Relationship between repetitive work and the prevalence of carpal tunnel syndrome in part-time and full-time female supermarket cashiers: a quasi-experimental study

OBJECTIVES: To investigate the prevalence of Carpal Tunnel Syndrome (CTS) in full-time and part-time supermarket cashiers exposed to a different weekly duration of biomechanical load. METHODS: All the 269 cashiers and 127 office workers were asked to participate. The protocol included ergonomic risk assessment, collection of personal and clinical data and bilateral electrodiagnostic study of the median nerve. CTS symptoms were defined as past and/or current nocturnal and/or diurnal numbness, tingling, burning or pain involving at least one of the first three fingers. Results were evaluated according to two case definitions based on current symptoms and on the combination of current symptoms and slowing of sensory conduction velocity from wrist to palm, respectively. Difference in proportions of CTS symptoms and cases was evaluated by the Pearson's chi-square (chi(2)) test, univariate and multivariate logistic regression analyses were performed to determine the impact of weekly exposure. RESULTS: The final female study population included 71 full-time cashiers, 155 part-time cashiers and 98 office workers. Ergonomic risk level was rated 5 for hand activity level and 4 for peak of force according to ACGIH. The intersection of the two values fell on the threshold limit value line, confirming the possible exposure to biomechanical risk factors for CTS. The prevalence of current CTS symptoms was higher among full-time (31.0%) than in part-time cashiers (19.3%) or controls (16.3%) (p = 0.055). A similar pattern was found for CTS past symptoms and cases. Univariate analysis showed that full-time cashiers had a 2.3 fold increased risk for CTS specific current symptoms than control subjects. A similar trend also emerged for CTS cases but was not significant (Odds ratios 1.23). Multivariate logistic regression analysis confirmed the increased risk for CTS current symptoms in full-time cashiers. CONCLUSIONS: Intensive manual work associated with inadequate recovery time might have generated an impairment of the median nerve at the wrist level proportionally increasing with duration of hand use. Our study can provide useful information both for ergonomic risk assessment and work organization.