To report mid-term results of total hip arthroplasty (THA) using the Opti-Fix Plus Hip System (Opti-Fix Hip), and to assess the correlations between peri-implant bone changes and the distal medullary occupancy rate.
11 men (13 hips) and 53 women (58 hips) aged 24 to 87 (mean, 61) years underwent THA using the Opti-Fix Hip, with a modular stem and a distal sleeve, and were followed up for a mean of 6.5 (range, 4.8-9.6) years. Clinical outcomes were evaluated using the Japanese Orthopaedic Association (JOA) hip score. Implant stability, bone changes around the implant, and the occupancy rate of the stem in the medullary space were examined radiologically. Bone changes around the implant were assessed based on the radiological evidence of a pedestal, osteolysis, stress shielding, and radiolucent lines.
The mean JOA score increased significantly after surgery and was maintained at the latest follow-up. Around the acetabular and femoral components respectively, 38 and 58 hips had radiolucent lines, whereas one and 54 hips developed osteolysis. A pedestal appeared in 21 hips and grade-III or higher stress shielding in 30 hips. Two hips showed loosening of the acetabular components, but none in the femoral components. Osteolysis around the stem was frequently observed in hips with poor distal medullary occupancy.
Clinical and radiological outcomes of the Opti-Fix Hip were favourable. The low incidence of osteolysis in the distal stem suggests that the proximal circumferential porous coating was effective. Minor osteolysis around the proximal stem was frequently observed, indicating early excessive wear of the polyethylene liner. Its high distal medullary occupancy rate could inhibit stem micromotion and aseptic loosening.