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Shoulder (AC) Separation


Three bones make up the shoulder girdle – the humerus (or arm bone), the scapula (or shoulder blade), and the clavicle (or collar bone). The upper part of the humerus attaches to a socket on the side of the shoulder blade (called the glenoid) and forms the shoulder joint, known as the “glenohumeral joint.” Above the glenohumeral joint and on the top part of the shoulder, the clavicle attaches to another part of the scapula called the acromion at a smaller joint called the acromio-clavicular (AC) joint. The AC joint is the only boney attachment of the scapula to the rest of the skeleton.

The AC joint is stabilized by two sets of ligaments:

  • The acromioclavicular (AC) ligaments connect the end of the clavicle to the acromion
    portion of the shoulder blade.
  • The coracoclavicular (CC) ligaments (including the “trapezoid” and “conoid” ligaments) stabilize the end of the clavicle to a small boney area on the front of the shoulder joint called the coracoid process.

Injuries to the AC joint, also known as “AC separations” or “shoulder separations,” occur when the AC and/or CC ligaments are sprained or torn. AC separations occur most commonly from direct contact, such as a fall to the ground directly on the shoulder. Occasionally, injuries to the AC joint can occur when a patient falls on a bent elbow and the ground drives the arm up into the collarbone. Shoulder separations are different from shoulder “dislocations” where the ball of the shoulder joint slides out of the socket.

AC separations range in severity from low-grade sprains (Type I) in which the AC ligaments are sprained but the CC ligaments are uninjured, to high-grade injuries (Type III) in which both the AC and CC ligaments are torn. Types IV, V, and VI are specific, more severe injuries that are less common


Pain on top of the shoulder, in the area of the AC joint, is the most common symptom of a shoulder separation. There may be associated swelling and bruising in the area of injury. With severe injuries, there may be an obvious deformity, such as the end of the collarbone sticking up and becoming prominent under the skin.


The diagnosis of shoulder separations is usually made by a history of the patient’s injury and location of pain and deformity on physical examination. X-rays confirm the diagnosis, rule out any associated fractures, and help to grade the severity of the injury.


Treatment of AC separations depends on the severity of the injury. Low-grade injuries, which are most common, are treated non-operatively with use of a sling for comfort, rest, ice, and anti-inflammatories. Most of these injuries heal within 4-8 weeks. Surgical treatment to repair or reconstruct the injured AC and CC ligaments is occasionally required in higher-grade injuries. Surgery is usually recommended in patients requiring high-level function of the arm. The goal of the surgery is to reconstruct the native AC and CC ligaments using a tendon graft to stabilize the end of the clavicle to the acromion.

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