The Strain Index (SI) and Threshold Limit Value (TLV) for Hand Activity Level (HAL): risk of carpal tunnelsyndrome (CTS) in a prospective cohort

Abstract

A cohort of 536 workers was enrolled from 10 diverse manufacturing facilities and was followed monthly for six years. Job physical exposures were individually measured. Worker demographics, medical history, psychosocial factors, current musculoskeletal disorders (MSDs) and nerve conduction studies (NCS) were obtained. Point and lifetime prevalence of carpal tunnel syndrome (CTS) at baseline (symptoms + abnormal NCS) were 10.3% and 19.8%. During follow-up, there were 35 new CTS cases (left, right or both hands). Factors predicting development of CTS included: job physical exposure (American conference of governmental industrial hygienists Threshold Limit Value (ACGIH TLV) for Hand Activity Level (HAL) and the Strain Index (SI)), age, BMI, other MSDs, inflammatory arthritis, gardening outside of work and feelings of depression. In the adjusted models, the TLV for HAL and the SI were both significant per unit increase in exposure with hazard ratios (HR) increasing up to a maximum of 5.4 (p = 0.05) and 5.3 (p = 0.03), respectively; however, similar to other reports, both suggested lower risk at higher exposures. Data suggest that the TLV for HAL and the SI are useful metrics for estimating exposure to biomechanical stressors.

Practitioner Summary: This study was conducted to determine how well the TLV for HAL and the SI predict risk of CTS using a prospective cohort design with survival analysis. Both the TLV for HAL and the SI were found to predict risk of CTS when adjusted for relevant covariates.

Keywords:

• epidemiology
• ergonomics
• cohort
• carpal tunnel syndrome
• Strain Index
• TLV for HAL

Acknowledgements

The authors also wish to acknowledge the major contributions of the subjects and employers who allowed this team to measure and assess them for several years of their lives. The authors wish to recognise the contributions of theresearch team as follows:

University of Wisconsin-Milwaukee:

James C. Foster, MD, MPH; David L. Drury, MD, MPH; Suzanna Tomich, MS, CPE, OTR; Gail Groth, MS, OTR; Karen Wahlgren, MS, OTR; Melissa Lemke, MS Jessica Gin, MS; Prithima Reddy Mosaly, PhD; Vivek Kishore, MS; Priyank Gupta, MS; Meenu Sagar, BS; Christopher Hoge, BA; and Bridget Fletcher, BS

University of Utah:

Matthew S. Thiese, PhD, MSPH; Andrew Merryweather, PhD; Richard Sesek, PhD, CSP, MPH; Xiaoming Sheng, PhD; Richard Kendall, DO; Donald Bloswick, PhD, PE, CPE; Eric Wood, MD, MPH; Hannah Edwards, MD, MPH; Jeremy Biggs, MD, MSPH; William Mecham, MS, CPE, CSP; Ulrike Ott, MS; Steven J. Oostema, MS; Riann Robbins, MS; Atim Effiong, MS; and Richard Holubkov, PhD.

Medical College of Wisconsin

Kevin White, MD;

Texas A&M University

J. Steven Moore, MD, MPH

This study was funded, in part, by grants from the National Institute for Occupational Safety and Health (NIOSH/CDC), 1 U 01 OH007917-01 and NIOSH Education and Research Center training grant T42/CCT810426-10.