A number of general and specific reviews were identified in which physical and psychosocial factors were examined in relation to musculoskeletal disorders of the upper extremities and back (see review refer- ences). These reviews served as a resource to supplement the panel’s efforts to identify relevant epidemio- logic studies. They also were examined to determine whether conclusions when drawn from the panel’s review were consistent with previous review efforts. The objectives of the reviews differed; some focused on specific industries, job, or exposures, but others were more general. As a whole, the findings from these other reviews are consistent with those arrived at in the panel’s review and provide additional support for the conclusions.
The approach for considering causal inferences described in Chapter 3 is useful for summarizing our review of the data from epidemiologic studies. As the tables in this chapter show, a number of studies were judged to be of sufficient quality for inclusion in this review, and these vary in terms of the types of designs and measurement approaches. While this variety complicates the generalization of causal inferences, the summary tables indicate meaningful associations between work-related physical and psychosocial exposures and musculoskeletal disorders. The tables show not only a preponderance Magnitude of Occupationally-Related Musculoskeletal Disorders 2-19
of evidence for some exposures (e.g., 26 of 32 studies found a significant association between vibration and upper extremity musculoskeletal disorders), but also a consistency of association for many of the exposures and outcomes. Although the literature contains mostly cross-sectional surveys, some work to establish temporality; combined with the available prospective studies, evidence for temporal associ- ation has been included in this chapter.
Most studies reviewed here also show a meaningful strength of association measured by both estimates of the relative risk and calculation of attributable risk. The attributable risk provides an estimate of the proportion of musculoskeletal disorders that might be prevented if effective interventions were implemented; the calculations are appreciable for most of the exposures summarized here.
While the measure of attributable risk is meaningful for conceptualizing public health impact, the calculations are presented for one factor at a time and do not account for other factors. As noted in this chapter, many studies did account for potential confounders that could provide alterna- tive explanations for the observed findings, but the number of confounders examined in each study tends to be limited. While this is due to multiple factors (including expense associated with satisfying sample size requirements), the fact that the associations persist after accounting for the confounders measured to date supports the fundamental association, but it also justifies more detailed investigation.
The joint effect of exposures is another element of the risk estimation suggested in Chapter 3 and illustrated in this chapter. The attributable fraction summarizes the impact of a single exposure.
However, scant attention has been paid to the joint effect, or interaction, of two (or more) exposures, increasing risk beyond the level of either alone. As noted in Chapter 3, some combinations of exposures might work jointly, although their individual actions may or may not be significant. The studies by Silverstein (e.g., Silverstein et al., 1987) showed an interaction between high force and high repetition for upper extremity disorders among industrial workers. Further investigation for joint effects of exposures is indicated from the current review. The effect of joint exposures can be investigated within physical (vibration, force, load, etc.), and psychosocial (job strain, job demand, etc.) domains.
This review indicated the utter lack of studies that were found to be of sufficient quality and that examine both physical and psychosocial factors together. Because evaluation of each has shown import- ant effects on the development of musculoskeletal disorders, and some of the current evidence (although modest) suggests that one does not explain the other, it is unlikely that more detailed investigation will demonstrate that the association of either with musculoskeletal disorders is due to confounding with the other. However, additional studies are needed to understand the degree to which each contributes to the overall incidence of musculoskeletal disorders, and the extent to which both work synergistically in selected work settings.
While the results presented in this chapter are consistent with one another, it is important to examine the degree to which they are consistent with the results from the basic science and the biomechanics studies (Chapter 5 and 6). Some of these studies have been mentioned in this chapter; their results are generally consistent, providing here some suggestion of biological plausibility for the association between physical forces and musculoskeletal disorders. The degree of consistency across different levels of study will be discussed in more detail in the integration chapter.
Most epidemiologic studies have been summarized as having exposure and outcome measures dichot- omized. The ability to make inferences about dose – response relationship is limited in this context. While there are step-wise differences in dichotomous measures across studies (e.g., see Boshuizen et al., 1992:
Bovenzi and Zadini, 1992) that make cross-comparisons tantalizing, the differences in comparison groups and other design features hinder the combining of results for generating inferences on dose – response relationships. Future studies can help generate strong inferences by paying greater attention to more refined levels of measurement. While this is a challenge, the strength of the current studies justifies this effort.
In conclusion, the epidemiologic evidence provides support for associations between workplace physical and psychosocial exposures and both back and upper extremity musculoskeletal disorders.
2-20 Fundamentals and Assessment Tools for Occupational Ergonomics
Panel on Musculoskeletal Disorders and the Workplace
Jeremiah A. Barondess (Chair), New York Academy of Medicine
Mark R. Cullen, Occupational and Environmental Medicine Program, School of Medicine, Yale University
Barbara de Lateur, Department of Physical Medicine and Rehabilitation, School of Medicine, Johns Hopkins University
Richard A. Deyo, Department of Medicine, Division of General Internal Medicine, University of Washington, Seattle
Sue K. Donaldson, School of Nursing and School of Medicine, Johns Hopkins University Colin G. Drury, Department of Industrial Engineering, State University of New York, Buffalo
Michael Feuerstein, Departments of Medicial/Clinical Psychology and Preventive Medicine/
Biometrics, Uniformed Services, University of the Health Sciences, Bethesda, Maryland, and Division of Behavioral Medicine, Georgetown University Medical Center
Baruch Fischhoff, Department of Social and Decision Sciences and Department of Engineering and Public Policy, Carnegie Mellon University
John W. Frymoyer (retired), McClure Musculoskeletal Research Center, Department of Orthopaedics and Rehabilitation, University of Vermont, Burlington
Jeffrey N. Katz, Division of Rheumatology, Immunology, and Allergy, Brigham and Women’s Hospital, Harvard University Medical School
Kurt Kroenke, Regenstrief Institute for Health Care and School of Medicine, Indiana University, Indianapolis
Jeffrey C. Lotz, Orthopaedic Bioengineering Laboratory and Department of Orthopaedic Surgery, University of California, San Francisco
Susan E. Mackinnon, Division of Plastic and Reconstructive Surgery, School of Medicine, Washington University, St. Louis
William S. Marras, Institute for Ergonomics and Department of Industrial, Welding, and Systems Engineering, The Ohio State University, Columbus
Robert G. Radwin, Department of Biomedical Engineering, University of Wisconsin, Madison David M. Rempel, School of Medicine, University of California, San Francisco
Robert M. Szabo, Department of Orthopaedic Surgery, School of Medicine, University of California, Davis
David Vlahov, Center for Urban Epidemiologic Studies, New York Academy of Medicine, and Johns Hopkins University School of Public Health
David H. Wegman, Department of Work Environment, University of Massachusetts, Lowell
Magnitude of Occupationally-Related Musculoskeletal Disorders 2-21
3
Legal Issues in Occupational Ergonomics
George A. Peters Barbara J. Peters
Peters and Peters