Baseball, returning to big-league action tonight, is a sport awash in superstition and lore—consider the long-standing Curse of the Bambino, said to have haunted the Boston Red Sox from the time the team sold Babe Ruth to the rival New York Yankees in 1919 until the Sox won a World Series in 2004. (The Chicago Cubs, another long-suffering franchise, are still struggling under their own Curse of the Billy Goat.)

So it's no surprise that a surgical operation resurrecting damaged elbows has taken on a legendary life of its own as a career-maker, rumored to tack a few extra miles onto a fastball and make a good pitcher great. Ulnar collateral ligament reconstruction, better known in the baseball world as Tommy John surgery after the left-handed Dodgers pitcher who first underwent the procedure in 1974, has often been rumored to leave pitchers better-equipped than ever to compete in the big leagues. After all, John himself went on to win 164 games post-op while making three All-Star teams. But the science on the surgery seems to indicate that the procedure provides little if any boost over pre-injury performance levels—in other words, its benefits may be just as real as the Bambino's curse.

The ulnar collateral ligament (UCL) connects the humerus, the upper arm bone, to the ulna, one of the two parallel forearm bones. (The ulna is the bone that reaches the wrist on the pinkie side.) The UCL can stretch or tear with stress such as that encountered in pitching a baseball or throwing a javelin. In 1974, Los Angeles orthopedic surgeon Frank Jobe replaced John's ruptured UCL with a grafted tendon (a band of tissue that usually connects muscle to bone) from the pitcher's right forearm, and Tommy John surgery was born. (Other tendons can be used as well.) Since that time countless athletes, primarily baseball pitchers, have gone under the knife for UCL reconstruction.

In 2003, Cubs fireballer Kerry Wood told USA Today that his velocity improved after Tommy John surgery. "I'm throwing harder, consistently," he said. And another hard thrower, reliever Billy Koch, then with the Chicago White Sox, joked to the newspaper that his elbow "felt so good when I came back, I said I recommend it to everybody ... regardless what your ligament looks like."

But the few studies tracking the impact of Tommy John surgery in the major leagues do not show the statistical improvement that would be expected of pitchers with improved velocity or command. A 2007 study by orthopedic surgeon Brett Gibson of the Penn Sports Medicine Center and his colleagues found "no significant change in mean earned run average or walks and hits per inning pitched" in players returning from UCL reconstruction.

Gregory Carolan, an orthopedic surgeon at St. Luke’s Hospital in Bethlehem, Pa., and his colleagues in February presented similar results at a meeting of the American Orthopaedic Society of Sports Medicine. Carolan's study compared athletes who had undergone Tommy John surgery before selection in the Major League Baseball draft with a matched control group, finding "no statistically significant difference between the [UCL-reconstructed] group and the control group with respect to placement on the disabled list, future shoulder or elbow injury, or level of professional advancement."

Even the inventor of the surgery refuses to credit his procedure for any career-making miracles. In a 2002 interview with ESPN.com, Jobe offered a few explanations for pitchers' perceived postoperative improvement. "When a pitcher comes in with elbow problems, you often see that their ligaments were already wearing out well before," Jobe said. A case in point: John first came to Jobe and his colleagues with UCL problems two years before the eponymous surgery. "Maybe four or five years ago they could throw a 95-mile-an-hour fastball, but they've had that ability diminished as the ligament's been stretched," Jobe told the sports Web site. "What the surgery does is restore the ligament's stability to where it was four or five years ago. A pitcher might say the operation did it, but it's just more stability in the arm contributing to better mechanics."

See our in-depth report on the science of baseball, just in time for Opening Day.

Photo of pitcher Shawn Estes in a 2007 rehab stint following Tommy John surgery courtesy of Tom Clifton on Flickr