Working Diagnosis:
Acromial apophysiolysis with type 1 acromioclavicular joint separation

Treatment:
After the initial visit, the patient was restricted from overhead activities and an MRI was ordered. After four weeks, his pain and physical examination was similar to his initial visit. A CT was then ordered and the patient was placed in a sling and restricted from weight lifting and football practice.

Outcome:
After two weeks of consistent sling use and restriction from activity, his pain was improved. His active range of motion increased with abduction to 100 degrees and anterior flexion to 110 degrees and his strength was 4/5 with resisted abduction. After nine weeks from his initial visit, he had no pain, full range of motion of his shoulder, full strength of his shoulder, and negative special tests. He was then cleared for a gradual return to play football. He was recommended to follow up if his shoulder pain returned. He has not followed up since.

Author's Comments:
Acromial apophysiolysis is characterized as incomplete fusion of the acromial apophyses. The acromion develops from three apophyses (meta-, meso-, and pre-acromion) that fuse from medial to lateral and from posterior to anterior between the age of 15 and 25. In one study, the frequency was 2.6% among patients between the age of 15 and 25 presenting with shoulder pain. It is associated with development of os acromiale, rotator cuff tear and/or shoulder impingement later in life. Risk factors include repetitive stress especially among throwing athletes with greater than 100 pitches per week, swimmers, and football players. The patient typically presents with superior shoulder pain and/or tenderness over the acromion. The treatment consists of rest for a period of 2-3 months with cessation of pitching or other sports activities, ice, and nonsteroidal antiinflammatory medication. Surgery may be considered if conservative therapy fails.

Editor's Comments:
Overhead athletes are at particular risk of developing acromial apophysiolysis due to the repetitive traction forces from the deltoid on the developing acromion in young athletes. As demonstrated in this case, the diagnosis of acromial apophysiolysis can be challenging. Shoulder radiographs may not show an abnormality at the growth plate. With an MRI, one can better differentiate apophysiolysis from a normally developing acromion. On axial images, the growth plate has a linear and transverse orientation with irregular margins with diffuse marrow edema and small foci of hyperintense signal adjacent to the growth plate in apophysiolysis. In comparison, a normal acromion growth plate has an arched and oblique orientation with uniform, lobulated margins on axial images.

References:
Kjellin I. Acromial apophysiolysis. MRI Web Clinic. Radsource; 2015. URL: https://radsource.us/acromial-apophysiolysis/. Accessed June 20, 2021.
Macalister A. Notes on acromion. J Anat Physiol. 1893; 27(pt 2): 244.1-251.
Roedl JB, Morrison WB, Ciccotti MG, Zoga AC. Acromial apophysiolysis: superior shoulder pain and acromial nonfusion in the young throwing athlete. Radiology. 2015;274(1): 201–209.
Sammarco VJ. Os acromiale: frequency, anatomy, and clinical implications. J Bone Joint Surg Am. 2000 Mar; 82(3): 394-400.
Scheuer L, Black S, Christie A. The pectoral girdle. In: Developmental juvenile osteology. San Diego, CA: Elsevier Academic Press, 2000: 244-271.
Winfeld, Matthew, et al. “Differentiating os acromiale from normally developing acromial ossification centers using magnetic resonance imaging.” Skeletal radiology 44.5 (2015): 667-672.

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