[Anatomical and mechanical studies of the extensor system of the knee joint]

The anterior thigh muscles were investigated with respect to their function in extending the knee joint and in patellar alignment . Anatomical dissections of the vastus medialis muscle in 115 fixed thigh-specimens could always demonstrate a clear separation between a long head of the muscle that inserts at the base ( VML ) and a short head ( VMO ) that inserts at the medial margin of the patella. The plane of separation could be identified by a femoral nerve's branch in every case. In 17 instances the nerve's localization was superficial, in 57 in an areolar fascial plane and in the depth between the muscles in 41 instances. The ramification of the femoral nerve's branch that runs along the separation plane showed four types of variation. The direction of pull of the individual heads of the quadriceps femoris muscle had different angulations from the long axis of the femur. These deviations were measured in 32 corpses, that were either fresh or fixed. The deviations were between 8 and 11 degrees medially and between 3 and 6 degrees anteriorly for the rectus femoris muscle (RF), between 12 and 16 degrees laterally for the vastus lateralis muscle (VL), between 15 and 18 degrees medially for the VML and between 46 and 52 degrees medially for the VMO . In every instance the direction of pull of the vastus intermedius muscle (VI) was parallel to the long axis of the femur. 28 fresh above-the-knee amputation specimens were used for strain tests of the extensor muscles as well as for measurements of tilting and shifting of the patella under a single strain. The strain tests of the VMO were carried out during the terminal phase of the knee-joint's extension and in order to assess its antagonistic function against the VL in various positions of the knee-joint. Furthermore the subluxation of the patella was measured after lateral and medial release and during single strain on VL or VML . The most effective extension was produced by pull in the direction of the VI as compared to other directions; single strain in the direction of each of the long extensor muscles always resulted in complete extension. Therefore loss of terminal extension cannot be due to the insufficiency of one single extensor muscle. Even with maximal weight loads pull in the direction of the VMO never achieved full extension, which indicates that the VMO does not contribute substantially to complete extension of the knee-joint.(ABSTRACT TRUNCATED AT 400 WORDS)