Total hip replacement for patients who have ankylosing spondylitis. The importance of the formation of heterotopic bone and of the durability of fixation of cemented components.

Fifty-three total hip replacements were performed in thirty-one patients who had ankylosing spondylitis. After an average period of follow-up of 6.3 years, cemented conventional hip prostheses proved to be very durable in this young population (average age, forty-three years). Only one primary conventional hip prosthesis was revised for aseptic loosening, seventeen years after implantation. Clinically important heterotopic bone (Classes III and IV of Brooker et al.) developed in 11 per cent of the patients, all of whom had had a previous operation on the hip, postoperative infection, or complete ankylosis preoperatively. If a patient has clinically important heterotopic bone after one operation on the hip, and an arthroplasty of the contralateral hip or reoperation on the same hip is to be done, prophylactic treatment should be considered for prevention of formation of heterotopic bone.