The human shoulder is primarily a ball-in-socket joint. The head of your upper arm bone fits loosely into a rounded socket in your shoulder blade. A patchwork of muscles and tendons called the rotator cuff keeps your arm bone centered in the socket.

Throwing a ball overhead places extreme stress on the shoulder to remain stable. It is one of the most violent actions you can inflict on any joint in the body. To accelerate the ball to top velocity, a person uses their entire torso in a kinetic chain to generate a high level of energy that ends up concentrated on the arm, launching the shoulder forward with tremendous force. With equal power, the soft-tissues – muscles, tendons, ligaments and cartilage (labrum) – must decelerate and dissipate the force after the ball is released.

The shoulder joint isn’t built for this. Yet the destructive push-pull of opposing imperatives is repeated thousands and thousands of times with baseball pitchers.

During an April 29 bullpen session, Raisel Iglesias said he felt a pinch in his right shoulder. The Reds assigned him to the disabled list two days later, diagnosed with a shoulder impingement.

Bryan Price described the impingement as a reinjury for Iglesias.

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Raisel Iglesias introduced himself to the international baseball scene playing for the Cuban national team in the 2013 World Baseball Classic. Iglesias pitched out of their bullpen, a role he performed extremely well according American scouts and Reds manager Bryan Price.

Soon afterward, at the age of 23, Iglesias chose to become one of more than two hundred baseball players who have defected from Cuba since 1991. Iglesias survived an odyssey of human trafficking, severe dehydration, capture, suspension and the bureaucracy of the U.S. Office of Foreign Asset Control. He risked all of this to play professional baseball in the United States.

Other organizations saw Iglesias as a reliever, though their reasons varied from his slight frame to mechanics to the number of pitches he had mastered. The Cincinnati Reds signed him to a surprising 7-year, $27 million contract in June 2014. Their plan was clear from day one.

“We feel he’ll be a starter in the next year or so,” said Reds general manager Walt Jocketty. In 2015, Iglesias made 22 starts, 16 for the Reds and 6 for Louisville. In his 95.1 major league innings, Iglesias struck out 104 and walked 26 batters. He posted a nifty 3.55 FIP and after normalizing his home run rate, a 3.28 xFIP.

Raisel Iglesias had displayed front-of-the-rotation promise in his new role as a starting pitcher.

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A medical diagnosis of impingement means two parts of the body are touching (impinging on) each other that shouldn’t. Devin Mesoraco’s tragic impingement last year consisted of his hipbones rubbing together. The shoulder is fragile compared to the hip joint.

There are a few types of shoulder impingements, but most involve the shoulder blade scraping the rotator cuff. Stress from throwing causes these structures to become pinched — the precise word Iglesias used. Inflammation (tendinitis) or tearing can occur. Muscles, tendons and other parts of the shoulder are at risk from impingement.

“There are so many nerves and other structures that run through there that any sort of inflammation throws things off and fast,” said Will Carroll, a sports injury expert. “It can be excruciating and tough to get under control.”

A single episode of impingement isn’t in itself serious. Treatment starts with non-surgical options of rest, anti-inflammation medicine and low-impact physical therapy.

Impingements limit the range of motion but also tend to become progressively worse. If the condition persists or recurs, the next step is surgery (subacromial decompression). Removal of scar tissue and bone spurs is possible, as is resection of a ligament to increase space by about 1 cm to avoid grinding.

Here’s the real rub: Chronic impingement can lead to career threatening shoulder damage like a rotator cuff tear or frayed labrum.

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Amidst the unbridled optimism about Raisel Iglesias following his 2015 performance lurked an ominous warning sign. The Reds had shut Iglesias down in September due to “shoulder fatigue.”

The Reds instructed the right-hander to take it easy with pitching in the off-season. They prescribed an aggressive training program in place of throwing, designed to strengthen his shoulder. The Reds accommodated the shoulder concerns even further in spring training when they delayed Iglesias’s first start to March 14. In total, he made just three appearances in Goodyear, throwing a total of six innings. By comparison, pitchers like Brandon Finnegan and Anthony DeSclafani started five games and pitched up to 19 innings.

“We shut him down to be cautious,” said Byran Price. “We were cautious in the offseason and cautious on the front end of spring training, not trying to do too much too soon.”

Discarding months of vigilance, on March 28 the Reds abruptly announced that Iglesias’s first start would be moved up a week so he could pitch on Opening Day. Iglesias would take the place of DeSclafani, who had been sidelined with an oblique injury.

On April 4, Raisel Iglesias started for the Reds against the Philadelphia Phillies, throwing 90 pitches. Four additional appearances followed, Iglesias never allowing more than three runs in a game. In 28 innings, he struck out 29 and walked just 7 batters. His ERA was 3.49 and FIP 3.65. On April 25, he threw 102 pitches against the New York Mets after throwing 107 the previous start against the Colorado Rockies.

Then came the bullpen session before a game with the Pirates and the pinch.

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Raisel Iglesias isn’t the only significant pitcher in the organization who the Reds have been trying to convert from a reliever to a starter. In fact, the front office has been running a large experiment with young former relief pitchers, large given the prominence of the draft picks involved.

Tony Cingrani, the Reds third round pick in 2011, was a reliever at Rice University. Michael Lorenzen, the club’s supplemental pick in 2013, was a closer at Cal State Fullerton. Nick Howard, the organization’s #1 pick in 2014, had been a closer at the University of Virginia.

The results so far have been discouraging. Cingrani spent most of 2014 on the disabled list with shoulder tendinitis and impingement. He returned to the DL last year with a shoulder issue. He’s back in the bullpen. Lorenzen has been on the DL this year with a sprained elbow ligament. He’ll return to the Reds in June as a reliever. Howard started 11 games in 2014 and made 5 starts in 2015. He was shut down at the end of 2015 with shoulder issues. He’s back in the bullpen in Daytona. Now you can toss Raisel Iglesias onto the pile of aborted starts and arm injuries.

Major league organizations, as a rule, don’t use early draft picks and 8-figure international signings on the bullpen. Pitchers who do spend time in the rotation and the bullpen begin as starters and move to the relief corps as they age or become ineffective. That was how it worked for Mariano Rivera and Dennis Eckersley as well as David Weathers and J.J. Hoover. Starters, then relievers.

As experience with the four Reds pitchers indicates, converting a reliever to a major league starter is a far-from-routine transition. The mental and physical preparation is radically different. Extensive studies by Tom Tango and ESPN’s Dan Szymborski show that pitchers, on average, have a one-run higher ERA, lower strikeout rates and higher weighted on-base average allowed as starters compared to when they were relievers. The added stress on the arm from starting can lead to injuries and setbacks.

Remember 2003 when the Reds moved closer Danny Graves to the starting rotation? His ERA/FIP rose from 3.19/3.56 to 5.33/5.48. Graves felt the move ruined his career.

Are there ways the Reds and other organizations can minimize the risk of future shoulder injuries? A great physical conditioning program aimed at developing strength and flexibility in pitching motions is a start. Guarding against overuse – pitching with shoulder fatigue – would help prevent the most common source of these injuries. Finally, biomechanical analysis can identify red flags in delivery. Delivery flaws place undue stress on smaller rotator cuff muscles instead of the stronger muscles of the back. Reds pitchers should undergo these tests as a matter of routine.

Again, in principle there is nothing wrong with a team trying to develop relievers with big arms into starters. The upside is enormous. 200 is a larger number than 70 in innings pitched. But attempting it, with the attendant health risks, with four top prospects is a big gamble.

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Casual baseball fans don’t pay attention to the details of injuries. They may be vaguely aware when a pitcher has an arm issue. They certainly don’t distinguish the most important types of arm injuries — elbows and shoulders. But the two are nowhere near the same in terms of long-term risk.

Research confirms that pitchers with shoulder injuries fail to recover to the degree that pitchers with elbow injuries do, even those with UCL tears. The elbow is a simple joint. It works like a hinge and does little more than that. Tommy John surgery is common now and successful recovery rates approach 90 percent.

Shoulder injuries often end careers. Pitchers who return can have recurring shoulder problems and face severe drop-offs in their first year after surgery. Treatment and recovery is difficult because the shoulder is a much more complicated network of muscles, ligaments, bones, tendons and nerves than is the elbow. Dr. Neal ElAttrache, a world-famous shoulder surgeon, compares fixing a shoulder with surgery to assembling a jigsaw puzzle without the box top.

“With your elbow, you go through the program, get the range of motion back, the pain goes away, everything feels good and off you go,” said Chris Carpenter, former Cy Young winning pitcher who had both elbow and shoulder surgery. “When you get into the shoulder, it’s a flip of the coin. You never have the same shoulder.”

On the bright side, there are pitchers who have overcome serious shoulder problems. Roger Clemens won all seven of his Cy Young awards after he underwent reconstructive rotator cuff surgery. Carpenter’s entire Cardinals career took place after he had labrum surgery in 2002.

Surgical techniques and rehab procedures have improved. Labrum surgery, for example, is no longer considered an automatic career-threatening event as it once was. Anibal Sanchez is a recent example of a pitcher returning after labrum surgery. But the odds against full recovery are steep.

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Bryan Price says Raisel Iglesias is now throwing with absolutely no soreness and the pitcher is expected to return to the Reds by late June. He has reported to AA Pensacola for rehab and threw 2 innings on Saturday.

That doesn’t mean Iglesias’ shoulder is no longer in jeopardy.

“The Reds have a good medical staff. There are few doctors I’d trust more than (Dr. Tim) Kremchek with a shoulder,” says Will Carroll. “But young pitchers with this problem almost always see it crop up again and again.”

There are limits to what rest and rehabilitation can accomplish. “We call it conservative treatment,” says Dr. Anthony Tropiano, a leading orthopedic surgeon. “But that’s just a euphemism for a little rehab and a lot of prayer.”

Even if he’s pain-free Raisel Iglesias’ role needs to change. The Reds have announced when Iglesias returns he will pitch out of the bullpen. That’s where he’ll stay for the indefinite future.

Carroll suggests the best-case template might be Trevor Hoffman. After spending a few years in the Reds organization as a light hitting infielder and then as a starting pitcher, Hoffman became a closer for Florida and San Diego. He had hurt his shoulder playing beach volleyball and football. Hoffman’s velocity fell from 95 to 91 mph after the injury and after shoulder surgery in 2003, it dropped to 85 mph. Meanwhile, Hoffman recorded 601 career saves, second most all-time.

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With eyes and minds wide open, the Cincinnati Reds chose a development course for Raisel Iglesias loaded with payoff and peril. They changed him from a reliever to starter, then back to reliever and once again to the rotation. In the face of shoulder issues last fall, they shut him down and put him on a special, slow recovery program through March. Then, they threw caution to the win in service of Opening Day headlines.

That’s not to say the Reds’ experiment with Iglesias wasn’t worth it. Short of finding another bullpen arm like Aroldis Chapman, the $27 million contract the Reds signed with Iglesias made sense mostly if the pitcher succeeded a starter.

Regarding his goal to pitch professionally in the United States, it would be a stretch to say that Raisel Iglesias’ journey with the Reds has been as harrowing as his escape from Cuba. But deep pitfalls await future decision-making. Moving Iglesias to the bullpen now is prudent. Even if he falls short of a second missile launch, Iglesias could become another brilliant Cuban star in relief.

However, the club won’t rule out trying Iglesias in the rotation again later this year or next. His glittering performance as a starter is powerful catnip.

Wise teams do what’s right even when it’s hard. Choices have repercussions. The Reds surely understand this.

They better. The health of Iglesias’ shoulder may hang like Damocles in the balance. There’s no assurance the Reds will receive another benign warning. If Iglesias’ impingement develops into a labrum or rotator cuff tear it could cut the pitcher’s promising career short. That’s the worst case. Three strikes and you’re out. Using Raisel Iglesias as a starter again makes that more likely.

With that risk in play, it’s time to edit the Rebuild Binder. The Reds and their fans may have to give up the vision of a 2017 rotation composed of Homer Bailey, Anthony DeSclafani, Cody Reed and Robert Stephenson and Iglesias. A Finnegan, Lorenzen, Amir Garrett or Rookie Davis can take his place.