Academic journal article Scandinavian Journal of Work, Environment & Health

Validation of the ACGIH TLV for Hand Activity Level in the OCTOPUS Cohort: A Two-Year Longitudinal Study of Carpal Tunnel Syndrome

Academic journal article Scandinavian Journal of Work, Environment & Health

Validation of the ACGIH TLV for Hand Activity Level in the OCTOPUS Cohort: A Two-Year Longitudinal Study of Carpal Tunnel Syndrome

Article excerpt

Objectives This study aimed to evaluate the risk of musculoskeletal disorders to the hand-wrist system. The American Conference of Governmental Industrial Hygienists (ACGIH) proposed threshold limit values (TLV©) based on hand activity level (HAL) and normalized peak force (PF). We validated ACGIH TLV© in OCTOPUS, a large cohort study on carpal tunnel syndrome (CTS).

Methods Industrial and service workers were followed from 2000-2003. We classified subjects with respect to action limit (AL) and TLV. Case definitions were: (i) self-reported symptoms; and (ii) combination of symptoms and positive nerve conduction studies. Poisson regression models including age, gender, body mass index, and presence of predisposing pathologies were conducted to estimate incidence rate ratios (IRR) of CTS.

Results There were 4097 eligible workers. Of these, 236 (5.8%) were non-responders, 2194 (53.6%) had a complete follow-up, 728 (17.8%) were lost after intermediate assessment, and 939 (22.9%) were lost after baseline. Among the 3860 subjects with complete information at baseline, 2599 (67.3%) were women [mean age 38.1 [standard deviation (SD) 9.5] years; mean body mass index (BMI) 23.8 (SD 3.9) kg/m^sup 2^]. ACGIH TLV© classification predicted both CTS symptoms [IRR between AL and TLV 2.43 [95% confidence interval (95% CI) 1.77-3.33]; above TLV 3.32 (95% CI 2.34-4.72)] and CTS confirmed by nerve conduction studies [IRR between AL and TLV 1.95 (95% CI 1.21-3.16); above TLV 2.70 (95% CI 1.48-4.91)].

Conclusions We found a dose-response relationship between ACGIH TLV© classification and risk of CTS. The increased risk observed for workers exposed between AL and TLV suggests that the current AL and TLV might not be sufficiently protective.

Key terms American Conference of Governmental Industrial Hygienists; biomechanical overload; CTS; hand force; industrial worker; MSD; musculoskeletal disorder; occupational exposure; repetition.

Carpal tunnel syndrome (CTS) continues to be a major cause of disability and cost to society. The prevalence of CTS in the general population has been estimated as between 1- 5% (1,2), while studies on its incidence have reported rates ranging from 0.5-3.8 per 1000 personyears (3-5). In Italy, a rate of 1.1 per 1000 person-years has been documented for surgically treated CTS (6).

Widely cited personal factors of CTS include gender, body mass index (BMI), height, marital status, familiar history, and other pathologies facilitating CTS onset (eg, rheumatoid arthritis, diabetes) (7, 8). There are a number of epidemiological studies that show a relationship between manual work (especially repetitive and forceful exertions) and CTS (9-11); however, many of these studies are cross-sectional and a causal relationship cannot therefore be concluded (9). Longitudinal studies are needed to investigate to what extent work is a primary cause of CTS.

A dose-response relationship for CTS and mechanical loads is supported by biomechanical models, laboratory studies and epidemiological studies. Early studies [eg, by Tanzer in 1959 (12)] demonstrated that certain postures of the wrist produce elevated pressure on the median nerve inside the carpal canal. Armstrong & Chaffin (13) proposed a pulley-belt model that showed the contact forces on the median nerve are related to tension in the finger flexor tendons and wrist flexion. Studies by Phalen (14) and Armstrong et al (15) showed fibrous connective tissue and thickening of the flexor synovia and the walls of arterioles inside the carpal tunnel in areas subjected to high contact stress tendon loads. Moore at al (16) showed that the tendon loads in the median nerve help explain the epidemiological findings of Silverstein et al (17) that CTS and hand-wrist tendonitis are related to repetitive work. Keir & Rempel (18) showed that deviation of the wrist from a neutral posture is associated with elevated fluid pressure inside the carpal tunnel. …

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