What is medial collateral ligament (MCL) injury?

Christopher C. Bell, MD
Sports Medicine
The medial collateral ligament (MCL) is a knee ligament that joins the lower end of the femur (thigh bone) to the upper end of the tibia (shin bone) on the medial (inner) part of the knee (part of the knee closest to the other knee). It prevents medial "folding" or bending of the knee towards the other knee, especially with lateral movements. Injuries most often occur when there are forces that drive the knee inward and separate the inner part of the femur and inner part of the tibia. The general term for ligament injuries are sprains, so MCL injuries are termed sprains also. There are different grades of sprains. Grade 1 is a stretch of the ligament such that there is trauma to it but no tear. This is the mildest form of injury. Grade 2 sprains involve partial tearing of the ligament. Grade 3 sprains involve full thickness tears. 

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