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, with the Rockwood system most commonly used to classify injuries into six grades. Other described grading systems include the Tossy and the Allman classification systems.
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.
- initial radiographs are normal, but an injury is suspected
- surgical intervention on a type 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
- which may be the only finding in type 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
- the 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 type of the injury. In general types I and II are treated conservatively, types IV, V and VI are treated surgically, and type III injuries are variably treated 4.
Type I and II (+/- III): conservative management consists of ice, analgesics and shoulder rest in a sling.
Type III: the current evidence does not support surgical intervention on type III injuries as a general rule. The selection of which patients with type 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.
Types 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
- type II: inferior border of clavicle not elevated beyond the superior border of the acromion
- type 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)
- type V: marked superior elevation of the clavicle with coracoclavicular distance more than twice normal
- direction of dislocation (use axillary view)
- posteriorly into trapezius: type IV
- inferiorly below the coracoid process: type 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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