title: The John Insall Award: no functional advantage of a mobile bearing posterior stabilized TKA.
abstract: BACKGROUND
  Mobile bearing (MB) total knee design has been advocated as a means to enhance the functional characteristics and decrease the wear rates of condylar total knee arthroplasty (TKA). However, it is unclear if these designs achieve these goals.
  
  
  OBJECTIVE
  We asked whether function of patients or survivorship would be greater or complications would be lesser in groups of patients with MB compared with fixed bearing (FB) TKA. We also sought to describe retrieval findings.
  
  
  METHODS
  We randomized 507 primary TKAs in 416 eligible patients to receive MB (n = 252) or FB (n = 255) devices from November 2001 to August 2007 (Investigational Device Exemption G000180, ClinicalTrials.gov registration number NCT00946075). Patients were blinded to treatment allocation. WOMAC Index, SF-12 Health Survey, knee range of motion, and Knee Society scores were collected and compared preoperatively and at 6, 12, and 24 months postoperatively. We recorded device failures and complications until October 2009. Kaplan-Meier survivorship was compared using the log rank test. Twelve retrieved MB devices underwent pathologic analysis. The minimum postoperative time was 2.2 years (mean, 5.9 years; range, 2.2-7.9 years).
  
  
  RESULTS
  We found no differences in mean clinical assessment scores or mean score changes from baseline at any postoperative interval through 2 postoperative years. Nineteen of the 252 MB and 13 of the 255 FB knees had undergone revision of any component. Estimated survival at 6 postoperative years was similar for the two devices: 90.1% (95% confidence interval [CI], 84.1-93.9) for MB and 94.2% (95% CI, 90.1-96.6) for FB. Two MB and no FB tibial components were revised for loosening. There was one case of MB insert dislocation. Retrieved MB devices demonstrated no unexpected wear or mechanical device failures.
  
  
  CONCLUSIONS
  We found no evidence of functional advantage of the MB design. Survivorship was similar, although the study is limited by short duration of followup.
authors: Athens Orthopedic Clinic, PA, 1765 Old West Broad Street, Building 2, Suite 200, Athens, GA 30606, USA. authors@aocfoundation.org
authors: Ormonde M
authors: OM
authors: Mahoney
authors: Tracy L
authors: TL
authors: Kinsey
authors: Theresa J
authors: TJ
authors: D'Errico
authors: Jianhua
authors: J
authors: Shen
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000379:methods* / Q000534:rehabilitation; D001363:Awards and Prizes; D016001:Confidence Intervals; D005260:Female; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000601:surgery*; D010147:Pain Measurement; D018579:Patient Selection; D011182:Postoperative Care / Q000379:methods; D011474:Prosthesis Design; D011475:Prosthesis Failure; D016059:Range of Motion, Articular / Q000502:physiology*; D018570:Risk Assessment; D012737:Sex Factors; D018709:Statistics, Nonparametric; D016896:Treatment Outcome; D016474:Weight-Bearing