Volume 4, Case 13
Alson S. Inaba, MD
Kapiolani Medical Center For Women And Children
University of Hawaiʻi John A. Burns School of Medicine
An 18-year old surfer presents to the Emergency Department complaining of right upper shoulder pain. He states that the tip of another surfer's board struck him on the top of his shoulder while he was paddling out to catch a wave. He immediately felt a pop when the surfboard struck his shoulder and states that he had difficulty paddling back to shore secondary to the pain. He denies any other trauma to his head, neck or chest. He also denies any paresthesias of his left hand.
Upon presentation to the ED, he prefers to hold his right arm adducted against his body. Inspection of the right shoulder region is only significant for superficial abrasions and mild erythema over the superior aspect of the shoulder joint without any obvious swelling or deformity.
View his shoulder.
The angle (contour) of the right shoulder appears symmetric when compared to the left shoulder (i.e., there is no obvious drooping of the affected shoulder). There is no fullness or tenderness in the deltopectoral groove. There is no tenderness over the humeral head or neck. With the right arm in the adducted position, he is able to fully internally and externally rotate the right arm without any exacerbation of the shoulder pain. Palpation of the clavicle does not reveal any crepitus or obvious fractures. His distal neurovascular examination is intact.
Questions:
a) What is the most likely diagnosis based on the above history and clinical examination?
b) What radiographic view(s) would you obtain to confirm your clinical diagnosis?
Based on the mechanism of injury and the clinical examination, the most likely diagnosis would be an acromioclavicular separation. To radiographically confirm this diagnosis, an AP view of the affected shoulder (specifically looking at the acromioclavicular and coracoclavicular joints) is obtained.
View shoulder radiograph.
Questions:
a) What is your radiologic diagnosis?
b) Would you classify this type of acromioclavicular injury as a type I, type II or type III acromioclavicular separation?
c) How should this type of injury be treated?
Discussion:
In order to thoroughly understand the clinical assessment, radiographic evaluation and treatment of acromioclavicular separations, one must first have a very clear understanding of the anatomy of this region of the shoulder.
View shoulder anatomy.
The function of the acromioclavicular (AC) joint is to elevate and abduct the arm. Although the term "AC separation" refers solely to the AC ligament, stability of the shoulder joint is actually dependent upon two ligaments; the AC ligament and the coracoclavicular (CC) ligament. The AC ligament anchors the distal tip of the clavicle to the acromion process of the scapula. The CC ligament consists of two separate ligaments which anchor the distal clavicle to the coracoid process of the scapula. The degree of injury to this CC ligament largely determines the classification of AC separation injuries.
The two most common mechanisms which cause AC separations are either direct trauma to the point of the shoulder (i.e., a direct blow to the AC joint region, as in the case of our patient) or secondary to falling and landing on the deltoid region with the arm in the adducted position. An indirect mechanism which can also produce an AC separation is when force is indirectly transmitted to the AC joint secondary to a fall on the outstretched hand.
The physical examination of a patient with an AC separation will depend upon the degree of AC separation. If there is no accompanying dislocation of the glenohumeral joint, one would not expect to see the typical signs of an anterior shoulder dislocation (i.e., asymmetric contour of the shoulder, fullness with tenderness in the deltopectoral groove, exacerbation of pain with external rotation, etc.). The majority of patients with AC separations will have some degree of tenderness directly over the AC joint. However, with severe AC separations (type III), the normal AC joint prominence may be exaggerated. This exaggeration of the AC joint prominence is secondary to the upward displacement of the distal tip of the clavicle and the downward pull of the shoulder (caused by the weight of the arm) and the loss of the integrity of the suspending CC ligament.
Although the term "AC injuries" refers to the AC ligament, the classification and treatment of "AC injuries" are dependent upon the degree of injury of both the AC and CC ligaments.
Type I (or first-degree) AC separation:
This degree of AC injury (typically referred to as an AC "sprain") involves an incomplete tear of the AC ligament. Because this tear is incomplete and the CC ligament remains intact, the radiographs are normal EVEN WITH stress views (i.e., no radiologic evidence of subluxation).
Type II (or second-degree) AC separation:
View the diagram of a type II injury.
This degree of AC injury involves a subluxation of the AC joint (secondary to a partial or complete tear of the AC ligament). As with type I injuries, the CC ligament also remains intact with type II AC separations. The subluxation of the AC joint (i.e., widening of the AC joint space as compared to the unaffected side) may or may not be evident on the routine shoulder radiographs (AP erect view). Therefore, when a type II AC separation is clinically suspected and the routine radiographs are within normal limits, stress views can be obtained. These AP stress views are obtained (in the erect position) with weights (5-15 pounds or 2-7 kg) suspended by the patient's wrist (Do not have the patient hold the weights). This stress view will bring out any degree of AC joint subluxation that was not evident on the initial routine radiographs. Subluxation of the AC joint is radiologically confirmed if the AC joint appears wider on the stress view (as compared to the routine nonstress views) and/or if the inferior border of the distal tip of the clavicle is not in alignment with the inferior border of the acromion process.
View this alignment of the inferior border of the clavicle and the inferior border of the acromion process.
With type II separations, this malalignment of the inferior borders of the distal clavicle and acromion process should not be more than half the diameter of the clavicle. Separation of the distal clavicle by more than one-half of its diameter from the acromion process indicates a type III AC injury.
Type III (or third-degree) AC separation:
View the diagram of a type III injury.
This type of injury involves a complete tear of both the AC and CC ligaments which then results in a complete dislocation of the AC joint. Clinically, type III injuries will present with an exaggeration of the normal AC prominence secondary to the upward displacement of the distal tip of the clavicle and the downward pull of the shoulder (caused by the weight of the arm) and the loss of the integrity of the suspending CC ligament. If a type III injury is clinically suspected, the AP view of the shoulder should be obtained in the erect position to allow the weight of the suspended arm to bring out the classic radiographic findings of a type III separation. The radiographic findings of a type III AC separation may not be evident if the AP radiograph of the shoulder is obtained with the patient in the supine position.
Radiographically type III injuries reveal: a) a widening of both the AC and CC joint spaces on the routine erect AP views (as compared to the AC and CC joint spaces of the unaffected shoulder) and b) the inferior border of the distal clavicle is clearly malaligned (i.e., separated by more than one-half the diameter of the clavicle) with the inferior border of the acromion process [Click on Align]. When a type III AC separation is confirmed on the routine AP erect views, stress views with weights are not necessary.
Treatment & Prognosis of AC separations:
The initial ED treatment of all three types of AC injuries involves placing the patient in a shoulder immobilizer with the arm adducted against the chest. This can be accomplished with any of the commercially available shoulder immobilizers or by placing the patient in a sling and swathe immobilizer. Early range of motion exercises are encouraged for type I injuries. Type II and type III injuries should be referred to an orthopedic surgeon for further evaluation and rehabilitation. Although internal fixation used to be advocated for the majority of type III injuries, some authorities are now attempting to treat these types of injuries with three weeks of immobilization in a Kenney-Howard sling or other similar shoulder immobilizers.
Post-Case Quiz Questions:
1. Name the two ligaments that make up the AC joint?
2. Describe the two most common mechanisms of injury that can cause an AC injury
3. The classification of AC separations is dependent upon the integrity of the coracoclavicular ligament. True or False?
4. If the line connecting the inferior border of the distal clavicle to the inferior border of the acromion process is malaligned, this is by definition a type III AC separation. True or False?
5. Stress views are always required to radiographically confirm the diagnosis of a type III AC separation. True or False?
References