A case-crossover study of occupational traumatic hand injury: Methods and initial findings

Background Acute hand injury is the beading cause of occupational injury cr eated in United States' hospital emergency departments (e.g., laceration, c rush or fracture). To identify risk factors for traumatic hand injuries, we conducted a case-crossover study of transient exposures (e.g., being rushe d) for acute occupational traumatic hand injury. Methods The case-crossover method, which uses subjects as their own control s, was used to identify risk factors for occupational hand injury. Two hund red and thirty-two subjects were recruited from 17 occupational health clin ics in New England and interviewed by telephone a median of 1.2 days after their injury. The a priori hazard period was defined as 10 min before the i njury. Two control periods were used: one was 60-70 min prior to the injury (matched-pair interval analysis); the other was the total work-time expose d, on average, in the previous month (usual frequency analysis). Results In the usual frequency analysis, the relative risk for using malfun ctioning dr different-from-usual equipment or tools in the hazard period wa s 25.5 (95% confidence interval = 18.4-35.2). Relative risks were also sign ificantly elevated for performing a task using an unusual work method, doin g an unusual task, being distracted, or being rushed. Wearing gloves appear ed to be protective (relative risk = 0.8, 95% CI = 0.5-1.2). Matched-pair i nterval analysis, where appropriate, provided similar findings but herd muc h wider confidence intervals. Conclusions This study demonstrates that the case-crossover design is a fea sible and efficient method for studying transient risk factors for sudden-o nset traumatic occupational hand injury. The usual frequency analysis prove d more useful than the match-pair approach to control period selection. Am. J. Ind. Med. 39:171-179, 2001. (C) 2001 Wiley-Liss, Inc.