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Teenage baseball pitchers have an increased risk of developing permanent shoulder injury. Researchers reported that young athletes who threw more than 100 pitches risked stunting normal shoulder development that could cause other problems, such as rotator cuff tears.

In this study, the researchers named the newly identified injury acromial apophysiolysis, which occurs when there is incomplete fusion and tenderness at the acromion, a bone that develops at the top of the shoulder during the teenage years. The acromion is made up of four bones.

"We kept seeing this injury over and over again in young athletes who come to the hospital at the end of the baseball season with shoulder pain and edema at the acromion on MRI, but no other imaging findings," said Johannes B. Roedl, M.D., a radiologist in the musculoskeletal division at Thomas Jefferson University Hospital in Philadelphia. "Among high school athletes, pitching is the most common reason for shoulder pain"

For this study, the team examined data on 2,372 patients between 15 and 25-years-old. The patients suffered from shoulder pain and underwent magnetic resonance imaging (MRI) from 1998 to 2012. The majority of the sample was made up of pitchers. Overall, 2.6 percent, or 61 patients experienced pain at the top of their shoulder. The researchers compared their shoulder health to a control group of participants.

The team found that 40 percent of the athletes from the injured group that threw more than 100 pitches per week had abnormal shoulder development. In the control group, only eight percent of them had shoulder problems.

Out of the 61 injured patients, one of them had surgery. The remaining 60 were treated conservatively. During the follow up, after the patients turned 25-years-old, the researchers managed to get MRIs or X-rays on 29 injured patients and 23 people from the control group. 25 out of the 29 patients had incomplete fusion of the acromion. In the control group, only one patient did.

"The occurrence of acromial apophysiolysis before the age of 25 was a significant risk factor for bone fusion failure at the acromion and rotator cuff tears after age 25," Dr. Roedl said in the press release. "Pitching places incredible stress on the shoulder. It's important to keep training in the moderate range and not to overdo it. This overuse injury can lead to potentially long-term, irreversible consequences including rotator cuff tears later in life."

The study, "Acromial Apophysiolysis: Superior Shoulder Pain and Acromial Nonfusion in the Young Throwing Athlete," was published in the journal, Radiology.