Mechanical behavior, wear surface morphology, and clinical performance of UHMWPE acetabular components after 10 years of implantation

The relationships between the mechanical behavior of ultra-high molecular weight polyethylene (UHMWPE) and the long-term clinical performance of acetabular component bearings remain poorly understood. During previous hip simulator validation studies, researchers have correlated the mechanical behavior and surface morphology of polymeric biomaterials with the wear performance in a hip simulator. For the present study, we sought correlations between clinical performance and quantitative metrics of the mechanical behavior and surface morphology of retrieved cups. Nine all-UHMWPE acetabular cups of the same cemented design, 32 mm head size, and manufacturer were retrieved after an average implantation time of 14.1 years (range: 11.5-16.4 years). The implants were manufactured from RCH-1000, sterilized by gamma radiation in air and implanted between 1980 and 1983. Mechanical behavior of the retrieved components was determined using the previously validated small punch test, which subjects miniature specimens to multi-axial loading conditions. Surface morphology of the retrievals was assessed using white light interferometry. No significant relationship was observed between the surface roughness measurements and patient related variables. However, statistically significant relationships were observed between the mechanical behavior determined by the small punch test and the implantation time and patient weight associated with the retrieved hip cups. These findings support the hypothesis that the mechanical behavior of UHMWPE is related, at least in part, to the clinical performance of acetabular component bearings for total hip replacement. (C) 2001 Elsevier Science B.V. All rights reserved.