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Symptom: Right Shoulder Pain

Wiler, Jennifer L. MD, MBA

doi: 10.1097/01.EEM.0000365881.68796.a3
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A 42-year-old man, intoxicated while riding his bike, strikes a parked car, and lands on his right shoulder. In the ED, he complains of right shoulder pain, but denies loss of consciousness, focal deficits, paresthesias, or neck, chest, or back pain.

What is the likely diagnosis, and how would you evaluate his shoulder injury?

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Diagnosis: Acromioclavicular Joint Dislocation

The acromioclavicular (AC) joint of the shoulder is located at the articulation of the distal end of the clavicle and the acromion of the scapula. Its purpose is to help raise the arm above the head. Despite being a strong complex, the lateral location of the joint makes it susceptible to direct trauma. AC joint ligament injuries account for as many as 10 percent of all shoulder injuries, and are five times more common in men.

The AC joint itself is comprised of superior and inferior fibers from the acromioclavicular ligament, a cartilaginous disk, and a synovial membrane, in addition to aponeurosis from the deltoid, trapezius, and supraspinatus muscles. The AC joint complex is stabilized by the coracoacromial and coracoclavicular ligaments. It can be injured by direct traumatic forces to the joint complex, or less commonly from indirect forces such as a fall on an outstretched hand or forced adduction of arm to chest mechanisms. The amount of traumatic force correlates with the degree of joint injury. Lesser traumatic forces strain and disrupt the AC ligament itself, while more significant forces can rupture the AC complex and rupture the strong coracoclavicular ligament. Disruption of the AC ligament results in AC joint dislocation, commonly known as AC separation, AC sprain, or separated shoulder. This is not to be confused with humeral head dislocations from the glenohumeral joint.

The diagnosis of AC joint dislocation is typically not difficult to make if direct shoulder trauma and pain at the joint are present. Referred cardiac, cervical, diaphragmatic, and gallbladder pain, biceps tendonitis, osteomyelitis, malignancy, immunologic conditions, and osteoarthritis should be considered in the differential diagnosis depending on the patient's presentation. Acromial and distal clavicular fractures with intact AC and coracoclavicular ligaments also can mimic type III AC injuries (pseudodislocations). Interestingly, the clavicle is the last joint in the body to fuse so Salter-Harris fractures can occur until age 25. (Prim Care 2004;31[4]:857.)



Patients often present with focal AC joint tenderness, swelling, often deformity, and occasionally extremity weakness with range of motion inversely proportional to the severity of injury. The AC joint is innervated by the suprascapular and lateral pectoral nerves. Pain is typically reproduced directly over the ligament, but may be more anterior or posterior depending on the innervation pattern. (Clin Sports Med 2008;27[4]:763.) Because AC injuries are the result of trauma, standard trauma protocols should be followed to evaluate for other concomitant traumatic injuries. A complete cervical spine and neurovascular examination is important in patients with suspected AC injury to rule out secondary injuries.

Radiological evaluation of the shoulder joint can rule out associated fractures and verify the diagnosis. Imaging is not needed in straightforward cases. Comparison films of the unaffected shoulder may be helpful to identify subtle injuries. Stress views are no longer recommended. (Clin Sports Med 2008;27[4]:763.) Zanca views (beam angled 10 degrees cephalad to eliminate clavicle and scapular spine overlap) can be helpful to quantify superior clavicular displacement.

AC joint dislocations are typed I-VI based on the severity of injury as classified by Rockwood (Fractures in Adults. Philadelphia: Lippincott-Raven; 1996. pp. 1341–413.) Type I is a mild tear in the AC ligament; radiographs are unremarkable, and treatment consists of ice, mild analgesia, and a sling for comfort with early range of motion. Type II injuries are more severe with complete rupture of the AC ligament and strain of the coracoclavicular ligament. There is no change in the relationship between the coracoid and the clavicle on radiographic evaluation between the affected and unaffected side, but the clavicle is displaced from the acromion no more than half the diameter of the clavicle, and is typically appreciated clinically as a bony prominence. A sling and orthopedic referral are recommended, usually with early return to full activity.

Intra-articular corticosteroid injections have no role in acute traumatic injury, but may help athletes return to play more quickly in the latent recovery period. Type III injuries are the most common, and are defined as a complete rupture of the AC and coracoclavicular ligaments with essentially a “free-floating” clavicle. Patients have severe pain with limited range of motion. A sling and early orthopedic referral are recommended for possible surgical intervention for cosmetically unacceptable cases, persistent pain, or dysfunction. Type IV injuries are those with a floating clavicle and posterior clavicle displacement. Type V injuries are associated with inferior displacement of the scapula and deltotrapezial fascial disruption. Type VI injuries are rare and associated with subcoracoid dislocation of the clavicle. These are commonly associated with significant trauma, brachial plexus injury, and subsequent neurological deficit, and other fractures. Surgical repair is recommended for Types IV–VI. (Clin Sports Med 2008;27[4]:763.) Chronic dislocations of the AC joint are common with Type III injuries that were not surgically repaired. This may be unacceptable to the patient and ultimately require surgical repair. (Prim Care 2004;31[4]:857.) Osteoarthritis and osteolysis are also common complications of AC injuries.

This patient was diagnosed with a type III AC injury, and was given a sling, analgesia, ice therapy instructions, and early orthopedic referral.



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