Akromions

Akromions, more commonly spelled acromions, are the lateral bony projections of the scapula that form the superior aspect of the shoulder. They extend from the scapular spine and, with the distal clavicle and coracoid process, contribute to the acromial arch that overhangs the glenohumeral joint. The acromion serves as an attachment site for muscles such as the deltoid and provides a roof over the tendons of the rotator cuff.

Structure and variation

The acromion varies in shape among individuals. The most widely used classification, derived from radiographic morphology, divides acromions into three types: Type I (flat), Type II (curved), and Type III (hooked). This variation can influence the size of the subacromial space and the risk of impingement. An accessory, unfused ossicle known as os acromiale can occur in some people, presenting as an extra piece of bone at the acromial tip.

Development

The acromion develops from ossification centers at the lateral border of the scapula and typically fuses with the scapular body during late adolescence. Variations in development can lead to anatomical differences that are clinically relevant for shoulder function and surgery.

Clinical significance

Acromial morphology affects shoulder mechanics and can contribute to conditions such as subacromial impingement and rotator cuff degeneration. Acromial spurs and degenerative changes may cause pain and limited motion. In some cases, surgical procedures such as acromioplasty are performed to reshape the acromion and relieve impingement. Imaging—radiographs, MRI, or CT—helps classify acromial type and assess associated pathology.