Ulnar collateral ligament reconstruction
Ulnar collateral ligament reconstruction, also known as Tommy John surgery, is a surgical graft procedure where the ulnar collateral ligament in the medial elbow is replaced with either a tendon from elsewhere in the patient's body, or with one from a deceased donor. The procedure is common among collegiate and professional athletes in several sports, particularly in baseball.
Source: Wikipedia — Ulnar collateral ligament reconstruction (CC BY-SA 4.0)