[In-vivo wear of the slide combinations ceramics-polyethylene as opposed to metal-polyethylene].

The present study deals with long-term dimensional changes in cemented Müller-type total hip endoprostheses. Creep and wear contribute to different extents to the dimensional changes in polyethylene. The total amount of polyethylene wear is represented by the displacement of the femoral head into the socket. Within the first postoperative years, the head shifts up to a relatively high rate of about 0.5 mm per year. This rate diminishes after 5 years to an average of about 0.1 mm (ceramics) and 0.2 mm (metal) per year. Values exceeding 0.2 mm per year for the shift of the femoral head are considered to be unfavourable with regard to a probable loosening of the prosthesis. In this study we determined the orientation of the centre of the prosthetic head in relation to the wire marker of the polyethylene cup, comprising in all 369 total hip prostheses. After an average of 77 months, 96% of the prostheses with ceramic heads (n = 109) had a wear rate of less than 0.2 mm per year. Using metal heads (Protasul-2 and Protasul-10) this rate could only be measured in 71% (n = 109) of the prostheses (61.5 months). The combination ceramics-polyethylene produces half of the total amount of wear produced by metal-polyethylene. Younger patients should preferably be treated with a ceramic ballhead.