Acromioclavicular Joint Injury: Causes, Symptoms, and Treatment
Acromioclavicular (AC) joint injury is a common shoulder injury that occurs when the ligaments that connect the collarbone (clavicle) to the shoulder blade (scapula) are damaged or torn. This can cause pain, swelling, and reduced range of motion in the affected shoulder.
In this article, we will discuss the causes, symptoms, and treatment options for AC joint injury.
What Causes AC Joint Injury?
AC joint injury can be caused by different mechanisms, such as:
- Direct impact: This is the most common cause of AC joint injury, resulting from a fall onto the shoulder with the arm close to the body, driving the shoulder blade down and inward.
- Indirect impact: This is caused by a fall onto an outstretched hand with force transmission through the upper arm and into the AC joint.
- Overuse: This is caused by repeated stress or strain on the AC joint from activities that involve overhead movements, such as throwing, lifting, or swimming.
AC joint injury is more common in young males who participate in contact sports or athletic activities that involve high-risk maneuvers or collisions.
What Are the Symptoms of AC Joint Injury?
The symptoms of AC joint injury depend on the severity and type of injury. There are six types of AC joint injury, ranging from mild sprains to complete dislocations (see Table 12.1 and Fig. 12.3).
The common symptoms of AC joint injury include:
- Pain in the front or top of the shoulder
- Swelling and bruising around the AC joint
- Difficulty raising or moving the arm
- A visible bump or step-off deformity on the top of the shoulder
- A popping or clicking sensation in the shoulder
The diagnosis of AC joint injury is based on a physical examination and imaging tests, such as X-rays or MRI scans. The doctor will assess the range of motion, strength, stability, and tenderness of the shoulder. The doctor will also compare the injured shoulder with the uninjured one to look for any differences in appearance or function.
Diagnosis
The diagnosis of an acromioclavicular joint injury is usually made by a doctor based on a physical examination and X-rays. In some cases, a computed tomography (CT) scan may be needed to confirm the diagnosis.
Classification
Acromioclavicular joint injuries are classified based on the severity of the separation:
- Type I: The AC ligaments are stretched but not torn. There is no displacement of the clavicle.
- Type II: The AC ligaments are torn, but the coracoclavicular ligaments remain intact. The clavicle is displaced slightly superiorly.
- Type III: The AC and coracoclavicular ligaments are torn. The clavicle is displaced more significantly superiorly.
- Type IV: The AC and coracoclavicular ligaments are torn, and the distal end of the clavicle is displaced posteriorly.
- Type V: The AC and coracoclavicular ligaments are torn, and there is a large amount of displacement of the clavicle superiorly.
- Type VI: The AC and coracoclavicular ligaments are torn, and the clavicle is displaced inferiorly to the acromion.
FIGURE Classification of ligamentous injuries to the AC joint. Type I: A mild force applied to the
point of the shoulder does not disrupt either the AC or the coracoclavicular ligaments. Type II: A moderate-to- heavy force applied to the point of the shoulder will disrupt the AC ligaments, but the coracoclavicular
ligaments remain intact. Type III: When a severe force is applied to the point of the shoulder, both the AC and the coracoclavicular ligaments are disrupted. Type IV: In a type IV injury, not only are the ligaments
disrupted but also the distal end of the clavicle is displaced posteriorly into or through the trapezius muscle.
Type V: A violent force applied to the point of the shoulder ruptures the AC and coracoclavicular ligaments
and also disrupts the muscle attachments creating a major separation between the clavicle and the acromion.
Type VI: This is an inferior dislocation of the distal clavicle in which the clavicle is inferior to the coracoid
process and posterior to the biceps and coracobrachialis tendons. The AC and coracoclavicular ligaments are also disrupted (type VI). (From Edgar C. Acromioclavicular and sternoclavicular joint injuries. In: Tornetta
P III, Ricci WM, Ostrum RF, et al., eds. Rockwood and Green’s Fractures in Adults. Vol 1. 9th ed.
Philadelphia: Wolters Kluwer; 2020:917–975.)
Treatment
The treatment of acromioclavicular joint injuries depends on the severity of the injury.
- Type I and II: These injuries are usually treated with rest, ice, compression, and elevation (RICE). A sling may be worn for comfort. Most patients recover within a few weeks.
- Type III: These injuries can be treated either non-surgically or surgically. Non-surgical treatment involves wearing a sling for 4-6 weeks. Surgical treatment may be recommended for patients who have persistent pain or weakness.
- Types IV to VI: These injuries are usually treated surgically. The goal of surgery is to stabilize the joint and prevent further displacement of the clavicle.
Complications
Complications of acromioclavicular joint injuries are rare but can include:
- Coracoclavicular ossification: This is the formation of bone in the area of the coracoclavicular ligaments. It is usually not a serious problem and does not require treatment.
- Distal clavicle osteolysis: This is the resorption (breakdown) of the distal end of the clavicle. It can cause pain and weakness in the shoulder.
- AC arthritis: This is the development of arthritis in the acromioclavicular joint. It can cause pain and stiffness in the shoulder.
Prevention
The best way to prevent acromioclavicular joint injuries is to wear protective gear when participating in sports that involve contact, such as football, hockey, and rugby. You can also reduce your risk of injury by strengthening the muscles around your shoulder.
AC Joint Injury: Causes, Symptoms, and Treatment Options
How Is AC Joint Injury Treated?
The treatment of AC joint injury depends on several factors, such as:
- The type and severity of injury
- The patient’s age, activity level, and preferences
- The presence of associated injuries or complications
The treatment options for AC joint injury include:
- Non-surgical treatment: This involves resting the shoulder, applying ice packs, taking anti-inflammatory medications, wearing a sling or a figure-of-eight brace, and doing physical therapy exercises to reduce pain, swelling, and stiffness. This is usually recommended for mild to moderate injuries (type I to III).
- Surgical treatment: This involves repairing or reconstructing the damaged ligaments using plates, screws, wires, pins, or grafts. This is usually reserved for severe injuries (type IV to VI) or those that do not respond well to non-surgical treatment.
The goal of treatment is to restore the normal function and appearance of the shoulder and prevent long-term complications, such as arthritis, instability, or chronic pain.
Conclusion
AC joint injury is a common shoulder injury that can affect anyone at any age. It can be caused by various mechanisms, such as falls, impacts, or overuse. It can involve different types of ligament damage, ranging from mild sprains to complete dislocations. It can cause pain, swelling, and reduced range of motion in the affected shoulder.
The treatment of AC joint injury depends on the severity and type of injury, as well as the patient’s preferences and goals. The treatment options include non-surgical and surgical methods, depending on the case. The recovery time for AC joint injury varies from person to person, but usually takes several weeks to months.
Acromioclavicular Joint Injury Epidemiology: The most common age group for AC joint injuries is the second decade of life and is associated with contact athletic activities. AC dislocations account for 9-10% of acute traumatic injuries to the shoulder girdle. These injuries are more prevalent in males with an approximate ratio of 5:1.
Anatomy: The AC joint is a diarthrodial joint with fibrocartilage-covered articular surfaces located between the lateral end of the clavicle and the medial acromion. The AC ligaments (anterior, posterior, superior, and inferior) strengthen the thin capsule, and the deltoid and trapezius muscles reinforce the superior AC ligament to strengthen the joint. The AC joint has minimal mobility through a meniscoid intra-articular disc that degenerates over time to become essentially nonfunctional beyond the fourth decade. The horizontal stability of the AC joint is conferred by the AC ligaments, whereas the vertical stability is maintained by the coracoclavicular ligaments (conoid medial, trapezoid lateral). The average coracoclavicular distance is 1.1 to 1.3 cm.
Mechanism of Injury: The most common mechanism of injury for AC joint injuries is direct trauma, resulting from a fall onto the shoulder with the arm adducted, driving the acromion medial and inferior. Indirect trauma is caused by a fall onto an outstretched hand with force transmission through the humeral head and into the AC articulation.
Associated Fractures and Injuries: Fractures of the clavicle, acromion process, and coracoid process may occur in AC joint injuries. Pneumothorax or pulmonary contusion may occur with type VI AC separations.
Clinical Evaluation: Patients should be evaluated while in the standing or sitting position with the upper extremity in a dependent position to stress the AC joint and emphasize deformity. A downward sag of the shoulder and arm is a characteristic anatomic feature. A standard shoulder examination should be performed, including assessment of neurovascular status and possible associated upper extremity injuries. Inspection may reveal an apparent step-off deformity of the injured AC joint, with possible tenting of the skin overlying the distal clavicle. Range of shoulder motion may be limited by pain, and tenderness may be elicited over the AC joint.
Radiographic Evaluation: A standard trauma series of the shoulder is usually sufficient for recognizing AC joint injury. Stress radiographs may assess ligamentous injury to the coracoclavicular joints. The Zanca view is taken with the x-ray beam in 10 to 15 degrees of cephalic tilt, allowing better visualization of the distal clavicle.
Classification: AC joint injuries are classified depending on the degree and direction of displacement of the distal clavicle.
Treatment: Treatment for type I injuries involves rest, ice packs, and a sling for 7 to 10 days. Type II injuries require a sling for 1 to 2 weeks and gentle range of motion as soon as possible. Refrain from heavy activity for 6 weeks. Nonoperative treatment for type III injuries is indicated for inactive, nonlaboring, or recreational athletic patients, especially for the nondominant arm. Younger, more active patients with more severe degrees of displacement and laborers who use their upper extremity above the horizontal plane may benefit from operative stabilization. Repair is generally avoided in contact athletes due to the risk of reinjury. Types IV to VI injuries typically require surgical treatment.
Complications: Coracoclavicular ossification is not associated with increased disability. Distal clavicle osteolysis may cause chronic dull ache and weakness, and AC arthritis may occur.