Acromioclavicular (AC) joint injury is not a benign injury, and it includes a large spectrum ranging from joint sprain to complete separation. It is among the most common injuries in athletes and in the general population. Despite the vast amount of clinical experience and literature, much controversy surrounds the appropriate approach to treatment of this injury.
Structure and function
The AC joint is located between the lateral aspect of the clavicle and the medial aspect of the acromion. It is a diarthrodial joint with an interposed firbocartilagenous disc. This disc is initially hyaline cartilage, but undergoes degeneration by the fourth decade, losing its functionality. The articulations of the AC joint and the sternoclavicular joint are the only attachments between the upper extremity and the axial skeleton.
A great deal of motion occurs around the AC joint, thus its ligaments and joint capsule are important for stabilization and strength as they surround the joint anteriorly, posteriorly, superiorly, and inferiorly. The deltoid and trapezius muscle fibers insert on the AC ligament superiorly, adding to its strength. The AC ligaments, particularly the posterior and superior ligaments, are essential in horizontal stability of the joint.
The coracoclavicular (CC) ligament is another important AC joint stabilizer. The fibers of the CC ligament run from the outer, inferior surface of the clavicle to the base of the coracoid process. The CC ligament has two components, the conoid ligament medially and the trapezoid ligament laterally. The conoid ligament attaches on the posteromedial base of the coracoid process, while the trapezoid ligament attaches anterior and lateral to the conoid. These ligaments are primarily responsible for vertical stability of the AC joint.
The AC joint is involved in anywhere from 3% up to 40% of traumatic shoulder girdle injuries, making it one of the more common athletic injuries. It generally occurs in males (5:1 to 10:1) between the ages of 20 and 30 years. The injury is twice as likely to be incomplete versus complete.
A focused history and physical exam are instrumental in leading to the diagnosis of AC joint injury. Injury to the AC joint can occur via direct or indirect mechanisms; a direct fall onto the dome of the shoulder with an adducted arm is the most common mechanism. This mechanism often occurs in football, rugby, and ice hockey players, as well as in falls from horses. A force exerted on the acromion from above in a downward, slightly anterior, and usually medial direction pushes the scapula down and medially. The displacement of the AC joint is directly related to the degree of damage that occurs in the ligament and muscular attachments. The AC ligaments are the first to be torn, followed by the CC ligaments, and finally the deltotrapezial fascia.
With a fall on the outstretched hand, the AC joint may be injured indirectly. The humeral head forces an upward moment onto the acromion, causing disruption of the AC ligaments. This mechanism does not involve the CC ligaments as they are relaxed with upward displacement of the scapula.
Associated injuries are quite common, such as fractures of the acromion, clavicle, and coracoid, and must not be overlooked.
Injury to the AC joint should be suspected in a patient with a history of trauma to the shoulder and associated pain localized to the acromion and clavicle. Depending on the extent of injury, there may be swelling, ecchymosis, and gross deformity with an unstable mobile distal clavicle. The clavicle may also be posteriorly dislocated, which is often evident on inspection of the joint. Patients will complain of tenderness with palpation at the joint with limited range of motion at the shoulder, depending on the extent of the injury.
Although rare, brachial plexus injuries have been reported to occur with severe AC joint injuries. If there is any suspicion of neurovascular compromise, it should be addressed immediately. Also, there may be associated clavicle or rib fractures which should not be overlooked in the initial evaluation of the patient.
AC joint injuries very commonly are associated with other injuries. In a patient complaining of pain at the AC joint, one must consider a distal clavicle or rib fracture in the setting of trauma. In the patient with an insidious onset of AC joint pain, consider AC joint arthritis or distal clavicle osteolysis. Other injuries to rule out include rotator cuff tear, acromion fracture, and os acromiale.
Plain radiography continues to be the most cost-effective, readily available method for evaluation of AC joint injuries. Only one-third to one-half of the x-ray penetration required to view the glenohumeral joint is needed for adequate radiographs of the AC joint. Therefore, unless the x-ray technician is specifically ordered to take x-rays of the “AC joint,” the film will be overpenetrated.
Routine radiographs include an AP, lateral, and axillary view of the shoulder as well as a Zanca view of the AC joint. The Zance view is taken with the patient in the upright position and the x-ray beam aimed at the AC joint with a 10- to 15-degree cephalic tilt. A cross arm adduction view may help assess the stability of the joint, as it would demonstrate movement of the joint with change of positioning in the case of instability. One may consider stress views, with the patient holding 10-pound weights in the hand of the injured side. Views of the uninjured shoulder are also very helpful for comparison.
Other imaging modalities such as MRI and bone scan have been suggested to further delineate the extent of injury; however, their role is still unclear and they are not routinely used for diagnosis.
Risk factors and prevention
Protective padding around the shoulders, seen particularly with football and ice hockey players, may be useful in preventing injury to the AC joint. This padding should be required in sports that involve routine tackling, falling, or checking to avoid these injuries.
Treatment of AC joint injuries is determined by the extent of ligamentous damage and the stability of the joint. The classification of AC joint injury is important to understand when determining treatment. Rockwood classified these injuries into six separate types. In its simplest form:
- Type I: Sprain of the AC ligament
- Type II: The AC ligaments are disrupted, but the CC ligaments remain intact
- Type III: Complete disruption of the AC and CC ligaments with increasing space between the coracoid and clavicle 25-100% greater than the uninjured side, as measured on x-ray (Figure 2)
Figure 2. Type III AC separation
- Type IV: Complete disruption of AC and CC ligaments with posterior displacement of the distal clavicle, detaching the deltoid and trapezoidal muscles
- Type V: Complete disruption of the AC and CC ligaments with increasing space between the coracoid and clavicle greater than 100% when compared with the uninjured side (Figure 3)
Figure 3. Type V AC separation
- Type VI: Inferior displacement of the distal clavicle, in which the clavicle is inferior to the acromion or the coracoid, with completely disrupted AC and CC ligaments
Most surgeons would agree that nonoperative treatment is the standard of care for acute Type I and Type II injuries. This consists of ice, analgesics, immobilization with a sling, early range-of-motion exercises, and return to activities as tolerated. Type II injuries may require immobilization for as long as 2 weeks with an early and gradual rehabilitation program. Contact sports and heavy lifting should be avoided for 8 to 12 weeks to allow for ligament healing. A protective pad worn over the AC joint may allow for earlier return to play.
The treatment for Type III injuries has been under debate for multiple decades, with current trends leaning toward nonoperative treatment.; Operative treatment may be recommended for thin patients with prominent distal clavicle, heavy laborers, athletes, and patients whose work requires shoulder abduction and flexion with overhead activities.
Most surgeons would agree on operative treatment of Type IV, V, and VI injuries. There is a wide variety of operative approaches with the similar goal of reducing the AC joint and creating a stable anatomical construct. The joint may be held in a reduced position with primary fixation using devices such as screws of sutures. It may also be reconstructed to recreate normal anatomy in the more chronic AC joint injuries. The reconstruction may be done with open or arthroscopic approaches. In these higher-grade injuries, acute reconstruction is preferable, as complete reduction of the joint is more difficult after several months have elapsed and the native ligaments are difficult to discern. Postoperatively, patients are placed in a sling and allowed early range of motion at around 2 weeks. Their activity is gradually increased and they can be expected to return to sport at about 6 months.
Patients with Type I, II, and III injuries who are treated nonoperatively generally do well and will return to their previous level of activity once their symptoms allow. There are reports that up to about 20% of those patients will fail nonoperative treatment (predominantly Type III) and will continue to have pain and limited mobility. Consideration for further surgical management is certainly an option and can help relieve those symptoms.
Results of operative treatment, whether primary fixation or reconstruction of the AC joint in Types IV, V, and VI injuries, as well as in Type III injured patients in whom surgery is indicated, has shown to be promising. The success rates for surgery have been reported to be around 70% to 90% depending on the technique used, the timing of surgery, and patient compliance.
Possible complications of surgical treatment include, but are not limited to, wound breakdown and infection, hardware migration and failure, clavicle and coracoid fracture, loss of reduction, and neurovascular injury. With older methods of fixation, screw failure, migration of pins, and loss of reduction during hardware removal are recognized complications. With introduction of foreign material into the reconstructed joint, there have also been reports of aseptic foreign-body reaction, as well as clavicle osteolysis. With careful surgical technique, an adequate rehabilitation and time to return to activity, and proper postoperative support, the complications can be minimized.
Despite the abundance of literature on the myriad techniques of repair and reconstruction of the AC joint, quality head-to-head clinical comparisons of these techniques are lacking. With ongoing biomechanical and clinical studies in the future, one can only hope for more convincing approach to the treatment of these injuries.
Acromioclavicular, shoulder separation, AC joint arthrosis, coracoclavicular, distal clavicle osteolysis
- Obtain a focused history and be able to perform a focused physical exam related to the injury and associated pathologies.
- Recognize deformity at the AC joint with superior migration of the distal clavicle.
- Be alert for neurovascular compromise, which needs immediate attention.
- Understand the patient’s expectations and goals when deciding treatment.
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