title: The association between a lifetime history of work-related low back injury and future low back pain: a population-based cohort study.
abstract: OBJECTIVE
  This population-based cohort study investigated the association between a lifetime history of a work-related low back injury, in those who had recovered to have no or mild low back pain, and the development of troublesome low back pain (LBP). A secondary analysis explored the possible effects of misclassification of the exposure by examining the association between a lifetime history of having taken time off work or performed light duties at work because of a work-related low back injury. Current evidence from cross-sectional studies suggests that individuals with a history of a work-related low back injury are more likely to experience future LBP. However, there is a need to examine this association prospectively in a large population-based cohort with adequate control of known confounders.
  
  
  METHODS
  We formed a cohort of 810 randomly sampled Saskatchewan adults with no or mild LBP in September 1995. At baseline, participants were asked if they had ever injured their low back at work. The secondary analysis asked if they had ever had to take time off work or perform light duties at work because of a work-related low back injury. Prospective follow-up 6 and 12 months later, asked about the presence of troublesome LBP (grade II-IV) on the Chronic Pain Grade Questionnaire. Multivariable Cox proportional hazards regression analysis was used to estimate these associations while controlling for known confounders.
  
  
  RESULTS
  The proportion followed up at 6 and 12 months was 76 and 65%, respectively. We found an association between a history of work-related low back injury and the onset of troublesome LBP after controlling for gender (adjusted HRR = 2.24; 95% CI 1.41-3.56). When covariates that may also be mediators of the association were added to the model, the effect estimate was attenuated (adjusted HRR = 1.37; 95% CI 1.41-3.56). We found a similar association between a lifetime history of having taken time off work or had to work light duties at work because of a work-related low back injury, adjusted for gender (adjusted HRR = 2.31; 95% CI 1.39-3.85) which was also diluted by the further adjustment for covariates that may also be mediators of the association (adjusted HRR = 1.80; 95% CI 1.08-3.01).
  
  
  CONCLUSIONS
  Our study suggests that a history of work-related low back injury or taking time off work or having to perform light duties at work due to a work-related low back injury may be a risk factor for the development of troublesome LBP. Residual confounding may account for some of the observed associations, but this was less in the group who took time off work or had to work light duties due to a work-related low back injury.
authors.affiliation: Department of Graduate Education and Research, Canadian Memorial Chiropractic College, Toronto, ON, Canada. pnolet@rogers.com.|Wellington Orthopaedic and Rehabilitation Associates, 86 Dawson Rd., Unit 3, Guelph, ON, N1H 1A8, Canada. pnolet@rogers.com.
authors.forename: Paul S
authors.identifier: http://orcid.org/0000-0002-3614-225X
authors.initials: PS
authors.lastname: Nolet
authors.affiliation: Department of Health Sciences, Lakehead University, Thunder Bay, ON, Canada.|Division of Human Sciences, Northern Ontario School of Medicine, Lakehead University, Thunder Bay, ON, Canada.|Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Ontario, Canada.|Institute for Work and Health, Toronto, ON, Canada.
authors.forename: Vicki L
authors.initials: VL
authors.lastname: Kristman
authors.affiliation: Department of Graduate Education and Research, Canadian Memorial Chiropractic College, Toronto, ON, Canada.|Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Ontario, Canada.|Faculty of Health Sciences, University of Ontario Institute of Technology, Oshawa, ON, Canada.|UOIT-CMCC Centre for the Study of Disability Prevention and Rehabilitation, Toronto, ON, Canada.
authors.forename: Pierre
authors.initials: P
authors.lastname: Côté
authors.affiliation: Department of Public Health Sciences, and the Alberta Centre for Injury Control and Research, School of Public Health, University of Alberta, Edmonton, AB, Canada.
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Carroll
authors.affiliation: Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Ontario, Canada.|Division of Health Care and Outcomes Research, Toronto Western Research Institute, University Health Network, Toronto, ON, Canada.
authors.forename: Cesar A
authors.initials: CA
authors.lastname: Hincapié
authors.affiliation: Department of Health Sciences, Lakehead University, Thunder Bay, ON, Canada.|Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Ontario, Canada.|Department of Sport Science and Clinical Biomechanics Faculty of Health, University of Southern Denmark, Odense, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: David Cassidy
mesh_terms: D000328:Adult; D019567:Back Injuries / Q000453:epidemiology*; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000453:epidemiology*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D060051:Occupational Injuries / Q000453:epidemiology*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012307:Risk Factors; D012525:Saskatchewan / Q000453:epidemiology; D011795:Surveys and Questionnaires; D013995:Time
keywords: Cohort studies; Low back pain; Occupational injuries; Risk factors