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

Abstract

Background Acute hand injury is the leading cause of occupational injury treated in United States' hospital emergency departments (e.g., laceration, crush or fracture). To identify risk factors for traumatic hand injuries, we conducted a case-crossover study of transient exposures (e.g., being rushed) for acute occupational traumatic hand injury. Methods The case-crossover method, which uses subjects as their own controls, was used to identify risk factors for occupational hand injury. Two hundred and thirty-two subjects were recruited from 17 occupational health clinics in New England and interviewed by telephone a median of 1.2 days after their injury. The a priori hazard period was de®ned as 10 min before the injury. 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 exposed, on average, in the previous month (usual frequency analysis). Results In the usual frequency analysis, the relative risk for using malfunctioning or different-from-usual equipment or tools in the hazard period was 25.5 (95% con®dence interval 18.4±35.2). Relative risks were also signi®cantly elevated for performing a task using an unusual work method, doing an unusual task, being distracted, or being rushed. Wearing gloves appeared to be protective (relative risk 0.8, 95% CI 0.5± 1.2). Matched-pair interval analysis, where appropriate, provided similar ®ndings but had much wider con®dence intervals. Conclusions This study demonstrates that the case-crossover design is a feasible and ef®cient method for studying transient risk factors for sudden-onset traumatic occupational hand injury. The usual frequency analysis proved more useful than the match-pair approach to control period selection.

A case-crossover study of work-related acute traumatic hand injuries in the People’s Republic of China

“…We previously reported on the development of our structured questionnaire (15), modeled after the studies by Sorock et al (11), translated into Chinese, and evaluated in the previous pilot study (13). The questionnaire recorded information on 8 self-reported transient expo- Jin et al sures starting at 90 minutes before the onset of the hand injury regarding the participant's work equipment, work practices, and worker-and workplace-related factors.…”

“…We utilized the case-crossover design to assess if the injury may have been "triggered" by one or more transient risk factors that occurred just prior to the injury. The same protocol was used as in a North American study by Sorock et al (11) and Lombardi et al (9) and in Hong Kong, China, by Chow et al (12). In these prior studies, wearing gloves was identified as a protective factor that was significant in Sorock et al's report (11) (RR 0.4, 95% CI 0.3-0.8) but insignificant in Chow et al's (RR 0.7, 95% CI 0.38-1.34).…”

“…Gloves do not protect workers from injury by high energy external forces. In the Sorock et al report (18), for example, glove use was not associated with a reduced relative risk of crush, avulsion, amputation, or fracture injuries to the fingers or hand (RR 0.93, 95% CI 0.62-1.39) but was associated with a reduced RR of a laceration injury [lacerations accounted for 63% of all injuries in the Sorock et al report (11)]; (ii) wearing gloves may also reduce operational flexibility and could actually cause a gloved hand to be caught in moving machinery; and (iii) wearing gloves might be confounded by other cooccurring risk factors. The last point has been referred to as multiple-correlated transient factors (19), for example, wearing gloves occurred most often with malfunctioning machine tools or work material, performing an unusual work task, being rushed, and performing a task with a different method.…”

“…For more information on limitations and study planning using case-crossover design, please see Maclure & Mittleman (8). This design has been used to study occupational injuries in the US by Lombardi et al (9) and Sorock et al (10,11), who identified modifiable transient risk factors for acute hand injuries.…”

“…In the Sorock et al (11) and Lombardi et al (9) studies, performing unusual work tasks, being distracted or rushed, equipment or tool malfunction, new work methods, or not wearing gloves were significantly associated with the occurrence of an acute work-related hand injury. A similar design was adopted to study occupational hand injuries among 192 workers from Hong Kong.…”