The influence of anterior displacement of the tibial tuberosity on patellofemoral biomechanics.

The effect of anterior displacement of the tibial tuberosity at distances of 5, 10, 15 and 20 mm on the mechanical behaviour of the patellofemoral joint has been investigated using a mathematical model, which describes movements and forces in the sagittal plane. Anatomical parameters for the model were obtained from five normal autopsy knees. The results show that anterior displacement: 1) increases the length of the contact paths on both patellar and femoral articulating surfaces, 2) produces a lengthening of the moment arm of the patellar ligament force, 3) may either decrease or increase the ratio between patellar ligament force and quadriceps muscle force and 4) decreases the ratio between patellar compression force and quadriceps muscle force. The magnitude of these effects depends on the flexion-extension angle of the knee and the displacement distance of the tibial tuberosity.