Heterotopic ossification (HO) of the hip after injury to the central nervous system can lead to joint ankylosis. Surgery is usually delayed to avoid recurrence, even if the functional status is affected. We report a consecutive series of patients with HO of the hip after injury to the central nervous system who required surgery in a single, specialised tertiary referral unit. As was usual practice, they all underwent CT to determine the location of the HO and to evaluate the density of the femoral head and articular surface. The outcome of surgery was correlated with the pre-, peri- and post-operative findings. In all, 183 hips (143 patients) were included of which 70 were ankylosed. A total of 25 peri-operative fractures of the femoral neck occurred, all of which arose in patients with ankylosed hips and were associated with intra-articular lesions in 18 and severe osteopenia of the femoral head in seven. All the intra-articular lesions were predicted by CT and strongly associated with post-operative complications. The loss of the range of movement before ankylosis is a more important factor than the maturity of the HO in deciding the timing of surgery. Early surgical intervention minimises the development of intra-articular pathology, osteoporosis and the resultant complications without increasing the risk of recurrence of HO.
At more than 15 years follow-up, the mean PMA hip functional score was 17.1. 66% of the hips was A, 4% were B and 30% were C according to the Charnley’s score. Of the 164 hips in the patients who had survived at least 15 years, 28 had femoral osteolysis in zone 7, and 31 had femoral osteolysis in one (or more) of the other 13 zones. 6 hips had an impingement sign on the neck of the femoral component, without aseptic loosening. According to Kaplan-Meier analysis, the fifteen year survival rate, was 84.36% with revision for any reason (infection, dislocation, osteolysis…) for end point. The young age of the patients at the time of the index surgery is correlated with loosening.