acromion

The acromion is a bony projection of the scapula that forms the highest point of the shoulder. It is a continuation of the scapular spine, extending laterally and anteriorly to overlie the glenohumeral joint. The acromion varies in shape and can be flat, curved, or hooked.

Articulations and attachments: The inferior surface of the acromion bears a facet that articulates with the acromial end of the clavicle to form the acromioclavicular joint. The acromion serves as an attachment site for the deltoid muscle and participates in the coracoacromial arch together with the coracoid process and the coracoacromial ligament, providing a protective roof over the glenohumeral joint.

Clinical relevance: The inferior surface contributes to the roof of the subacromial space through which the rotator cuff tendons and adventitious bursae pass. Narrowing of this space or acromial spur formation can contribute to shoulder impingement, particularly of the supraspinatus tendon. Acute acromial fractures, osteoarthritis at the acromioclavicular joint, and degenerative changes may involve the acromion.

Development and variants: The acromion develops from bony ossification centers that typically fuse in late adolescence or early adulthood. Variants in acromion shape are clinically recognized; a hooked (type III) acromion is more frequently associated with subacromial impingement than a flat (type I) form.

In summary, the acromion is a key scapular landmark that forms the lateral shoulder roof, participates in the acromioclavicular joint, and serves as an important attachment and protective structure for shoulder function.