Load distribution at the patellofemoral joint during walking

We combined computational modelling with experimental gait data to describe and explain load distribution across the medial and lateral facets of the patella during normal walking. The body was modelled as a 13-segment, 32-degree-of-freedom (DOF) skeleton actuated by 80 muscles. The knee was represented as a 3-body, 12-DOF mechanical system with deformable articular cartilage surfaces at the tibiofemoral (TF) and patellofemoral (PF) joints. Passive responses of the knee model to 100 N anterior-posterior drawer and 5 Nm axial torque tests were consistent with cadaver data reported in the literature. Trajectories of 6-DOF TF and PF joint motion and articular joint contact calculated for walking were also consistent with measurements obtained from biplane X-ray imaging. The force acting on the lateral patellar facet was considerably higher than that on the medial facet throughout the gait cycle. The vastus medialis, vastus lateralis and patellar tendon forces contributed substantially to the first peak in the PF contact force during stance whereas all three portions of the vasti and rectus femoris were responsible for the second peak during swing. A higher lateral patellar contact force was caused mainly by the laterally-directed shear force applied by the quadriceps muscles, especially the vastus lateralis, intermedius and rectus femoris. A better understanding of the contributions of the individual knee muscles to load distribution in the PF compartment may lead to improved surgical and physiotherapy methods to treat PF disorders.