I don't know, I've seen that piece of footage many times, and it just doesn't make any sense how he could have done it. The injury doesn't occur to the leg that he kicks with (meaning that there's no snapping motion), nor the leg that he lands on (meaning that there's no hyper-extension, or buckling as his weight collapses on it.) The leg in question just doesn't appear to suffer any trauma whatsoever, and yet there it is. It just looked so innocuous.