title: Exclusion of patients with sequential primary total joint arthroplasties from arthroplasty outcome studies biases outcome estimates: a retrospective cohort study.
abstract: OBJECTIVE
  Total joint arthroplasty (TJA) outcome studies have largely focused on recipients of a single primary TJA, which may bias outcome estimates.
  
  
  METHODS
  This retrospective cohort study utilized health administrative databases from Ontario, Canada, to assemble a cohort that received a first primary elective hip or knee TJA for osteoarthritis (OA) between 2002 and 2009 (index TJA). Characteristics of TJA recipients at their index TJA were compared for those who did vs did not go on to receive one or more subsequent primary, elective hip/knee TJAs (multiple TJAs - yes/no) over a 2-year follow-up period. Cox proportional hazards, censored on death, was used to examine the relationship of receipt of multiple TJAs (yes/no) on rates of surgical complications for the index TJA, controlling for confounders.
  
  
  RESULTS
  Among 97,374 eligible patients, 19,856 (20.4%) received a second primary elective TJA procedure within 2 years. In bivariate analyses, recipients of multiple primary TJAs were significantly more likely than single TJA recipients to be female, younger, with fewer co-morbidities (P < 0.0001), and to experience surgical complications with the index surgery, including early revision (P < 0.0001). Controlling for patient differences, receipt of >1 primary TJAs over 2 years was independently and significantly associated with lower odds of having experienced a surgical complication following the index arthroplasty (adjusted HR 0.65, 95%CI 0.59-0.72).
  
  
  CONCLUSIONS
  One in five patients receiving their first elective primary hip or knee TJA received a second hip/knee TJA within 2 years. Our results indicate that exclusion of this large subsample of TJA recipients from TJA outcomes studies over-estimates surgical risks and may underestimate patient-reported benefits.
authors.affiliation: Division of Orthopaedics, Department of Surgery, University of Toronto, Toronto, Canada; Institute of Health Policy, Management and Evaluation, University of Toronto, Toronto, Canada. Electronic address: bheesh@rocketmail.com.
authors.forename: B
authors.initials: B
authors.lastname: Ravi
authors.forename: R
authors.initials: R
authors.lastname: Croxford
authors.forename: G
authors.initials: G
authors.lastname: Hawker
mesh_terms: D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000379:methods / Q000706:statistics & numerical data*; D019645:Arthroplasty, Replacement, Knee / Q000379:methods / Q000706:statistics & numerical data*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000601:surgery*; D020370:Osteoarthritis, Knee / Q000601:surgery*; D017063:Outcome Assessment, Health Care / Q000379:methods; D018579:Patient Selection; D016016:Proportional Hazards Models; D012086:Reoperation / Q000706:statistics & numerical data; D012189:Retrospective Studies; D015983:Selection Bias; D016896:Treatment Outcome
keywords: Arthroplasty; Bias; Joint revision; Osteoarthritis; Post-operative complications