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 w eight polyethylene (UHMWPE) and the long-term clinical performance of aceta bular component bearings remain poorly understood. During previous hip simu lator validation studies, researchers have correlated the mechanical behavi or and surface morphology of polymeric biomaterials with the wear performan ce in a hip simulator. For the present study, we sought correlations betwee n clinical performance and quantitative metrics of the mechanical behavior and surface morphology of retrieved cups. Nine all-UHMWPE acetabular cups o f the same cemented design, 32 mm head size, and manufacturer were retrieve d 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 radiati on in air and implanted between 1980 and 1983. Mechanical behavior of the r etrieved components was determined using the previously validated small pun ch test, which subjects miniature specimens to multi-axial loading conditio ns. Surface morphology of the retrievals was assessed using white light int erferometry. No significant relationship was observed between the surface r oughness measurements and patient related variables. However, statistically significant relationships were observed between the mechanical behavior de termined by the small punch test and the implantation time and patient weig ht associated with the retrieved hip cups. These findings support the hypot hesis 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.