Uncemented acetabular cups in dysplastic and protrusio acetabuli.

Total hip arthroplasties using the Ring uncemented polyethylene to metal system were carried out in 84 hips with either protrusio or dysplasia of the acetabulum. The results of the operation, the stability and function of the acetabular implant, and radiologic changes in the medial wall of the acetabulum in the protrusio hips were assessed over a two- to five-year follow-up period. Annual assessment over the follow-up period showed that an excellent functional result was achieved in all patients. Six of the eight hips with severe protrusio showed an increase in the thickness of the medial acetabular wall one year from the time of operation. Lack of bony cover over the lateral surface of the acetabular cup in the dysplastic hips did not have any adverse effect on the stability and function of these hips.