About the AC Joint
The acromioclavicular joint, or AC joint, is a joint at the top of the shoulder. It is the junction between the acromion (part of the scapula that forms the highest point of the shoulder) and the clavicle. The AC joint allows the ability to raise the arm above the head. This joint functions as a pivot point (although technically it is a gliding synovial joint), acting like a strut to help with movement of the scapula resulting in a greater degree of arm rotation.
The AC joint is stabilized by three ligaments:
The acromioclavicular ligament: attaches the clavicle to the acromion of the scapula.
The coracoacromial ligament: runs from the coracoid process to the acromion.
The coracoclavicular ligament: consists of two ligaments, the conoid and the trapezoid ligaments.
A common injury to the AC joint is dislocation, often called AC separation or shoulder separation. This is not the same as a “shoulder dislocation,” which refers to dislocation of the glenohumeral joint. A shoulder separation is almost always the result of a sudden, traumatic event that can be attributed to a specific incident or action. The two most common descriptions of a shoulder separation are either a direct blow to the shoulder (often seen in football, rugby, or hockey), or a fall on to an outstretched hand (commonly seen after falling off a bicycle or horse).
Although a shoulder separation is a common injury, there are a few different types:
Type 1: is an injury to the capsule that surrounds the AC joint. The bones are not out of position and the primary symptom is pain.
Type 2: involves an injury to the AC joint capsule as well as one of the important ligaments that stabilizes the clavicle. This ligament, the coracoclavicular ligament, is partially torn. Patients with a type II separated shoulder may have a small bump over the injury.
Type 3: involves the same type of injury as a type II separated shoulder, but the injury is more significant. These patients usually have a large bump over the injured AC joint.
Type 4: is an unusual injury where the clavicle is pushed behind the AC joint.
Type 5: is an exaggerated type III injury. In this type of separated shoulder, the muscle above the AC joint is punctured by the end of the clavicle causing a significant bump over the injury.
Type 6: also exceedingly rare. In this type of injury the clavicle is pushed downwards, and becomes lodged below the coracoid (part of the scapula)
Arthroscopic surgical technique:
The patient is placed in the lateral or beach chair position under a general anesthesia, supplemented with a scalene block. The arthroscope is introduced into the glenohumeral joint via a standard posterior portal. An anterior portal is created with an outside/in technique using a spinal needle to verify position. An 8.25 mm cannula is then introduced through the anterior portal. A full radius shaver blade is put in position through the anterior cannula and worked through the rotator interval. The dead or damaged tissue is removed until the base of the coracoid can be seen.
A hole is drilled in the clavicle typically 35 mm from the distal clavicle. Once the hole is drilled, a graft is attached with a coracoid button on either side. The clavicle is reduced while the blue fiberwire is tightened. The excess graft and wire is then cut and the portals are sutured.