Influence of mediolateral tibial baseplate position in TKA on knee kinematics and retropatellar pressure.

Purpose: Anterior knee pain is a major reason for unsatisfied patients after total knee arthroplasty (TKA). Since malposition and increased retropatellar peak pressure are supposed to contribute to pain, we conducted this in vitro study to analyse the influence of mediolateral tibial component position on tibiofemoral and patella kinematics as well as retropatellar pressure.

Methods: Eight fresh frozen cadaver specimens were tested after a fixed-bearing TKA. To evaluate the influence of mediolateral tibial component position, special inlays with 3 mm of medialization and lateralization were constructed. For the analysis, a weight-bearing knee rig under a loaded squat from 20° to 120° of flexion was used. Tibiofemoral and patella kinematics were measured with an ultrasonic-based three-dimensional motion analysis system. Additionally, retropatellar pressure distribution was registered with a pressure-sensitive film.

Results: Alteration of mediolateral tibial component position by 3 mm did not reveal a significant influence on retropatellar peak pressure (7.5 ± 2.5 vs. 7.2 ± 2.6 MPa). Regarding tibiofemoral kinematics, 3-mm medialization of the tibial baseplate significantly increased lateral femoral rollback and femorotibial external rotation. Medialization of 3 mm also significantly increased the relative medial patella shift and decreased lateral patella tilt.

Discussion: Medialization of the tibial baseplate came along with more lateral rollback and external femorotibial rotation. For the positioning of the tibial baseplate, rotational alignment seems to be more important than mediolateral orientation. Since retropatellar peak pressure remained rather unchanged, the tibial baseplate should be placed by the surgeon looking for a maximal tibial coverage without overhang.