Mechanical properties and fatigue performance of crosslinked polyethylene in total knee applications

Abstract

Abstract There has been increasing concern about the structural fatigue resistance of crosslinked ultra-high molecular weight polyethylene (UHMWPE) components due to deterioration of certain mechanical properties. However, due to the lack of clear correlation between specific mechanical properties and clinical performance, these concerns remain theoretical. To mimic clinical use and thus evaluate the potential risks and benefits of various crosslinked polyethylene materials for knee and hip bearing applications, two clinically relevant, worst-case scenarios were simulated on functional devices. In the first scenario, cemented all-polyethylene patellar components were tested under simulated stair-climbing conditions with femoral component rotational malalignment. In the second scenario, thin, metal-backed, polyethylene acetabular liners were tested in a hip joint simulator under rim-loading conditions. To compare the mechanical properties of these materials, various types of crosslinked UHMWPE were prepared according to published process descriptions of commercial materials. These materials were then subjected to standardized tensile strength testing. The results indicated that material performance was more significantly affected by the postirradiation thermal treatment history than by the total dose of irradiation. Remelting following irradiation led to catastrophic fractures of the pegs of the rotationally malaligned patellar components and the rim-loaded liners. The ultimate tensile strength appeared to be the key mechanical property that correlated with the structural fatigue performance of crosslinked polyethylene materials, whereas tensile elongation within the 250 to 400% range had no effect on structural integrity.