We investigated the influence of the length of the patellar ligament on (1) the relative positions of the ligament, patella, and quadriceps tendon, (2) the location of the patellofemoral contact point, (3) the force of the quadriceps femoris muscle, and (4) the patellofemoral compression force for 0-120 degrees flexion-extension angles of the knee. For this purpose, we used a mathematical model, describing movements and forces in the sagittal plane. The anatomic parameters for the model were obtained from five autopsy knees. The patellar ligament length appeared to influence the mechanical behavior of the patellar articulation considerably. The magnitude of the induced changes was determined by the length of the ligament and by the flexion-extension angle of the knee.