Tommy John surgery is a procedure that replaces the ulnar collateral ligament, or UCL, of the elbow. The UCL is a ligament on the inside, or medial side of the elbow. It helps to stabilize the elbow joint. The injury is common in throwing or overhead athletes and can occasionally result from acute trauma, but more often it occurs with wear-and-tear over time. Non-athletes or non-throwing athletes can often recover without surgery, but throwing athletes frequently require surgery to return to pla