In vivo and in vitro surface changes in a highly cross-linked polyethylene

Highly cross-linked, ultrahigh-molecular-weight polyethylenes (UHMWPEs) were developed to reduce UHMWPE wear in arthroplasty. These UHMWPEs have manifested an improvement in the wear resistance. Examination of the first retrievals revealed surface features not usually observed on conventional retrievals. A flattening of the machining marks is evident, together with the presence of ripples with microfissures. These ripples were investigated in vitro and on retrievals having a follow-up of up to 15 months. The examinations of all specimens showed that the ripples may be described as folds with microcracks. The depth of the microcracks extended to a maximum of 5 microm and is independent of the mode of loading (up to 27 million cycles). Because of the extreme wear resistance of these UHMWPEs, the folds accumulate on the surface of components.