RETRIEVED TOTAL HIP PROSTHESES - PART II - WEAR BEHAVIOR 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 Muller 32 mm Co-Cr-Mo alloy ball) were observed by the naked-eye and s canning electron microscopy. Cross-linked cups irradiated with gamma r adiation in heavy high doses of 100 Mrad were included. On the weight- bearing surface of the cups non-gamma irradiated, carpet-like conspicu ous 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, mainl y. On the whole, the number of crevices for the 32 mm ball was fewer t han that for the 22 and 28 mm balls. The weight-bearing areas of the g amma-irradiated cups presented a clearly outlined pattern, irregularly lined with smooth ripples of about 0.1 mu m. The scratching, flaking and delamination, characteristic of non-gamma irradiated polyethylene, were not observed at all. These findings indicate that wear is very s mall for gamma-irradiated polyethylene. For references, the weight-bea ring surfaces of retrieved total knee prostheses were compared.