The fibular collateral ligament is one of the ligaments that make up the knee joint. Ligaments are bands of fibrous, durable tissue that connect and strengthen joints. They can be likened to rubber bands.

The fibular collateral ligament 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 collaborates with the tibial collateral ligament to form the system of bone, ligament, and tendon that is known as the knee joint.

The fibular collateral ligament is called an extracapsular ligament because it lies outside the knee joint capsule. Together, both ligaments control the adduction and extension (motion towards the midline and straightening of the joint) of the leg at the knee joint.

Injury to this ligament can lead to gait (walking) problems. The most common injury for the fibular collateral ligament is tearing, typically 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.