Mobile-bearing prosthesis did not improve mid-term clinical results of total knee arthroplasty

Abstract

A prospective study was performed to compare the clinical and radiological results of mobile- and fixed-bearing total knee arthroplasty with specific attention to rotational alignment and range of motion. Sixty-one knees were assigned to total knee arthroplasty with either the NexGen LPS Flex fixed-bearing or with the NexGen LPS Flex mobile-bearing prosthesis. Postoperatively, knees were compared with regard to range of motion, clinical score, and radiographic findings. Rotational alignment of the femoral and tibial components was evaluated by computed tomography. The median follow-up period was 5.9 years (range 2.1-8.8 years). Median postoperative Knee Society scores were 99 points (68-100) for the fixed-bearing group and 100 points (66-100) for the mobile-bearing group (n.s.). The median postoperative flexion angles of 120° (90°-150°) for the fixed-bearing group and 125° (90°-145°) for the mobile-bearing group were not significantly different from each other (n.s.). No knee required revision surgery due to wear of polyethylene or loosening of the component in either group. Computed tomography showed that 11 knees had rotational mismatches of more than 10° between the femoral and tibial components, but no significant difference was found in the postoperative extension and flexion angles or in the clinical score between the two treatment groups. Using the identical design for both fixed- and mobile-bearing prostheses, this prospective, randomized study did not show any clinical advantages of the mobile-bearing knee. Analysis of rotational alignment by CT scan did not reveal a particular advantage of the self-aligning mechanism of mobile-bearing implants.