Last post we discussed ACL injuries, the granddaddy of knee pain. Equally common are medial collateral ligament (MCL) injuries. The MCL crosses the inside of the knee, and provides stability to prevent valgus stress, the stress that would occur to the knee if you were to push one knee in towards the other from the outside, and also contributes to rotational stability. Forceful movement into valgus or rotation can cause ligament failure, and, unlike the ACL, we have more varie