title: Influence of body mass index on revision rates after primary total knee arthroplasty.
abstract: OBJECTIVE
  Studies demonstrate that revision rates after primary total knee arthroplasty (TKA) tend to be higher in obese patients. However, the existence of a body mass index (BMI) threshold remains unexplored.
  
  
  METHODS
  We conducted a prospective cohort study of 2442 primary TKAs in 2035 patients (69.1 % women; mean age 72 years; mean follow-up 93 months, range 38-203). We evaluated the influence of BMI in five categories on all-cause revision after TKA using incidence rates (IR), hazard ratios (HR), and Kaplan-Meier survival analysis. Adjustment for baseline imbalances was performed using Cox regression analysis.
  
  
  RESULTS
  Over the study period, 71 revisions occurred. Revision rates were 3.2 cases/1000 patient-years for patients of normal weight, 3.4/1000 for overweight patients and 3.0/1000 for patients classified as obese class I. At BMI ≥ 35, a significant increase in revision was noted. Comparing BMI ≥ 35 vs. < 35, there were 6.4 vs. 3.2 /1000. Crude HR was 2.0 [95 % confidence interval (CI) 1.2-3.3, p = 0.009], and the adjusted HR was 2.1 (95 % CI 1.2-3.6, p = 0.008).
  
  
  CONCLUSIONS
  All-cause revision rates after primary TKA doubled in patients with a BMI of 35 but were similar in those with a BMI <35.
authors.affiliation: Division of Orthopaedics and Trauma Surgery, Geneva University Hospitals, 4 rue Gabrielle-Perret-Gentil, 1211, Genève 14, Switzerland. matthieu.zingg@hcuge.ch.
authors.forename: Matthieu
authors.identifier: http://orcid.org/0000-0002-7937-2960
authors.initials: M
authors.lastname: Zingg
authors.affiliation: Division of Orthopaedics and Trauma Surgery, Geneva University Hospitals, 4 rue Gabrielle-Perret-Gentil, 1211, Genève 14, Switzerland.
authors.forename: Hermès H
authors.initials: HH
authors.lastname: Miozzari
authors.affiliation: Division of Orthopaedics and Trauma Surgery, Geneva University Hospitals, 4 rue Gabrielle-Perret-Gentil, 1211, Genève 14, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Fritschy
authors.affiliation: Division of Orthopaedics and Trauma Surgery, Geneva University Hospitals, 4 rue Gabrielle-Perret-Gentil, 1211, Genève 14, Switzerland.
authors.forename: Pierre
authors.initials: P
authors.lastname: Hoffmeyer
authors.affiliation: Division of Orthopaedics and Trauma Surgery, Geneva University Hospitals, 4 rue Gabrielle-Perret-Gentil, 1211, Genève 14, Switzerland.
authors.forename: Anne
authors.initials: A
authors.lastname: Lübbeke
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D015992:Body Mass Index; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000601:surgery*; D050177:Overweight / Q000150:complications / Q000601:surgery*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012044:Regression Analysis; D012086:Reoperation
keywords: Body mass index (BMI); Obesity; Revision; Threshold; Total knee arthroplasty (TKA)