AC Joint Separation
The acromioclavicular (AC) joint is located at the top of the shoulder, where the collarbone (clavicle) meets the highest point of the shoulder blade (acromion). An AC joint separation, sometimes called a shoulder separation, occurs when the stabilizing ligaments are stretched or torn. This can cause the clavicle to move out of its normal position, leading to pain, swelling, and difficulty using the arm. While often confused with a dislocated shoulder, an AC joint separation is a different injury and requires its own approach to diagnosis and care.
The key ligaments involved are:
- Acromioclavicular (AC) ligaments – These are small ligaments directly connecting the clavicle (collarbone) to the acromion (part of the shoulder blade). They provide horizontal stability. A sprain or tear here usually indicates a mild (Grade I) injury.
- Coracoclavicular (CC) ligaments – This pair includes the conoid ligament and the trapezoid ligament. They connect the clavicle to another part of the shoulder blade called the coracoid process. These ligaments provide vertical stability and are stronger than the AC ligaments. When they are torn, the injury is more severe (Grade III or higher), and the clavicle often becomes visibly displaced upward.
Symptoms usually appear right after the injury. The most common symptoms include:
- Sudden pain at the top of the shoulder, particularly after a fall or direct impact.
- Swelling and bruising may develop quickly.
- Many people notice tenderness when pressing on the joint and a reduced ability to lift the arm.
- In more severe injuries, a visible bump may appear at the end of the collarbone where it has shifted upward. Some patients also report a grinding or popping sensation when moving the shoulder.
The most frequent cause is trauma, such as falling directly onto the shoulder. This often happens in contact sports like football, hockey, or rugby. Cyclists may experience an injury if they fall off a bike and land on their shoulder. It can also result from accidents, such as slipping on ice or being involved in a motor vehicle collision. Less commonly, repetitive stress or heavy overhead lifting may strain the joint and increase the risk of separation.
AC joint separations are typically graded based on severity, ranging from mild sprains to complete tears of the supporting ligaments.
- Grade I: A mild sprain where ligaments are stretched but the joint remains stable.
- Grade II: A partial tear that causes some displacement of the clavicle.
- Grade III: A complete ligament tear with visible displacement of the clavicle.
More severe grades (IV–VI) are rare but involve significant displacement or damage to surrounding tissues.
Certain individuals are at higher risk of experiencing an AC joint separation.
- Athletes who participate in contact or high-impact sports face the greatest risk because of frequent collisions and falls.
- Occupations that involve heavy lifting or repetitive overhead movement may also increase susceptibility.
- Previous shoulder injuries can weaken the ligaments, making another separation more likely.
- Age may play a role as well, since ligament strength and flexibility tend to decrease over time.
- Although anyone can suffer this injury, young and active adults are the most common group affected.
Diagnosis begins with a medical history and physical examination. Your doctor will ask about how the injury occurred, your symptoms, and any previous shoulder problems. During the exam, the doctor will look for tenderness, swelling, and deformity around the joint. They may gently move your arm to assess pain, stability, and range of motion. Imaging tests are often used to confirm the diagnosis. X-rays can show whether the clavicle has shifted out of place and help determine the severity of the separation. In certain cases, an MRI may be ordered to evaluate the surrounding ligaments, cartilage, or other shoulder structures.
Treatment depends on the severity of the separation. Mild cases often improve with rest, ice, a sling for support, and over-the-counter pain relievers. Gentle physical therapy exercises may be introduced as pain decreases to restore motion and strength. For more moderate injuries, longer periods of immobilization and structured rehabilitation may be necessary. Severe separations that cause ongoing pain, deformity, or loss of function may require surgery to stabilize the joint and restore alignment. Each treatment plan is tailored to the patient’s activity level, injury severity, and personal goals.
If you have suffered a shoulder injury and are experiencing pain, swelling, or loss of motion, it is important to seek expert care. At Ortho Illinois, our team of orthopedic specialists offers exceptional evaluation and treatment for AC joint separations and other shoulder conditions. With five convenient clinic locations—two in Rockford and one each in Algonquin, Elgin, and McHenry— where you can access experienced, compassionate care close to home. Contact Ortho Illinois today to schedule an appointment and begin your path to recovery.
