Acromioclavicular joint dislocation (ACD) is one of the most common shoulder injuries and is usually sports related. Acromioclavicular (AC) joint injuries account for about 12% of all shoulder injuries in clinical practice, a rate that increases to almost 40% in athletes participating in contact sports.
Epidemiological studies showed that most AC joint injuries occur in the third decade of life, and the gender distribution is 5:1 in favor of men. Acromioclavicular joint (ACJ) injuries have been reported to especially occur in 20- to 30-year-old male patients engaging in high-contact sports.
The mechanism of injury leading to AC joint dislocation can be direct or indirect. A direct force on the superior aspect of the acromion process, it happen due to fall onto the outer aspect of the shoulder, is the most common scenario. The acromioclavicular capsule-ligamentous structures fail with consecutive loading of the coraco-clavicular (CC) ligaments.
The Four components of the acromioclavicular (AC) capsular ligaments and the two components of the coracoclavicular (CC) ligaments contribute to AC joint stability depending upon the direction and magnitude of the force applied. The trapezoid ligament provides the major support against compressive loads applied along the axis of the clavicle and acts as a secondary restraint to superior translation. On the other hand, the conoid ligament contributes to both superior and anterior stability. Among the 4 AC capsular ligaments, the superior and posterior capsular ligaments, reinforced by the deltoid and trapezius muscle, are important due to their primary role in prevention of posterior translation. Despite the different contribution of each ligament on the stability of the AC joint, most current surgical techniques for complete AC joint dislocation focus on CC interval fixation to restore the CC ligaments.
Nonsurgical management is the mainstay of treatment for type I and II injuries, whereas surgery is usually recommended for type IV to VI injuries. The treatment for type III remains instead controversial as no clear treatment algorithm has been established.
Because of the distinct functional anatomy of the AC and CC ligaments, several studies provided good results focusing on anatomical surgical techniques that recreate those structures, rather than non-anatomical procedures that aim to improve function and stability regardless of restoration of anatomy of the torn ligaments. Although several anatomic reconstruction techniques are available, most of them showed promising results after conducting underpowered studies at short-term follow-up. Moreover, no gold standard has been identified yet.
Several surgical techniques have been described in the literature. Rockwood classified the early surgical treatments for AC joint instability into 4 groups: (1) AC ligament repairs, (2) CC ligaments repairs, (3) excision of the distal clavicle, and (4) dynamic muscle transfer. In addition, K-wires, screws, and plates have been used for temporary fixation of the AC joint. A better understanding of the anatomy and biomechanics of the AC joint and the coracoclavicular (CC) ligaments has led to advances in surgical techniques. Anatomic reconstructions using free grafts have become popular in recent years. In addition, arthroscopically assisted procedures using cortical fixation devices have become more popular.
