Principles and mechanisms of automatic rotation during terminal extension in the human knee joint
Fuss, F.K.
Journal of Anatomy 180: 297-304
1992
ISSN/ISBN: 0021-8782 PMID: 1506284 Document Number: 390601
The mechanisms solely responsible for the automatic rotation during terminal extension were investigated by means of destruction experiments of knee joint structures. These are: the posterior cruciate ligament (PCL), the anterior cruciate ligament (ACL) and the curavature of the medial femoral condyle. The first mechanism is based on the extraordinary obliquity of the constantly taut PCL guiding bundle which produces torque in the final extension stage. The second mechanism depends on the fact that the ACL becomes "too short" towards the final extension stage which in turn is due to the shape of the articular surfaces. The third mechanism is caused by the deflection of the medial femoral condyle by the intercondylar eminence of the tibia. Each of the collateral ligaments can, in their own right, prevent excessive automatic rotation. On the one hand, the mechanism of the automatic rotation is reversed during initial flexion by the medial collateral ligaments (this would be "too short" in the case of non-reversal). On the other hand it is reversed by the popliteus muscle. It is suggested that automatic rotation is not related to securing an amuscular stance (locking mechanism).