Your acromioclavicular joint is located where your collarbone and shoulder blade meet. Acromioclavicular joint separation is an injury that occurs when a force to your shoulder pulls these bones apart. It’s more commonly known as shoulder separation.

Acromioclavicular (AC) joint separation is very common. It’s estimated to make up about 4% to 12% of shoulder injuries and occurs in about 3 to 4 people per 100,000 every year. People who participate in contact sports like ice hockey or American football are particularly at risk of AC joint injuries.

Low-grade AC joint separation can often be treated conservatively with a sling or harness to rest your injured shoulder. Severe injuries may require surgical repair of the ligaments and other tissue around the joint.

Read on to learn more about AC joint separation, including symptoms, how it’s managed, and treatment options.

Your AC joint is where a part of your shoulder blade called the acromion process attaches to your collarbone. You may be able to feel this joint as a notch in the front of your shoulder at the end of your collarbone.

Your AC joint is held together by a strong piece of connective tissue called the AC ligament. Other ligaments such as the coracoclavicular ligament also support this joint.

AC joint separation occurs when a sudden force to your shoulder pulls your shoulder blade and collarbone apart and damages the ligaments. The most common cause of AC joint separation is a sudden direct trauma to your shoulder, such as during a fall or collision.

Types of AC joint separation

Medical professions subdivide AC joint separation into different types depending on the severity of the injury. The Rockwood system, developed in the 1980s, is the most common classification system. It divides AC joint separation into six categories.

Type Isprain of the AC ligament
Type IIrupture of AC ligament without damage to coracoclavicular (CC) ligament
Type IIIcomplete rupture of AC and CC ligaments but no injury to the surrounding fascia (collarbone is displaced less than its width)
Type IVouter part of your collarbone is displaced backward (a complete rupture of your AC ligaments and a partial rupture of the CC ligaments)
Type Vcomplete rupture of AC and CC ligaments and a rupture in your surrounding fascia (outer part of your collarbone is raised more than its width)
Type VIlateral part of your collarbone is below one or both parts of your shoulder blade, called the acromion and coracoid processes

Symptoms of AC joint separation may include:

  • pain in the front of your shoulder
  • tenderness around your AC joint
  • bruising
  • swelling
  • visible deformity, such as a visible bump in the front of your shoulder
  • weakness in your arm and shoulder

Pain is often worse when raising your arm in front of you or moving your arm away from the midline of your body.

AC joint separation is usually caused by a direct blow to your shoulder or a fall on an extended arm. These types of impacts can cause the head of your arm bone to push against your shoulder blade and overstretch the ligaments keeping your AC joint together.

Your doctor will perform a physical exam where they examine your shoulder. They will likely press on your AC joint and have you move your arm into certain positions to see if they cause pain.

AC joint separation is relatively easy to diagnose if you have a noticeable deformity to your shoulder. Your doctor will likely order X-rays to visualize the extent of the damage, even if they highly suspect shoulder separation. You may be told to hold a weight during your X-ray to make the deformity in your shoulder clearer.

Treatment for type I and II AC joint separation is usually conservative, whereas types IV, V, and VI usually require surgery. There remains controversy about how to best treat grade III injuries.

Conservative treatment options include:

Your doctor may recommend surgery if these conservative treatments aren’t effective. Surgery often involves surgically repairing damaged ligaments and stabilizing the joint with screws and plates.

Arthroscopic surgery is becoming progressively more common. Arthroscopic surgery is when your surgery uses a narrow tube with special tools to perform the operation instead of using a large incision.

Injuries to the acromioclavicular joint are common among younger adults, especially those engaged in contact sports or sports with a high risk of falling.

AC joint separation is 5 times more common in men than women.

Most people regain full range of motion and strength in their shoulder after AC joint separation. Type I and type II injuries generally only require 1 to 2 weeks in a sling. Recovery from more severe injury may take 12 weeks or more.

Here are some frequently asked questions people have about acromioclavicular joint injuries.

Are acromioclavicular injuries common?

Acromioclavicular joint injuries are very common. They make up more than 40% of shoulder injuries and about 10% of injuries in impact sports.

What sports put you at risk of AC joint injury?

Sports where AC joint injuries are common include:

  • ice hockey
  • rugby
  • American football
  • handball
  • skiing

Will an AC joint separation heal by itself?

Low-grade AC joint separation often heals with conservative treatment. Your doctor will likely recommend keeping your arm inactive with a sling for a week or 2. Surgery may be required if your injury is severe.

Your AC joint is located where your shoulder blade and collarbone meet. AC joint separation occurs when these bones are pulled apart by a sudden force to your shoulder. It’s usually caused by a fall or collision, especially during impact sports.

Mild AC joint separations can often be treated conservatively. Serious injuries or injuries that don’t respond to conservative treatment may require surgery.