Work-Related Musculoskeletal Disorders Report, Workshop Summary, and Workshop Papers (1999) / Chapter Skim
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I Steering Committee Report
I Steering Committee Report
Pages 1-32
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Work-Related dusculoskelelal Disorders
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A disorder is work related when work procedures, equipment, or environment contribute significantly to the cause of the disorder. There is great variation in the diagnostic criteria for musculoskeletal disorders, ranging from clinical diagnoses based on symptoms and signs for some, to diagnoses based on structural and functional criteria for others.
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Estimated costs associated with lost days and compensation claims related to musculoskeletal disorders range from $13 to $20 billion annually (National Institute for Occupational Safety and Health, 1996; AFL-CIO, 1997~. The multiplicity of factors that may affect reported cases including work procedures, equipment, and environment; organizational factors; physical and psychological factors of the individual; and social factors has led to much debate about their source, nature, and severity.
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This framework serves as a useful heuristic to examine the diverse literatures associated with musculoskeletal clisorclers, reflecting the role that various factors work procedures, equipment, anc3 environment; organizational factors; physical anc3 psychological factors of inclivicluals; non~work~relatec3 activities; organizational factors; anc3 social factorscan play in their development. Its overall structure suggests the physiological pathways by which musculoskeletal clisorclers can occur or, conversely, can be avoiclec3.
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6 .o In m~ ~ as o ~ cc .O ~ ~ o 4- o A .2 o ~5 o In o Q In o ._ Q ci In E o Q E En In A ~ EN ~ ~ Q ~ ~0 E ._ Q E t E lo · _ ._ Q In ._ 1 .
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To the left of the shaclec3 area in Figure I, the framework shows environmental factors that might affect the development of musculoskeletal clisorclers, including work procedures, equipment, anc3 environment; organizational factors; anc3 social context. For example, physical work factors (reaching, close vision work, lifting heavy loads)
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For exam' pie, there are highly controlled studies of soft tissue responses that are based on work with cadavers, animal models, anc3 human biomechanics; survey anc3 cross~sectional studies that examine the relationship between musculoskeletal clisorclers anc3 work, organizational, social, anc3 incliviclual factors; anc3 experimental, quasi-experimental, anc3 time~series studies that are clesignec3 to examine the effects of various interventions. In order to make sense of such a multifaceted body of research, we have extenclec3 our analysis beyond the traditional criteria used in epiclemiological studies; we rely, instead, on five commonly accepted criteria for establishing causal linkages among factors.
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offer plausible explanations for the observed effect (e.g., a lower average level of sick clays in the post~reclesign period of observation) , it is necessary to identify anc3 test whether other plausible factors might have been operative, mimicking the effect of the target cause (e.g., change in sick leave policy, turnover in personnel)
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By applying these criteria to evaluate the credibility of scientific evidence, one need not place heavy emphasis on the types of research design that have been used in a given study. It is a clisciplinec3 way to take advantage of the research proviclec3 by a wide variety of methods anc3, thus, it has substantial implications for the manner in which a science base is consiclerec3.
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Data from cadaver studies provide ranges within which such failures occur, and animal models of some tissue provide support for the laboratory data. Even at levels of force clearly below the failure level, however, there is scientific evidence, from these types of studies, that tissue response to deformation can produce inflammation, failure at micro' scopic levels, and muscle fatigue.
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have been stucliec3 extensively, using both theoretical models anc3 human laboratory studies. Theoretical models make use of mathematical models that are widely applied to design mechanical structures in aircraft, automobiles, bridges, anc3 buildings.
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The relationship between external anc3 internal loacis is also based on Newtonian mechanics. Internal loacis have been shown to produce mechanical, physiological, anc3 psychological responses, such as tissue deformation, altered metabolism, altered circus latory patterns, anc3 perceived exertion (see discussion of soft tissue responses above)
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However, continuous scales would be useful for primary prevention anc3 work design. EPIDEMIOLOGICAL EVIDENCE THAT PHYSICAL FACTORS CAN CAUSE MUSCULOSKELETAL DISORDERS One of the factors prompting our review of the scientific relationship between biomechanical stressors at work anc3 the occurrence of musculoskeletal clisorclers has been controversy regarding human studies in working populations.
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These presentations anc3 discussions led us to the following summaries of the scientific evidence: · Strong associations between measured biomechanical stressors at work anc3 musculoskeletal clisorclers were observed in most studies; however, temporal contiguity between the stressors anc3 onset of effects, as well as evidence of amelioration after reduction of stressors, could not always be established, nor could the clinical course of the observed effects. This shortcoming, though inherent to practical requirements of such research, makes it difficult to make strong causal inferences on the basis of the evidence from any incliviclual study.
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Examples include the excesses of musculoskeletal clisorclers of the upper extremities among sawyers anc3 auto assembly workers anc3 the excesses of musculoskeletal clisorclers of the back among materials handlers anc3 health care workers who lift patients. · There is compelling evidence from numerous studies that as the amount of biomechanical stress is reclucec3, the prevalence of musculoskeletal clisorclers at the affected body region is likewise reclucec3.
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Organizational and Social Factors A number of studies have grouped non-biomechanical factors at the workplace anc3 within social support groups as "psychosocial factors." These are often the factors directly associated with levels of workplace stress, such as job content anc3 clemancis, job control, anc3 social support. However, variables such as job satisfaction or job enjoyment have also been incluclec3.
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Social support is seen as a mediating variable in studies of psychological stress; it fincis strong support in the NIOSH review anc3 the commissioned review, but somewhat less in other reviews presented by workshop discussants. Across organizational anc3 social variables, psychological stress has some causal plausibility, but in general its biological plausibility is weaker than for some other incliviclual anc3 biomechanical factors.
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Overall, there is a great clear of diversity regarding the nature anc3 quality of research methods used in intervention studies (Smith et al., 1998~. There are a number of laboratory studies involving the use of random assignment of participants to interventions.
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Further evidence for effective intervention is found in several well~uesigneu studies that show that alternative hand tool designs result in improved hand and wrist posture, thereby minimizing the risk of musculoskeletal disorder. And there is some evidence that weight handling devices reduce the risk of musculoskeletal disorders (Smith et al.
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In all areas, aciclitional research would shed light on the models arid mechanisms that underlie the established relationships between causal factors anc3 outcomes. For example, it is obvious that a tissue will fail when loaclec3 above its ultimate strength.
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22 WORK-RELATED MUSCULOSKELETAL DISORDERS 5. Although a good clear is known about musculoskeletal clisorclers, a better uncler' stancling of the clinical courses of these clisorclers would be possible with improved models and measures.
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The musculoskeletal conditions that may be caused by (non~acciclental) physical work activities include clisorclers of inflammation, degeneration, anc3 physiological clis' ruption of muscles, tendons, ligaments, nerves, synovia, anc3 cartilage involving limbs anc3 trunk.
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In the classification of back pain, a symptom classification is often used because the precise etiology of the painful process often cannot be iclentifiec3. For specific disease entities, such as herniated disks, there are accepted diagnostic criteria that are based on clinical symptoms anc3 signs, as well as imaging information.
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specific occupational groups? Specific interventions can affect the reported rate of musculoskeletal clisorclers in specific industries anc3 for specific occupations.
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Question 7: What scientific questions remain unanswered, and may require further research, to determine which occupational activities in which specific industries cause or contribute to work related musculoskeletal disorders? Looking at this web of evidence, we have reached three major conclusions: · Musculoskeletal clisorclers are a serious national problem: estimates of costs range from $13 to $20 billion annually.
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· There is a strong biological plausibility to the relationship between the incidence of musculoskeletal clisorclers and the causative exposure factors in high exposure occu' pational settings. · Research clearly demonstrates that specific interventions can reduce the reportec3 rate of musculoskeletal clisorclers for workers who perform high~risk tasks.
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improve the caliber of measurements for risk factors, outcome variables, anc3 injury data collection anc3 reporting systems; anc3 (5) provide better unclerstancling of the clinical course of these clisorclers.
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Rempel 1994 Investigation of applied forces in alphanumeric keyboard work. American Industrial Hygiene Association Journal 55~1~:30-35.
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Lavender 1998 Work Factors, Personal Factors, and Internal Loads: Biomechanics of Work Stressors. Paper prepared for the Steering Committee for the Workshop on Work-Related Musculoskeletal Injuries.
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Wegman, D.H. 1998 Workshop on Work-Related Musculoskeletal Injuries: Examining the Research Base Panel on Epidemiology: Physical Factors: Summary Comments.
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