The resurgence of one previously out-of-work major league pitcher has increased demand for a controversial new procedure utilizing stem cells that could usher in advances in athletic-injury treatment so effective they seem to turn back the clock.

But there are questions about the extent to which the attention-grabbing stem cell aspect of this new therapy helped Bartolo Colon, who has become the poster boy in this nascent area — or whether he benefitted primarily from particularly successful, but decidedly traditional, surgery.

Colon was an elite hurler for the Cleveland Indians and Anaheim Angels before age, injuries and workload took their gradual toll on his right shoulder. His baseball career seemed to be over when he was released by the Chicago White Sox during the summer of 2009, thanks to recurring bone spurs in his elbow.

His fastball speed had dropped several ticks. For a power pitcher like Colon, that often signals the beginning of the end.

And yet Colon has emerged this season with a fastball on par with his 2007 numbers, and his strikeout rate (if it keeps up) would be the best of his career since 2000. Testing for performance-enhancing drugs has never been more rigorous in baseball, so how did this happen to a 38-year-old has-been?

What no one knew until recently — not even the New York Yankees, who signed Colon to a minimum contract last offseason — was that Colon had a semi-experimental procedure done in the spring of 2010 in the Dominican Republic.

Fat and bone-marrow stem cells were extracted from Colon and then re-injected into his elbow and shoulder, a move designed to help regenerate and repair tissue — including his rotator cuff, which had been torn.

In some circles, the use of stem cells has become commonplace in treating athletes with stress injuries and ligament damage. By “some circles,” though, I mean “those who train thoroughbred racehorses.” For several years now, thousands of racehorses around the world have been treated with stem-cell-rich injections, with some analyses suggesting a 50 percent reduction in repeat leg injuries.

(Of course, even innocuous-looking injuries can be far more fatal in horses than people, so the stakes are higher to find faster, less invasive treatment options.)