Acromion process

Acromion
Left scapula. Posterior view. Acromion shown in red.
Details
Identifiers
Latin	Acromion
TA	A02.4.01.009
FMA	23260
Anatomical terms of bone []

In human anatomy, the acromion (from Greek: akros, "highest", ōmos, "shoulder", plural: acromia) is a bony process on the scapula (shoulder blade). Together with the coracoid process it extends laterally over the shoulder joint. The acromion is a continuation of the scapular spine, and hooks over anteriorly. It articulates with the clavicle (collar bone) to form the acromioclavicular joint.

The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the glenoid cavity.

Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibers of the deltoideus, and in the rest of its extent is subcutaneous. Its inferior surface is smooth and concave.

Its lateral border is thick and irregular, and presents three or four tubercles for the tendinous origins of the deltoid. Its medial border, shorter than the lateral, is concave, gives attachment to a portion of the trapezius, and presents about its center a small oval surface for articulation with the acromial end of the clavicle.

There are three morphologically distinct types of acromia and a correlation between these morphologies and rotator cuff tear:

The acromion has four ossification centers called (from tip to base) pre-acromion, meso-acromion, meta-acromion, and basi-acromion. In most cases, the first three fuse at 15–18 years, whereas the base part fuses to the scapular spine at 12 years. However, in between 1% and 15% of cases, this osseous union fails and the acromion remains a separate bone. This condition is referred to as os acromiale, but rarely causes pain. Earlier estimates of its prevalence were as low as 1.4%, and this higher estimate was made by Sammarco in the year 2000, based on radiographic and anatomical studies.