Polyethylene Wear Debris From a Knee Simulator Model: Effect of Crosslinking and Counterface Material

INTRODUCION: Improved wear resistance of crosslinked UHMWPE has been well demonstrated in both hip and knee [1-4]. A reduction of 70% can be shown in knee simulators from conventional crosslinked tibial inserts (CXPE) gamma-irradiated at 3.5Mrad to 7Mrad highly crosslinked inserts (HXPE). Hip simulator models indicated that debris size decreased with increased crosslinking [5]. In the knee it has been suggested that ceramic femoral condyles also reduced UHMWPE wear compared to CoCr [4,6]. Both alumina and zirconia condyles have been used in Japan (but not approved in USA). The expectation with use of both HXPE and ceramic condyles was that the polyethylene wear rate would be exceedingly low. Hence, even with small volumes of wear an adequate quantity of particles can be easily obtained for analysis. Therefore, an “un-measurable” weight change in the gravimetric wear estimation does not signify zero wear or an insufficient sample size of particles. This prompted some to develop advanced techniques in wearrate estimation employing wear debris [8]. . However, little is known about these combined effects on wear debris production. It seemed likely that analysis of wear debris would be a useful adjunct for examining the combined wear effects of HXPE and zirconia condyles. Therefore, the objective of this study was to determine how 1) increased crosslinking from 3.5 to 7Mrad and 2) counterface material (zirconia ceramic versus CoCr femoral condyles) influenced the wear debris morphology in a knee simulator model.