What an MCL Does. The MCL is one of the four main ligaments in the knee joint. It's located on the side of the knee that's closer to the other knee. One end of the ligament is attached to the femur, while the other end is attached to the tibia. With the lateral collateral ligament (LCL), which is in the same location on the outside of the knee, the MCL helps prevent the knee joint from bending too far from side-to-side.