Avery Jenkins wrote:
The knee is actually composed of two joints, the patellofemoral and the tibiofemoral joint. The latter is generally considered to include two degrees of freedom; in addition to flexion/extension, this joint rotates in the sagittal plane (up to 70 degrees with the knee in 90 degrees of flexion).
Grood and Noyes(sp?) say this joint actually has 6 degrees of freedom, but I'm not buying it.
The patella also rotates on the femur as the knee flexes.
Thus, when done properly, the rotation caused by shikko and suwariwaza techniques probably don't overstress a healthy knee joint, because the knee is primarily in flexion during these techniques. Other pressures, I'll grant you, can cause injury in these joints.
The two-joint business is obviously red herring nitpickery.
I'll look into the rotation. Seventy degrees, though? I don't know what kind of hypermobile yogi they took that measurement off of, but I'd pay money to see him run or take a jump-shot. Mine only rotates a few degrees in that postion, and a few when the knee is fully extended and 'locks out'. I don't think either position is necessarily a healthy one to heavily load the joint in, however. As with squatting, lunging, and jumping, the knee works best when the foot and knee are kept in line. In practical terms, the knee functions as a hinge, and should be strengthened for mobility in this capacity, as well as stability in resistance to twisting or ab/adducting.
Just because it is theoretically possible for the knee to rotate while flexed, it does not even remotely follow that it is a good idea to do so under load, or that the torquing forces involved in suwari waza are within healthy knee-functioning parameters. The only way to settle such an argument would be controlled experiments, which probably don't exist. Next would be epidemiological-style studies. I would be willing to bet that I could find a high correlation between amount of knee-walking activity undertaken over a period of years and deterioration of the knee in terms of pain and reduced pain-free function.