The purpose of the present retrospective study was to report the clinical and radiological results of 31 total hip arthroplasties of 28 patients with bony ankylosed hip.

Conversions to cementless total hip arthroplasty between August 1983 and May 1999 were reviewed after followups ranging from 3 years 1 month to 18 years. The mean age of the patients at the time of operation was 35.0 years. The mean duration of the ankylosis was 15 years 7 months.

At the time of the last follow-up, the mean arc of flexion was 84.6 °. The mean Harris hip score improved from 47.7 to 84.9. There were no significant differences in clinical results according to the type and duration of ankylosis. Radiographs showed one acetabular loosening, six acetabular osteolysis and five femoral osteolysis. In cases of osteolysis, the average wear rate was 0.28 mm/year.

The conversion of bony ankylosed hip to a cementless total hip arthroplasty revealed a favorable outcome, and the risk of failure was found to be unrelated to the type and the duration of ankylosis. However, since some patients show excessive wear with osteolysis, polyethylene liner wear will be of critical importance in terms of long-term results.