Fibular collateral ligament
Ligaments are bands of fibrous, tough tissue that connect and strengthen joints. They act very much like rubber bands. The fibular collateral ligament, which is one of the ligaments that make up the knee joint, is attached to the femur (thigh bone) on one end, goes through the biceps femoris muscle, and attaches to the fibula (calf bone) on the other end. It works together with the tibial collateral ligament to form the system of bone, ligament, and tendon that is the knee joint. The fibular collateral ligament is called an extracapsular ligament because it lies outside the knee joint capsule. In tandem with the tibial collateral ligament, the fibular collateral ligament controls the adduction and extension (motion towards the midline and straightening of the joint) of the leg at the knee joint. Hence, injury to this ligament can lead to great difficulty walking. The typical injury to the fibular collateral ligament is for it to become torn after a blow to the inside of the knee. Symptoms of a torn fibular collateral ligament include swelling on the outside of the knee, a feeling of instability in the knee, numbness in the foot, and a catching or popping in the knee joint.
Written and medically reviewed by the Healthline Editorial Team
In Depth: Fibular collateral ligament