Medial Collateral Ligament
The medial collateral ligament (MCL) is one of four ligaments that is responsible for keeping the knee joint stable. (The other three are the anterior and posterior cruciate ligaments [ACL and PCL] and the lateral collateral ligament [LCL].) The MCL connects the inner (medial) surfaces of the thigh bone (femur) and the shin bone (tibia) and is on the outside of the knee joint. Its function is to prevent stress from widening the medial portion of the knee joint.