Rotational alignment of the tibial component affects the kinematic rotation of a weight-bearing knee after total knee arthroplasty.

PURPOSE: The purpose of this study is to elucidate how the rotational malalignment of prosthesis after total knee arthroplasty affects the rotational kinematics in a weight-bearing condition.

METHODS: In this study of 18 knees replaced with the posterior stabilizing fixed-bearing system, which has a relatively low-restricting design, rotational angles between the femoral and tibial components and between the femur and tibia during stair climbing were evaluated in vivo in three dimensions using radiologically based image-matching techniques. Rotational alignments of the components were assessed by postoperative CT. The correlations between the rotational alignments and the rotational angles during stair climbing were evaluated.

RESULTS: Rotational alignment of the tibial component significantly correlated with rotational angles between the components as well as between bones during stair climbing. Rotational malalignment of the tibial component toward internal rotation caused a rotational mismatch of the tibial component toward internal rotation relative to the femoral component in 0° extension and caused a rotational mismatch of the tibia (bone) toward external rotation relative to the femur (bone). The knee in which the tibial component was placed close to the AP axis of the tibia did not show any rotational mismatch between either components or bones.

CONCLUSIONS: Rotational alignment of the tibial component affects the kinematic rotation of the replaced knee during a weight-bearing condition even though using a low-restricting designed surface, and the AP axis can be a reliable reference in determining rotational alignment for the tibial component.