Patellofemoral (PF) disorders remain complex and multi-factorial. PF pathology, such as PF knee pain, excessive lateral pressure, and PF arthritis have been linked to excessive contact forces and pressure between the patella and femur [1]. Antero-medial transfer of the tibial tuberosity and tibial attachment of the patellar tendon is a procedure that was designed to reduce the PF contact pressure, thereby decreasing pain symptoms of early PF arthritis. The transfer procedure alters the angle between the patellar tendon and the quadriceps muscle force, and increases the patellar moment arm. These changes result in a reduction in the quadriceps force required for a given knee flexion strength, and in reduced contact pressure between the patella and femur. However, the tubercle movement also changes the flexion of the patella in the sagital plane, which alters not only regions of contact at various degrees of motion, but may also alter the contact area at these flexion ranges. PF forces, contact pressures and kinematics have been evaluated both prior to, and following, antero-medialization procedures in several cadaveric studies, e.g. [2]. Computational studies have evaluated the potential of anterior and medial tuberosity transfer to reduce PF contact pressure, including a study utilizing patient-specific models to analyze isolated anterior transfer at 15 and 20 mm, and combined antero-medial transfer at two different treatment levels for single, static flexion positions [3]. However, this study suggested that optimal tuberosity transfer required to decrease contact pressure was widely variable between patients and had less absolute decreases than earlier studies. This variability of contact pressure may translate clinically to patient comfort and thus, to maximize surgical outcome, it is likely necessary to identify a patient-specific parameter. Therefore, the purpose of the present study was to evaluate the feasibility of optimization, specifically simulated annealing, to determine the optimal amounts of anterior and medial transfer of the tibial tuberosity required to minimize peak patellofemoral contact pressure during a deep flexion cycle.
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