The medial collateral ligament (MCL) is the most commonly damaged ligament in the knee. The MCL can be sprained or torn as a result of a blow to the outer side of the knee, by twisting the knee, or by quickly changing directions while walking or running. MCL injury most often occurs in athletes. The MCL is a small, thick band of tissue on the inner side of the knee joint. It connects two bones—the thighbone and the shin bone—preventing the knee from bending inward toward the other knee. When the knee is hit on the outer side of the leg or if the knee is twisted violently, the MCL can overstretch resulting in a partial or complete tear. Healing times vary from a couple of weeks to a couple of months, depending on the severity of the injury.