Clinical significance of the heterotopic ossification after total hip arthroplasty.

Heterotopic ossification represents one of the most frequent complications following any type of hip arthroplasty. However, disagreement exists regarding the clinical significance of heterotopic ossification after total hip arthroplasty (THA). This study evaluated the effect of different grades of heterotopic ossification on range of hip motion, pain, and the clinical outcome in patients after THA. The study included 198 patients with primary THA because of unilateral hip osteoarthritis, followed for a minimum of 1 year after THA. Diagnosis and classification of heterotopic ossification according to Brooker was achieved on anteroposterior radiograph of the hips 1 year postoperatively. The clinical outcome was assessed at 1-year follow-up with the use of the Harris hip score. Pain was assessed as the pain component of the Harris hip score. Hip range of motion was measured passively in the lying position with a goniometer and recorded in degrees according to the method suggested by the American Academy of Orthopaedic Surgeons 1988. The incidence of heterotopic ossification was 47% and the incidence of severe ossification was 11%. The severe heterotopic ossification significantly reduced clinical outcome, overall range of hip motion and certain components such as flexion, abduction and external rotation, but had no significant effect on pain, while the lower degree of ossification did not significantly influence the clinical outcome, hip motion and pain. This study has shown that only severe heterotopic ossification is of clinical significance.