Distal aspect of the extensor apparatus of the knee joint above the patella. The rectus femoris muscle is reflected medially displaying the anterior insertion of the vastus medialis into the vastus intermedius (see also Fig. 3a). The vastus medialis further inserts into the rectus femoris and patella. The medial deep and medial superficial layer of the vastus intermedius aponeurosis are covered by the inserting muscle fibers of the vastus medialis and therefore not visible. The aponeurosis of the vastus lateralis is separated into two fiber bundles. The fibers of the vastus lateralis and the tensor vastus intermedius are oriented towards the medial femoral condyle. Together with parts of rectus tendon the vastus medialis occupies the supero-medial half of the upper semi-circle of the patella (green dotted line). The strong muscle belly of the vastus lateralis inserts at the supero-lateral semi-circle of the patella (red dotted line)