OS ACROMIALE

UNFUSED ACCESSORY OSSIFICATION CENTRE OF ACROMION OF SCAPULA

 

 

There are normally 3 acromial ossification centers that fuse between 22 and 25 years of age.

An os acromiale results from the failure of 1 of these centers to fuse.

The anterior ossification center is termed the pre-acromion, the middle is the meso-acromion, and the posterior is the meta-acromion.

The basi-acromion forms the point of attachment of these 3 ossification centers to the scapula.

A number of subtypes of os acromiale have been described.

The most common variant is nonfusion between the meso- and meta-acromion.

The prevalence of os acromiale in radiographic and anatomic studies ranges between 1% and 15%.

An os acromiale can contribute to shoulder impingement symptoms.

Contraction of the deltoid muscle may pull the os acromiale downward, causing it to impinge on the rotator cuff.

Abnormal motion may lead to an osteophytic spur at the pseudarthrosis, which may also impinge on the cuff.

The diagnosis of os acromiale may be made on axillary projection radiographs, computed tomography (CT) or magnetic resonance imaging (MRI).

MRI may show marrow edema and degenerative changes at a pseudarthrosis.