Heterotopic ossification after total hip arthroplasty: our experience.

Heterotopic ossification is a condition characterized by the presence of mature lamellar bone and often bone marrow in soft tissues surrounding a major joint. It represents a common complication after total hip arthroplasty (THA). The etiology and predisposing factors are not completely known, but some authors reported that the implant of a non-cemented prosthesis seems to be associated with a greater incidence of HO. Two hundred and two non-cemented total hip arthroplasties were performed between October 1997 and February 2002. The mean age was 70.2 years. The average follow-up for 181 hips included in the study was 96 months (range, 72-120 months). A standard lateral approach (Hardinge) was performed for the implant of a non-cemented femoral component and a non-cemented acetabular component. Radiographs were done before and after surgery, at 1, 4 and 12 months postop, then every year. The incidence of HO was assessed in the antero-posterior view at each interval and graded according to Brooker classification. Out of 181 implants, HO was observed in 52 hips (28,7%). Heterotopic bone was graded as class I in 32 (17.7%) hips, class II in 14 (7.73%) hips, class III in 6 (3,3%) hips and class IV in none (0%). The mean preoperative Harris hip score was 48; at the last follow-up, the mean postoperative score was preoperatively to a mean of 89 points (range, 76-97 points) in HO Hip and of 91 points (range, 78-100 points) in the other Hip. In our experience, non-cemented THA led to a higher incidence of class I and II HO according to Brooker Classification, the incidence of HO is comparable to the rates reported in recent studies about the HO finding after a non-cemented THA, the importance of clinical symptoms in the presence of HO is very low.