The Tommy John procedure is an ulnar collateral ligament reconstruction (UCLR) named after the pitcher Tommy John, who underwent the procedure for the first time in 1974. He successfully had his elbow reconstructed and was able to win a ton of games after.
The procedure restores stability to the elbow by reconnecting the ligament from the humerus to the olecranon. This is the ligament that undergoes stress during repetitive throwing.
The Tommy John surgery has an 80 percent return-to-play rate. It’s not perfect. The procedure does not improve performance, but has a goal of returning the athlete to the field.
The best thing you can do as an athlete is to avoid the surgery in the first place by adhering to proper rest periods from throwing, which by U.S.A. Baseball standards, includes taking three months a year off from competitive throwing.