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.