Young baseball pitchers who throw more than 100 pitches per week are at risk for a newly identified overuse injury that can impede normal shoulder development and lead to additional problems, including rotator cuff tears, according to a study published online ahead of print October 14 in Radiology.
The injury, termed acromial apophysiolysis by the researchers, is characterized by incomplete fusion and tenderness at the acromion. The acromion, which forms the bone at the top of the shoulder, typically develops from four individual bones into one bone during the teenage years.
Johannes B. Roedl, MD
“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, MD, a radiologist in the Musculoskeletal Division at Thomas Jefferson University Hospital in Philadelphia.
Dr. Roedl and a team of researchers conducted a retrospective study of 2,372 consecutive patients between the ages of 15 and 25, who underwent magnetic resonance imaging (MRI) for shoulder pain between 1998 and 2012. The majority of the patients, which included both males and females, were baseball pitchers.
Patients with edema at the acromial apophyses and no other abnormalities on MRI were included in the study group. Association of acromial edema with incomplete fusion , pitching, and clinical findings was determined in the study group and in an age- and sex-matched control group. Association with the development of an os acromial and rotator cuff tears later in life was assessed with follow-up imaging after age 25.
Edema at the acromial apophyses was found in 2.6% (61 of 2,372) and was associated with incomplete fusion of the acromial apophyses and superior shoulder tenderness.
A pitch count of more than 100 pitches per week was a substantial risk factor for developing acromial apophysiolysis (odds ratio 6.5). Among the patients with this overuse injury, 40% threw more than 100 pitches per week, compared to 8% in the control group.
All 61 injured patients took a three-month rest from pitching. One patient underwent surgery while the remaining 60 patients were treated conservatively with non-steroidal pain medication. Follow-up imaging conducted a minimum of two years later after the patients turned 25 were available for 29 of the 61 injured patients and for 23 of the 61 controls. Follow-up imaging revealed that 25 of the 29 patients (86%) with the overuse injury showed incomplete fusion of the acromion, compared to only one of the 23 (4%) controls.
Twenty-one of the 29 patients with the overuse injury continued pitching after the rest period, and all 21 showed incomplete bone fusion at the acromion. Rotator cuff tears were significantly more common among this group than in the control group (68% versus 29%, respectively). The severity of the rotator cuff tears was also higher in the overuse injury group compared with the control group.
“More and more kids are entering sports earlier in life and are overtraining,” said Dr. Roedl. “Baseball players who pitch too much are at risk of developing a stress response and overuse injury to the acromion. It is important to limit stress to the growing bones to allow them to develop normally.”