Acromioclavicular (AC) Joint Injuries
The bones of the shoulder girdle create two distinct joints: 1) the glenohumeral joint is the ball and socket joint, where most of the shoulder motion occurs; 2) the acromioclavicular (AC) joint is where the collar bone (clavicle) attaches to the shoulder blade (acromion).
The acromioclavicular (AC) joint is stabilized by two sets of ligaments: 1) the acromioclavicular (AC) ligaments connect the end of the collarbone to the end of the shoulder blade; 2) the coracoclavicular (CC) ligaments, connect a bony projection of the shoulder blade, known as the coracoid process, to the collarbone.
Injuries to the AC joint, also known as a separated shoulder, occur when the AC and/or CC ligaments are sprained or torn. Injuries to the AC joint occur most commonly from direct contact, such as in contact sports. Also falls, in which a patient lands directly on their shoulder, can cause injuries to the AC joint. Occasionally injuries to the AC joint occur when a patient falls on a bent elbow and the ground drives the arm up into the collarbone.
AC joint injuries range in severity from low-grade injuries, in which the AC ligaments are sprained but the CC ligaments are uninjured, to high-grade injuries, in which both the AC and CC ligaments are torn (see picture below).
Signs & Symptoms:
Pain on the top of the shoulder, in the area of the AC joint, is the most common symptom of a separated shoulder. Often there is associated swelling and bruising in this area. If the injury is severe, there may be an obvious deformity as the end of the collarbone sticks up and becomes prominent under the skin.
Diagnosis:
The diagnosis of an AC joint injury is typically made on the basis of the patient’s history of injury, the physical examination findings, and x-rays.
Treatment:
The treatment of AC joint injuries depends on the severity of the injury. Low-grade injuries, which represent the majority of shoulder separations, are treated non-operatively with conservative methods. Treatment modalities include: rest, ice, anti-inflammatory medications, pain medications as needed, and the use of a sling for comfort. Most of these injuries will heal within 4-8 weeks.
Occasionally a high-grade injury will require surgery to either repair or reconstruct the injured AC and CC ligaments. The decision to perform repair versus reconstruction depends upon the time that has elapsed from injury until surgery and the tissue quality of the remnants of the AC and CC ligaments at the time of surgery.
