title: Biomechanical and psychosocial exposures are independent risk factors for carpal tunnel syndrome: assessment of confounding using causal diagrams.
abstract: 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.
authors.affiliation: Division of Occupational and Environmental Medicine, University of California, San Francisco, San Francisco, California, USA Department of Environmental Health Sciences, University of California Berkeley, Berkeley, California, USA.
authors.forename: Carisa
authors.initials: C
authors.lastname: Harris-Adamson
authors.affiliation: Department of Environmental Health Sciences, University of California Berkeley, Berkeley, California, USA.
authors.forename: Ellen A
authors.initials: EA
authors.lastname: Eisen
authors.affiliation: Department of Environmental Health Sciences, University of California Berkeley, Berkeley, California, USA.
authors.forename: Andreas
authors.identifier: http://orcid.org/0000-0001-7327-5361
authors.initials: A
authors.lastname: Neophytou
authors.affiliation: Center for Ergonomics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA.
authors.forename: Jay
authors.initials: J
authors.lastname: Kapellusch
authors.affiliation: Center for Ergonomics, University of Wisconsin-Milwaukee, Milwaukee, Wisconsin, USA.
authors.forename: Arun
authors.initials: A
authors.lastname: Garg
authors.affiliation: Rocky Mountain Center for Occupational and Environmental Health (RMCOEH), University of Utah, Salt Lake City, Utah, USA.
authors.forename: Kurt T
authors.initials: KT
authors.lastname: Hegmann
authors.affiliation: Rocky Mountain Center for Occupational and Environmental Health (RMCOEH), University of Utah, Salt Lake City, Utah, USA.
authors.forename: Matthew S
authors.initials: MS
authors.lastname: Thiese
authors.affiliation: Division of General Medical Science, Washington University School of Medicine, Saint Louis, Missouri, USA.
authors.forename: Ann Marie
authors.initials: AM
authors.lastname: Dale
authors.affiliation: Division of General Medical Science, Washington University School of Medicine, Saint Louis, Missouri, USA.
authors.forename: Bradley
authors.initials: B
authors.lastname: Evanoff
authors.affiliation: Washington State Department of Labor and Industries, Safety and Health Assessment and Research for Prevention (SHARP) Program, Olympia, Washington, USA.
authors.forename: Stephen
authors.initials: S
authors.lastname: Bao
authors.affiliation: Washington State Department of Labor and Industries, Safety and Health Assessment and Research for Prevention (SHARP) Program, Olympia, Washington, USA.
authors.forename: Barbara
authors.initials: B
authors.lastname: Silverstein
authors.affiliation: Department of Occupational and Environmental Health, University of Iowa, College of Public Health, Iowa City, Iowa, USA.
authors.forename: Fred
authors.initials: F
authors.lastname: Gerr
authors.affiliation: formerly with National Institute of Occupational Safety & Health, Atlanta, Georgia, USA.
authors.forename: Susan
authors.initials: S
authors.lastname: Burt
authors.affiliation: Division of Occupational and Environmental Medicine, University of California, San Francisco, San Francisco, California, USA Department of Bioengineering, University of California, Berkeley, Berkeley, California, USA.
authors.forename: David
authors.initials: D
authors.lastname: Rempel
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002349:Carpal Tunnel Syndrome / Q000453:epidemiology* / Q000209:etiology* / Q000523:psychology; D015984:Causality; D015986:Confounding Factors, Epidemiologic; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009784:Occupational Diseases / Q000453:epidemiology* / Q000209:etiology* / Q000523:psychology; D016273:Occupational Exposure / Q000009:adverse effects*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D013315:Stress, Psychological / Q000453:epidemiology / Q000209:etiology; D011795:Surveys and Questionnaires; D014481:United States; D017132:Workplace / Q000523:psychology; D055815:Young Adult
keywords: biomechanical exposure; carpal tunnel syndrome; confounding; prospective; psychosocial exposure