency vibration is unlikely to affect the lower extremities. Highly repetitive, monotonous work can cause a variety of problems in the joints, bones, tendons, and peripheral nerves. These types of loading conditions are not often seen in the lower extremities in relation to occupation but can occur during sports activities.
Tendinitis Tendinitis, tenosynovitis, myalgia, and other conditions of muscles and tendons are uncommon in the lower extremities.
Table 7a.1 Occupational injuries of the lower extremities as a percentage of all injuries: U.S. data.25 Diagnosis Fracture Sprain and strain
Hip 0.3 0.3
Knee 2.6 7.9
Lower leg 2.0 0.3
Multiple 1.2 0.8
Bursitis Eighteen bursae surround the hip joint, and approximately 10 surround the knee joint. Specific diagnoses are often difficult
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Epidemiology of the lower extremity
to make. Bursitis caused by sports overuse is not uncommon, but bursitis around the hip as an occupational illness is rarely seen. Bursitis of the knee, especially prepatellar or infrapatellar, is often seen in jobs that require kneeling, for example, floor layers, fishermen, and plumbers.28-30
Nerve entrapments Only occasionally is nerve entrapment seen in the lower extremities. Ischial neuralgia, or “wallet sciatica,” a sensation along the ischial nerve caused by compression at the infrapiriforme foramen, may be encountered by sitting, particularly when having a well-filled wallet in the back pocket. Peroneal nerve compression at the side of the knee may cause palsy and can result from work activities. This may happen to tractor drivers during prolonged sitting in a twisted position and from accidents. Ilioinguinal neuralgia and lateral cutaneous nerve neuralgia are reported as occupational illnesses. The mechanism is often some type of pressure over the anterior part of the iliac crest from heavy belts or other equipment, especially if loaded with tools or other weights. Edema, tiredness, and dull pain in the legs are more common in those with static sitting or standing occupations than in those who work in a more varied posture.37 Compartment syndromes are rarely due to occupational loading of the lower extremities. This syndrome is more often seen as a result of sports activities and as a complication of fractures and other traumatic injuries.
Rheumatic diseases Arthritis and rheumatism account for 66% of the musculoskeletal conditions among women and 51% among men. Osteoporosis accounts for an additional 11% of musculoskeletal disease, occurring predominantly in females.25 Rheumatic diseases are not caused by occupational loading but may be worsened by it.
Table 7a.2 Prevalence of osteoarthritis as diagnosed by history or examination by gender and age group: rate per 100 persons Diagnosis by history
Diagnosis by examination
Age
Males
Females
Males
Females
Less than 20 years 20–39 years 40–59 years Over 60 years All ages All ages over 20 years
— 0.2 3.4 17.0 1.9 4.5
— 0.4 8.4 29.6 4.0 7.3
— — 4.0 20.3 2.2 4.2
— 0.2 8.9 40.8 5.0 9.0
Perthes disease). Primary OA has been shown to have a multifactorial background. Bilateral hip and knee OA has been suggested to have an etiology different from that of unilateral OA. Hochberg13 reported on a group of 1337 students who graduated from The Johns Hopkins University School of Medicine from 1948 through 1964. The cumulative incident of knee OA at age 65 was 6.3%, whereas hip OA existed in 2.9% of individuals. Cumulative knee OA relative rise was three times higher in those with a history of knee injury (13.9% vs. 6%). The incidence of knee OA was 7.5 per 1000 person-years among those with a knee injury compared with 1.2 per 1000 person-years, for a relative risk (RR) of 5.2. Similarly for the hip, the incidence was 3.2 per 1000 person-years among those with hip injury compared with 0.7 without a hip injury (RR, 3.5). The increased risk remained significant even after adjustment for age, sex, body mass index, and physical activity at study entry. Clearly, lower leg injuries should be prevented to reduce the risk of knee and hip OA.
Heredity
Osteoarthritis The prevalence of OA is greater in women than in men. Physical examination more often results in a diagnosis of OA, as compared with radiographic examination, when narrowing of the joint space is used as the criterion. If osteophytosis is included as a sign of OA, the prevalence is much higher. Around 12% of the U.S. population have OA in any joint.8,12,18 Table 7a.2 shows the prevalence of OA diagnosed by radiographic examination in different age groups.18,25 Diagnosis by examination revealed more OA than diagnosis by history. The explanation is that many individuals are symptom free. In the NHANES I study,2 the prevalence of OA of the knee was 2.3% to 18% in those aged 45 to 74 years, with a larger prevalence in the elderly and in women. Hip OA was found in 0.2% to 6.6% in those aged 25 to 74 years, more in the elderly but with less sex difference than OA in the knee. OA of the hip and knee has been studied in relation to occupational and other factors. These results were confirmed in recent studies.1,6 Secondary OA is due to previous known trauma (e.g., fracture, surgery) or disease (e.g., hip dysplasia, osteochondritis,
Most OA is not attributable to single genes. Rather, common OA appears to result from interactions between multiple genes and the environment. In a comparative population study in San Francisco, standardized rates of primary hip OA, expressed as numbers per 100,000 population per year, were 1.5 in Japanese, 1.5 in Chinese, 1.6 in Filipinos, 5.1 in Hispanics, 8.3 in blacks, and 29.4 in whites. The hereditary factor often results in a more generalized OA in different locations of the body.22 The percentage of hip OA, defined as lowered height of the joint cartilage, at 70 years of age in Sweden is about 2% in both sexes. Knee OA has a prevalence of 2% in men and 3% in women at 70 years of age in Sweden. However, a relation to occupational loading or sports is more clearly shown in men, whereas obesity correlates more with knee OA in women. Consequently, a hereditary factor increasing the risk for females to contract OA of the knee is likely.22 Obesity correlates with symptomatic OA in the hip31 and also in the knee, which is clearly shown in females, and has an RR of about 4.10,22
Hip OA Sports Lindberg and Montgomery20 found a 2.8% prevalence of hip OA in control subjects as compared with 5.6% in athletes
Chapter 7a
●
References
and 14% in elite athletes (soccer players). Similar results have been shown by Klunder et al.16 Among those undergoing a total hip procedure because of OA, Vingård et al32-34 found an RR of 4.5 for athletes. Those athletes who also had a physically demanding job had an RR of 8.5. Different results have been shown in studies of long-distance runners.9
carry an increased risk for OA. Other physically demanding jobs have less of an increase in RR for OA, around 2 to 3, similar to the RR for obesity and lower than the increased risk in some elite athletes.22
Occupation Vingård et al32-36 found more symptoms caused by hip OA in men exposed to greater physically demanding jobs. Farmers, construction workers, firefighters, and food processing workers had significantly more OA than expected (RR, 2.4). For those exposed to both occupational loading and sports activities the RR was 8.5, and for sports alone the RR was 4.5. In this study, being overweight had an RR of 2.5. Disability pension for hip OA was more often received by those with high occupational load exposure than by those with low exposure (RR, 12.4).33 The risk occupations were construction workers, metal workers, farmers, and forestry workers. An increased risk for hip OA has been shown in farmers, with RRs of 9.7 to 12 in several studies.4,7,11,15,19,27 In female farmers, no difference from control subjects was found.4
REFERENCES
Knee OA
8.
Sports A Swedish study22 found a knee OA prevalence of 7% in
9.
soccer players as compared with 1.6% in control subjects. The prevalence was higher in those with known meniscal tears or anterior cruciate ligament ruptures.
1.
2.
3. 4. 5. 6.
7.
10.
11.
Occupation The Framingham study showed an odds ratio of 2.2 for OA of the knee in jobs requiring knee bending and at least a medium level of physical activity.10 The etiologic fraction or attributable proportion of knee OA to occupational physical loading was 15%. Obesity accounted for 10%. Only a few females had physically demanding jobs in the study, and no gender association was found.10 In the NHANES study, knee OA was increased among men and women with physically demanding jobs: odds ratios of 1.88 in women (not significant) and 3.13 in men of younger ages, and odds ratios of 3.49 and 2.45, respectively, at higher ages. The occupational etiologic fraction was estimated to be 32%.2 Dock workers have been shown to have more knee OA than office workers.24 Lindberg and Montgomery20 found an increasing risk for knee OA in shipyard workers as compared with office workers and teachers. Vingård et al32-34,36 found an increased risk for knee OA among farmers, construction workers, and firefighters. That study also showed an increased risk of knee OA symptoms in female janitors and letter carriers. Therefore, a moderately increased risk of symptom-giving knee OA has been shown in physically demanding occupations.4,17,21 Overweight and some sports activities seem to increase the risk of symptom-giving knee OA more than any occupation. A consensus discussion in 1992 in Malmö on the etiology of OA concluded that unfavorable weight bearing and repeated minor trauma may contribute to OA.22 This is in agreement with the current etiologic hypotheses. Static load, repeated trauma over long periods, and an unnatural use of joints are likely to contribute to OA. Regarding occupation, farmers, professional ballet dancers,3 and professional soccer players have a much higher frequency of OA than expected and are therefore considered to
12. 13.
14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.
30.
Andersen RE, Crespo CJ, Ling SM, Bathon JM, Bartlett SJ: Prevalence of significant knee pain among older Americans: results from the Third National Health and Nutrition Examination Survey. J Am Geriatric Soc 47(12):1435-1438, 1999. Andersson JJ, Felson DT: Factors associated with osteoarthritis of the knee in the first National Health and Nutrition Examination Survey (NHANES I): evidence for an association with overweight, race, and physical demands of work. Am J Epidemiol 128(179):89, 1988. Andersson S, Nilsson B, Hessel T, et al: Degenerative joint disease in ballet dancers. Clin Orthop 238:233-236, 1989. Axmacher B, Lindberg H: Coxarthrosis in farmers. Clin Orthop 287:82-86, 1993. Bergenudd H: Talent, occupation, and locomotor discomfort. Doctoral thesis. Malmö, Sweden, 1989, Lund University. Christmas C, Crespo CJ, Franckowiak SC, Bathon JM, Bartlett SJ, Andersen RE: How common is hip pain in older adults? Results from the Third National Health and Nutrition Examination Survey. J Fam Pract 51(4):345-348, 2002. Croft P, Coggon D, Cruddas M, Cooper C: Osteoarthritis of the hip: an occupational disease in farmers. BMJ 304:1269-1272, 1992. Cunningham LS, Kelsey JL: Epidemiology of musculoskeletal impairments and associated disability. Am J Public Health 74:574-579, 1984. Ernst E: Jogging-for a healthy heart and worn out hips? J Intern Med 228:295-297, 1990. Felson DT, Hannan MT, Naimark A, et al: Occupational physical demands, knee bending and knee osteoarthritis: results from the Framingham study. J Rheumatol 18:1587-1592, 1991. Forsberg K, Nilsson B: Coxarthritis on the island of Gotland. Increased prevalence in a rural population. Acta Orthop Scand 63:1-3, 1992. Hadler NM: Occupational musculoskeletal disorders. New York, 1993, Raven Press. Hochberg MC: Prevention of lower limb osteoarthritis: Data from the John Hopkins Precursor Study. In VC Hascall, KE Kuettner, eds: The many faces of osteoarthritis. Berlin, 2002, Birkuauser. Hult L: The Monkfors investigation. Acta Orthop Scand Suppl 16:1-76, 1954. Jacobsson B, Dalén N, Tjörnstrand B: Coxarthrosis and labour. Int Orthop 11:311-313, 1987. Klunder KB, Rud B, Hansen J: Osteoarthritis of the hip and knee joint in retired football players. Acta Orthop Scand 51:925-927, 1980. Kohatsu N, Schurman D: Risk factors for the development of osteoarthritis of the knee. Clin Orthop 261:242-246, 1990. Lawrence RC, Hochberg MC, Kelsey JL, et al: Estimates of selected arthritic and musculoskeletal diseases in the U.S. J Rheumatol 16(4):427-441, 1989. Lindberg H, Axmacher B: Coxarthrosis in farmers. Acta Orthop Scand 59:607, 1988. Lindberg H, Montgomery F: Heavy labor and the occurrence of gonarthrosis. Clin Orthop 214:235-236, 1987. Nicolaisen T: Health among postmen. Copenhagen, 1983, General Directorate for Post and Telegraph (in Danish). Nilsson BE: The Tore Nilson Symposium on the etiology of degenerative joint disease. Acta Orthop Scand Suppl 64(253): 54-61, 1993. Nordin M, Frankel VH: Basic biomechanics of the musculoskeletal system, ed 2. Philadelphia, 1989, Lea & Febiger. Partridge REH, Dulthie JJR: Rheumatism in dockers and civil servants. Ann Rheum Dis 27:559-568, 1968. Praemer A, Furner S, Rice DP: Musculoskeletal conditions in the United States. Park Ridge, IL, 1992, AAOS. Praemer A, Furner S, Rice DP. Musculoskeletal conditions in the United States. Rosemont, IL, 1999, American Academy of Orthopedic Surgeons, pp. 1-182. Thelin A: Hip joint arthrosis: an occupational disorder among farmers. Am J Ind Med 18:339-343, 1990. Törner M: Musculoskeletal stress in fishery: causes, effects, and preventive measures. Doctoral thesis. Sweden, 1991, University of Göteborg. Törner M, Zetterberg C, Anden U, Hansson T, Lindell V: Workload and musculoskeletal problems: a comparison between welders and office clerks. Ergonomics 34:1179-1196, 1991. Törner M, Zetterberg C, Hansson T, Lindell V, Kadefors, R: Musculoskeletal symptoms and signs and isometric strength among fishermen. Ergonomics 33:1155-1170, 1990.
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31. 32. 33.
34.
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Epidemiology of the lower extremity
Vingård E: Overweight predisposes to coxarthrosis. Body mass studied in 239 males with hip arthroplasty. Acta Orthop Scand 62:106-109, 1991. Vingård E: Work, sports, overweight and osteoarthrosis of the hip. Arbete och Hälsa 25, doctoral thesis, 1991, Karolinska Institute, Stockholm, Sweden. Vingård E, Alfredsson L, Fellenius E, Hogstedt C: Disability pensions due to musculoskeletal disorders among men in heavy occupations. Scand J Soc Med 20:31-36, 1992. Vingård E, Alfredsson L, Goldie I, Hogstedt C: Sports and osteoarthrosis of the hip. Am J Sports Med 21(2):195-200, 1993.
35.
36. 37.
Vingård E, Alfredsson L, Hogstedt C, Goldie I: Ökad risk för arthros i knän och höfter för arbetare i yrken med hög belastning på benen. Läkartidningen 87:4413-4416, 1990. Vingård E, Hogstedt C, Alfredsson L, Fellenius E, Goldie I, Koster M: Coxarthrosis and physical work load. Scand J Work Environ Health 17:104-109, 1991. Winkel J: On fast swelling during prolonged sedentary work and the significance of leg activity. Arbete och Hälsa, doctoral thesis, Stockholm, 1985, National Institute of Occupational Health.
CHAPTER
7b
Biomechanics of the Hip and the Knee Ali Sheikhzadeh
Biomechanical analysis of the hip and knee joints during daily activities that occur in the home and work environment can identify tasks that are potentially harmful for a healthy and an injured joint. A kinematics and kinetic profile of uninjured joints provides an understanding of joint contribution during functional tasks, provides a baseline to identify abnormalities, and thereby assists with diagnosis and treatment. Moreover, it facilitates the design and performance of reconstructive surgery and rehabilitation programs. The kinematics and kinetics of the hip and knee joints and the joint forces that occur during activities of daily living are the focus of this chapter. The application of biomechanical models for calculating external forces and moments at the hip and knee joints is explained first. The application of biomechanical concepts in reducing joint forces and thereby risk of injury is then discussed. The activities discussed are mainly physical activities of daily living and those commonly performed at work such as gait, stair climbing, rising from a chair, and lifting weights.
KINEMATICS OF THE HIP AND KNEE A three-dimensional measurement of relative motion among adjacent limb segments, comprehensive kinematics analysis is expressed by 6 degrees of freedom, generally three translational and three rotational angles. However, kinetics analysis involves both static and dynamic analysis of internal and external forces and moments acting on a joint. In the musculoskeletal system, external forces frequently include the ground reaction forces, the weight of the limb segment, and the force of one segment on another. Muscle contractions, passive soft tissue stretch, and articular reaction forces generate primarily internal forces.
Kinematics of the knee The knee joint is composed of the tibiofemoral joint and the patellofemoral joint. The tibiofemoral joint has the greatest motion in the sagittal plane, 0 to approximately 140 degrees. Provided by articulations between large convex femoral condyles and smaller or nearly flat tibia condyles, this large range allows extensive knee motion in the sagittal plane for the activities such as walking, running, squatting, and climbing. The knee motion in the transverse plane (internal and external rotation) and in the frontal plane (abduction and adduction) is affected by the amount of joint flexion. The interlocking of the
femoral condyles in the knee in extension precludes almost any motion in the frontal and transverse planes. The knee motion in the transverse plane increases as the knee is flexed toward 90 degrees, with a maximum of approximately 45 degrees in internal rotation and 30 degrees in external rotation, and then decreases primarily due to the soft tissue restrictions. Similarly, motion in the frontal plane increases as the knee is flexed toward 30 degrees, reaching a maximum of only a few degrees of abduction and adduction, and then decreases as the knee flexion goes beyond 30 degrees. Values for the average range of motion of the knee joint in the sagittal plane during 11 common activities are reported in Table 7b.1. A range of motion of 130 degrees is required for common daily living activities. Excluding the range of motion required to bathe, 11061 to 117 degrees51 of knee flexion would seem a reasonable goal for the rehabilitation of its motion for the general population. The inability of the knee to move within the range of motion required for daily living activities would be compensated for by increasing the motion of other joints51 or avoiding trying to perform the task.
Kinematics of the hip The hip joint is a synovial ball-and-socket joint with articulation between the large nearly spherical head of the femur and the acetabulum of the pelvis. With its inferior anterolateral and inferior opening, the acetabulum provides a wide range of motion. The concave acetabulum covers about two thirds of a spherical femur head. As the hip joint is loaded, the acetabulum deforms about the femoral head. The unloaded acetabulum has a smaller diameter than that of the femoral head.21 Hip motion takes place in all three planes, with the greatest motion in the sagittal plane. The extreme motion of the hip joint is limited by passive tension of the surrounding ligaments and muscles (Table 7b.2). Passive hip flexion is approximately 140 degrees, whereas active hip flexion with the knee flexed is 125 degrees and with it extended is 90 degrees. Passive hip extension is approximately 30 degrees, whereas active extension is 20 degrees.59
Table 7b.1 The mean of the left knee joint angle performed by 20 normal elderly subjects during 11 functional activities Function
Mean
Level walking Ascend slope Descend slope Ascend stairs Descend stairs Sit down low chair Sit to stand low chair Sit down standard chair Sit to stand standard chair Into bath Out of bath
64.5 61.6 69.0 80.3 77.8 92.5 95.0 91.0 89.8 123.3 131.3
Rowe PJ, Myles CM, Walker C, Nutton R. Gait Posture 12:143-155, 2000.
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Magnitude of hip range of motion and associated limiting ligaments and muscular tissues
Hip motion
Magnitude of hip motion
Examples of tissues that may limit the extremes of motion
Flexion
80° (with knee extended) 120° (with knee fully flexed)
Extension
20° of extension (with knee extended)*
Abduction Adduction
0° (with knee fully flexed) 40° 25°
Internal Rotation Extrenal Rotation
35° 45°
Hamstrings and gracilis muscles Inferior fibers of ischiofemoral ligament Inferior capsule Predominantly iliofemoral ligament and anterior capsule; some components of the pubofemoral and ischiofemoral ligaments Rectus femoris muscle Pubofemoral ligament, inferior capsule, adductor and hamstring muscles Superior fibers and ischiofemoral ligament, iliotibial band, and abductor muscles such as the tensor fasciae latae Ischiofemoral ligament external rotator muscles (e.g., piriformis) Lateral fasciculus of iliofemoral ligament, iliotibial band, and internal rotator muscles (e.g., gluteus minimus, tensor fasciae latae)
*Implies 20° of extension beyond the neutral zero degree position. From Neumann, DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation. St. Louis, 2002, Mosby; p. 400.
The hip abduction range is about 30 degrees, and adduction range is about 25 degrees. The external and internal rotations of the hip are 90 and 70 degrees, respectively, when the joint is flexed. The internal and external rotations of the hip, when it is extended, are approximately 15 and 35 degrees, respectively.59 Most common daily activities require flexion, abduction, and external rotation. The mean of motion during selected daily activities is shown in Table 7b.3. Most daily activities require more than 100 degrees of hip flexion.30 Squatting and shoe tying with the foot across the opposite thigh require the greatest motion in the frontal and transverse planes. Walking on a level surface requires about 30 degrees of flexion and 10 degrees of extension, with minimal abduction-adduction and internal-external rotation. Approximately 80 to 104 degrees of flexion and extension, respectively, is required to sit on or rise from a chair. The range of motion during daily activities should be interpreted cautiously. The reported range has been shown to be influenced by age,23 speed of movement,15 and environmental task constraints such as chair46 and stair height. Mulholland and Wyss44 demonstrated the significance of cultural sensitivity in the interpretation of daily activities. In many parts of Asia and the Middle East, a chair is not commonly used at home or work, and sitting on the floor without support, sitting cross-legged, or kneeling are more common than in Western countries.22,44 Mulholland and Wyss44 suggested that even rural as opposed to urban life-styles in different geographic locations might demand significantly different analytical approaches and should be considered in evaluations of daily physical activities. The current related literature on daily living activities, including data reported in Tables 7b.1 and 7b.3, reflects mainly the Western life-style and would not apply to the actual life-styles of many people in Asian and Middle Eastern cultures. There is a growing need for culturally and racially sensitive data that allow for individual variation in the normal range of motion.
require gross oversimplification of forces and coincide with the theoretical assumption of the model itself. However, the reliability and validity of biomechanical models depend on realistic assumptions and representations of the mechanical system and accuracy of the experimental data that constitute the inputs and/or outputs. In addition, an important aspect of developing a model is to decide what should be included or neglected. Although it is not always possible, generally the simplest model that provides a valid representation of reality should be used.
Table 7b.3 Mean values for maximum hip range of motion measured in three planes during several common activities for 33 healthy men
KINETICS OF THE HIP AND KNEE Generally, a biomechanical model attempts to represent a simplified version of a complex task. Often these representations may
Johnston RC, Smidt GL: Hip motion measurement for selected activities of daily living, Clin Orthop 72:205-215, 1970.
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(cm) 10.0
Glut eu s
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Figure 7b.1 A side view of the femoral head with the line-of-action of several muscles crossing the hip in the sagittal plane. (From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation. St. Louis, 2002, Mosby, p. 400.)
The formulation of a comprehensive dynamic model of the knee and hip joints is challenging because of the complexity of internal forces acting on the joints and the difficulty of measuring anatomic parameters precisely. For instance, a comprehensive model of the hip joint should include the line-of-action of muscles crossing it with respect to its axes of rotation in the sagittal and frontal plane, as presented in Figure 7b.1. In addition to the line-of-action of muscles, such a model should consider the dynamic changes of these parameters during joint motion. The following methods are used to overcome the difficulty and complexity of estimating the internal joint forces during dynamic tasks.
Analytical joint models Often, even the simplest model of external forces generated by gravity acting on the body provides crucial functional and clinical information about a joint. As illustrated in Figure 7b.2, for instance, a simplified free-body diagram of the lower extremity during a single leg stand phase of stair climbing presents a reasonable estimate of the tibiofemoral joint forces and patella tendon force. The flexion moment of the lower leg is the product of the body weight (BW) and its lever arm, the perpendicular distance of the BW to the center of the tibiofemoral joint motion. The sensitivity
Figure 7b.2 Free-body diagram of moments acting around the center of motion of the tibiofemoral joint during stair climbing. The ground reaction force (W) and its lever arm (a) are counterbalanced by moments produced by the quadriceps muscle force through the patellar tendon (P) and its lever arm (b). (From Nordin M, Frankel VH: Biomechanics of the knee. In M Nordin, VH Frankel, eds: Basic biomechanics of the musculoskeletal system. New York, 2001, Lippincott Williams & Wilkins, pp. 176-201.)
of the knee flexion moment to the carrying of objects during occupational tasks can be determined by adding the weight of an object to the external weights acting on the body. Despite the oversimplification of the joint forces that may be estimated based on a free-body diagram, a two-dimensional static model can be used to analyze occupational tasks or to design rehabilitation training. Typically, a person with arthritis pain or patellofemoral joint pain is advised to avoid large forces created by the quadriceps.12 Figure 7b.3 illustrates the magnitude of the external forces on the knee during two physical tasks requiring knee extension, tibial-on-femoral knee extension (the line between D and B) verses the femoral-on-tibial knee extension during the 0 to 90-degree joint angle (the line between A and C). During tibial-on-femoral knee extension, the external moment arm of the weight of the lower leg increases from 90 degrees to 0 of knee flexion. In contrast, during femoral-on-tibial knee extension, the external moment arm of the upper BW decreases from 90 degrees to 0 of knee flexion. A more realistic biomechanical model of the knee should include a better representation of the patellofemoral stresses and forces within the quadriceps muscle. The single line of quadriceps force in Figure 7b.2 should be replaced by four lines. The four heads of the quadriceps muscle consist of distinct fibers that
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B
A External Torque-Angle Plot 100%
70%
Relative external torque (% maximum)
0% D
90º
70º
45º
20º
0º
C
Knee angle (degrees) EXTENSION
Figure 7b.3 The relative external torque generated by body weight acting on the knee joint between 90-degree flexion and full extension (0 degree) during two styles of knee extension: (1) during femoral-on-tibial extension (A to C line), the external moment arm of the weight of the lower leg increases from 90-degree knee flexion to full knee extension, and (2) during tibial-on-femoral extension (D to B line), the external moment arm of the upper-body weight decreases from 90 degrees to 0 knee flexion. (From Neumann DA: Kinesiology of the musculoskeletal system: foundations for physical rehabilitation. St. Louis, 2002, Mosby, p. 458.)
approach the patella at different angles, especially the vastus medialis fibers, which approach from two distinct directions. The more distal oblique fibers approach the patella at 50 to 55 degrees, and the remaining more longitudinal fibers approach it at 15 to 18 degrees, both medial to the quadriceps tendon.49 Cohen et al12 presented a more comprehensive model of the knee joint, computer simulated with geometric and anatomic details, to compare the patellofemoral stresses and quadriceps force during open (with 0, 25-N, and 100-N load at ankle) and closed kinetic chain leg exercises in the flexion range of 20 to 90 degrees. As demonstrated in Figure 7b.4, the quadriceps muscle force and the average patellofemoral contact forces increase progressively from 20 to 90 degrees. To achieve a more realistic estimate of joint forces, a biomechanical model of the hip and knee joint should include the soft tissues forces such as agonist-antagonist muscle forces in threedimensional dynamic environments. The exclusion of agonistantagonist muscle forces underestimates the internal joint forces. However, the inclusion of these forces adds another layer of complexity to the model and demands more advanced analytical methods to solve indeterminate systems. Generally, inverse dynamic models47 or optimization methods4,56 are used to solve the indeterminate problem of determining muscle and contact forces. For example, with the large number of muscles crossing the hip (Fig. 7b.1) and with at least 27 separate musculotendinous units crossing the joint, a unique demonstration of individual muscle force can be achieved only by oversimplification. Today’s advances in computer science and technology provide the possibility of creating “virtual human” reality.10 The virtual
human concept aims at understanding human activities through the simulation of accurate physiologic and anatomic models and data. This type of simulation combines biomechanical models of joints and mechanical properties of connective tissues to visualize
Figure 7b.4 Quadriceps muscle force exertion simulation based on anatomical data from five cadavers for closed kinetic chain (CKC) and open kinetic chain (OKC) exercises for knee flexion range of 20 to 90 degrees. The three OKC loading simulated conditions are OKC 0N, knee extension with no load; OKC 25N, leg extension with 25-N external force at the ankle; OKC 100N, leg extension with 100-N external force at the ankle. (From Cohen ZA, Roglic H, Grelsamer RP, et al: Patellofemoral stresses during open and closed kinetic chain exercises: an analysis using computer simulation. Am J Sports Med 29:480-487, 2001.)
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the results in both static and animated forms. For surgical implantation of a proximal femur/hip prosthesis, for example, graphic information about implants that is available directly from the manufacturers or CAD/CAM files can be added to real images of the patients’ anatomic parameters taken from computed tomographies. It can also be incorporated into the biomechanical models of joints and soft tissues in functional tasks. For surgical and medical education and for device development applications, it is worthwhile to incorporate adaptive anatomic models, which include prosthetic implants and fracture fixation devices. Advanced computation environments for static posture, kinematics, kinetics, and stress analysis under physiologic boundary and loading conditions can be incorporated.
In vivo direct measurement of joint forces Although biomechanical models deal with indirect estimates of internal forces, the real-time continuous signal from an instrumented telemetric prosthesis has been used for direct measurement of internal forces acting on the distal or proximal femur during daily activities such as walking and stair climbing.69 Direct measurement of the hip contact forces was first obtained by Rydell.62 The peak hip forces during gait vary from 1.8 to 4.3 times the BW, with peak pressure occurring during heel strike and early midstance.4 These hip forces are related to the ground reaction forces acting on the superior anterior acetabulum. For patients measured at 11-31 months postoperatively, the average hip forces during fast walking and climbing stairs was about 250% BW and slightly less than going downstairs.7 Taylor and Walker69 studied two patients over 2.5 years during various daily activities. The average peak distal femoral shaft forces for one patient during various activities were jogging 3.6 BW, stair descending 3.1 BW, walking 2.8 BW, treadmill walking 2.75 BW, and stair ascending 2.8 BW. Bending moments about the mediolateral axis (flexion-extension) and anteroposterior axis (varus-valgus) peaked in the range of 4.7-7.6 BW cm and 8.5-9.8 BW cm, respectively, over the follow-up period. During similar activities, however, forces and moments for the second subject were generally 45-70% less than those for the first subject due to inadequate musculature around the knee.69 The joint forces and moments of patients who have had joint arthroplasty are expected to return to the values of healthy individuals within approximately 6 months after surgery.2 The discrepancy between forces and moments reported by various authors, for example, Bergmann et al7 and Taylor and colleagues,69,70 reflect the variation among individuals, success of surgery, location of measured forces, and time of study with respect to surgery. For example, Taylor and Walker offer a good estimate of the loading conditions (distal femoral) acting at the knee and are assumed to offer data different from what Bergmann and colleagues found with respect to hip arthroplasty surgery. In comparison with biomechanical models, direct measurement produces valid data on internal forces. The information serves mostly as validation9,39,65 for biomechanical models and provides useful insight into wear, strength, and fixation stability. Direct measurement is otherwise difficult because of technologic restrictions and ethical considerations, and because of a variety
of practical reasons only a limited number of subjects can be studied.69 Because the validity of collected information depends on the extent to which joint mechanics and surrounding tissues have been altered, generalizations cannot be made.
REDUCING INTERNAL JOINT LOAD: APPLICATION OF BIOMECHANICAL CONCEPTS Determining the consequence of daily physical activities of work and leisure on lower extremity joints is difficult because of the complexities of structural anatomy and dynamic movements combined with the calculation of internal and external forces acting on joints. Musculoskeletal loading is influenced by a number of individual differences such as age, weight, and gender; the activity itself; and the variables of the task. Such factors help explain individual variation in functional abilities, biomechanical consequences of physical performance on internal tissues, and potential risk or mechanism of injury. Biomechanical analysis of physical activities such as walking, running, and stair climbing provides understanding of internal and external forces acting on a joint and their significance for injury and pain. Biomechanical analysis of task variables such as stair or chair height influence and gait speed demonstrate the degree to which selected characteristics of a task may influence the physical demands of executing it and its consequences for joints and surrounding tissues. The following is a brief description of selected variables that directly or indirectly influence physical ability and musculoskeletal loading during daily living activities.
Individual factors Individual factors such age, gender, anatomic variation, and medical history and disease stage are known directly or indirectly to influence ability, internal resources for executing a task, and distribution of internal forces and tissue tolerance. Except for weight, individual factors cannot be controlled or altered, but understanding a mechanism by which these factors may influence joint loading is important to explain injury mechanism, prevent injury risk, and design rehabilitation programs for special groups of individuals.
Age, weight, and gender Individual factors such as age,1,15,16,21,34,58 weight,1,11 and gender35,36,67 influence the internal joint forces and ultimately the injury mechanism and risk. Biomechanical properties of soft tissues and the hip and knee joints are known to be different between genders and to change with age in a highly individualized process and rate. They may be modified negatively or positively by many factors such as activity types and frequency, medical conditions, and nutritional factors. The alteration of posture, active and passive range of motion of the hip and knee joints, and gait during physical activities are associated with age and gender as well.51 An individual’s weight and height directly influence the hip and knee joint moments.71 Height can influence limb size and therefore lever arm. Daily physical activities such as walking and
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stair climbing exert 3.5 BW on hip and knee forces. A change of 5 pounds of BW, for instance, may therefore result in 17.5 pounds of excess force in the knee and hip. Additionally, an individual’s weight has been associated with the prevalence of joint pain1 and change in properties of tissue characteristics.11 Aging is associated with a decrease in neuromuscular control characterized by the decline of maximum muscle force production, the velocity of contraction, and the dynamic stability.33 Human muscle strength attains its peak between the ages of 20 and 30 years and declines gradually until the age of 60 and rigorously thereafter.31 During the single-leg support phase of walking and stair climbing, while the body is moving forward, lower extremity muscular strength is required to control and support it.34 Often a lack of joint strength or an inability to develop torque within the appropriate time may contribute to the risk of injury.71 Stair descent by the elderly has previously been described as a “controlled fall” due to the lack of ankle flexibility and strength as well as the delay in developing torque rapidly.72 It has been suggested that absolute task demands for performing activities of daily living are not significantly high; however, older adults’ difficulty in performing these activities must take
into account their decrease in capacity.23 Using inverse dynamics analysis, Figure 7b.5 compares the knee joint moments of healthy young and older adults during stair ascent and descent and when rising from a chair compared with maximal isometric effort in supine leg press. Although there is no significant difference between absolute knee moments during physical activities, motor tasks demand substantially greater effort relative to available maximum capacity of elderly compared with young adults. As illustrated in Figure 7b.5, relative effort was significantly higher for stair ascent, 54% for younger compared with 78% for older adults, stair descent required 42% compared with 88% relative effort, and chair rising required 42% compared with 80%. Compared with young adults, the elderly walk at a significantly higher rate of oxygen uptake (about 20% more) and physiologic relative effort, that is, the ratio of the required oxygen uptake to the available maximal capacity.5,23 Age has been hypothesized to cause a redistribution of joint torques and power during gait. DeVita and Hortobagyi15 reported that during self-selected walking speed, elderly adults had 58% greater angular impulse and 279% more work at the hip and 50% less angular impulse and 29% less work at the knee compared with young adults. Similarly, they reported 23% less angular
Figure 7b.5 Mean of body mass-normalized knee joint moments for healthy young adults of 22 years and old adults with a mean age of 74 years during stair ascent (A), stair descent (B), and sit-to-stand (C). For stair ascent and descent, one cycle represents the initial foot contact (0) with the stair to toe-off (100%). For rising from a chair, one cycle corresponds to lift-off (0) to fully erect position at the end of the rise (100%). The bar graphs represent the group mean of the maximal isometric knee joint moments measured at specific knee joint positions in a leg press task. Solid lines and filled columns indicate older adults, and dashed lines and open columns denote young adults. (From Hortobagyi T, Mizelle C, Beam S, DeVita P: Old adults perform activities of daily living near their maximal capabilities. J Gerontol A Biol Sci Med Sci 58:M453-M460, 2003.)
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impulse and 29% less work at the ankle for the elderly compared with young adults. The elderly use less of the ankle plantar flexors and knee extensors and more of the hip extensors.15
Anatomic variation In addition to variation in the size of muscle and bone, many known anatomic variations directly influence the hip and knee joint forces. For instance, the femoral neck has two angular relationships with the femoral shaft: the neck-to-shaft or inclination angle and the torsion or anteversion angle. The inclination angle of the femur is referred to the relation of the femur neck with the shaft in the frontal plane. The inclination angle is about 140 to 150 degrees at birth and usually reduces to approximately 125 degrees, with a range of 90 to 135 degrees in adulthood. These abnormal angles alter the alignment between the acetabulum and femoral head and thereby alter the hip moments by changing the lever arm and the effect of upper body forces on the joint. The inclination angle may have positive and negative biomechanical effects.49 The torsion angle of the femur is the relative rotation that exists between the neck and the shaft. Normally, an infant is born with about 30 degrees of torsion angle that usually decreases to 15 degrees by 6 years of age.55,75 Excessive anteversion is often associated with a tendency toward internal rotation of the leg during gait, change of contact area between the femoral head and the acetabular,50 and wear on the articular cartilage. The Q-angle is another reported anatomic variation. During active knee extension and passive stretch, several structures guide the patellar movement with respect to the tibiofemoral joint. Although each structure alone may force medial or lateral movement of the patella, the net result of these forces moves it through the groove with minimal stress to the articular surfaces. The degree that the quadriceps tends to pull the patella is known as the Q-angle, which varies between the genders24 and is not bilaterally symmetric.37,38 A Q-angle of greater than 15-20 degrees is often thought to contribute to high articular stress and the poor tracking of the patella, thereby leading to arthritis, chondromalacia, recurrent patellar dislocation, or patellofemoral joint pain syndrome. Although in apparently normal anatomic structure the Q-angle and femoral neck angle of inclination and torsion is not necessarily consistent with the appropriate knee and hip joint loading during physical activities, the abnormal range of these angles is usually an indication of abnormal joint loading and pain.
Medical history and disease stage Medical history such as osteoarthritis45 and ligament deficiency35,67 may alter the kinematics and kinetics of the hip and knee joints directly or indirectly. Hip and knee osteoarthritis results from degenerative changes in cartilage that to some extent result from arbitrary increases in joint loading.19 For instance, patients with advanced knee osteoarthritis walk with lower ground reaction forces and reduced sagittal plane range of motion,45,66 increased knee adduction moment,6 decreased stride length,3 and increased angling out of the toes.73 Although self-selected walking speed has been reported to explain only 8.9% of the variation in the maximum knee adduction moment, a patient’s walking style is associated with the severity of knee osteoarthritis.45 One study has shown that knees with more severe osteoarthritis have greater
adduction moments and more varus alignment than those in which osteoarthritis is less severe.45 Figure 7b.6 demonstrates the magnitude and slope of the theoretical relationship between the maximum knee adduction moments and the walking speeds for two groups of patients with different degrees of knee osteoarthritis severity compared with asymptomatic control subjects matched for age and sex. The variation of the slopes in Figure 7b.6 indicates that adopting different walking speeds may not equally benefit osteoarthritis patients. Patients with less severe knee osteoarthritis walk with unique gait mechanics that are different from those of the control group and those of patients whose knee osteoarthritis is more severe.45 Similarly, other studies have demonstrated the effects of hip osteoarthritis and pain on the hip forces and gait.25 In summary, the kinematics and kinetics of the knee and hip joints are directly or indirectly influenced by individual factors. A brief discussion of some of these factors mainly serves as an example of how they may influence hip and knee joint forces. Although these individual factors cannot be controlled or modified, understanding their relationship with their influencing mechanism helps to explain the individual’s tolerance, ability to perform physical tasks, neuromuscular adaptation, and variation in the magnitudes of joint forces. Whereas most reported studies in this section discuss and compare healthy individuals with certain groups such as the elderly or individuals with severe osteoarthritis, who may not represent the working population, the information can still demonstrate the process and direction of biomechanical change.
Less severe knee OA
Maximum knee adduction moment (% body weight • height)
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2.0
More severe knee OA
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Walking speed (m/s) Figure 7b.6 Relationship between maximum knee adduction moment and self-selected walking speed for three groups of subjects: patients with knee osteoarthritis (OA) of lesser and greater severity and matched control subjects. (From Mundermann A, Dyrby CO, Hurwitz DE, Sharma L, Andriacchi TP: Potential strategies to reduce medial compartment loading in patients with knee osteoarthritis of varying severity: reduced walking speed. Arthritis Rheum 50:1172-1178, 2004.)
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Reduction of joint forces and moments Many physical activities such as walking, running, and stair climbing involve coordinated cyclic movements of several joints. Often, the comprehensive kinetic and kinematics analysis of single joints such as the hip or knee requires understanding their function in relation to other joints and their crossing muscles. The internal joint forces during dynamic physical activities are produced by BW, externally carried loads, and internal soft tissue forces such as muscles. A practical method of reducing joint force is to reduce the lever arm and impact of external forces. Several biomechanical and physiologic factors underlie the mechanism to reduce joint loads during physical activities and thereby risk of injury.
Reducing the lever arm The primary function of the hip joint is to support the weight of the head, arm, and trunk both in static erect posture and in dynamic activities such as walking, running, and stair climbing. The most effective means of reducing the joint forces during daily activities is to find a practical method of reducing the magnitude of either these forces or the lever arm. The hip and knee joint forces need to be understood largely in the context of action of the upper BW on the lower extremity. For example, the magnitude of the torques on the hip joint during upright standing is equal to the weight of the upper body (W), which is equal to two thirds of BW50 times the distance of this force from the hip joint axis. As shown in Figure 7b.7A, during a single-legged stance, assuming the lever arm is 4 inches,52 for a 180-pound individual, the gravitational force at the hip is as follows: Hip joint moment = (upper BW + lower leg weight) × lever arm Assuming the weight of lower leg is one sixth of BW, the acting moment is as follows: = (2/3 BW + 1/6 BW) × lever arm = 5/6 BW × 4 = 150 × 4 = 600 lbs/in Often individuals with painful hip or abductor weakness may lean their upper bodies over the painful hip to reduce the pain or may display a Trendelenburg (abductor lurch) gait pattern.59
When the pelvis rotates and the trunk is laterally flexed toward the stance limb, the moment arm may reduce substantially with respect to the neutral trunk. If the lever arm decreases from 4 to 2 inches (Fig. 7b.7B), the hip joint moment proportionally reduces to half. In a series of three experiments, Neumann48 compared the electromyography activity of the hip abductor muscles in subjects with hip prostheses adopting different methods of walking while using canes and carrying external loads. Twenty-four subjects with unilateral hip prostheses carried loads weighing 5%, 10%, or 15% BW and held by either their contralateral or ipsilateral arms relative to their prosthetic hips. As shown in Figure 7b.8, it was assumed that during the midstance phase of walking, the hip abductor muscle generated a very large force proportional to the BW and varied with a relatively small moment arm. Neumann found that the use of a cane on the contralateral side and the ipsilateral load condition could reduce the muscle activities by 40% of baseline as compared with walking without a load or a cane.
Synergic movement and muscular coactivation The force produced by a given muscle with specific size and structure depends on the activation level, length, and speed of contraction. The interaction of these parameters and their influence on muscle force production has been discussed in most basic textbooks of skeletal muscle biomechanics and physiology. Generally, it is known that tension generated in a skeletal muscle is a function of its length and the magnitude of overlap between the actin and myosin filaments. As the load increases, the velocity at which a muscle shortens while undergoing maximal stimulation decreases. During physical activities involving the lower extremity, muscle length changes due to the synergy among the monoarticular and biarticular muscles of the hip and knee joints. During functional activities, often the biarticular muscles have antagonistic activities at one joint and agonistic activities at another.4 During stair climbing, for example, the rectus femoris acts as the knee agonist muscle by providing the knee extension moment and as the hip antagonist muscle by providing the hip flexion moment.4 At times a muscle is even antagonist in one plane and agonist in another. Except for the short head of the
Weight Moment Arm Weight Moment Arm
A
B
Figure 7b.7 Normal pelvis and hip orientation during upright standing (A) and pelvis position during abductor lurch and Trendelenburg (B). (From Robertson DD, Britton CA, Latona CR, Armfield DR, Walker PS, Maloney WJ: Hip biomechanics: importance to functional imaging. Semin Musculoskelet Radiol 7:28-41, 2003.)
Chapter 7b
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Reducing internal joint load: application of biomechanical concepts
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flexors
