Objectives

This paper aimed to quantify exposure-response relationships between the American Conference of Governmental Industrial Hygienists' (ACGIH) threshold limit value (TLV) for hand-activity level (HAL) and incidence of carpal tunnel syndrome (CTS).

Methods

Manufacturing and service workers previously studied by six research institutions had their data combined and re-analyzed. CTS cases were defined by symptoms and abnormal nerve conduction. Hazard ratios (HR) were calculated using proportional hazards regression after adjusting for age, gender, body mass index, and CTS predisposing conditions.

Results

The longitudinal study comprised 2751 incident-eligible workers, followed prospectively for up to 6.4 years and contributing 6243 person-years of data. Associations were found between CTS and TLV for HAL both as a continuous variable [HR 1.32 per unit, 95% confidence interval (95% CI) 1.11-1.57] and when categorized using the ACGIH action limit (AL) and TLV. Those between the AL and TLV and above the TLV had HR of 1.7 (95% CI 1.2-2.5) and 1.5 (95% CI 1.0-2.1), respectively. As independent variables (in the same adjusted model) the HR for peak force (PF) and HAL were 1.14 per unit (95% CI 1.05-1.25), and 1.04 per unit (95% CI 0.93-1.15), respectively.

Conclusion

Those with exposures above the AL were at increased risk of CTS, but there was no further increase in risk for workers above the TLV. This suggests that the current AL may not be sufficiently protective of workers. Combinations of PF and HAL are useful for predicting risk of CTS.

Background

Six research groups independently conducted prospective studies of carpal tunnel syndrome (CTS) incidence in 54 US workplaces in 10 US States. Physical exposure variables were collected by all research groups at the individual worker level. Data from these research groups were pooled to increase the exposure spectrum and statistical power.

Objective

This paper provides a detailed description of the characteristics of the pooled physical exposure variables and the source data information from the individual research studies.

Methods

Physical exposure data were inspected and prepared by each of the individual research studies according to detailed instructions provided by an exposure subcommittee of the research consortium. Descriptive analyses were performed on the pooled physical exposure data set. Correlation analyses were performed among exposure variables estimating similar exposure aspects.

Results

At baseline, there were a total of 3010 participants in the pooled physical exposure data set. Overall, the pooled data meaningfully increased the spectra of most exposure variables. The increased spectra were due to the wider range in exposure data of different jobs provided by the research studies. The correlations between variables estimating similar exposure aspects showed different patterns among data provided by the research studies.

Conclusions

The increased spectra of the physical exposure variables among the data pooled likely improved the possibility of detecting potential associations between these physical exposure variables and CTS incidence. It is also recognised that methods need to be developed for general use by all researchers for standardisation of physical exposure variable definition, data collection, processing and reduction.