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cially those that can be supported by objective ancillary diagnostic tests, such as carpal tunnel syndrome. Others, such as work-related low back pain, are in some instances supported by objective change, which must be considered in concert with the history and physical findings. In the case of radicular syndromes associated with lumbar intervertebral disc herniation, for example, clinical and X-ray findings tend to support each other. In other instances, in the absence of objective support for a specific clinical entity, diagnostic certainty varies but may nevertheless be substantial. The clinical picture of low back strain, for example, while varying to some degree, is reasonably characteristic.

Epidemiologic definitions for musculoskeletal disorders, as for infectious and other reportable diseases, are based on simple, unambiguous criteria. While these are suitable for data collection and analysis of disease occurrence and patterns, they are not appropriate for clinical decisions, which must also take into account personal, patient-specific information, which is not routinely available in epidemiologic databases.

    3. What is the state of scientific knowledge, characterized by the degree of certainty or lack thereof, with regard to occupational and non-occupational activities causing such conditions?

The panel has considered the contributions of occupational and non-occupational activities to the development of musculoskeletal disorders via independent literature reviews based in observational epidemiology, biomechanics, and basic science. As noted in the chapter on epidemiology, when studies meeting stringent quality criteria are used, there are significant data to show that both low back and upper extremity musculoskeletal disorders can be attributed to workplace exposures. Across the epidemiologic studies, the review has shown both consistency and strength of association. Concerns about whether the associations might be spurious have been considered and reviewed. Biological plausibility for the work-relatedness of these disorders has been demonstrated in biomechanical and basic science studies, and further evidence to build causal inferences has been demonstrated in intervention studies that show reduction in occurrence of musculoskeletal disorders following implementation of interventions. The findings suggest strongly that there is an occupational component to musculoskeletal disorders. Each set of studies has inherent strengths and limitations that affect confidence in the conclusions; as discussed in Chapter 3 (methodology), when the pattern of evidence is considered across the various types of studies, complementary strengths are demonstrated. These findings were considered collectively through integration of the information across the relevant bodies of scientific evidence. Based on this approach, the panel concludes, with a high



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