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What is the Acromion Process?

By Shelby Miller
Updated Mar 03, 2024
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The acromion process, also known as the acromion, is a bony structure on the top of the scapula, or shoulder blade. It arises from a ridge that horizontally crosses the upper portion of the scapula on the back side and protrudes at the peak of the shoulder, forming a club-like shape. Paired with the coracoid process, a similar club-shaped protrusion that arises from the front side of the shoulder blade and crosses laterally toward the shoulder joint, the acromion process serves as a point of attachment for the deltoid and trapezius muscles. Its superior, or upper, surface is convex and rough, angling upward and outward above the shoulder joint, while its inferior, or lower, surface is concave and smooth.

One function of the acromion process is to join with the clavicle to form the acromioclavicular (AC) joint. Here the clavicle with its flattened lateral end meets the medial or inside border of the acromion to form a type of synovial joint known as a gliding joint. In a gliding joint, the adjoining bony surfaces glide past one another. As the articulating surfaces of the clavicle and acromion slide against each other, they make possible the action of raising the arm above the head.

Another purpose of the acromion process is to act as a site of muscle attachment. At the shoulder, the fibers of the middle deltoid originate on the lateral border of the acromion, crossing the shoulder joint and inserting into the deltoid tuberosity partway down the outside of the humerus bone of the upper arm. The main function of the deltoid muscle, particularly its middle fibers, is to abduct the arm, or lift it laterally away from the body. This action occurs at the glenohumeral, or shoulder, joint, but the attachment of the muscle to the acromion provides the leverage that helps to lift the weight of the arm.

The trapezius muscle of the upper back, particularly its middle fibers, also attaches to the acromion process. Originating on the spinous processes of the thoracic vertebrae, the middle trapezius crosses the upper back horizontally and inserts into the medial margin of the acromion. The function of the middle fibers of the trapezius is to retract the scapulae, pulling them back and together. This in turn pulls the arms backward at the shoulder joint, a movement that begins between the shoulder blades and ends with the movement of the shoulders.

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Discussion Comments
By shmiller — On Jul 26, 2011

@alFredo: Thanks for your question, it's a good one. A very common cause of pain at this site is known as supraspinatus impingement syndrome, and yes, it's an overuse injury. Basically, the supraspinatus, which is one of the four muscles of the rotator cuff, forms a tendon that crosses the top of the shoulder by running beneath the acromion process. When that tendon becomes inflamed for any reason, say after a rigorous weight-lifting session, it tends to swell, which causes it to rub against the process and essentially fray like a rope. If the tendon is not given a chance to heal properly, it can become a chronic condition--i.e. tendinitis--and the risk of a rotator cuff tear increases.

By tolleranza — On Jul 14, 2011

@aLFredo - I'm not sure how you get it, as I am just learning about it as part of my physical therapy program, but there is such thing as acromion process pain and there is another disorder... what was it called... I think it was impingement syndrome of the shoulder and it occurs around the area where your acromion process is.

By aLFredo — On Jul 14, 2011

With this process being a part of the anatomy of the shoulder it seems you could pain there from overuse in working out or if your work involved lifting items.

Is this possible, to feel pain there or is actually something else?

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