An acromioclavicular joint (AC) separation is also referred to as a shoulder separation. An AC separation is a very common injury in sports and in falls onto the shoulder from a bike for example. The AC joint is the connection between the scapula (shoulder blade) and the clavicle (collarbone). An AC separation is not a shoulder dislocation. During the injury, the clavicle is forced upward and can be elevated in relation to the acromion. Falls directly on the shoulder are the usual cause of this injury. Football, biking, skiing, snowboarding and other sports which allow contact with the shoulder and the ground are the commonest causes of this injury.
During the injury varying degrees of injury to the structures that hold the AC joint together occur. The AC joint capsule and two ligaments, the coracoclavicular ligaments, hold the clavicle down level with the acromion.
AC joint separations are graded from mild to severe, depending on which ligaments are sprained or torn and how high the clavicle is elevated in relation to the acromion. The mildest type of injury is a simple sprain of the AC joint capsule (grade I). A grade 2 separation is a partial tear of the coracoclavicular ligaments with partial elevation of the clavicle. A complete tear of the AC ligaments and the coracoclavicular ligaments is a results in 100 % elevation of the clavicle with respect to the acromion. Grade 4, 5, and 6 separations are severe injuries with high degree of displacement of the clavicle with respect to the acromion and usually require surgery. Figure one summarizes the classification of AC joint injuries.
Treatment of AC joint separations depends on the type (severity) of the AC joint injury. This classification is based on the severity of the injury (degree of elevation of the clavicle with respect to the acromion on x-ray and clinical exam.
The type of surgery performed to reconstruct the AC joint after a severe separation (Type 3-6) is controversial. Recently, there has been a renewed focus on improving the surgery to reconstruct the AC joint. This is called an anatomic AC joint reconstruction and was well studied both clinically and in the laboratory by a physician named Dr. Mazzocca at the University of Connecticut. Severe injury to the AC joint results in a tear of not only the AC joint capsule but also the coracoclavicular ligaments which serve as a strong connection from the coracoid process to the clavicle.
During this surgery, the torn coracoclavicular ligaments are reconstructed (replaced) using cadaver tissue. The cadaver graft is placed in the exact location of the torn ligaments and is fixed with bio-compatible screws. The new ligaments heal and serve to restore the normal anatomy of the shoulder. Dr. Gamradt performs part of this operation arthroscopically, but the graft must be secured through a small open incision.
Rehabilitation after the surgery involves six weeks in a sling followed by three months of supervised physical therapy to restore motion and strength. Return to contact sports is probably not advisable until 5-6 months after surgery. Despite surgery, the clavicle can still remain prominent and the surgery is not 100 percent successful. Recurrence of the AC separation can also occur, especially in contact athletes.
Figure 2a. Type 5 AC separation with 200% elevation of clavicle with respect to AC joint
Figure 2b. Postoperative x-ray after anatomic coraco-clavicular ligament reconstruction with tibialis anterior allograft.
Figure 2c: Arthroscopic exposure of coracoid process
Figure 2d: Arthroscopic passage of coracoclavicular ligament graft around coracoid process to restore normal AC joint anatomy.