Risk factors for poor hip flexion after total hip arthroplasty for the treatment of ankylosing spondylitis a multivariate analysis.

The purpose of this study is to investigate the clinical and radiographic results of total hip arthroplasty (THA) for the treatment of ankylosing spondylitis (AS) and to evaluate the effects of patient, prosthesis design, and surgical technique-related risk factors on postoperative functional results. We retrospectively reviewed the clinical and radiographic results of THA performed in 167 hips for 100 patients with AS. The average follow-up period was 54.8 months (range, 32-129 months). The hip passive-flexion arc averaged only 0 ° (0-40.0 °) before surgery, compared with 100.0 ° (85.0-110.0 °) at the most recent follow-up examination (P < 0.001). Multivariate regression demonstrated that significant variables for postoperative hip flexion were degree of preoperative flexion contracture, preoperative level of C-reactive protein, use of a 32-mm femoral head, and postoperative heterotopic ossification. In patients with AS with severe pain, limited motion and posture, as well as deformity, the overall outcomes after THA were found to be favorable with an encouraging midterm prosthetic survivorship, a low complication rate and a high level of patients' satisfaction. It seemed these patients were particularly predisposed to relative poor range of motion of the involved hips after THA which was closely related to patients' satisfaction. The surgeons should pay careful attention to all possible risk factors perioperatively and develop a comprehensive treatment regimen.