In-depth morphological changes and embrittlement near the wear surface of UHMWPE inserts from uncemented hip systems

Polyethylene hip cups were examined with optical and electron microscopy af ter permanganic etching, a technique that allows in-depth examination from the articulating surface downward. In addition to wear features present on the surface, novel defects were revealed in implants after retrieval from t he body but not in as-manufactured controls. They were incipient cracks tha t indicated the existence of an embrittled layer extending 10 mum or more i nto the implant from the wear surface after exposure to the body environmen t. The lengths of the cracks, which were perpendicular to the tensile stres ses responsible for their formation, were mostly more or less parallel to t he wear surface. The embrittlement and cracking revealed are probably major contributors to the wear of polyethylene implants in the body. Poor partic le consolidation may be a contributory factor, but it was not observed to b e the primary cause of implant wear within the body. (C) 2001 John Wiley & Sons, Inc.