By age 17, the acromion has consolidated to form three separate ossification centers along the periphery: the 1) PRE-ACROMIAL center which serves as the attachment for the coracoacromial ligament and the anterior tendinous origin of the deltoid; the 2) MESO-ACROMIAL center which anchors the middle tendinous fibers of the deltoid; and the 3) META-ACROMIAL center from which the posterior deltoid fibers originate. These three centers consolidate over the next year and ossify medially toward the clavicular facet by the time that the individual is eighteen years old (see illustration). The most common form of symptomatic os acromiale is failure of fusion between the meso-acromion and meta-acromion. Treatment is challenging and includes nonoperative management, ORIF of the fragment, open fragment excision or arthroscopic fragment decompression. All treatment modalities are fraught with benefits and disadvantages.
Kurtz CA, Humble BJ, Rodosky MW, Sekiya JK. Symptomatic os acromiale. J Am Acad Orthop Surg. 2006 Jan;14(1):12-9.
PMID:16394163 (Link to Abstract)
Sammarco VJ. Os acromiale: frequency, anatomy, and clinical implications. J Bone Joint Surg Am. 2000 Mar;82(3):394-400.
PMID:10724231 (Link to Abstract)