Teenage baseball pitchers at risk for permanent shoulder injury

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 new study published online in the journal 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 or roof of the shoulder, typically develops from four individual bones into one bone during the teenage years.

"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.

To investigate the unexplained pain, 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.

"Among high school athletes, pitching is the most common reason for shoulder pain," Dr. Roedl said.

Sixty-one of the patients, (2.6 percent) had pain at the top of the shoulder and an incomplete fusion of the acromion but no other findings. The patients were then age and sex-matched to patients who did not have the condition to form a control group.

Pitching history was available for 106 of the 122 patients included in the study. Through statistical analysis, the researchers found that throwing more than 100 pitches per week was a substantial risk factor for developing acromial apophysiolysis. Among the patients with this overuse injury, 40 percent threw more than 100 pitches per week, compared to 8 percent in the control group.

"We believe that as a result of overuse, edema develops and the acromion bone does not fuse normally," Dr. Roedl explained.

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 MRI or X-ray imaging studies 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 percent) with the overuse injury showed incomplete fusion of the acromion, compared to only 1 of the 23 (4 percent) controls.

"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.