In vitro comparison of fixed- and mobile meniscal-bearing unicondylar knee arthroplasties: effect of design, kinematics, and condylar liftoff.

Unicondylar knee arthroplasty (UKA) has become a popular alternative to total knee arthroplasty or high tibial osteotomy for unicompartmental knee conditions. This study investigated the effects of kinematics and femoral liftoff on the wear of fixed and mobile versions of a UKA design. The fixed bearing had lower wear than the mobile bearing under all conditions. Wear was higher in lateral bearings than medial bearings, indicating that the increased sliding distance laterally had a greater effect than the greater loading medially. Femoral condylar liftoff resulted in increased wear in the medial UKAs but reduced wear in the lateral UKAs for both the bearing designs. The reduced wear rates observed for the fixed UKA bearings highlight the potential for a longer osteolysis-free clinical outcome for these devices.