AC Joint Fixation
The acromioclavicular, or AC joint is a joint in the shoulder where two bones meet. One of these bones is the collarbone or clavicle. The second bone is part of the shoulder blade (scapula), the big bone behind the shoulder that also forms part of the shoulder joint. The portion of the shoulder blade that meets the clavicle is called the acromion. As a result, where the clavicle meets the acromion is called the AC joint.
AC joint serves as a primary link between the axial skeleton and the upper extremity. Like most joints in the body where bones meet, the cartilage between the two bones is the white tissue between bones that allows them to move on each other. The joint has dynamic and static stabilizers, and it is movable in all planes, so it is not a rigid structure. Its complex ligamentous structure is critical to the normal function of the shoulder girdle. The acromioclavicular and Coracoclavicular ligaments are the static stabilizers, whereas the deltoid and trapezoid muscles are the dynamic stabilizers.
What is an AC joint injury?
AC joint injury is the separation of the acromioclavicular joint; it means that the ligaments are torn, and the collarbone no longer lines up with the acromion. The injury to the AC joint ligament can be graded as mild to severe.
Type I is a sprain injury of the AC ligament; there is no complete tear, and both AC and CC ligaments are intact.
Type II is a tear of the AC ligament but not of the CC ligaments. A type III injury involves tears of both the AC and CC ligaments, with 25% to 100% displacement of the clavicle than that on the contralateral side.
In a type IV injury, both the AC and CC ligaments are torn, and there is a posterior displacement of the distal clavicle into the trapezius fascia.
In a Rockwood type V injury, the AC and CC ligaments and both the origin of the deltoid and the trapezius insertion are torn, causing extreme instability of the AC joint. It is a complex injury where the deltotrapezial fascia is stripped from its attachment and displacement of the clavicle is more than three times the diameter of its distal part. The CC distance is increased to 100% to 300%.
Type VI injuries are the result of inferior displacement of the distal clavicle into the subcoracoid position.
The traditional literature supports non-operative treatment for grade I and II injuries. Patients with grade IV, V and VI injuries benefit from operative treatment, whereas grade III injuries' treatment remains a controversial issue.
Many surgical procedures have been described; these are screws, plates, muscle transfers, ligamentoplasty procedures and ligament reconstruction using either autograft or allografts. Open and arthroscopic methods can perform anatomical ligament reconstruction using a tendon graft. Open surgery requires deltoid detachment from the clavicle and extensive soft-tissue dissection to access the coracoid process; neurovascular structures are placed at risk because of the suboptimal visibility during tendon transfer around the coracoid.
Recent treatment modalities for AC joint dislocation have focused on either CC ligament reconstruction or CC interval fixation. Many devices such as screws, plates, suture anchors or synthetic tapes have been used as fixation material; however, none of these methods is free of complications such as implant failure or implant migration, bony erosions and fractures of the clavicle, and recurrent dislocation. With the advancement of arthroscopic intervention techniques, AC joint injuries' management has been shifted from open surgical procedures towards less invasive, arthroscopically-assisted or all-arthroscopic procedures.
The principle advantage of arthroscopy is that it allows the patient early release from the hospital with a shorter rehabilitation period and early return to activity.
Arthroscopy allows a better, greater and clearer visibility around the coracoid, and extensive dissection of the deltotrapezial fascia is not required. This clearer visibility also puts the important neurovascular structures at less risk. The suprascapular nerve and the suprascapular artery are the structures with the closest proximity to any implanted material. Besides, arthroscopy makes it possible to get a straight vision of the inferior aspect of the coracoid base – a particularly important anatomical area, especially when placing CC fixation systems.