The incidence of heterotopic ossification after cementless total hip arthroplasty.

The purpose of this study was to determine the incidence of heterotopic ossifications (HOs) after total hip arthroplasty in Japanese patients and the predisposing factors associated with this condition. One thousand hips of 885 patients undergoing cementless total hip arthroplasties were examined with respect to the incidence and severity of HO; the data analysis was conducted by using the univariate and multivariate methods. The overall incidence of HO was 5.2%, with severe HO in 0.9% of the patients. A significant increase in the frequency of HO was observed in patients with ankylosed hips (odds ratio, 11.1; 95% confidence interval, 2.5-49.9), hypertrophic osteoarthritis (odds ratio, 2.7; 95% confidence interval, 1.2-5.9), and with a particular type of prosthesis used (ceramic-on-ceramic vs ceramic-on-polyethylene) (odds ratio, 2.5; 95% confidence interval, 1.3-4.8).