gms | German Medical Science

Objectives: Femoral component malrotation in total knee arthroplasty (TKA) is clinically proven to cause dissatisfaction and impaired function. This study is an attempt to characterize the poorly understood knee biomechanics with focus on tibiofemoral kinematics following malrotation of the femoral component in posterior stabilized (PS) TKA.

Methods: Six fresh frozen cadaver specimens were mounted in a kinematic rig. Three motion patterns were applied with the native knee and following PS TKA (passive motion, open chain extension, and squatting) while infrared cameras recorded the trajectories of markers attached to femur and tibia. Three different femoral implants were tested: a conventional posterior stabilized component, and custom made components with five degrees of intrinsic external and internal rotation respectively.

Results and Conclusion: The implantation of the PS TKA resulted in less tibial internal rotation and the medial femoral condyle shifted posterior especially in deep flexion.

Internal component malrotation caused internal rotation and abduction of the tibia in flexion, an elevated and more anterior located medial femoral condyle and a lateral femoral condyle located more posterior and inferior.

External component malrotation caused only little changes under passive motion. Under a squat there was less internal rotation and more adduction to the tibia. The medial femoral condyle was moved more posterior, the lateral femoral condyle more superior.

The greatest differences to the native tibiofemoral kinematics were introduced by internal rotation of the femoral component. With respect to the alterations introduced to kinematics internal malrotation should be avoided when performing PS TKA. Also neutrally and externally rotated femoral components introduce kinematic changes, but to a lesser extent.