Tommy John Surgery, known in medical practice as ulnar collateral ligament (UCL) reconstruction, is a surgical graft procedure in which the ulnar collateral ligament in the medial elbow is replaced with a tendon from elsewhere in the body. The procedure is common among collegiate and professional athletes in several sports, most notably baseball. The patient’s arm is opened up around the elbow. Holes to accommodate a new tendon are drilled in the ulna and humerus bones of the elbow. A harvested tendon (often the palmaris tendon) from the forearm of the same or opposite elbow, from below the knee (known as the patellar tendon), or from a cadaver—is then woven in a figure-eight pattern through the holes and anchored. The ulnar nerve is usually moved to prevent pain as scar tissue that forms can apply pressure to the nerve.