What Is Acromion

The acromion is the extension of the spine of the scapula. The acromioclavicular joint is the point of articulation between the acromion and the clavicle or collarbone of the pectoral girdle.

Acromion

The acromion is a bony process located on the scapula or shoulder blade of the pectoral girdle.

The spine of the scapula bone is an elevated ridge present on its dorsal surface, dividing it into two unequal parts. The acromion, a flat process which projects out laterally, is curved upwards.

The acromion of the scapula (acron = summit;omos = shoulder) is a flattened piece of bone that lies subcutaneously forming the top of the shoulder. The posterior end of its lateral border is called the acromial angle, where it is continuous with the scapula. The anterior end of its medial border articulates with the clavicle at the acromioclavicular joint.

Acromion Structure

The acromion has two borders: medial and lateral; two surfaces: superior and inferior; and a facet for the clavicle.

Acromion Surfaces - The superior surface is convex and rough, while the inferior surface is concave and smooth. The lateral border has three or four tubercles for the origin of the deltoid, and the medial side gives attachment to the trapezius and articulates with the clavicle.

Acromion Borders

  • Its lateral border is irregular and thick.
  • The medial border is comparatively shorter and is concave.

Any type of shoulder injuries, such as osteoarthritis and rotator cuff tears, can lead to acromion pain.

Acromion Types

Acromion bone can be morphologically classified (Bigliani classification) into three types:

  1. Type Ⅰ - Flat Acromion

2. Type II – Hooked Acromion

Type Ⅲ – Curved Acromion

The curved acromion bone shape is the most common type, followed by flat, which is the most inferior type. Additionally, some recent classifications include a fourth type comprising upturned or convex acromion.

Acromioclavicular Joint

The acromioclavicular joint is the junction between the acromion and the clavicle. It is a plane synovial joint located at the top of the shoulder.

The clavicle lies horizontally at the root of the neck, separating it from the front of the chest. The bone is subcutaneous, and therefore, palpable, throughout its length. Medially, it articulates with the sternum at the sternoclavicular joint, and laterally with the acromion at the acromioclavicular joint. Both the joints are palpable because of the upward projecting ends of the clavicle.

The acromioclavicular ligaments connect the acromial end of the clavicle to the acromion. The ligament covering the superior part of the articulation is called the superior acromioclavicular ligament and the ligament covering the inferior part of the articulation is called the inferior acromioclavicular ligament.

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