Degradation of mechanical properties of UHMWPE acetabular liners following long-term implantation.

We tested the hypothesis that the mechanical and chemical behavior of gamma radiation-sterilized ultrahigh-molecular-weight polyethylene (UHMWPE) changes after implantation. Relationships between the mechanical behavior and oxidation index were explored in a cohort of 16 consecutive traceable Hexloc acetabular components (Biomet, Warsaw, IN) that were machined from extruded, stearate-containing UHMWPE and gamma sterilized in air. Shelf aging time (average, 0.4 years) and implantation time (average, 11.5 years) were determined for all 16 inserts. The retrieved liners exhibited significant mechanical degradation, which was most severe in the unloaded surface regions. Analysis of the Fourier transform infrared spectroscopy data revealed a significant association between the oxidation index and mechanical degradation of the UHMWPE. The results of this study strongly support the hypothesis that the degradation of mechanical properties for the liners occurred during implantation.