Ulnar collateral ligament (UCL)

The ulnar collateral ligament (UCL) is a band of fibrous tissue on the inside of your elbow that helps stabilize the joint, especially during activities like throwing. It connects the humerus (upper arm bone) to the ulna (one of the forearm bones). The UCL prevents the elbow from valgus stress—where the forearm swings outward from the body—and maintains joint stability during motion. Injuries to the UCL are common in athletes who perform repetitive throwing or similar motions, often leading to pain and instability, sometimes requiring surgical repair or reconstruction.