Long-term results of rotational total hip arthroplasty: radiological analysis

We developed a rotational total hip prosthesis that has a 30 mm diameter metal-covered head with a polyethylene liner with which it can rotate around the neck of the stem. Long-term results of the rotational total hip arthroplasty with cement were evaluated in 55 hips of 52 patients. The diagnosis was degenerative osteoarthritis in all patients. The mean follow-up was 11.2 years (range 5-19 years). Eight of thirty 7mm thick acetabular components were revised 7.6-14.3 years (mean 10.4 years) afterward. Two of twenty five 9.5 mm thick acetabular components and two femoral components were revised at 12 and 15 years, respectively. The mean polyethylene wear in the 9.5 mm thick acetabular components was significantly less than that in the 7mm thick components. The mean polyethylene wear inside the rotational head removed during the revision surgeries was 0.01 mm in diameter and 0.03mm in depth per year, respectively. Fifty percent of the patients with 7 mm thick acetabular components, 9.5 mm thick components, and femoral components had surviving prostheses at 13.4, 15.2, and 16.3 years, respectively. It is possible that the rotational system reduces the stress against acetabular and femoral components, but the 30mm diameter head caused high friction torque and required at least 9.5mm thickness in the acetabular component.