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Disorders of the Acromioclavicular Joint (AC Joint)


Updated June 04, 2009

The acromioclavicular joint (AC joint) is located at the end of the collar bone, or clavicle, above the shoulder region. It is where the clavicle meets a part of the scapula called the acromion. Two disorders commonly occur at the acromioclavicular joint -- shoulder separation and acromioclavicular arthritis. Both of these conditions result in significant pain and discomfort at this joint site above the shoulder.

Shoulder Separation

A shoulder separation injury involves a disruption of the AC joint. This joint is composed of the collar bone, or clavicle, and the highest portion of the shoulder blade, the acromion of the scapula. These two bones meet on top of the shoulder and form the acromioclavicular joint, as mentioned above.

The most common cause of shoulder separation, or AC joint disruption, is a direct fall onto the shoulder. This fall injures the ligaments that provide stability to the joint. The laxity that results allows a degree of separation between the acromion and the clavicle. The degree of separation can range from mild to severe with a noticeable deformity.

Treatment of this condition can vary from conservative management with a period of immobility followed by gentle shoulder strengthening to surgery.

Acromioclavicular Arthritis

Arthritis of the acromioclavicular joint can be the cause of significant pain at this region. AC joint arthritis may result from previous injury, natural wear and tear that occurs with aging, or weight lifting activities. As the joint wears out, the ends of the bones rub against each other and cause pain.

If this condition becomes severe enough, surgery may be necessary in order to relieve the pain. This procedure involves removing the end portion of the clavicle bone.


Shaffer BS. "Painful conditions of the acromioclavicular joint" J Am Acad Orthop Surg. May-Jun 1999;7(3):176-188

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