Patients with longstanding hip fusion are predisposed to symptomatic degenerative changes of the lumbar spine, ipsilateral knee and contralateral hip¹. In such patients, conversion of hip arthrodesis to hip replacement can provide relief of such symptoms^{2 – 4}. However, this is a technically demanding procedure associated with higher complication and failure rates than routine total hip replacement.

The aim of this study was to determine the functional results and complications in patients undergoing hip fusion conversion to total hip replacement, performed or supervised by a single surgeon.

Twenty-eight hip fusions were converted between 1996 and 2016. Mean follow up was 7 years (3 to 18 years). The reasons for arthrodesis were trauma 11, septic arthritis 10, and dysplasia 7. The mean age at conversion was 52.4 years (26 to 77).

A trochanteric osteotomy was performed in all hips. Uncemented components were used. A constrained liner was used in 7 hips. Heterotopic ossification prophylaxis was not used in this series.

HHS improved a mean of 27 points (37.4 pre-op to 64.3 post-op). A cane was used in 30% of patients before conversion and 80% after.

Heterotopic ossification occurred in 12 (42.9%) hips. There was 2 peroneal nerve injuries, 1 dislocation, 1 GT non-union and 1 infection.

There have been 5 revisions; 2 for aseptic loosening, 1 for infection, 1 for recurrent dislocation and 1 for leg length discrepancy.

Conversion of hip fusion to hip replacement carries an increased risk of heterotopic ossification and neurological injury. We advise prophylaxis against heterotropic ossification. When there is concern about hip stability we suggest that the use of a constrained acetabular liner is considered. Despite the potential for complications, this procedure had a high success rate and was effective in restoring hip function.