Total hip arthroplasty in patients with ankylosing spondylitis: longterm followup.

OBJECTIVE: To evaluate the longterm functional effects of total hip arthroplasty (THA) on 46 patients.

METHODS: Clinical and radiographic examinations were performed on 46 patients (74 THA) with ankylosing spondylitis (AS). The mean followup period was 100 months (range 37-174 months); 32 hips were followed for more than 10 years.

RESULTS: Significant benefit was obtained in pain control (all but 2) and function (mean improvement in range of motion 128 degrees) in the early stage so that patients could be gainfully employed. An average 100 months after THA, the overall functional results were rated excellent in 21 hips, good in 28, fair in 7, and poor in 18. Only 6 hips (8%) in our series developed clinically significant (Class III or IV) heterotopic ossification. Seventeen hips needed a 2nd operation because of loosening (11 hips), deep infection (3), malposition of acetabular component (2), and prosthetic failure (1). Another 6 hips showed definite loosening on radiographs and needed to be revised. The total incidence of failure was 31% (23 hips). The average time from the index operation to loosening was 9.5 years (range 4-13 years). Factors contributing to component loosening were young age, short stature, and decreased postoperative range of motion.

CONCLUSION: Total hip arthroplasty can be very important and beneficial to patients with AS, but the patients, being young and active, and with their rigid spines, do not treat their prostheses gently and are very dependent upon their mobility. They must be kept under supervision long after THA, probably for the rest of their lives, to identify possible longterm complications.