Review Question - QID 219939

This patient has an acromioclavicular (AC) joint injury with posterior displacement, which would be Type 4 in the Rockwood classification scheme (Answer 4).

AC joint injuries are common injuries in athletes who suffer direct trauma to the shoulder. The AC joint is stabilized by the AC ligament, which provides sagittal plane stability, and the two coracoclavicular ligaments that provide axial stability. The Rockwood classification categorizes AC joint injuries into six types based on the direction and degree of displacement. Types I and II are milder injuries where the AC joint remains relatively stable. Type I involves a sprain of the AC ligament without displacement or instability, while Type II injuries present with slight horizontal instability. Type III injuries involve complete tears of both the AC and coracoclavicular (CC) ligaments, leading to noticeable joint separation. Types IV through VI represent more severe injuries with increasing displacement of the clavicle, ranging from posterior displacement in Type IV, to superior and inferior displacement in Types V and VI, respectively. Typically, Type I and II injuries are managed nonoperatively with a brief period of rest followed by progressive return to activity. Type IV-VI injuries are typically managed operatively. The management of Type III injuries is controversial, often depending on the activity level, athletic considerations, and degree of symptoms of the patient.

The Alexander view can be used to identify posterior displacement of the clavicle. This view is similar to the scapular Y view except that the center of the beam is at the AC joint with a 15 degree cranial tilt. Superior translation can also be seen on this view, but is easier to assess using the Zanca AP view (which is an AP radiograph with a 15 degree cranial tilt). Additionally, both of these views can be taken with weight to stress the AC joint. A CT scan can be used to further characterize the degree and direction of displacement, but may not be necessary.

Waldrop and colleagues discussed the importance of lateral radiographs in identifying posterior dislocations of the distal clavicle. They found that the Alexander view was the most helpful in identifying posterior dislocations. They concluded that these lateral radiographs could help make more accurate diagnoses and allow clinicians to make more informed decisions.

The Upper Extremity Committee of the International Society of Arthroscopy, Knee Surgery, and Orthopaedic Sports Medicine (ISAKOS) released a consensus statement on the Rockwood classification for AC joint injuries. Although the Rockwood classification is widely used for AC joint injuries, it can miss nuances needed for treatment decisions. The committee recommends additional modifications to include biomechanical stability and variations in injury patterns.

Figure A is a CT scan demonstrating posterior displacement of the distal clavicle.

Illustration A is a table of the Rockwood classification of AC joint injuries.
Illustration B is an example of the Alexander view demonstration posterior displacement of the clavicle.

Incorrect answers:
1, 2, 4, and 5: these answers denote other types in the Rockwood classification that do not involve posterior dislocation of the distal clavicle.