Uncemented acetabular replacement.

An uncemented Polyethylene acetabular component has been developed using a cup of conical outer configuration locked in position with the Freeman osseous peg. This cup is available in four sizes and is normally used with an uncemented femoral component. During the last 3 years 875 implants of this sort have been inserted and the results in these patients who are between 1 and 3 years post-operatively have been compared with the results in 236 replacements of a similar configuration but secured with bone cement in the usual way. The two groups have been demonstrated to be comparable in pre-operative diagnosis, age and sex. The results using the uncemented articulation are broadly the same as those using the cemented joint during the period of study but the acetabular component in 30% of the cemented joints showed a zone of demarcation between cement and bone whereas only one of the uncemented acetabular components showed similar radiological changes. The examination of the radiographs of the uncemented group suggests that the pelvic bone responds favourably to the stresses which are imposed upon it provided that the centre of the joint movement is relocated in the anatomical position, under these circumstances bone will usually build up to support the cup in a dysplastic acetabulum and in the floor of a central protrusion.