Strengthening the vastus medialis muscle leads to increased internal tibial rotation, thus optimizing patella tracking by lowering the Q-angle. In contrast, weakness of the vastus medialis muscle causes decreased tibial internal rotation and is associated with lower patellofemoral contact pressure and contact area. Vastus medialis exercise is advisable to improve patella tracking but may not be recommended in patients with disorders due to increased patellofemoral contact pressure.

Simulating knee movement under physiological muscle loading is a prerequisite in order to improve surgical treatment and rehabilitation techniques. An apparatus is presented which can simulate five knee muscles to control a definite amount of body weight using the ankle force as the target value for the control mechanism. The influence of different amounts of simulated ankle forces upon the knee movement was investigated. The apparatus was constructed in a closed kinetic chain design similar to the so-called Oxford rig. Three quadriceps muscles and two hamstring muscles were controlled by electrical servo motors via tendon clamps in order to adjust a target value for the simulated body weight. Three fresh frozen cadaveric specimens were used to validate the apparatus and to examine the difference between loaded and unloaded knee flexion from 10 degrees to 90 degrees . In one specimen, up to 250 N simulated ankle force could be achieved for a single leg knee flexion. Among the kinematic variables, tibial rotation was influenced the most when varying the amount of simulated body weight. Although the knee kinematics changed considerably with increasing simulated bodyweight, the shapes of the kinematic profiles remained similar, indicating that qualitative clinical insights can still be elucidated with partially (but reasonably) loaded knees.

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