AC Joint Separation

AC joint separation occurs when the ligaments that stabilize the AC joint are damaged, leading to varying degrees of displacement/ dislocation between the collarbone and shoulder blade. The injury typically results from a direct blow to the shoulder or a fall onto the point of the shoulder. When the force is severe enough, the ligaments are torn causing the shoulder blade to move downward due to the weight of the arm which creates a bump or bulge above the shoulder.

The severity of AC joint injuries is categorized by the extent of the injury and the number of ligaments involved.

• Type I: A mild sprain or partial tear of the AC ligament without displacement. The joint remains stable, and the CC ligament is intact.
• Type II: A complete tear of the AC ligament with a sprain or partial tear of the CC
• Type III: A complete tear of the AC ligament and CC ligament, leading to significant separation between the clavicle and acromion. They take longer to heal.
• Type IV and V: This is severe injury that often requires surgery.

An AC joint separation happens most often from a fall onto the shoulder. The impact damages the ligaments that hold the joint together, causing pain, swelling, and sometimes a bump on the top of the shoulder. It’s common in contact sports like football or in accidents like falling off a bike.

Patients with an AC joint separation often present with:

• Pain: Acute shoulder pain at the time of injury, which may worsen with arm movement or lifting.
• Deformity: In more severe cases (Type III or higher), a visible bump or displacement may be seen at the top of the shoulder.
• Swelling and Bruising: Soft tissue inflammation and discoloration around the joint.
• Limited Range of Motion: Difficulty lifting the arm or performing overhead activities.
• Tenderness: Sensitivity upon palpation of the AC joint.

A thorough medical history and physical examination are crucial in diagnosing AC joint separations. During the evaluation, physicians assess for deformity, swelling, and tenderness around the AC joint. Special attention is given to any loss of shoulder function or abnormal mobility in the joint.

To confirm the diagnosis and determine the severity of the injury, imaging studies are typically utilized:

• X-Rays: Standard shoulder X-rays, often including stress views, are used to assess joint alignment and ligament integrity. Stress views involve applying weight or resistance to the affected arm to reveal subtle displacements.
• MRI: This advanced imaging technique is used when soft tissue damage, such as ligament tears or concurrent injuries like rotator cuff tears, is suspected.
• Ultrasound: A dynamic and non-invasive tool to visualize ligament integrity and detect fluid or inflammation around the joint.

AC joint separations can significantly affect an individual’s quality of life and athletic performance. For athletes, even a mild separation can temporarily disrupt training and competition. Moderate to severe injuries (Types III and above) may lead to prolonged recovery times, persistent discomfort, and, in some cases, residual instability or deformity.

The long-term impact of AC joint separations depends on the severity of the injury and how well it is managed. While most low-grade injuries heal without complications, higher-grade separations may lead to chronic pain, joint arthritis, or weakness if not addressed appropriately.