Work-Related Musculoskeletal Disorders A Review of the Evidence (1998) / Chapter Skim
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2 State of Evidence
2 State of Evidence
Pages 6-18
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From page 6... ...
For example, there are highly controlled studies of soft tissue responses that are based on work with cadavers, animal models, and human biomechanics; survey and cross-sectional studies that examine the relationship between musculoskeletal disorders and work, organizational, social, and individual factors, and experimental, quasiexperimental, and time-series studies that are designed to examine the effects of various interventions. In order to make sense of such a multifaceted body of research, we have extended our analysis beyond the traditional criteria used in epidemiological studies; we rely, instead, on five commonly accepted criteria for establishing causal linkages among factors.
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From page 7... ...
offer plausible explanations for the observed effect (e.g., a lower average level of sick days in the post-redesign period of observation) , it is necessary to identify and 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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From page 8... ...
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 microscopic levels, and muscle fatigue.
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From page 9... ...
On all of these highly controlled studies, the causal criteria are met: the load or stress occurs before the response, confounding factors are controlled to eliminate other plausible responses, and the size and temporal proximity of the load and effect can be consistently measured and predicted. Work Factors and Biomechanics The relationships among external work factors, loads, and responses (see Figure I)
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From page 10... ...
Although external stresses can be produced by activities of recreation and daily living, the duration of exposures rarely equals the 40-60 hours per week that commonly occur in work settings. External loads impose internal loads on underlying tissues (e.g., muscles, tendons, tendons sheaths, bones, ligaments, and nerves)
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From page 11... ...
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 and the occurrence of musculoskeletal disorders has been controversy regarding human studies in working populations. These studies, although numerous, have used diverse methods for measuring both exposure to mechanical factors and the health outcomes of interest.
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From page 12... ...
These presentations and discussions led us to the following summaries of the scientific evidence: · Strong associations between measured biomechanical stressors at work and musculoskeletal disorders were observed in most studies; however, temporal contiguity between the stressors and 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 individual study.
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From page 13... ...
Many of these factors are discussed below. Epidemiological Evidence that Non-Biomechanical Factors Can Cause Musculoskeletal Disorders The framework in Figure ~ shows individual, organizational, and social factors as sources of variation that might directly affect the physiological pathways leading from tissue load, through impairment, to disability.
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From page 14... ...
Organizational and Social Factors A number of studies have grouped non-biomechanical factors at the workplace and within social support groups as "psychosocial factors." These are often the factors directly associated with levels of workplace stress, such as job content and demands, job control, and social support. However, variables such as job satisfaction or job enjoyment have also been included.
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From page 15... ...
Overall, there is a great deal of diversity regarding the nature and quality of research methods used in intervention studies (Smith et al., ~ 998~. There are a number of laboratory studies involving the use of random assignment of participants to interventions.
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From page 16... ...
Another class of field studies involves comparisons of alternative forms of intervention (e.g., back school versus exercise) rather than pure control group conditions, where the participants receive little or no specialized attention.
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From page 17... ...
How tissue responds to repetitive loading, what triggers inflammatory responses, and how these are influenced by individual factors have not been explained in detail. A similar argument can be made for intervention studies, especially those that involve multiple components.
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From page 18... ...
5. Although a good deal is known about musculoskeletal disorders, a better understanding of the clinical courses of these disorders would be possible with improved models and measures.
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