The lateral collateral ligament (LCL) is a thin band that runs along the outside of the knee and connects the thighbone (femur) to the fibula, which is the small bone that runs down the side of the knee and connects to the ankle.
Similar to the medial collateral ligament (MCL), the LCL’s primary function is to stabilize the knee as it moves.
Tears to the LCL commonly occur as a result of direct blows to the inside of the knee, which can over-stretch the ligaments on the outside of the knee and, in some cases, cause them to tear.
The most common symptoms of an LCL tear are pain, stiffness, swelling and tenderness along the outside part of the knee. Your knee may feel loose, as though it will give way under stress, or it may lock.
More severe tears can cause numbness or weakness in the foot, which occurs in the peroneal nerve (located near the LCL) if it is stretched at the time of injury or squeezed by swelling of the surrounding tissues.