Stephen Strasburg returns to a major league mound for the first time in over a year when he pitches against the visiting Dodgers on Tuesday night. (Jonathan Newton/WASHINGTON POST)

The baseball world will take a break from its pennant races Tuesday night and watch Stephen Strasburg hurl fastballs at close to 100 mph, mesmerized again with his talent. It will possess only a vague understanding of the medical advances that allowed him to do so now and, the Washington Nationals hope, for years to come.

Strasburg will return to the major leagues one year, one month and 16 days after he threw a change-up and snapped the ulnar collateral ligament in his right elbow. One year ago Saturday, Lewis Yocum bored holes in a bone in Strasburg’s elbow and attached to it a tendon removed from Strasburg’s thigh. Over time it transformed into a replacement ulnar collateral ligament, a thin strand of tissue that gave Strasburg new pitching life.

The procedure known as Tommy John surgery has changed baseball for 37 years, ever since Frank Jobe performed the first ligament-replacement surgery on the left-handed pitcher for which the operation is named. A torn UCL was once a death sentence for pitchers’ careers. Tommy John surgery was once regarded as a risky, last-resort operation. It has become commonplace and, at the highest level of baseball, a virtually sure-fire means to restore a pitcher’s career.

“As long as it’s in the right hands,” said Tim Kremchek, a leading Tommy John practitioner, “the player has over a 95 percent chance of coming back.”

The surgery Strasburg underwent last year struck a devastating blow to the Nationals’ 2011 hopes and presented Strasburg a grueling year of rehabilitation. But because of the evolution and prevalence of Tommy John surgery, Strasburg will join the horde of major leaguers who have returned with a four-inch scar on the inside of their pitching elbow.

“I would never have thought it would happen,” said Jobe, the orthopedic surgeon who pioneered the surgery. “It’s been a very fortunate experience for me. It just turned out very well.”

‘Immense creativity’

Tommy John met Jobe in 1972. John was pitching for the Los Angeles Dodgers and needed bone chips removed from his left elbow. Jobe, then the Dodgers’ team physician, performed the surgery. They stayed in touch. Jobe performed an operation on John’s wife. A friendship formed.

Late in the summer of 1974, John felt a pain in his left elbow so severe he could no longer pitch. He learned he had snapped the ulnar collateral ligament. He went to Jobe.

Early in his career, Jobe had performed tendon grafts for children who had polio diagnosed. When he examined John’s torn ligament, the idea to perform a similar operation struck him.

“Immense creativity,” said Yocum, the surgeon who performed Strasburg’s operation and now practices with Jobe.

“Brilliant,” Kremchek said.

At the time, Jobe was confident but was not certain the idea would work.

“I trusted Jobe,” John said. “He was a friend. I knew he wouldn’t BS me. He would lay it on the table and tell me what was good for me. He told me, ‘You do not have to have the surgery. But if you don’t, you will never pitch again.’ I said, ‘Okay, if I have the surgery, what are the chances?’ He said, ‘You probably won’t pitch again.’ I wanted to play baseball. I would do whatever it took to play baseball again. So we had the surgery.”

When Jobe operated, he sliced John’s elbow wide open and moved the ulnar nerve in order to reach the bone. He took a tendon from a cadaver’s leg and attached it with screws. Then he hoped John’s body would react favorably and the tendon would serve the same role as the ligament.

“We didn’t really know whether we could do it or not,” Jobe said. “We didn’t know whether we could heal it or not. We didn’t know whether a tendon would be accepted by the body and receive blood supply and become part of the body.”

Jobe and John waited. John did not throw a ball again for 16 weeks. Jobe decided he should not pitch in a major league game again until one year of rigorous rehab. Every step of the way, the recovery unfolded as Jobe hoped. John returned in 1974, and in seven of the next eight seasons he threw more than 200 innings.

“I would never have thought it would happen,” Jobe said. “I didn’t do it again for another two years. After another year or so, I had a couple successes. I thought, ‘This may be something we ought to use a little more routinely.’ ”

Some differences

Tommy John surgery has become more reliably successful, and so more pitchers have had it. As more pitchers undergo the surgery, doctors are able to perform more studies and gain more knowledge, and it becomes more reliably safe.

Last year, 10 pitchers who had undergone the surgery were named to the all-star team. Kremchek, the Reds’ team physician, said he once performed 15 to 20 ligament-replacement surgeries per year. In 2010, he performed Tommy John surgery about 150 times.

“It’s becoming much more of an accepted procedure,” Kremchek said. “Our comfort level with doing this is better. The public opinion as well as the baseball opinion has changed.”

(John enjoys his association with the procedure. “I’ll be dust in the grave,” he said, “and people will still be having Tommy John surgery.”)

The fundamental concept of the operation has not shifted since John’s surgery — “the basic principles have always been the same,” Yocum said. But four crucial differences have made the surgery more consistent:

●The placement of the tendon graft has become more uniform, which leads to fewer complications for surgeons.

●The operation is less invasive and requires less damage to soft tissue. Doctors no longer cut the elbow wide open, as Jobe did for John.

●Surgeons don’t move the ulnar nerve anymore. About 10 percent of recoveries once either failed or were slowed because of nerve damage. Surgeons learned how to operate around the nerve.

●The most significant development has been a more predictable and comprehensive rehab plan. Pitchers still throw for the first time at around 16 weeks after surgery. Doctors now, though, have a better understanding of how pitchers should strengthen their shoulder and core muscles to take stress off the elbow.

The advances have not eliminated risk. Even a 95 percent success rate means, “not everybody that has that the Tommy John surgery comes back,” Jobe said.

Many pitchers have come to believe the fallacy that Tommy John surgery enhances velocity. It doesn’t, experts say. Pitchers sometimes throw harder when they return, but that comes from the increased shoulder strength from rehab, not the surgery. Also, pitchers often threw with diminished velocity before the operation, and in comparison, when healthy, they just seem to throw harder.

Cubs reliever Kerry Wood underwent Tommy John surgery in 1999 at age 22. His electric first season and high-90s fastballs were a precursor to Strasburg’s rookie year. Wood’s injury-filled career is often held up as an example for pitchers who do not return to full strength after the procedure.

But that, Wood said, is inaccurate. From 2001 to 2003, he struck out 700 batters in 599 innings and compiled a 3.41 ERA. He later pitched only 110 innings from 2005 to 2007 because of injury. But those complications arrived because of his shoulder. Wood attributes none of the damage to Tommy John surgery.

“I missed a year,” Wood said. “That’s the way I look at it. That’s about the only effect it had. I haven’t had any issues with [my elbow] since.”

Dedicated to rehab

Strasburg flew to Los Angeles for his surgery in early September of last year. “There was some concern,” Yocum said. “I think anybody would be concerned. It’s appropriate. It’s a potential end to their career.”

Strasburg’s initial doubt ceded quickly to drive. He had always wanted to be the best pitcher. Now, “he said he was going to be best at rehab,” Nationals pitching coach Steve McCatty said.

“That’s one of the nice things about doing the professional athletes,” Yocum said. “They’re very focused and they’re very dedicated to their rehabilitation. That’s one of the very exciting things about working with them, that motivation and drive. Stephen definitely fit that bill.”

As well as Strasburg has progressed, challenges remain. Pitching is an unnatural act, especially when ligaments and tendons are forced to absorb the torque necessary to throw 100 mph.

The Nationals will take every precaution they can, starting with limiting Strasburg to four innings and 60 pitches in his first start back. They will keep a close eye on him, for a different reason than the rest of the baseball world.