Heterotopic ossification in total hip arthroplasty: the significance for clinical outcome.

This study evaluates 706 patients with 835 primary total hip replacements documented in a prospective fashion in a multicenter study with respect to correlation between heterotopic ossification (HO) and clinical outcome. Only patients without prophylaxis against HO entered the study. The mean clinical and radiological follow-up was 3.1 years (+/- 0.7). Heterotopic ossification was noted in 47% of all total hips replaced. It was graded as mild (Brooker I) in 29.1%, moderate (Brooker II) in 12.7%, and severe (Brooker III and IV) in 5.2%. All clinical parameters investigated were significantly affected with the increasing amount of heterotopic ossification. The strongest correlation was found in flexion range and spreading distance. Both factors were significantly decreased with higher degrees of ossification. The other clinical parameters investigated, walking capacity, limp, and use of analgesics, were altered to a lesser extent and only with higher degrees of heterotopic bone formation. Finally, patient satisfaction was significantly influenced by the degree of heterotopic ossification and dropped from almost 90% good or excellent patient satisfaction in the non-ossification group to less than 30% in the group with severe ossification.