[Metaanalysis for the evaluation of risk factors for carpal tunnel syndrome (CTS) Part II. Occupational risk factors]

The expert committee of the German Ministry for Labour and Social Affairs suggested carpal tunnel syndrome (CTS) as an "occupational disease". This systematic literature review and metaanalysis was aimed at identifying associated and risk factors for CTS. Part II addresses the occupational factors of CTS.

A systematic literature review was performed by examining papers in PubMed, Cochrane, EMBASE and Web of Science databases that were published on or before February 15th, 2011. A total of 87 studies (27 longitudinal and 60 cross-sectional) were included in this metaanalysis. The PRISMA (preferred reporting items for systematic reviews and metaanalyses) guidelines for performing a metaanalysis were strictly followed. All of the effect sizes were calculated using a random-effects model.

The prevalence of CTS in working populations [10.9 % (95 % CI 7.9-14 : 9)] was significantly higher than in the general population [8.2 % (95 % CI 2.3-25.1), p < 0.001]. Working people had a CTS incidence of 17.3 (95 % CI 14.5-20.1)/1,000 person years. In contrast, the crude incidence in the general population was 1.8 (95 % CI 1.4-2.2)/1.000 person years (p < 0.001). The heterogeneity of the different study designs made it impossible to detect concrete prevalence or incidence rates for specific job groups. However, "blue-collar work" was a significant risk factor for CTS [OR = 3.1 (95 % CI 1.9-5.3), p < 0.001]. Thus, it makes sense to evaluate concrete hand burdens. In numerous studies, some factors were associated with CTS: repetition [OR = 2.7 (95 % CI 1.8-39), p < 0.001), chronic wrist flexion [OR = 1.7 (95 % CI 1.0-2.6), p = 0.033], powerful grip [OR = 4.4 (95 % CI 1.4-13.6), p = 0.009], and chronic vibration load [OR = 2.6 (95 % CI 1.7-4.0)]. Primarily, combined hand loadings were estimated. For this evaluation, the hand activity level threshold limit values (HAL TLVs®) of the ACGIH (American Conference of Governmental Hygienists) were useful. Manual work in the 4th quartile of this score was significantly associated with the prevalence of CTS [OR = 2.9 (95 % CI 1.5-5.7), p = 0.001]. These score values were identified as a significant risk factor for occupational CTS.

It was impossible to define exact prevalences or incidences of CTS for specific job titles. However, it was possible to identify manual loadings with a significantly higher risk or association with CTS, including repetition, wrist flexion, powerful grip, and vibration. These loadings are usually combined during occupational work. Subsequent experts' reviews have to respect these complex hand loadings. It may be useful to use instruments, such as HAL TLVs®.