Results of the administration of diphosphonate for the prevention of heterotopic ossification after total hip arthroplasty.

We evaluated the results in 177 patients with 200 total hip arthroplasties that had been performed for primary osteoarthritis. Severe postoperative heterotopic-bone formation (grades III and IV according to the classification of Brooker et al.) was found in thirty-six hips (18 per cent). The incidence of heterotopic bone formation was found to be slightly higher in the patients who had received diphosphonate than in the control group of patients who had received either a placebo or no drug therapy. The postoperative range of motion of the hips as well as ratings for pain, walking, and function did not differ significantly between the treated and untreated groups. The results of this study were consistent with those of previously published reports that demonstrated that while diphosphonates did not prevent heterotopic bone formation in laboratory animals they did result in a delay of mineralization of osteoid. This delay did not, as was hoped, significantly improve the range of motion of the involved hips in our series.