The flattened acromion projects anteriorly from the lateral end of the spine, sloping gently upwards. There is a small oval facet at the anterior aspect of its medial border for articulation with the clavicle. The posterior border of the spine and the lateral border of the acromion meet at the acromial angle.

The acromion gives attachment to the deltoid laterally and anteriorly, with fibers from the trapezius attached to the medial margin.

With the exception of the medial aspect, the borders are all easily palpable, as is the upper surface.

Acromioclavicular joint

The acromioclavicular (AC) joint is a plain synovial joint between the small oval facet on the lateral end of the clavicle and the facet at the medial aspect of the acromion. The articular surfaces are lined with fibrocartilage.

A wedge-shaped articular disc is often found in the AC joint, partially separating the joint surfaces. The capsule is attached to the articular margins and reinforced by superior and inferior acromioclavicular (AC) ligaments. The coracoclavicular ligament, with its conoid and trapezoid components, provides major stability to the joint.