The medial collateral ligament, commonly referred to as the MCL, is a ligament located along the inner side of the knee. The MCL stretches from the thighbone (femur) to the shinbone (tibia) and helps to stabilize the inner (or medial) part of the knee. While several other ligaments and tendons, such as the hamstring tendons, provide additional support, the MCL is the most important structure that prevents the inner part of the knee from “gapping open” when the tibia bone is pulled outward (laterally).

The medial collateral ligament is commonly injured in soccer players as well as skiers and football players. Most injuries occur during a sliding tackle when the knee is subjected to a force (known as valgus force) that causes the tibia to bend outwards relative to the femur. An example of this is when an opposing player forcefully strikes the inside of one’s lower leg and forces it out during a slide tackle. During these episodes, the MCL can be injured by itself (isolated) or can be injured with the anterior cruciate ligament (ACL) and/or the medial meniscus, which is directly connected to the MCL.

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