Another question has been whether epidemiological case definitions represent "real" clinical disorders. Many MSDs are self-limited or cause minimal disability, while others are more severe. Case definitions can be designed to capture a broad or a narrow spectrum of illness; it is probably not true that only the most severe cases are clinically "real." Case definitions used in the weighted studies required both symptoms and physical examination findings by an experienced clinician, and were analogous to common clinical diagnostic practices. For CTS, the issue of diagnosis without EDS is controversial as noted above. Many clinicians make the working diagnoses of CTS, and start therapy in individual patients, based on the same symptom and physical examination criteria used in those weighted studies which did not use EDS.
4. What does the evidence tell us about incidence in the general population versus specific groups of workers?
MSDs are common in the general population. Epidemiological studies of occupational risk factors must include appropriate referent groups for valid comparisons. Many studies show much higher than expected rates of MSDs among workers with high exposures to physical risk factors. The prevalence and incidence of MSDs is highly dependent on the reporting mechanisms and case definitions adopted.
The current best evidence shows consistent, strong associations between certain physical factors and MSDs. The quality of evidence is adequate but not perfect. It seems unlikely that future longitudinal studies will invalidate causal inferences drawn from current studies.