Os acromiale

• Os acromialeis relatively common, seen in ~8% (range 1-15%) of the population and can be bilateral in 60% of individuals .
• The subtypes develop due to the fusion pattern of the three acromial ossification centres (preacromion, mesoacromion and meta-acromion)  and are classified on their pattern of articulation with the acromion (from proximal to distal) :
• basiacromial
• meta-acromial
• mesoacromial
• preacromial

Meta- and mesoacromial are the most common .

An Os acromiale is readily identified if care is taken to examine the acromion in the superior axial plane as it can easily be mistaken for the normal acromioclavicular joint.