The well-documented dissatisfaction of patients with the results of their total knee replacement surgery has been the incentive for deeper research into the optimisation of knee prostheses. One way to optimise total knee replacements is to develop patient-specific 3D musculoskeletal models, enabling a better understanding of the kinematics and kinetics affecting the lower limbs of the patient. This paper suggests a particular methodology to build such personalised models, by implementing data of additional measurement systems. MRI scanning ensures a morphological match between the model and the patient. Additionally, ground reaction force measurements coupled with motion capture provide the kinematic input. A squat test was performed to illustrate the usefulness of the data obtained through the force plates. The combination of this data into the 3D models allows for a more precise calculation and simulation of knee joints. This will ultimately improve the quality of prosthesis testing in a knee-rig setup by providing more accurate boundary conditions.