Medial collateral ligament
The medial collateral ligament (MCL or tibial collateral ligament) is one of the four major ligaments of the knee. It is on the medial (inner) side of the knee joint in humans and other primates. Its primary function is to resist valgus forces on the knee.
Structure
It is a broad, flat, membranous band, situated slightly posterior on the medial side of the knee joint. It is attached proximally to the medial epicondyle of the femur immediately below the adductor tubercle; below to the medial condyle of the tibia and medial surface of its body. It resists forces that would push the knee medially, which would otherwise produce valgus deformity.
The fibers of the posterior part of the ligament are short and incline backward as they descend; they are inserted into the tibia above the groove for the semimembranosus muscle.
The anterior part of the ligament is a flattened band, about 10 centimeters long, which inclines forward as it descends.
It is inserted into the medial surface of the body of the tibia about 2.5 centimeters below the level of the condyle.