[Factors affecting the primary stability of acetabular components. An in vitro study].

The aim of the present study was to investigate the micromotion under physiological loading of various acetabular components with and without screws, to determine the most suitable anchoring, cup design and optimal surface structure. Six acetabular components with varying cup geometry and surface configuration were implanted with a 2 mm press-fit into polyethylene pelves. In the first set of trials, the uncemented cups with two peripheral screws were tested under an axial load of 240 kg (2,354 N). The screws were then removed and the cups, held in place only by press fit, were tested again. None of the uncemented cups achieved the high initial stability of the cemented reference cups. It was not possible to determine an optimal cup design. In this study, titanium plasma-spray-coated cups achieved the best results. Stability is determined only in part by the configuration of the prosthesis. Of equal importance is the quality of the preparation of the cup bed. The use of screws cannot be unreservedly recommended. With a good press fit, the use of screws enhances stability only minimally.