The acromioclavicular (AC) Joint is stabilized by a joint capsule and ligaments. The AC ligament controls the AP translation (horizontal stability). The coracoclavicular (CC) ligament controls the vertical stability.
There are two separate coracoclavicular ligaments that stabilize the distal clavicle. These ligaments are the primary stabilizers to superior or vertical migration of the distal clavicle. The conoid ligament is medial (inserts about 4.5 cm from the end of the clavicle) and the trapezoid ligament is lateral (inserts about 3 cm from the end of the clavicle). The distance from the top of the coracoid to the inferior surface of the clavicle is called the CC distance that is less than 12 mm.
The coracoacromial (CA) ligament does not provide stability to the AC joint; however, this ligament can be used for surgical stability of the AC joint. The CA transfer alone gives only 20% of the native strength of the CC ligaments.
What is the classification of AC joint injuries?
Injury to the AC joint occurs in a progressive degree to the stabilizing structures. You will be able to predict the pathology by carefully assessing the degree and direction of the displacement. These injuries are classified according to the degree of the injury, the amount and direction of displacement, into six types.
Type I – AC joint sprain that distributes pain at the point of the shoulder.
Type II – The AC ligament ruptures and there is partial displacement of the AC joint (the CC ligament is intact).
Type III – The AC and CC ligaments are ruptured with superior displacement of the clavicle up to 100% of the clavicle width. There is an increase in the CC ligament distance and the deformity is reducible.
Type IV – The ligaments are ruptured and the AC joint is dislocated and displaced posteriorly through the trapezius muscle. Axillary view x-rays will show this posterior displacement very well. In the axillary view, the anterior aspect of the clavicle and the acromion should align.
Type V – Greater than 100% displacement of the clavicle superiorly. Marked increase in the CC distance and the deformity is not reducible. There will be marked, gross disparity between both the injured and normal shoulder.
Type VI – Inferior displacement of the clavicle, this type is rare. The distal clavicle lies under the acromion and the coracoid.
Watch out for sleeve fracture off the distal clavicle in skeletally immature patients! The distal clavicle fracture is usually a sleeve fracture that resembles an AC joint separation. No surgery is needed for this deformity because it remodels well in the pediatric patient.
Injuries to the AC joint are sometimes apparent due to the pain and deformity. Injury results from direct trauma such as a direct fall on the point of the shoulder and if the distal clavicle is prominent, then the patient probably has a high grade injury.
If you can reduce the deformity with manual pressure, this probably means that the clavicle did not button hole through the trapezius or deltoid muscles and this determines if the patient will need surgery or not. Be sure to examine the patient carefully because the neurovascular status may be affected especially if it is a violent trauma that may cause a brachial plexus injury or scapulothoracic dissociation.
The amount of displacement can often be difficult to assess on plain x-rays. Zanca view is an x-ray which is very useful for identifying the AC joint. The beam is directed with cephalic angle of 10 degrees and 50% of normal penetration. Sometimes weight bearing views will be obtained to differentiate type II from type III, but they are not widely used.
The treatment for a shoulder separation can be either conservative or surgical. Some people believe that if the deformity is up to 2 cm, complication rate is probably less with non-surgical treatment. If the deformity is more than 2 cm, then you probably need to do surgery. The idea is that there is a higher risk of complications with surgical treatment. The result of conservative treatment is usually better with a quick recover and return to work. With types I, II and type III the trend is to do conservative treatment. Conservative treatment in type III injuries is controversial, especially in athletes. Some surgeons are treating these injuries arthroscopically, so there may be a better result. Surgery is better with Type Iv, V and Type VI injuries.
Treat the patient with a sling for about 7 days followed by range of motion exercises. The patient may develop painful arthritis of the AC joint. The patient may have a residual prominence of the distal clavicle and pain with nonoperative treatment that may last for about 6 months. There is no correlation between reduction of the AC joint and pain, strength or the motion. In fact, there are similar outcomes between nonoperative and operative treatment for Type III injuries; however, there is a higher risk of complications with operative treatment.
When will doctors perform surgery involving Type III injuries?
Surgery should be done in young, active athletes, people who perform manual labor and also in those who have chronic injury with pain. Less than 4 weeks, will probably not need a graft augmentation if reduction and stabilization is done. The physician should not use K-wires or pins, a Hook plate is okay to use in acute injuries, but it has complications.
The physician should work on and stabilize the CC interval. Healing of the ligament will occur with no need for graft augmentation (CC interval fixation will be done). The physician will use suture anchors, buttons placed in the coracoid, or sutures passed around the coracoid (both probably have the same result). They may do a distal clavicle excision and also add AC joint fixation with a Hook plate, to support the CC ligament repair. CC ligament fixation in isolation could translate the clavicle anteriorly due to the lack of an anterior AC ligament.
For a chronic symptomatic dislocation, a tendon reconstruction will be done if greater than 4 weeks (augmented Weaver-Dunn procedure). The Weaver-Dunn procedure is a good operation, when it is performed acutely. It may not be good alone in chronic injuries. It does not matter which procedure is done, loss of reduction may occur and it usually does not affect the result of the treatment.
The Weaver-Dunn procedure will first start with resecting the distal end of the clavicle. The joint will then be reduced. Following that, the augmentation with a tendon graft to the coracoid will occur. A transfer of the CA ligament to the distal end of the clavicle will happen. The bottom line is that if the injury is chronic, use an augmented tendon graft.