The Mets said the 34-year-old left-hander was operated on at the Hospital for Special Surgery. Mets medical director David Altchek repaired a tear in the capsule in the front of his left shoulder. The team said the two-time Cy Young Award winner will be hospitalized overnight.
Santana will miss the entire season for the second time in three years. He had surgery on Sept. 14, 2010, to repair tears in the front and bottom of the shoulder's anterior capsule and did not make it back to the major leagues until April 5, 2012.
New York still owes Santana $31 million from his $137.5 million, six-year contract. General manager Sandy Alderson said the remainder of the contract is not covered by insurance.
The surgery to repair a torn anterior capsule had been performed previously on only a handful of pitchers, beginning with Bret Saberhagen on May 28, 1996, Altchek told ESPNNewYork.com last year. The surgery on Santana left a two-inch scar at the front of his prized shoulder.
Because anterior capsule surgery has been performed so infrequently on pitchers, how Santana's recovery unfolds will contribute to determining the procedure's effectiveness in extending careers, Altchek had added.
The capsule is the set of ligaments that run between the ball and socket, holding them in place. The ligaments nearly completely encircle the shoulder. They span the front, bottom and back of the shoulder, but not the top.
Tearing the anterior capsule can result in the ball slipping forward in the shoulder socket during the delivery. Young actually felt discomfort in the back of his right shoulder before his surgery May 16, 2011 -- even though the tear was in the front of the capsule -- because the rear ligaments that remained intact were stretching as the ball slipped forward in the socket.
If the tear occurs on the socket side, the repair can be done through a less invasive arthroscopic procedure, as was the case with Braden, as well as former New York Yankees catcher Jorge Posada. If the tear is on the ball side, the surgeon is required to make an incision and go in through the front. That was the case with both Santana and Young.
Torn anterior capsules very likely are not new injuries among pitchers. Standard MRIs often are not conducive to revealing the tears. A more sophisticated MRI usually is required, or some other sleuth work.
Information from ESPNNewYork.com's Adam Rubin and The Associated Press was used in this report.