Causes

Ligaments are tough, non-stretchable fibers that hold bones that span the knee joint together. The medial and lateral collateral ligaments in your knee give you stability on your feet. The most common cause of a collateral ligament injury is a direct blow to the knee either from the inside or outside.

Torn collateral ligaments usually occur during contact sports such as football or hockey. A blow to the outside of the knee while the foot is planted can push the knee inward toward the opposite leg, tearing the MCL. A blow to the inside of the knee that forces the lower leg to bend out can damage the LCL.