Injury to the acromioclavicular (AC) joint is a common finding in the emergency department, usually resulting directly from an impact on the superior aspect of the acromion. The classification system for AC joint includes six types. A type I injury is equivalent to a stretching of the acromioclavicular ligament. A type II injury consists of tearing of the AC ligaments and stretching of the coracoclavicular ligaments. Complete disruption of the AC and coracoclavicular ligaments is seen in types III to VI.
Patients complain of pain at the AC joint and will actively splint the injured shoulder. Ecchymosis may be present; however, an obvious deformity is not always seen. There is significant tenderness upon palpation of the AC joint.
Standard radiographs should include anteroposterior (AP) and axillary lateral views of the shoulder. Type I injuries will appear normal. Type II injuries may show 0% to 50% displacement at the AC joint but no increase in the coracoclavicular interval. Types III to VI will demonstrate displacement at the AC joint and the clavicle will appear to be displaced superiorly (the acromion actually is rotated inferiorly) 50% to greater than 100% its width when compared with the normal side.
Emergency Department Treatment and Disposition
Type I and type II injuries are treated with rest, ice, analgesics, and a simple sling until acute pain with movement is relieved. Treatment of type III injuries is controversial with the literature supporting both nonoperative and operative management. Types IV, V, and VI are treated operatively. Referral to a musculoskeletal specialist is essential for all AC joint injuries since many patients who initially appear to have minor injuries will have more obvious deformity after the swelling and pain have subsided.
AC Joint Separation. Subtle prominence of the left distal clavicle. The upward displacement of the clavicle is due to stretching or disruption of the suspending ligaments. (Photo contributor: Frank Birinyi, MD.)
Acromioclavicular Joint Injuries. Types of acromioclavicular joint injuries. Classification schemes may subdivide type III injuries into III through VI depending on the position of the clavicle.
AC Joint Separation. Large deformity at the right distal clavicle suggesting complete ligament disruption. (Photo contributor: R. Jason Thurman, MD.)
The early AC joint stress radiograph can be negative due to splinting of the shoulder girdle muscles.
Differentiating between types I and II versus types III to VI is the goal of the ED physician since the treatment is significantly different.
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