Ulnar collateral ligament reconstruction, also known as Tommy John surgery, is a surgical procedure performed to repair a torn ulnar collateral ligament (UCL) in the elbow. The UCL is a vital stabilizing structure in the elbow, and its injury can lead to pain, instability, and reduced elbow performance. During the surgery, a tendon from another part of the patient's body or from a donor is used to replace the damaged ligament.