Acromioclavicular Joint Dislocation (AC Joint Separation) is one of the most occurring injuries in the shoulder gridle. The majority of AC joint injuries occurs in young to middle aged males.
Mechanism of Injury
- AC Joint Separation usually results from a force applied downward on the acromion.
- The most common mechanism of injury of AC Joint Separation is a fall directly onto the dome of the shoulder.
- The clavicle rests against the first rib, and the rib blocks further downward displacement of the clavicle.
- As a result, if the clavicle is not fractured, the acromioclavicular and coracoclavicular ligaments are ruptured and the acromioclavicular joint dislocation occurs.
- AC Joint Separation is associated mostly with contact or collision sports like football, rugby, and hockey.
Anatomy of the AC Joint
Acromioclavicular (AC) joint is a diarthrodial joint with a fibrocartilaginous disc.
Ligaments of the AC Joint
- AC ligaments: prevent anteroposterior displacement.
- Coracoclavicular ligaments: prevent superior displacement of distal clavicle:
- Trapezoid (anterolateral): approximately 25 mm from AC joint
- Conoid (posteromedial and stronger): approximately 45 mm from AC joint
See Also: Clavicle Anatomy
Ac Joint Separation Symptoms & Signs
- Pain and swelling at the anterior-superior aspect of the shoulder.
- Unstable acromioclavicular joint with a mobile distal clavicle.
- The clinical triad confirm the AC joint injury:
- Point tenderness at the AC joint.
- Pain exacerbation with cross-arm adduction.
- Relief of symptoms by injection of a local anesthetic agent.
- The cross-body adduction test is positive.
- Anteroposterior Views:
- Both AC joints should be imaged simultaneously.
- Zanca View:
- By tilting the x-ray beam 10° to 15° toward the cephalic direction.
- This view is now routinely used in the evaluation of AC joint separation.
- Axillary Lateral View:
- This will reveal any posterior displacement of the clavicle as well as any small fractures that may have been missed on the AP view within the coracoid.
- Stryker Notch View:
- To evaluate fracture of the coracoid process (should be suspected when there is an AC joint dislocation on the AP projection, but the CC distance is normal, or equal to that on the opposite, uninvolved side)
- Weighted stress views:
- No longer used.
- Helps differentiate Type II from Type III.
- Ultrasonography, computed tomography (CT), and magnetic resonance imaging are not required In the typical patient.
See Also: Anterior Shoulder Instability
Classification of AC Joint Separation
Rockwood Classification of AC Joint Dislocation
|Type||AC Ligs.||CC Ligs.||Radiography||Treatment|
|Type II||Injuried||Sprain||Vertical Displacement < 25 %||Sling|
|Type III||Injuried||Injuried||Vertical Displacement 25-100 %||Controversial|
|Type IV||Injuried||Injuried||Posterior Displacement of the lateral end of the clavicle (through trapezius muscle).||Surgery|
|Type V||Injuried||Injuried||Vertical Displacement > 100 % (clavicle herniated|
through deltotrapezial fascia, resulting in subcutaneous distal clavicle)
|Type VI||Injuried||Injuried||Rare injuries, the distal clavicle lies either in a subacromial or subcoracoid position (infero-lateral under conjoined tendon).||Surgery|
Ac Joint Separation Treatment
- Type I and II
- Type III (controversial)
- Non-operative treatments include:
- Use of mild analgesics,
- Immobilization with a sling
- Early range of motion exercises.
- If the distal clavicle is displaced no more than one half of its thickness, strapping, splinting, or immobilization with a sling for 2 to 3 weeks usually is successful.
- Failing of conservative treatment may be due to the interposition of the articular disc, frayed capsular ligaments, and fragments of articular cartilage between the acromion and the clavicle.
- The disadvantages of nonsurgical treatment by strapping, bracing, or splinting techniques include:
- Skin pressure and ulceration,
- Recurrence of deformity.
- Necessity of wearing the sling or brace for 8 weeks.
- Poor patient cooperation.
- Interference with activities of daily living.
- Loss of shoulder and elbow motion (in older patients).
- Soft tissue calcification.
- Late acromioclavicular arthritis.
- Late muscle atrophy, weakness, and fatigue.
- Type III (controversial).
- Type IV, V, VI.
- Operative Treatments of AC joint separation can be divided into five major categories:
- Acromioclavicular reduction and fixation:
- Usually with smooth or threaded Kirschner wires or with hook plate.
- Acromioclavicular reduction, coracoclavicular ligament repair, and coracoclavicular fixation.
- A combination of the first two categories.
- Distal clavicle excision:
- In older patients with painful, disabling, old acromioclavicular dislocations with degenerative changes.
- Muscle transfers.
- Acromioclavicular reduction and fixation:
- Any surgical procedure for acromioclavicular dislocation should fulfill three requirements:
- The acromioclavicular joint must be exposed and débrided.
- The coracoclavicular and acromioclavicular ligaments must be repaired or reconstructed.
- Stable reduction of the acromioclavicular joint must be obtained.