The medial and lateral muscle fibers of the extensor apparatus lie opposite each other and join 5 to 10 mm medial to the mid-line of the tendon. This arrangement and its orientation towards the medial and lateral femoral condyles support the view that medial and lateral forces of the quadriceps muscle group balance each other. The vastus lateralis, the tensor vastus intermedius and the lateral part of the vastus intermedius counterbalance the medial parts of the vastus intermedius (superficial and deep layer) and the inserting vastus medialis. The rectus femoris also predominantly inserts into the medial aspect of the superior border of the patella. The vastus intermedius and rectus femoris provide an extensive area for the attachment of the vastus medialis (Fig. 3a).