Introduction

Within the reconstruction of unicondylar femoral bone defects with morselized bone grafts in revision total knee arthroplasty (TKA), a stem extension appears to be critical to obtain adequate mechanical stability. Whether the stability is still secured by this reconstruction technique in bicondylar defects has not been assessed. Long, rigid stem extensions have been advocated to maximize the stability in revision TKAs. The disadvantage of relatively stiff stem extensions is that bone resorption is promoted due to stress shielding. Therefore, we developed a relatively thin intramedullary stem which allowed for axial sliding movements of the articulating part relative to the intramedullary stem. The hypothesis behind the design is that compressive contact forces are directly transmitted to the distal femoral bone, whereas adequate stability is provided by the sliding intramedullary stem. A prototype was made of this new knee revision design and applied to the reconstruction of uncontained bicondylar femoral bone defects.

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

Materials and Methods: 30 bipolar hemiarthroplasties were performed in 24 patients with an average age of 34 years. Twenty-six hips had osteonecrosis of the femoral head and 4 hips had secondary osteoarthritis. All prostheses were Osteonics Omnifit collarless stems 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, 11 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 found 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 destruction of the polyethylene (PE) inserts 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. Extensive proximal femoral bone loss is seen predominately in the HA group. The loosening rate in the HA-coated group showed no difference with the non-coated group although the reason for this is different.