Doctors who specialize in sports medicine, including leading authorities on the type of ligament replacement surgery performed on the throwing arm of Stephen Strasburg, say they aren’t surprised by the Washington Nationals’ decision to end their star pitcher’s season early sometime next month.

Even so, they acknowledge there is no consensus on whether it is a necessary step.

The approach the Nationals are taking — shutting Strasburg down once he reaches a yet-to-be-decided cap, possibly between 160 and 180 innings — is being scrutinized and studied carefully by many across the sport.

“It’s been conservative, more conservative than what we’ve done in the past,” said Kevin Wilk, whose group, Champion Sports Medicine, handles rehabilitation for the practice of James Andrews, one of the nation’s foremost orthopedic surgeons. “But this may turn out to be the model that teams use as a result of it. It’s very interesting to watch, especially because it’s such a high-prized player and the Nationals are doing so well.”

Since the surgery was first performed on the elbow of Los Angeles Dodgers pitcher Tommy John in 1974, broad timelines have been hammered out, mostly by trial and error, over how to treat pitchers in their first full season after the procedure.

There’s no proof that limiting the number of innings for a pitcher in his first full season back from the surgery will prevent another injury, but some leading medical experts on the subject agree that being cautious and limiting the workload of a talented, young pitcher such as Strasburg, 24, is a sound practice.

Recovery from Tommy John surgery is typically a two-year process. Pitchers don’t start throwing at full throttle off the mound until eight to nine months after surgery, and don’t start pitching competitively until nine to 12 months after. In the first full season back, or the second year of the recovery, a pitcher starts to feel completely comfortable with the reconstructed elbow, the feel of pitching and grip of the ball, and finds consistency. But there is no way to truly tell when the transplanted tendon fully becomes a new ligament, nor is there a consensus on when the restraints on a pitcher can be fully removed.

“There is no book, no number, no magic, no ‘you can pitch all the way until October,’ ” said Timothy Kremchek, the Cincinnati Reds’ team doctor. He performs nearly 60 Tommy John surgeries a year on major and minor league pitchers from across the country. “Nobody knows that and many of us are afraid to take the chance with these guys.”

Template for shutdown

The Nationals have used fellow starter Jordan Zimmermann as a model for their approach with Strasburg. Zimmermann had Tommy John surgery to replace his torn ulnar collateral ligament in 2009 and pitched 1611 / 3 innings last year in his first full season back, just over his prescribed 160-inning limit. While that proved successful for Zimmermann, who has emerged as one of the league’s best pitchers, Strasburg won’t be held to the same number.

The worst-case scenario would be if the tendon graft is damaged, but that’s a rare occurrence since the surgery is extremely successful if performed by a capable surgeon and rehabilitated correctly by the player. (According to a 2010 study, 83 percent of athletes studied returned to the same level of competition or higher within a year of surgery.) But experts worry that tendinitis could develop or a pitcher could become fatigued by overuse, possibly leading to poor mechanics or more serious shoulder injuries.

Not all teams rely on a strict innings limit in the first full season back. Kremchek said the Reds keep a close eye on innings but don’t prescribe a number. Instead, the team carefully scrutinizes the players’ starts, especially beginning around the 10th start, watching for a loss in bite on breaking balls, comparing film and consulting with catchers and coaches. If needed, Kremchek said a pitcher can skip a start or be shut down.

If a team has playoff potential, Texas Rangers team doctor Keith Meister said he works with Rangers coaches to manage the pitcher’s innings: skipping starts, adding an extra day of rest or pushing them to the back of the rotation. He said he generally sticks to the 150- to 200-inning range in the first full season back, and anything beyond that is worrisome.

“I wish I could tell you there was science behind it,” he said. “But there is none.”

A firm decision

Nationals General Manager Mike Rizzo — with the direction of Lewis Yocum, who performed the surgeries on Strasburg and Zimmermann; the team’s medical and pitching staff; and other medical resources — will ultimately decide when to stop Strasburg. He will also look at how strongly and consistently Strasburg is pitching, and how many stressful innings he has thrown.

Rizzo has held firm that Strasburg’s schedule would not be manipulated so that he can pitch in the postseason, believing a regular schedule would help him recover but also because he has yet to experience the rigors of a full major league season.

Strasburg was 22 at the time of injury in 2010, having thrown 1231 / 3 innings in both the minors and majors. He had surgery on Sept. 3, 2010, and the following season, he threw only 441 / 3 combined innings. With his six innings in Wednesday’s 6-4 victory over the San Francisco Giants, he has thrown 139 1/3 innings.

Some experts say a pitcher’s age and pitching style matter in the recovery process. If the pitcher is an experienced veteran, he could adjust his body, mind and arm to adapt to the challenges of the first full season after the procedure. A pitcher who hasn’t thrown a lot of innings in professional baseball could be more susceptible to injury if there’s a large increase in work. And a power pitcher who gives maximum effort on every throw should be monitored a little more closely, some experts said.

Given that there is no evidence to explain the effects of limiting a pitcher in his first full season, medical experts said it is likely best to err on the side of caution, especially given Strasburg’s potential and future.

“It’s a risk-reward situation,” said James C. Walter, an orthopedic surgeon who trained under Andrews and serves as the medical director for FC Dallas of Major League Soccer. “We don’t have a perfect science on what you can rehab and when you can come back. It’s trial and error. It makes you nervous with someone that talented, I think, it’s as much financial as medical.”

Kremchek said he has wondered what he would do if faced with the same situation as the Nationals. When Strasburg is shut down in a postseason push, fans will be upset, he said. If he continues to pitch and gets hurt, the Nationals will also be scrutinized. Kremchek believes they are taking the correct approach for the future of the Strasburg and the Nationals by being cautious.

“The kid is obviously a No. 1 pitcher and a No. 1 pitcher for the next 12 years on a team that is very young and potentially going to contend for the next eight years,” he said. “There’s no right or wrong answer.”