Os Acromiale: Reviews and Current Perspectives

Abstract

Os acromiale is a developmental defect which results from the lack of an osseous union between the ossification centers of the acromion, leading to the fibrocartilaginous tissue connection. The prevalence of os acromiale is 1% to 15%, and is quite common in the African American population. Os acromiale in adults is easily diagnosed by symptoms and X-ray, particularly on the axillary view; however, the differential diagnosis of adolescents may require MRI or SPECT-CT. Generally, nonoperative therapy for symptomatic os acromiale should be started, including physiotherapy, nonsteroidal anti-inflammatory drugs, and injections. Surgical treatment is indicated after failed conservative treatment. In symptomatic patients with fixable acromiale, the tension band technique should be used to make the anterior aspect of the acromion elevated from the humerus head. In patients with small fragments which are unsuitable for reattachment, excision might be the best therapeutic option and lead to good outcomes. Whether using internal fixation or resection, the arthroscopic technique results in a better outcome and fewer complications, especially in older patients or athletes with overhead movement, because of the high incidence of shoulder impingement or rotator cuff tears which can be treated concurrently.

Keywords: Arthroscopy; Os acromiale; Reverse shoulder arthroplasty; Rototar cuff tear; Shoulder impingement.

Figure 1

The types of os acromiale: (A) the space between the os pre‐acromiale and the acromion; (B) the space between the os meso‐acromiale and the acromion (note there is a communication with the acromioclavicular joint, found in all our patients); and (C) the space between the os meta‐acromiale and the acromion14.

Figure 2

(A) Os acromiale without step‐off deformity. T1‐weighted sagittal MRI of the shoulder shows an os acromiale without step‐off deformity (arrow) relative to the inferior cortex of the acromion. A, acromion; H, humeral head; O, os acromiale; P, posterior. (B) Os acromiale with step‐off deformity. T1‐weighted sagittal MRI of the shoulder shows malalignment (white arrowhead) between the inferior cortex of the os acromiale (arrow) and the acromion. A, acromion; C, clavicle; P, posterior24.

Figure 3

Axillary lateral radiograph demonstrating a meso‐acromion (arrow)28.

Figure 4

(A) Anteroposterior radiograph demonstrating the double‐density sign, with the cortical margin of a meso‐acromion (OS) superimposed over the cortical margin of the base of the acromion (Ac) at the nonunion site. The margins of this os acromiale appear smooth, sharp, and well circumscribed. DC, distal part of the clavicle. (B) Diagrammatic representation of the radiograph28.

Figure 5

Axial proton density‐weighted fat‐saturated image of the left shoulder of a 17‐year‐old boy demonstrates an ununited ossicle adjacent to the acromion suggestive of os acromiale. There is a fluid‐like signal at the interface (arrow) and marrow edema along the opposing surfaces (curved arrows) of the distal acromial ossification center (asterisk) and the rest of the acromion33.

Figure 6

Top row shows static bone scan and blood‐pool images, middle row images shows fused SPECT/CT images, and bottom row shows attenuation correction CT. Arrows are placed at ossification centers of apophyses. Center is at meso‐acromion on the left (white arrow) but at preacromion on the right (black arrow). The right apophysis is nearly fused and has less activity than the unfused apophysis of the left acromion34.

Figure 7

(A) Deltoid‐off approach: Terminal branches of thoracoacromial artery have been divided. Hence, unfused acromial epiphysis is devascularized. (B) Transacromial approach. Terminal branches of thoracoacromial artery remain intact. Acromial epiphysis remains vital and maintains full healing potential36.

Figure 8

(A) Schematic drawing shows compression of the acromion and the os acromiale fragment. (B) Arthroscopic view shows compression of the acromion and the os acromiale fragment8.