Approach Considerations
Distinguishing acromioclavicular injuries from other shoulder injuries (ie, clavicular fractures, shoulder dislocations, proximal humeral fractures) is difficult.
Standard radiographs are usually adequate to confirm the diagnosis of acromioclavicular joint injury. The clavicle and scapula should also be assessed for any associated fractures.
To optimally image the acromioclavicular joint, obtain a cross-body adduction radiograph. Additionally, a radiograph of the entire upper thorax is useful to compare the vertical distance between the clavicle and the coracoid process on both sides. Radiographic results according to severity of injury are as follows:
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Type I: Normal
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Type II: Subluxation of the acromioclavicular joint space is less than 1 cm; normal coracoclavicular space
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Type III: Subluxation of the acromioclavicular joint space is greater than 1 cm; widening of the coracoclavicular space is more than 50%
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Types IV-VI: Subluxation of the acromioclavicular joint space is more than 1 cm, and widening of the coracoclavicular space is more than 50%; there is associated displacement of the clavicle
With complete acromioclavicular/coracoclavicular ligament rupture, cross-body adduction films will show the scapula rotated anteromedially, and the acromion will migrate medially.
Athletes with a previous history of acromioclavicular injury or a history of heavy weight lifting may present with relatively acute shoulder pain over the distal clavicle, and they may have classic radiographic findings of distal clavicle osteolysis or of acromioclavicular osteoarthritis (ie, joint narrowing, distal clavicle or acromial spurring). When these radiographic findings are present, the clinician may expect that seemingly little trauma can result in significant pain.
Radiography
As with all skeletal injuries, in cases of suspected acromioclavicular joint injury a minimum of 2 radiographic views (eg, anteroposterior [AP], lateral, axillary views of the shoulder; lateral projection of the scapula [scapular Y]) is necessary to evaluate the individual injury. [29] For pediatric injuries, plain radiographs may reveal fractures at the base of the coracoid.
If the athlete has sustained concomitant rib fractures with shortness of breath, good quality chest radiographs are indicated. A consultation from a pulmonary physician or cardiovascular chest surgeon may be necessary.
AP, lateral, and axillary views of the shoulder
The AP view should be taken with the patient’s arms at the side, and both acromioclavicular joints should be imaged for comparison. If a true AP view is obtained, the acromioclavicular joint can be seen superimposed on the spine of the scapula; hence, some authorities have recommended the Zanca view, in which 10-15° of cephalic tilt of the radiographic beam provides a clearer image of the acromioclavicular joint. (See below.)
Anteroposterior (AP) radiograph of right shoulder showing step-off of the acromioclavicular (AC) joint.
An axillary lateral view is also needed in suspected acromioclavicular joint injuries to account for any anterior or posterior displacement of the distal clavicle.
Stress views of the shoulder
Stress radiographs can be used to more accurately assess the integrity of the ligamentous structures by showing the degree of displacement of the acromion relative to the clavicle. If an unstable acromioclavicular joint injury is suspected, yet not confirmed on routine AP and lateral views, stress views may be indicated.
A 10- to 15-lb weight is attached to the wrist of the affected side, and an AP view can be taken. This stress tests the integrity of the coracoclavicular ligament and, if the ligament has been disrupted completely, the test will demonstrate the complete dislocation.
Routine use of stress radiographs is not recommended in the acute setting. Although these radiographs may help distinguish type I from type II injuries, many authorities consider such studies unnecessary, as any involuntary splinting by the patient prevents full visualization of the acromioclavicular joint and may simply serve to increase the patient's pain.
Weighted stress tests may be valuable in follow-up care if the clinician has any doubt about the instability of the acromioclavicular joint. Even with conservative care of type III-VI acromioclavicular disruptions, this test may be helpful for determining a timetable for the athlete’s return to conditioning and sporting activities.
Ultrasonography
Heers and Hedtmann reported that ultrasonographic examination of the acromioclavicular joint in experienced hands had 100% sensitivity for diagnosis of deltoid muscle detachment and fascial disruption. [30] The study also showed 80% sensitivity and 100% specificity for disruption of the trapezius muscle. A study by Faruch Bilfeld et al also found that ultrasound is an effective examination for the diagnostic work-up of lesions of the coracoclavicular ligaments in the acute phase of an acromioclavicular injury. [31] However, more studies are necessary to evaluate the potential for additional information provided by ultrasonography in the routine examination of suspected acromioclavicular injury.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is not routinely ordered in the management of straightforward acromioclavicular disruptions, although it has been shown to be helpful in differentiating between type II and type III injuries. [32] Such detailed knowledge of acromioclavicular and coracoclavicular ligamentous injury is generally not needed for conservative or, in rare cases, surgical care. [29]
Clinicians may consider an MRI to evaluate for a possible rotator cuff tear in middle-aged and older patients who continue to have disabling shoulder pain after the acute pain of an acromioclavicular disruption abates. In highly competitive athletes, MRI may be considered to further delineate the extent of the acromioclavicular injury.
Very rarely, athletes with persistent pain over the acromioclavicular joint merit an MRI to determine whether or not the cartilaginous disk has been damaged irreversibly and to determine whether or not the process of distal clavicle osteolysis or early osteoarthritis has begun.
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Acromioclavicular joint anatomy.
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Classification of acromioclavicular joint injuries.
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Allman/Rockwood classification of acromioclavicular injuries.
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Anteroposterior (AP) radiograph of right shoulder showing step-off of the acromioclavicular (AC) joint.
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Type III acromioclavicular joint separation.
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Type III acromioclavicular joint separation.
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Postoperative coracoclavicular ligament reconstruction. The clavicle is back to its normal position. The anchor in the clavicle keeps the allograft tendon from coming off of the clavicle. Also note the distal clavicle has been excised, because it had traumatic arthritis from the injury.
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Type V separation, characterized by wide displacement of the clavicle in a superior direction relative to the acromion. The radiographic findings denote disruption of the acromioclavicular AC ligaments and coracoclavicular (CC) ligament, as well as the deltoid attachment to the distal clavicle.
