Risk factors for heterotopic ossification in total hip arthroplasty.

This study prospectively evaluated 928 patients with 1318 primary total hip replacements for heterotopic ossification (HO). The mean clinical and radiological follow-up was 2.5 years (range 1.5-3.6 years). HO was noted in 44.6% of all total hips replaced. It was graded as mild (Brooker 1) in 29.2%, moderate (Brooker 2) in 10.5%, and severe (Brooker 3 and 4) in 4.2%. The following factors showed a significantly increased risk of HO: hypertrophic osteoarthritis, HO after contralateral total hip replacement, trochanteric osteotomy, lateral or anterolateral approach, previous hip surgery, subtrochanteric femoral osteotomy, and male gender (p < 0.05 in chi-square analysis of independence and multivariable analysis). Patients with rheumatoid arthritis showed less HO. A combination of any of these factors resulted in a significant increase in the risk of developing HO.