Acromioclavicular joint injuries are common and range from a mild sprain to complete disruption of the acromioclavicular joint (ACJ) and injury to surrounding structures.
Acromioclavicular joint injuries usually occur from a direct blow or following a fall onto the shoulder with an adducted arm. This pushes the acromion forcibly inferiorly and medially with respect to the clavicle 7.
Imaging can be used to classify acromioclavicular injuries, and a six-grade system is most commonly used.
In most cases, plain films (including an axillary view) are sufficient for accurate grading although CT or MRI may be useful in cases where plain films are thought to underrepresent the degree of injury.
Clavicle series consists of an AP and cephalic angled oblique (10-15º) view are obtained.
Additionally, stress views (weight bearing) can be obtained if:
- initial radiographs are normal, but an injury is suspected
- surgical intervention on a grade III injury would be contemplated (see below) 7
These are performed with the patient erect and holding a weight in the arm. If the joint is normal, then acromioclavicular alignment should remain normal and symmetric.
Features of acromioclavicular joint injury include 6:
- soft tissue swelling/stranding
- may be the only finding in grade I injuries
- widening of the AC joint
- normal: 5-8 mm (narrower in the elderly)
- greater than 2-4 mm asymmetry (compared to radiographs of the contralateral side)
- increased coracoclavicular (CC) distance
- normal: 10-13 mm
- greater than 5 mm asymmetry (compared to radiographs of the contralateral side)
- superior displacement of the distal clavicle
- undersurface of the acromion should be level with the under the surface of the clavicle
Treatment and prognosis
Treatment largely depends on the age and lifestyle of the patient as well as the grade of the injury. In general grades I and II are treated conservatively, grades IV, V and VI are treated surgically, and grade III injuries are variably treated 4.
Grades I and II (+/- III): conservative management consists of ice, analgesics and shoulder rest in a sling.
Grade III: the current evidence does not support surgical intervention on grade III injuries as a general rule. The selection of which patients with grade III injuries for surgical intervention is difficult, but patients who are particularly thin, require great range of motion or do heavy lifting may benefit from operative repair 4-5.
Grades IV-VI (+/- III): surgical internal fixation is typically achieved with a hook plate, which in most cases needs to be eventually removed. K-wires have also been used, although rare cases of wire migration into vital organs, has dissuaded many surgeons from using them 4.
Just as an injury to other joints, prior acromioclavicular dislocation predisposes the joint to osteoarthritis. Surgical complications include migration of hardware and infection.
In addition to commenting on whether or not a subluxation/dislocation is present a number of features should be examined and commented upon:
- presence of soft tissue swelling
- degree of subluxation of the clavicle
- grade II: inferior border of clavicle not elevated beyond the superior border of the acromion
- grade III: inferior border of the clavicle is elevated beyond the superior border of the acromion, but coracoclavicular distance is not greatly increased (less than twice normal)
- grade V: marked superior elevation of the clavicle with coracoclavicular distance more than twice normal
- direction of dislocation (use axillary view)
- posteriorly into trapezius: grade IV
- inferiorly below the coracoid process: grade VI
- any fractures present
- glenohumeral joint alignment
A careful inspection of the periphery of the film is also required, to ensure no rib fracture, pneumothorax or incidental lung, mediastinal or osseous lesion is present. These do not usually constitute 'relevant negatives' and as such, no comment is required.
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