Influence of tibial rotation in total knee arthroplasty on knee kinematics and retropatellar pressure: an in vitro study

Although continuous improvements have been made, there is still a considerable amount of unsatisfied patients after total knee arthroplasty (TKA). A main reason for this high percentage is anterior knee pain, which is supposed to be provoked by post-operative increased retropatellar peak pressure. Since rotational malalignment of the implant is believed to contribute to post-operative pain, the aim of this study was to examine the influence of tibial component rotation on knee kinematics and retropatellar pressure. Eight fresh-frozen knee specimens were tested in a weight-bearing knee rig after fixed-bearing TKA under a loaded squat from 20A degrees to 120A degrees of flexion. To examine tibial components with different rotations, special inlays with 3A degrees internal rotation and 3A degrees external rotation were produced and retropatellar pressure distribution was measured with a pressure-sensitive film. The kinematics of the patella and the femorotibial joint were recorded with an ultrasonic-based motion analysis system. Retropatellar peak pressure decreased significantly from 3A degrees internal rotation to neutral position and 3A degrees external rotation of the tibial component (8.5 +/- 2.3 vs. 8.2 +/- 2.4 vs. 7.8 +/- 2.5 MPa). Regarding knee kinematics femorotibial rotation and anterior-posterior translation, patella rotation and tilt were altered significantly, but relative changes remained minimal. Changing tibial rotation revealed a high in vitro influence on retropatellar peak pressure. We recommend the rotational alignment of the tibial component to the medial third of the tibial tuberosity or even more externally beyond that point to avoid anterior knee pain after TKA.