A medial collateral ligament (MCL) injury is a sprain or tear of the MCL, one of four knee ligaments. 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.

MCL injuries often occur during twisting, bending, or quick changes of direction, such as might happen if a knee is hit from the side while it is locked in position.

Minor injuries are treated with rest, ice, compression, and elevation (RICE). Knee movement may also be restricted for a period of time with a knee brace. Severe MCL tears may require surgery.