Retrieved total hip prostheses: part II. Wear behaviour and structural changes.

Polyethylene cups and femoral heads of retrieved total hip prostheses (Charnley 22 mm stainless steel ball, Bioceram 28 mm alumina ball and Müller 32 mm Co-Cr-Mo alloy ball) were observed by the naked-eye and scanning electron microscopy. Cross-linked cups irradiated with gamma radiation in heavy high doses of 100 Mrad were included. On the weight-bearing surface of the cups non-gamma irradiated, carpet-like conspicuous fine fibres, scratches and fine crevices for the 22 mm ball, scale-like with rough and fine crevices for the 28 mm ball, and scale-like structures and many scratches for the 32 mm ball, were observed, mainly. On the whole, the number of crevices for the 32 mm ball was fewer than that for the 22 and 28 mm balls. The weight-bearing areas of the gamma-irradiated cups presented a clearly outlined pattern, irregularly lined with smooth ripples of about 0.1 microm. The scratching, flaking and delamination, characteristic of non-gamma irradiated polyethylene, were not observed at all. These findings indicate that wear is very small for gamma-irradiated polyethylene. For references, the weight-bearing surfaces of retrieved total knee prostheses were compared.