title: Polyethylene thickness is a risk factor for wear necessitating insert exchange.
abstract: OBJECTIVE
  The aim of this observational study was to investigate the optimal minimal polyethylene (PE) thickness in total knee arthroplasty (TKA) and identify other risk factors associated with revision of the insert due to wear.
  
  
  METHODS
  A total of 84 TKA were followed for 11-16 years. All patients received the same prosthesis design (Interax; Howmedica/ Stryker) with halfbearings: separate PE-inserts medially and laterally. Statistical analysis comprised Cox-regression to correct for confounding.
  
  
  RESULTS
  Eight knees (9.5%) had been revised due to thinning inserts and an additional patient is scheduled for revision. PE thickness, diagnosis, BMI and weight are risk factors for insert exchange. For each millimetre decrease in PE thickness, the risk of insert exchange increases 3.0 times, which remains after correction for age, gender, weight, diagnosis and femoral-tibial angle. Insert exchange was 4.73 times more likely in OA-patients compared to RA-patients. For every unit increase in BMI and weight the risk for insert exchange increases 1.40 times and 1.14 times, respectively.
  
  
  CONCLUSIONS
  In conclusion we therefore advise against the use of thin PE inserts in modular TKA and recommend PE inserts with a minimal 8-mm thickness.
authors: Department of Orthopaedics, Leiden University Medical Center, Albinusdreef 2, P.O. Box 9600, Postzone J-11-S, 2300 RC, Leiden, The Netherlands. b.g.c.w.pijls@lumc.nl
authors: Bart G
authors: BG
authors: Pijls
authors: Henrica M J
authors: HM
authors: Van der Linden-Van der Zwaag
authors: Rob G H H
authors: RG
authors: Nelissen
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation / Q000379:methods*; D000075202:Contraindications; D005260:Female; D006801:Humans; D007720:Knee Prosthesis / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D020959:Polyethylene; D011474:Prosthesis Design; D011475:Prosthesis Failure / Q000209:etiology*; D012086:Reoperation; D012307:Risk Factors
chemical_list: D020959:Polyethylene