Musculoskeletal model is a useful tool to evaluate the complex biomechanical problems, simulate and evaluate the injuries, estimate the muscle-tendon forces, and joint the torques during motion and predict the effects of orthopedic surgeries. Moreover, the musculoskeletal model is a rich source of information to develop robotics exoskeleton aiming to restore the normal gait after some injuries. This paper presents a full musculoskeletal model in an open-source framework to perform the biomechanical analysis of the human lower limb in order to simulate both healthy and pathological gait; 14 bones, 88 Hill-type muscle-tendon segments, ten ligament segments for each knee, and six joints for each lower limb were modeled. The model allows us to simulate different injuries of the lower limb, such as ictus, stroke, and so on, by sending different signal profiles to muscle-tendon segments, emulating the functional electrical stimulation (FES). At the same time, forces and torques could be computed for muscles and joints. Hence, the proposed model can be suitable not only to perform a complete biomechanical analysis for medical purposes but also for the exoskeleton controller design and actuators dimensioning. In order to validate the model, it was exported to Simulink environment to simulate the joints range of motion, muscle moment arm, and joint torque, and then, these data were compared with the medical literature. All simulations results show that the data from the model are according to the previously published works. Furthermore, the model was validated using the real data obtained by our own gait capture system and by CODA motion software for normal and pathological gait. Finally, the goodness-of-fit of our model was assessed using the root mean square error (RMSE) and the normalized mean square error (NMSE); the values of these indices suggest that the model estimated the kinematics and kinetics parameters of healthy and pathological gait successfully.