The purpose of this thesis was to quantify the mechanical effects of quadriceps muscle weakness and imbalance on patellofemoral joint kinematics and kinetics, and to determine the independent action of individual quadriceps muscles on the patellofemoral joint. The rabbit knee joint was used for approaching this purpose and a novel experimental technique was developed allowing for controlled activation of the individual muscles of the quadriceps group, thereby permitting simulation of any experimental joint loading scenario of interest. The primary outcome measures were the 3-dimensional patellar kinematics, and the patellofemoral joint contact pressure distribution as a function of quadriceps force, muscle weakness, and muscle imbalance. The key findings were:​ (i) that pressure distribution in the patellofemoral joint changed when simulating muscle imbalance and vastus medialis (VM) weakness;​ (ii) that patellar tracking depended greatly on knee extensor force/torque;​ and (iii) that the VM shifts, rotates, and tilts the patella medially throughout the range of motion. We conclude from these results that VM weakness changes the mechanics in the rabbit patellofemoral joint, and that, due to the anatomical similarity of the rabbit patellofemoral joint with other animals’ joints, including those of humans, the results may have important clinical implications. Furthermore, even though muscle imbalance induced by VM weakness altered patellar tracking, these new paths of the patella did not go beyond the range of tracking paths observed when knee extensor torques were changed from zero (passive) to maximal, thus, they may be considered within the normal range.