Newly described shoulder injury spotted on MRIs of young pitchers

A new study has revealed that young baseball pitchers who throw more than 100 pitches per week are at risk for acromial apophysiolysis, a newly identified overuse injury characterized by incomplete fusion and tenderness at the acromion, which forms the bone at the top of the shoulder.

“Little leaguer’s acromion would be an inappropriate term for this entity, because the mean age of presentation of acromial apophysiolysis (19.6 years in our study) is later than in little leaguer’s elbow and little leaguer’s shoulder (mean age at presentation, approximately 13 years for both),” wrote Johannes B. Roedl, MD, of Thomas Jefferson University Hospital in Philadelphia, and colleagues.

The findings were published online October 14 in Radiology.

The acromion typically develops during the teenage years when four individual bones fuse into one, however Roedl and colleagues noticed young athletes, particularly pitchers, were often presenting with shoulder pain and edema at the acromion on MRI.

Roedl and colleagues devised a retrospective study that first looked at 2,372 consecutive patients who underwent MRI for shoulder pain between 1998 and 2012. All patients were between the ages of 15 and 25, and the majority were pitchers. A total of 61 patients had incomplete fusion of the acromion but no other findings, and these patients were matched with a control group that did not have the condition.

Of this final group of 122 patients, pitching history was available for 106, and statistical analysis revealed that throwing more than 100 pitches per week was a significant risk factor for developing acromial apophysiolysis (odds ratio 6.5). Among patients with acromial apophysiolysis, 40 percent threw more than 100 pitches per week, compared with 8 percent in the control group.

Follow up imaging revealed lingering effects for those with the overuse injury. MRI or x-rays conducted a minimum of two years after the patients turned 25 were available for 29 of the injured patients and 23 of the controls. These follow up scans showed 86 percent of patients who previously had acromial apophysiolysis later demonstrated incomplete fusion of the acromion, compared with only 4 percent of the controls.

All injured patients took a three-month rest from pitching, though rotator cuff injuries were significantly more common in patients with the overuse injury who continued to pitch after the rest period, according to the authors.

“Pitching places incredible stress on the shoulder,” Roedl said in a press release. “It’s important to keep training in the moderate range and not to overdo it.”