The effects of tibial tray orientation on Weight-Bearing kinematics of the patellofemoral joint for total knee arthroplasty.

Abstract

While alternative alignment strategies gain traction in total knee arthroplasty (TKA), limited investigation into how component orientation influences patellar mechanics and loading has been done. This study employed a validated forward solution mathematical (FSM) model of the knee to evaluate the effects of tibial tray orientation in the axial and coronal planes on patellar mechanics across multiple TKA designs. The FSM incorporated bone and soft tissue geometries reconstructed from CT imaging of 10 unique subjects, each virtually implanted with three distinct cruciate-retaining TKA designs. Standard mechanical alignment was the control, while rotations of ± 5° in the axial plane (internal/external) and ± 4° in the coronal plane (valgus/varus) of the tibial tray were the experimental groups. Subjects underwent simulated deep knee bends from full extension to 120° flexion. Examined parameters included patellotibial spin, tilt, and shift, as well as quadriceps, patellar ligament, and patellofemoral contact forces. Valgus alignment increased patellar spin, tilt, and lateral shift throughout flexion, with internal rotation similarly increasing tilt and lateralization. Conversely, varus and external rotations reduced these parameters. TKA design also influenced peak forces, with increased trochlear conformity leading to higher patellofemoral forces and greater sensitivity to malalignment. These findings suggest that valgus and internal tibial tray orientations may contribute to anterior knee pain and that greater patellofemoral constraint elevates joint reactive forces.