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Acromial apophysiolysis: superior shoulder pain and acromial nonfusion in the young throwing athlete.

PURPOSE
To describe the frequency of acromial apophysiolysis and its association with incomplete fusion and superior shoulder pain, to determine risk factors of acromial apophysiolysis, and to assess whether acromial apophysiolysis is associated with the development of an os acromiale and rotator cuff tears.


MATERIALS AND METHODS
Institutional review board approval was obtained for this HIPAA-compliant study; requirement for informed consent was waived. A retrospective report review of 2372 consecutive patients between 15 and 25 years of age who underwent shoulder magnetic resonance (MR) imaging for shoulder pain was performed. Individuals with edema at the acromial apophyses and no other abnormalities on MR images 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, with both univariate and multivariate binary logistic regression analyses. Association with the development of an os acromiale and rotator cuff tears later in life was assessed with follow-up imaging after age 25 years.


RESULTS
Edema at the acromial apophyses was found in 2.6% (61 of 2372) of patients and was associated with incomplete fusion of the acromial apophyses (χ(2), P < .001) and superior shoulder tenderness (P < .001). The entity was named acromial apophysiolysis. A pitch count of more than 100 pitches per week was shown to be a risk factor for acromial apophysiolysis (odds ratio [ OR odds ratio ] = 6.5, P = .017). Follow-up imaging showed that acromial apophysiolysis was significantly associated with the development of an os acromiale ( OR odds ratio = 138, P < .001) and rotator cuff tears ( OR odds ratio = 5.4, P = .015) after age 25 years.


CONCLUSION
Acromial apophysiolysis is characterized by incomplete fusion and edema at the acromial apophyses. It is associated with superior shoulder pain in young patients (< 25 years old), and pitching is a risk factor. It predisposes the patient to the development of an os acromiale and rotator cuff tears after age 25 years.