A medial collateral ligament (MCL) injury is a sprain or tear to the medial collateral ligament. The MCL is a band of tissue on the inside of your knee. It connects your thighbone to the bone of your lower leg. The MCL keeps the knee from bending inward.

You can hurt your MCL during activities that involve bending, twisting, or a quick change of direction. For example, the MCL can be injured in football or soccer when the outside of the knee is hit. This type of injury can also occur during skiing and in other sports with lots of stop-and-go movements, jumping, or weaving.