Kinematics of mobile-bearing total knee arthroplasty.

In a comparison of in vivo knee kinematic patterns of mobile-bearing total knee arthroplasty with thosefrom studies of fixed-bearing total knee arthroplasty and the normal knee, no major differences in the "average" kinematic patterns of fixed- versus mobile-bearing implants was observed. However, there was less AP translation of both the medial and lateral femoral condyles during gait in patients with mobile-bearing implants. This is probably the result of the increased sagittal femorotibial conformity of most mobile-bearing implants, which reduces polyethylene shear stresses and should lessen polyethylene wear rates. In rotating-platform mobile-bearing implants, axial rotation occurs primarily on the inferior surface of the polyethylene bearing instead of on the superior surface, which reduces shear forces on the superior aspect of the polyethylene bearing, thereby lessening wear: Although the average axial rotational values after total knee arthroplasty were limited (< 10 degrees), a significant number of patients exhibited higher magnitudes of rotation (> 20 degrees), which exceeds the rotational limits of most fixed-bearing implants. Rotating-platform mobile-bearing implants may therefore be advantageous in that they can accommodate a wider range of axial rotation without creating excessive polyethylene stresses.