A 29-year-old, right-hand-dominant male presented to the Emergency Department with right shoulder pain after falling while riding his mountain bike. He reports that he “flew over his handle bars.” The patient was wearing a helmet and denies loss of consciousness. He denies numbness or tingling in the left, upper extremity. He notes increased swelling and pain over the clavicle. On examination, the patient’s skin is tenting over the distal end of the clavicle, and he has tenderness to palpation over the coracoclavicular interspace. He is diagnosed with an acromioclavicular (AC) joint separation and is unable to reduce the injury in the ED.

What is the mechanism of this injury?

1. Hyperabduction and external rotation of the arm combined with retraction of the scapula

2. Anterior and inferior displacement of the scapula

3. Inferior displacement of the scapula in relation to the clavicle

4. Lateral translation of the acromion in relation to the clavicle

5. Medial displacement of the clavicle in relation to the acromion

Discussion

The correct answer is (C). The mechanism of an AC joint separation is inferior displacement of the scapula in relation to the clavicle. AC joint separation can occur from direct or indirect mechanisms. Direct injuries result from a direct force to the acromion with the shoulder adducted. The acromion moves inferiorly and medially and the clavicle remains stabilized by the sternoclavicular ligaments. This is the mechanism of most AC joint separations and is usually caused by a fall onto the superolateral portion of the shoulder. The force applied during this type of injury results in a systematic failure of the stabilizing ligaments. The failure of the acromioclavicular (AC) ligaments and capsule is followed by failure of the

coracoclavicular (CC) ligaments and deltotrapezial fascia. The indirect mechanism results in the same injury, but due to a fall on an outstretched arm or elbow with a superiorly direct force. Hyperabduction and external rotation of the arm combined with retraction of the scapula is thought to be the mechanism for the exceedingly rare Type VI AC joint dislocation. Anterior and inferior displacement of the scapula from a force applied to the acromion is thought to be the mechanism of the relatively rare Type IV AC joint dislocation. Lateral translation of the acromion in relation to the clavicle and medial displacement of the clavicle are not described as mechanisms of AC joint separations.

What structure provides the most resistance to AC joint compression?

1. Conoid ligament

2. Trapezoid ligament

3. AC ligaments

4. Coracoacromial (CA) ligament

5. Deltotrapezial fascia

Discussion

The correct answer is (B). The AC joint is a diarthrodial joint that has both static and dynamic stabilizers. The trapezoid and conoid ligaments comprise the CC ligaments. The trapezoid ligament is a static stabilizer, which attaches more lateral than the conoid ligament on the undersurface of the clavicle and provides resistance to AC joint compression. The conoid ligament inserts more medially on the undersurface of the clavicle providing approximately 60% of the restraint to anterior and superior displacement and rotation of the clavicle. The AC ligaments (Answer C) are static stabilizers that reinforce the joint capsule and predominately control horizontal motion (anterior and posterior) of the clavicle. The coracoacromial (CA) ligament is used in CC ligament reconstruction and does not play a significant role in AC joint stability. The deltotrapezial fascia is a dynamic stabilizer of the AC joint and must be considered when AC joint reconstruction is performed.

A radiograph of the patient is shown in Figure 2–68. Based on the information obtained thus far, what is the most likely classification of this injury?

1. Type II

2. Type III

3. Type IV

4. Type V

5. Type VI

Figure 2–68

Discussion

The correct answer is (D). Based on the amount of distance between the coracoid process and the clavicle (CC interspace); the fact that the distal clavicle is tenting the skin and that the joint is irreducible, this AC joint separation can best be classified as a type V. The remaining answer choices are incorrect based on the information provided in Table 2–10 describes the Rockwood classification of AC joint injuries.

Table 2–10 CHARACTERIZATION OF ACROMIOCLAVICULAR JOINT INJURIES BY THE ROCKWOOD CLASSIFICATIONa

What is the most appropriate way to manage this patient’s injury?

1. Sling immobilization and early range of motion

2. Sling immobilization for 7 to 10 days until pain resolves

3. Figure-of-eight sling for immobilization for 7 to 10 days until pain resolves

4. Open reduction, ligamentous repair, coracoclavicular ligament repair supplementation, and repair of the deltoid and trapezial fascia

5. Open Mumford procedure

Discussion

The correct answer is (D). Type IV, V, and VI injuries all require surgical intervention. Answer E is a distal clavicle resection. Because this injury is unstable, this procedure would likely accentuate the instability.

Type I injuries can usually be treated with a simple sling for 7 to 10 days or until pain has subsided. Type II injuries can require as long as 2 weeks of immobilization to achieve resolution of symptoms. When pain has subsided, passive- and active-assisted range of motion and strengthening exercises are instituted. Contact sports and heavy lifting should be avoided for 2 to 3 months. There is controversy regarding treatment of Type III injuries. Most studies support nonsurgical management. However, discrepancies exist when managing young patients who frequently engage in activities that place high demands on the shoulder. A rigorous rehabilitation program should be undertaken when nonsurgically managing type III injuries because this may have an impact on the outcome.

There are several different ways to surgically manage AC joint separations. All have the same goal of obtaining and retaining anatomic reduction. There are three main groups of surgical techniques: primary fixation, fixation between the coracoid process and the clavicle, and ligament reconstruction. Some of these techniques can be combined, such as hook plate fixation with ligament reconstruction. Primary fixation with Kirschner wires has been abandoned due to risk of pin migration. Fixation with hook-plates, which is more commonly performed in Europe, can be performed. The plate must be removed at 8 weeks. Fixation between the coracoid process and the clavicle can be performed using a screw, synthetic loops (i.e., 6-mm PTFE surgical tape). Ligament reconstruction can be performed with the Weaver and Dunn procedure or some of its modifications in which the CA ligament is detached from the acromion and is then transferred to the clavicle. Alternative techniques for ligament reconstruction use semitendinosus tendon autograft or anterior tibialis tendon allograft with different fixation methods to the coracoid process and clavicle.

Objectives: Did you learn...?

Recognize the mechanism of AC joint separations? Recognize different types of AC joint separations?

Appropriately treat a patient with AC joint separation based on the type of injury while considering the individual?