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.