Sagittal Plane Dynamic Model Using Tibiofemoral Articular Geometric Center and Experimental Tibiofemoral Center of Rotation to Predict Joint Forces During Knee Extension Exercise

Abstract

Abstract A 2-dimensional anatomical dynamic model of the patellofemoral joint was developed for investigating the forces that contribute to patellar motion during the knee extension exercise. Sagittal bone profiles were aligned to kinematic experimental data to simulate bone motion. Kinematic experimental data was collected using VICON motion analysis system. Marker coordinate data was used to set body-fixed coordinate systems on femur and tibia. These body-fixed coordinate systems were used to drive the femur and tibia geometric profiles during the knee extension exercise. Kinematic experimental data was used to calculate the relative instant center of rotation of markers on tibia with respect to femur’s body-fixed coordinate system. The instant center was then used as an alignment point for the geometric center of femur’s posterior lateral condyle. A geometric approach was implemented to predict patellar motion. The position of patella’s center of mass was assumed to be a function of the position of the tibial tuberosity and the geometric center of the femoral condyle. Newton’s second law of motion was used to calculate the force exerted by the quadriceps muscle during the knee extension exercise. The patellofemoral contact was modeled as a deformable articular surface, which was represented mathematically as the overlapping area between bone profiles. Overall, the forces calculated for the quadriceps force were greater than those observed for the patellofemoral contact. The quadriceps force displayed an increasing trend as the flexion angle decreased until reaching its maximum value of 1,920 N at full extension. On the other hand, the patellofemoral contact force displayed an increasing trend as the flexion angle decreased until reaching its maximum value of 805 N at 37° of flexion.