The effect of different quadriceps loading patterns on tibiofemoral joint kinematics and patellofemoral contact pressure during simulated partial weight-bearing knee flexion

The purpose of this in vitro study was to investigate the influence of different quadriceps loading patterns on tibiofemoral joint kinematics and patellofemoral pressure. A dynamic muscle-loaded knee squat was simulated on eight knee specimens with an upright knee simulator while measuring tibiofemoral joint kinematics and patellofemoral pressure distribution. The quadriceps muscle was attached to three actuators simulating the three main extensor muscles, and five different quadriceps loading patterns were tested. Tibial axial and varus-valgus-rotation are affected most while changing quadriceps loading patterns from lateral to medial. Higher internal tibial rotation is associated with higher medial muscle load compared to the symmetrical loading condition. Contact force, contact area and maximum peak pressure rise with increasing flexion angles. Accentuating the vastus lateralis muscle induces a significant reduction in patellofemoral contact force and a 30% diminished contact area at 90A degrees of flexion. Strengthening the vastus medialis muscle leads to increased internal tibial rotation, thus optimizing patella tracking by lowering the Q-angle. In contrast, weakness of the vastus medialis muscle causes decreased tibial internal rotation and is associated with lower patellofemoral contact pressure and contact area. Vastus medialis exercise is advisable to improve patella tracking but may not be recommended in patients with disorders due to increased patellofemoral contact pressure.