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Biomechanical and psychosocial exposures are independent risk factors for carpal tunnel syndrome: assessment of confounding using causal diagrams
  1. Carisa Harris-Adamson1,2,
  2. Ellen A Eisen2,
  3. Andreas Neophytou2,
  4. Jay Kapellusch3,
  5. Arun Garg3,
  6. Kurt T Hegmann4,
  7. Matthew S Thiese4,
  8. Ann Marie Dale5,
  9. Bradley Evanoff5,
  10. Stephen Bao6,
  11. Barbara Silverstein6,
  12. Fred Gerr7,
  13. Susan Burt8,
  14. David Rempel1,9
  1. 1Division of Occupational and Environmental Medicine, University of California, San Francisco, San Francisco, California, USA
  2. 2Department of Environmental Health Sciences, University of California Berkeley, Berkeley, California, USA
  3. 3Center for Ergonomics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA
  4. 4Rocky Mountain Center for Occupational and Environmental Health (RMCOEH), University of Utah, Salt Lake City, Utah, USA
  5. 5Division of General Medical Science, Washington University School of Medicine, Saint Louis, Missouri, USA
  6. 6Washington State Department of Labor and Industries, Safety and Health Assessment and Research for Prevention (SHARP) Program, Olympia, Washington, USA
  7. 7Department of Occupational and Environmental Health, University of Iowa, College of Public Health, Iowa City, Iowa, USA
  8. 8formerly with National Institute of Occupational Safety & Health, Atlanta, Georgia, USA
  9. 9Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA
  1. Correspondence to Dr Carisa Harris-Adamson, University of California, San Francisco, 1301 South 46th Street, Bldg 163, Richmond, CA 94804, USA; carisa.harris-adamson{at}


Background Between 2001 and 2010, six research groups conducted coordinated prospective studies of carpal tunnel syndrome (CTS) incidence among US workers from various industries to estimate exposure–response relationships.

Objective This analysis examined the presence and magnitude of confounding between biomechanical and workplace psychosocial factors and incidence of dominant-hand CTS.

Methods 1605 participants, without CTS at enrolment, were followed for up to 3.5 years (2471 person-years). Demographic information, medical history and workplace psychosocial stress measures were collected at baseline. Individual workplace biomechanical exposures were collected for each task and combined across the workweek using time-weighted averaging (TWA). CTS case criteria were based on symptoms and results of electrophysiological testing. HRs were estimated with Cox proportional hazard models. Confounding was assessed using causal diagrams and an empirical criterion of 10% or greater change in effect estimate magnitude.

Results There were 109 incident CTS cases (IR=4.41/100 person-years; 6.7% cumulative incidence). The relationships between CTS and forceful repetition rate, % time forceful hand exertion and the Threshold Limit Value for Hand Activity Level (TLV-HAL) were slightly confounded by decision latitude with effect estimates being attenuated towards the null (10–14% change) after adjustment. The risk of CTS among participants reporting high job strain was attenuated towards the null by 14% after adjusting for the HAL Scale or the % time forceful hand exertions.

Conclusions Although attenuation of the relationships between CTS and some biomechanical and work psychosocial exposures was observed after adjusting for confounding, the magnitudes were small and confirmed biomechanical and work psychosocial exposures as independent risk factors for incident CTS.

  • prospective
  • carpal tunnel syndrome
  • psychosocial exposure
  • biomechanical exposure
  • confounding

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  • Contributors CH-A was the primary data analyst and author of this paper. She received technical advice from EAE and AN. Other authors were integral in designing studies at their respective universities and collecting data. As part of the Upper Extremity MSD Consortium, all authors contributed to the pooling and analysis of data, as well as summarising findings in this and other papers.

  • Funding Centers for Disease Control/National Institute for Occupational Safety and Health (R01OH009712).

  • Competing interests None declared.

  • Ethics approval University of California, San Francisco.

  • Provenance and peer review Not commissioned; externally peer reviewed.