Contrary to popular belief, the kneecap does not just move up and down. It also moves side to side, and can rotate in some instances. This makes that little piece of bone very diverse and also very unstable.

However, there is an exception to the rule. If the ROM is less than 45 degrees, it could be that the medial hamstrings are restricting the movement of passive abduction. To differentiate between the short adductors and the medial hamstrings, the knee is flexed to 90 degrees (figure 8.27); if the range now increases, this indicates shortness in the

as the cartilaginous articular surfaces of the bones. These articulating surfaces keep the bones apart, and the soft tissues around the joint keep the bones together.