Your Anatomy Teacher was WRONG!
By Art Horne
Your college anatomy teacher will have you believe that the knee is a simple hinge joint that’s only action is flexion and extension. Of course they probably mentioned the “screw home” mechanism and its related rotational component at some point, but this motion was most likely reviewed only as a side note to the main lecture with no further mention.
Unfortunately, this critical motion is often forgotten about during both the evaluation and rehabilitation of knee pain and for those with limited rotation in either direction, or an inappropriate axes of rotation, traditional knee pain management strategies aimed at limitations in flexion and extension will only lead to frustration.
Why care about tibio-femoral rotation?
Ignoring knee rotation and only examining the flexion-extension component is akin to checking the wheels on a train and then ignoring the tracks beneath them. Both are required if you’re hoping to efficiently move from A to B. So what happens when this critical motion is off? Inappropriate arthrokinematic motion will cause excessive motion or friction on adjacent structures – think train grinding around a corner and the screeching of wheels on the tracks.
“Fixed rotation of either the femur or tibia has a significant influence on the patellofemoral joint contact areas and pressures. This is due to the anatomic asymmetry in the knee with respect to all planes, as well as the laterally directed force vector that naturally exists in bipedal lower-limb biomechanics. Specifically, femoral rotation results in an increase in patellofemoral contact pressures on the contralateral facets of the patella, and tibial rotation results in an increase in patellofemoral contact pressures on the ipsilateral facets of the patella. This difference can be elucidated when one considers that rotation of the femur is biomechanically different than rotation of the tibia. For both tibial and femoral rotations, the patella’s distal attachment to the tibial tubercle influence the direction of patellar movement.” (Lee et al, 2003 p.686)
This influence on the patella by the relative motion between the tibia and femur is echoed by Kapandji,
“During movements of axial rotation the patella displacements relative to the tibia occur in a coronal plane. In the neutral position of rotation the patellar ligament runs a slightly oblique course inferiorly and laterally. During medial rotation the femur is laterally rotated with respect to the tibia, dragging the patella laterally, and the patellar ligament now runs obliquely inferiorly and medially. During lateral rotation, the opposite movements take place: the femur drags the patella medially and the patellar ligament now runs inferiorly and laterally with a greater obliquity than in the neutral position.”(Kapandji, pg.106)
“Patella displacements relative to the tibia are therefore indispensable for movement of both flexion-extension and axial rotation.”(Kapandji, pg. 106)
What exactly is happening?
“During lateral rotation of the tibia on the femur the lateral condyle moves forward on the lateral tibial surface, while the medial condyle moves backwards on the medial tibial surface. During medial rotation of the tibia on the femur the converse is true: the lateral condyle moves backwards and the medial condyle forwards on their corresponding tibial surfaces. In reality, the anteroposterior movements of the condyles on their corresponding tibial surfaces are not identical.” (Kapandji, pg. 90)
Because of this unequal movement, the axis of rotation is NOT between the two intercondylar tubercles as many people would think, or what your college professor lead you to believe, but actually through the articular surface of the medial tubercle which serves as the central pivot point of the knee joint.
So now you’ve identified a limitation, how would you treat it?
Treatment Example: Below is an example taken from Greenman (Greenman’s Principles of Manual Medicine, Fourth Edition. Page 453), in an effort to restore normal tibia internal rotation
Position: Tibia