New Overuse Injury Identified in Young Baseball Pitchers

Laird Harrison

October 14, 2014

Young baseball players who throw more than 100 pitches per week run the risk for a newly identified overuse injury that can impede normal shoulder development and lead to other injuries, a new study shows.

"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 [magnetic resonance imaging (MRI)], but no other imaging findings," first author Johannes B. Roedl, MD, PhD, said in a press release.

Dr Roedl, a radiologist in the musculoskeletal division at Thomas Jefferson University Hospital in Philadelphia, Pennsylvania, and colleagues published their findings online October 14 in Radiology.

They call the injury acromial apophysiolysis because it 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.

To investigate the unexplained pain, the researchers reviewed records of 2372 consecutive patients between the ages of 15 and 25 years who underwent MRI for shoulder pain between 1998 and 2012.

Most of the patients, both male and female, were baseball pitchers. "Among high school athletes, pitching is the most common reason for shoulder pain," Dr Roedl said.

The researchers identified 61 patients (2.6% of the population) who had pain at the top of the shoulder and an incomplete fusion of the acromion but no other findings. They created a comparison group by matching these patients by age and sex with patients who did not have the condition.

They were able to obtain pitching history for 106 of the 122 patients included in the study. Through statistical analysis, they found that throwing more than 100 pitches per week was a substantial risk factor for acromial apophysiolysis (odds ratio [OR], 6.5; P = .017).

Among the patients with this injury, 40% threw more than 100 pitches per week compared with 8% in the comparison group.

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

The condition can lead to future problems. All 61 injured patients took a 3-month rest from pitching. One patient underwent surgery; the remaining 60 patients were treated conservatively with nonsteroidal pain medication.

The researchers obtained follow-up MRI or X-ray imaging studies at least 2 years later, after the patients turned 25 years old, for 29 of the injured patients and for 23 of the comparison group.

These images showed that the acromion was incompletely fused in 25 (86%) of the patients with the overuse injury (os acromiale) compared with only one (4%) of the patients in the comparison group (OR, 138; P = .001).

Of the 29 patients with the overuse injury, 21 continued pitching after the rest period, and all of these 21 patients showed incomplete bone fusion at the acromion.

The prevalence of rotator cuff tears was significantly 68% in this group vs 29% in the comparison group (OR, 5.4; P = .015).

The severity of the rotator cuff tears was also significantly higher in the overuse injury group compared with the control group.

Dr Roedl and colleagues suggest teenage and young adult pitchers limit the number of pitches thrown in a week to 100. This fits the recommendation of the American Sports Medicine Institute that pitchers between 15 and 18 years of age play no more than two games per week, with 50 pitches per game.

"Pitching places incredible stress on the shoulder," Dr Roedl said in the news release. "It's important to keep training in the moderate range and not to overdo it."

Dr Roedl added that many successful professional baseball pitchers played various positions, and even other sports, as young athletes, and thereby avoided overuse shoulder injuries.

The authors have disclosed no relevant financial relationships.

Radiology. Published online October 14. 2014.

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