FACTORS INFLUENCING INITIAL STABILITY OF UNCEMENTED 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 withou t screws, to determine the most suitable anchoring, cup design and opt imal surface structure. Six acetabular components with varying cup geo metry and surface configuration were implanted with a 2 mm press-fit i nto polyethylene pelves. In the first set of trials, the uncemented cu ps with two peripheral screws were tested under an axial load of 240 k g (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 achi eved the high initial stability of the cemented reference cups. It was not possible to determine an optimal cup design. In this study, titan ium plasma-spray-coated cups achieved the best results. Stability is d etermined only in part by the configuration of the prosthesis. Of equa l 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.