A medial collateral ligament (MCL) is a broad band on the inside of the knee. An MCL injury involves some degree of stretching of this ligament. MCL injuries commonly occur when force is exerted on the outside of the knee and pushes the joint sideways. This places stress on the inside of the joint, resulting in ligament damage.

There are three degrees of ligament injuries. A first-degree injury consists of only mild stretching of the ligament. There is no looseness of the joint. A second-degree MCL is a partial tear of the ligament. In a third-degree injury, the ligament is completely ruptured, and the joint is unstable.

What are the causes and risks of the injury?

Most frequently, the MCL is injured during sports when there is a twisting injury or blow to the outside of the knee. This might occur in a clipping injury in football or in a skiing accident if the knee is twisted. An MCL injury may also be caused by overuse of the joint, or by a fall in an elderly individual.