TOTAL HIP-ARTHROPLASTY IN PATIENTS WITH ANKYLOSING-SPONDYLITIS - LONG-TERM FOLLOW-UP

Objective. To evaluate the longterm functional effects of total hip ar throplasty (THA) on 46 patients. Methods. Clinical and radiographic ex aminations were performed on 46 patients (74 THA) with ankylosing spon dylitis (AS). The mean followup period was 100 months (range 37-174 mo nths); 32 hips were followed for more than 10 years. Results. Signific ant benefit was obtained in pain control (all but 2) and function (mea n improvement in range of motion 128 degrees) in the early stage so th at patients could be gainfully employed. An average 100 months after T HA, the overall functional results were rated excellent in 21 hips, go od in 28, fair in 7, and poor in 18, Only 6 hips (8%) in our series de veloped clinically significant (Class III or IV) heterotopic ossificat ion. Seventeen hips needed a 2nd operation because of loosening (11 hi ps), deep infection (3), malposition of acetabular component (2), and prosthetic failure (1). Another 6 hips showed definite loosening on ra diographs 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 l oosening were young age, short stature, and decreased postoperative ra nge of motion. Conclusion. Total hip arthroplasty can be very importan t and beneficial to patients with AS, but the patients, being young an d active, and with their rigid spines, do not treat their prostheses g ently and are very dependent upon their mobility. They must be kept un der supervision long after THA, probably for the rest of their lives, to identify possible longterm complications.