Heterotopic ossification after uncemented hydroxyapatite-coated primary total hip arthroplasty.

A total of 134 patients who had a cementless hydroxyapatite-coated total hip arthroplasty (THA) and had no recognized risk factors for heterotopic ossification (HO) were reviewed retrospectively. The average follow-up period was 83 months. Pharmacologic or radiotherapeutic prophylaxis against HO was not used. HO was seen in 90 (67.2%) of the 134 patients reviewed. HO was rated as Brooker class I in 68 (50.7%) patients, class II in 17 (12.7%) patients, class III in 3 (2.2%) patients, and class IV in 2 (1.5%) patients. The average Merle d' Aubigne score in patients with mild forms of HO (Brooker classes I and II) was 16 compared with 13.2 in patients with severe HO (Brooker classes III and IV). A statistically significant negative correlation was found between the presence of HO and the postoperative hip score. Based on our study findings and on a comparison with data in the literature, hydroxyapatite-coated cementless THA alone does not seem to increase the likelihood of HO over other types of THA. The presence of a hydroxyapatite coating does not result in more class III or IV HO, which are the only classes of HO with real clinical significance. Fear of HO should not be a factor in the choice of fixation for THA.