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specifically defined disorders of the upper extremities. The studies are summarized in Table 8.3. The report does not state that interventions prevent carpal tunnel syndrome or, indeed, any other upper-extremity disorder. The emphasis, rather, is on amelioration of symptoms, which is the end point in the relevant literature. Furthermore, the comments on upper extremity interventions carefully state that interventions influence symptoms, not the incidence of specific disorders ( Chapter 8, p. 313):

Studies of engineering interventions for computer-related work that reduce static postural loads, sustained posture extremes, and rapid motions have demonstrated decreases in upper extremity pain reports. Further study of these interventions is needed to determine the amount of pain reduction possible, the duration of salutary effect, and which upper extremity clinical conditions could benefit from these interventions.

Dr. Szabo uses the case of carpal tunnel syndrome with regard to lowforce, high-repetition exposures (primarily the use of computer keyboards) as the causal factor to suggest that the relationship of musculoskeletal disorders to work exposure may not be sound. The panel has recognized that the evidence for low-force, high-repetition exposures is weaker than for other relationships among risk factors and musculoskeletal outcomes; however, strong evidence for causal relationships between physical work and musculoskeletal disorders is provided throughout the report.

The epidemiology section as it relates to the upper extremity was carefully written. We discuss the cross-sectional designs of most studies and possible implications for causal inference, including the potential for the “healthy worker” effect. In 9 studies, carpal tunnel syndrome was defined by a combination of a history of symptoms and physical examination or nerve conduction testing. In these studies there were 18 estimates of risk based on various specificities of carpal tunnel syndrome diagnosis and varying degrees of work exposure. Of these, 12 showed significant odds ratios greater than 2.0 (range 2.3 to 39.8), 4 showed nonsignificant odds ratios of greater than 2.0, and 2 showed nonsignificant odds ratios of between 1.7 and 2.0. The epidemiology section, however, does not draw specific conclusions regarding carpal tunnel syndrome. The report points out that just three articles dealt with keyboard work; indeed, keyboard work is not a major consideration or focus in the report.

Dr. Szabo's dissent provides an incomplete view of a study published in the Journal of the American Medical Association (Atroshi, 1999). He states: “In the general population the prevalence of Carpal Tunnel Syndrome is the same whether people perform repetitive activities or not.” In the panel's view, the nature of the design in that study and its survey instruments were such that the power to demonstrate this association was not

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