The acromioclavicular (AC) joint located on top of the shoulder is commonly injured in athletes and active individuals. The superficial position of the AC joint just beneath the skin makes the joint susceptible to direct trauma. The most common mechanism of injury involves a fall onto the top of the shoulder. The AC joint is comprised of the articulation between the end of the clavicle (collarbone) and the acromion (part of the shoulder blade).
Diagnosis of an AC joint injury is made by a careful history, physical examination and plain radiographs (xrays). Patients commonly report a history of fall onto the top of the shoulder with the arm at their side. A direct trauma or force to the top of the shoulder is another common mechanism of injury. Physical examination may show swelling and bruising to the top of the shoulder. Tenderness to palpation is present at the AC joint. Shoulder range of motion may be restricted secondary to pain. A visible deformity is present in higher grade injuries with the end of the clavicle dislocated completely from the acromion. Plain radiographs allow confirmation of injury to the AC joint as well as show amount and direction of displacement of the clavicle from the acromion. AC joint injuries are classified as types I through VI based on the magnitude and direction of displacement of the clavicle from the acromion.
Treatment of AC joint injuries is dictated by the type of injury. Types I and II are injuries with minimal displacement and are treated conservatively with a short period of immobilization followed by early shoulder range of motion, strengthening and gradual return to activity. Types IV, V and VI are complete AC joint dislocations in the posterior (to the back), superior (to the top) and inferior (to the bottom) directions respectively. These types of AC joint injuries are usually treated with surgery to reduce and stabilize the AC joint to its anatomic position. Treatment of type III injuries (dislocation superiorly but with less displacement than type V) is a subject of debate. Some physicians recommend early surgery, especially for high level throwing athletes. For most patients an initial trial of nonoperative treatment is recommended. Surgical treatment may be necessary in some patients with continued pain following conservative treatment. In order to properly diagnose and treat AC joint injuries, an evaluation by an orthopedic surgeon is recommended.
