title: Wear of contemporary total knee replacements--a knee simulator study of six current designs.
abstract: BACKGROUND
  Compared to conventional ultra-high molecular weight polyethylene (UHMWPE), crosslinked polyethylene showed significantly reduced wear rate in hip simulation and early prospective-randomized clinical studies. The crosslinking process can reduce the mechanical properties of UHMWPE, particularly the fatigue strength. UHMWPE fatigue occurs more frequently in the knee joint than in the hip joint due to its higher contact stresses and there is therefore an increased concern of mechanical failure. Therefore, the purpose of this study was to determine the wear behaviour and the wear rates of different current knee designs and bearing materials.
  
  
  METHODS
  In a knee-joint-simulator four kinds of crosslinked polyethylene (one produced by sequential irradiation and annealing process, three by different remelting processes, including fixed- and mobile-bearing-types) and two UHMWPE- (fixed- and mobile-bearing) inserts were tested with the appropriate femoral and tibial component recommended from the manufacturer.
  
  
  RESULTS
  All types of crosslinked polyethylene produced statistically significant (P<0.05) lower wear rates than the conventional UHMWPEs without any traces of fatigue. There were no differences in the wear rates between fixed-and mobile-bearings (crosslinked polyethylenes and UHMWPEs; P>0.05). The crosslinked polyethylene tibial inserts manufactured by sequential irradiation and annealing (X3) combined with the Scorpio-knee-design had the lowest wear rates (P<0.05) overall.
  
  
  CONCLUSIONS
  Fixed- as well as mobile-bearing crosslinked polyethylene tibial inserts are suitable for total knee arthroplasty and showed reduced wear rates compared with conventional UHMWPE. The combination of the fixed-bearing Scorpio-knee-design with a sequential irradiated and annealed crosslinked polyethylene tibial insert (X3) seems to have an advantage in wear generation compared with other fixed- and mobile-bearing knee designs.
authors.affiliation: Orthopaedic Department, Grosshadern Medical Center, University of Munich, Marchioninistr. 15, 81377 Munich, Germany. sandra.utzschneider@med.uni-muenchen.de
authors.forename: Sandra
authors.initials: S
authors.lastname: Utzschneider
authors.forename: Norbert
authors.initials: N
authors.lastname: Harrasser
authors.forename: Christian
authors.initials: C
authors.lastname: Schroeder
authors.forename: Farhad
authors.initials: F
authors.lastname: Mazoochian
authors.forename: Volkmar
authors.initials: V
authors.lastname: Jansson
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D007720:Knee Prosthesis; D008422:Materials Testing; D011095:Polyethylenes
chemical_list: D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene