Methodological limitations in the study of video display terminal use and upper extremity musculoskeletal disorders.

Upper extremity musculoskeletal disorders may occur as a result of work with keyboard-equipped video display terminals. Many studies of the associations between keyboard use and upper extremity disorders have appeared in both the human factors and occupational epidemiologic literature. Methodological limitations and inconsistent results have limited conclusions that can be made from these studies, however. Although exposure conditions can be carefully controlled, human factors studies are limited by relatively small sample sizes, short exposure durations, and reliance on outcome measures with unknown relevance to chronic adverse health effects. Epidemiologic studies have been limited by poor ascertainment of both exposure and health outcome. Many have failed to control for any potential confounding. An almost exclusive reliance on cross-sectional study designs has resulted in possible bias from selective survival, exposure-effect reversal, and poor estimates of exposures occurring prior to development of the disorder. Given the inconsistency in the literature and the growing controversy surrounding this issue, prospective study of this question using objective methods for assessment of exposure and health outcome is recommended. This design allows identification of incident cases and minimizes bias from selective survival. In addition, ergonomic and psychosocial variables prior to onset of symptoms can be ascertained periodically. Given estimates for up to 100 million video display terminals to be in use in the United States by the year 2000, clarification of the health effects of their use is critical.