This project contains an OpenSim model with enhanced knee structures, which based on the a lower extremity model with a torso and back joint (Delp et al. 1990; Anderson and Pandy 1999). The knee joint in this model included three rotations and three translations. The three knee rotations and mediolateral translation were independent, with proximodistal and anteroposterior translations occurring as a function of knee flexion/extension. Ten elastic elements described the geometrical and mechanical properties of the anterior and posterior cruciate ligaments, and the medial and lateral collateral ligaments.