The sequence of events has been a topic of great interest in St. Louis since it was announced that Carpenter would need ligament replacement, known as Tommy John surgery. The procedure, which Carpenter underwent on Tuesday, will sideline the 2005 Cy Young winner for approximately 12 months beyond the three months that he has already missed due to elbow troubles.
Carpenter was initially diagnosed in April with bone spurs and arthritis in his pitching elbow. He and the team first attempted a non-surgical program of rest and rehabilitation. When he still experienced trouble, Carpenter had an operation to remove the spurs and ease the arthritis.
The early part of Carpenter's rehabilitation following the first operation went well. But in his second rehabilitation start following the operation, he came down with more swelling and discomfort, which eventually necessitated the second surgery.
"In May, the main problem appeared to be related to the spurs and the arthritis," Paletta said. "But the potential existed that those spurs and arthritis were there because the ligament was gradually failing. But at the time, it was impossible to tell the player that that was the fact. And it was impossible to tell the player that he needed to have the elbow reconstructed."
What was determined with time was that the problem with the ligament was in fact the root cause of the other issues Carpenter was experiencing. Paletta said he originally estimated that possibility as about a one-in-three chance. But after the spurs and arthritis were addressed, and Carpenter was still having discomfort, it was clear that the ligament damage was the ultimate problem.
"In this particular case," Paletta said, "the question that had to be asked, and that was asked in depth, was, 'Is the arthritis the main problem here? Or is the arthritis there because this ligament is gradually starting to fail?'
"The consensus opinion ... was that we were hopeful that the arthritis was the main problem, in and of itself, and was not a sign of this underlying ligament failure. We dealt with the arthritis in an ideal way, cleaning out the spurs, smoothing out the arthritis, and he had continued problems, which made it more clear that the cause of that arthritis and the cause of those spurs was that this ligament was gradually failing over time."
According to Paletta, the ulnar collateral ligament in Carpenter's right elbow had not deteriorated dramatically in recent months. In fact, he said that scans of the ligament from 2007 do not look all that different from scans taken years earlier. However, once the elbow became symptomatic and problematic, the equation changed.
While the ligament did not worsen dramatically, the results of its failure grew more significant as time went on. But repairing the results was not enough -- the cause itself had to be addressed.
"As the ligament starts to fail, and gets gradually a little bit looser, it allows a little bit more play in the elbow," Paletta said. "The way the elbow responds to that is to try to stabilize itself by forming these bony spurs that increase the stability of it. That little bit of shear and play lets the cartilage surfaces wear a little faster and get arthritis. So the body is trying to basically counteract the gradual failure of that ligament by forming these spurs, and the arthritis is a manifestation of that little bit of extra play."
Paletta explained that the problem in Carpenter's elbow was not a complete rupture of the UCL. Rather, it was a slow deterioration of the ligament. According to a Cardinals source, opinions from leading doctors varied on whether Carpenter needed to undergo reconstructive surgery. But ultimately the pitcher decided that his preferred course of action was to have the operation, rather than wait and hope -- and possibly end up needing the procedure later anyway.
"This is unfortunately a classic example of slow, gradual failure of the ligament," Paletta said. "Not all ligaments suddenly tear and rupture. And sometimes the way the ligament fails is over the course of many months or many seasons, and it doesn't become as obviously apparent except through things like spurs and arthritis."
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.