title: Effect of Body Mass Index on Reoperation and Complications After Total Knee Arthroplasty.
abstract: BACKGROUND
  High body mass index (BMI) is associated with increased rates of complications after total knee arthroplasty. To date, to our knowledge, studies have examined risk as a dichotomous variable using specific BMI thresholds. The purpose of this investigation was to quantify implant survival and the risk of common complications after total knee arthroplasty using BMI as a continuous variable.
  
  
  METHODS
  Using prospectively collected data from our institutional total joint registry, we analyzed 22,289 consecutive knees, in 16,136 patients, treated with primary total knee arthroplasty from 1985 to 2012. The mean BMI of these patients at the time of the surgical procedure was 31.3 kg/m (range, 11 to 69 kg/m). The Kaplan-Meier survival method was used to estimate survivorship, reoperations, and common complications, with associations of outcomes assessed using a Cox regression model.
  
  
  RESULTS
  Utilizing smoothing spline parameterization, we found that reoperation (p < 0.001) and implant revision or removal rates (p < 0.001) increased with increasing BMI after total knee arthroplasty. Increasing BMI also was associated with increased rates of wound infection (hazard ratio [HR], 1.07; p < 0.001) and deep infection (HR, 1.08; p < 0.001) per unit of BMI over 35 kg/m. A BMI of 35 to 40 kg/m was associated with a higher rate of implant revision for aseptic loosening (p < 0.001) and for polyethylene wear (p < 0.001) compared with a BMI of 18 to 24.99 kg/m. There was no correlation between BMI and risk of venous thromboembolism, tibiofemoral instability, or need for knee manipulation.
  
  
  CONCLUSIONS
  The rates of reoperation, implant revision or removal, and many common complications after total knee arthroplasty were strongly associated with BMI.
  
  
  METHODS
  Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: 1Departments of Orthopedic Surgery (E.R.W., A.F.K., and D.J.B.) and Biostatistics and Health Sciences Research (K.F. and W.S.H.), Mayo Clinic, Rochester, Minnesota.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Wagner
authors.forename: Atul F
authors.initials: AF
authors.lastname: Kamath
authors.forename: Kristin
authors.initials: K
authors.lastname: Fruth
authors.forename: William S
authors.initials: WS
authors.lastname: Harmsen
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Berry
mesh_terms: D000328:Adult; D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D015992:Body Mass Index; D005260:Female; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D011183:Postoperative Complications / Q000601:surgery; D011475:Prosthesis Failure; D016459:Prosthesis-Related Infections / Q000209:etiology / Q000601:surgery*; D012086:Reoperation; D012189:Retrospective Studies; D013530:Surgical Wound Infection / Q000209:etiology / Q000601:surgery*