Five Year Results of Hydroxyapatite Coated Hip System: Early Severe Wear and Acetabular Osteolysis

Purpose: To assess the midterm results of the hydroxyapatite hip system with acetabular cups, with particular emphasis upon cup wearand loosening, using a computer assisted-3 dimensional technique. Materials and Methods: From March 1992 to December 1996, 52 patients (61 hips) were available for inclusion in this study after an average duration of follow up of 6 years and 4 months. Clinical evaluation was performed using the Harris hip scoring system. Initial postoperative and long term follow up films were digitized, and 2 dimensional linear and 3 dimensional wear was measured by using a computer assisted-3 dimensional technique. Acetabular bone changes are described using previous published methods. Results: An analysis of the clinical results showed a mean Harris hip score of 47.2 points preoperatively and 89.8 points at the final visit. The mean polyethylene 3D-linear wear rate was 0.26 mm/year and mean volumetric wear rate was 105.9 /year. In 16 hips (26.2%) the linear wear rate was more than 0.3 mm/year (0.30-0.74 mm/year). Osteolytic changes of the acetabulum were recorded in 51% around acetabular cups, in which considerable wear of the acetabular polyethylene was evident by the five-year radiographic findings. Conclusion: Midterm results of hydroxyapatite coated acetabular cups were disappointing in terms of acetabular cup and liner wear, despite early accelerated bone remodeling by hydroxyapatite and excellent early clinical results.