Bipolar Endoprosthesis for Osteonecrosis of the Femoral Head: A 12-year Follow-up of 29 Hips
K Yamano, T Atsumi, T Kajiwara, Y Hiranuma, S Tamaoki, Y Asakura
Department of Orthopaedic Surgery, Fujigaoka Hospital, Showa University
School of Medicine, Yokohama, Japan

Results of noncemented press-fit bipolar hip endoprosthesis were reviewed in 29 hips of 24 patients with osteonecrosis of the femoral head. The average follow-up period was 12 years and 5 months (range from 9 years 2 months to 17 years 11 months). All hips were classified at stage 3 or 4 (osteoarthritis) before surgery by classification of Japanese investigation committee and acetabular reaming was performed in 5 hips with stage 4 osteonecrosis. Four prosthesis had been revised to a total hip arthroplasty at the time of follow-up examination. The average clinical hip score of Japanese Orthopaedic Association was 88.9 (98-82) with 23 hips rated excellent and good, 6 hips rated fair. Radiologically, stem subsidence more than 5 mm occurred in 5 hips and stem loosening in 6 hips (21%). 5 hips with stage 4 osteonecrosis (3 hips received acetabular reaming, 2 hips in elderly patients with osteoporosis) developed to outer head migration more than 4 mm in both superior and axial direction. Osteolytic lesions, seen on 11 hips of femur and 3 hips of pelvis, appeared at an average of 4.2 years postoperatively. These results suggest that cementless press-fit bipolar endoprosthesis for osteonecrosis demonstrate high incidence of acetabular protrusio and osteolysis. Cementless THA with a porous coating stem should be recommended for treatment of necrosis of the femoral head.