Kinesiology Of The Knee Joint

Knee flexion or extension is accompanied by a gliding motion of the tibia upon the femur during knee extension and an internal rotation during flexion. The first 20

of flexion causesa rocking motion. After 20

, further flexion is accomplished with a gliding motion. After 20

of flexion, the ligaments become relaxed and permit both gliding and axial rotation.Most rotation occurs during the final phase of full flexion and during the last 30

of extension. Some rotation, however occurs throughout the entire flexion and extensionaction. At 90

or rotation is possible. In full extension, no axial rotation is possible andalso no significant lateral or medial adduction – abduction of the tibia on the femur ispossible.Rotation of the tibia upon the femur during flexion – extension is passive because of theanatomical configuration of the articular surfaces. The muscles acting upon the joint have arotatory torque, but this is secondary. During flexion – extension, the tibia follows theconfiguration of the medial condyle of the femur which is longer then the lateral condyle. As the femur glides upon the tibia it stops when the surface contour of the lateral condylehas been traversed but continues to move along the longer and more curved medialcondyle, which curves in a lateral direction. During extension the tibia rotates upon thefemur on a distance equal to half the width of the patella. The knee extensors run mediallyand thus help rotate the tibia during extension.In flexion, from the fully extended position, begins with simultaneous internal rotation (tibiaupon femur) by contraction of the popliteus muscle. Further active flexion results fromharmstring contraction. The capsular ligaments which are taut during full extension, relax asflexion begins. The femur glides forward upon the tibia placing the smaller rounded posterior surface of the femoral condyles upon the tibial plateau. The posterior cruciate ligament becomes taut and acts as a drag to any further forwardgliding. An axis now exists around which the tibia rotates upon the femur.