Cementless Bipolar Hemiarthroplasty with and without Hydroxyapatite in Patients under 55 Years
JWM Gardeniers, HJ Meijerink, BW Schreurs
Orthopaedic Department, University Medical Center St. Radboud, UMCN, Nijmegen, the Netherlands

Introduction: Between 1985 and 1995 an uncemented Osteonics hipprosthesis with bipolar Universal Head was the implant of choice in young patients with osteonecrosis of the femoral head and with posttraumatic secundary osteoarthritis of the hip.

Materials and Methods: 30 bipolar hemiarthroplasties were performed in 24 patients with an average age of 34 years. 26 hips had osteonecrosis of the femoral head and 4 hips had secundairy osteoarthritis. All prostheses were Osteonics Omnifit collarless stem with an UHR universal head. 11 were non-HA-coated prostheses (NG) and 19 proximal HA-coated prostheses (HA). The mean duration of follow-up was 10.4 years.

Results: Clinically at final follow-up the Harris Hip Score increased from a preoperative average of 41 points to 76 points (NG 70 and HA 80 points). Thigh or groin pain was present in 16 of 30 hips (NG 3/11 and HA 10/19). Radiographically a subsidence of 5 mm or more was the major problem in the non-coated prostheses, 1 of 30 hips (NG 10/11, HA 1/19), but osteolysis was mainly seen in the HA-coated group, 20 of 30 hips (HA 17/19, NG 3/11). Total proximal migration of 5 mm or more of the bipolar head was determined in 18 prostheses (NG 5/11 and HA 13/19). The revision rate for aseptic loosening was 8 of the 30 hips (NG 3/11 and HA 5/19). During the revisions major destructions of the polyethylene (PE) insert were found.

Discussion: The revision rate of the Osteonics Omnifit Prosthesis with bipolar UHR is too high to use this implant in young patients with ON. Bone destruction due to third body wear is probably the main cause. The loosening rate in the HA-coated group shows no difference with the non-coated group although the reason for this is different.