What to Know About an AC Joint Sprain

Medically Reviewed by Poonam Sachdev on October 18, 2022
Written by Kristen Drummey
5 min read

AC joint sprains are a fairly common type of shoulder injury that affects the joint connecting the shoulder blade and collarbone. This sprain is particularly common in athletes and can result from a direct hit to the shoulder or a fall. AC joint sprains can vary in severity, but many can be treated without surgery.

The AC joint, short for the acromioclavicular joint, connects the shoulder blade and the collarbone. 

What are joints? In the body, joints are where two or more bones come together. Joints are essential for movement — they’re necessary for swinging your arms or moving your legs. 

Joints are made up of several different components that ensure smooth movement and connect parts of the joint with the surrounding tissue. 

Some components of a joint include:

  • Ligaments. Ligaments are a type of connective tissue that support the joint and keep its movement within a reasonable range. Ligaments can stretch to support joint movement.
  • Tendons. Like ligaments, tendons are a type of connective tissue. They connect muscles and bones so that they move together. 
  • Cartilage. The part of a bone connected to a joint is covered with cartilage, which helps the bone move smoothly in the joint. 

What happens when the AC joint is sprained? AC joint sprains are caused by damage to the ligaments that support the AC joint and help keep it in place. Damage to ligaments can destabilize a joint and cause pain or limit movement. AC joint sprains may also impact surrounding connections with muscles.

Who is at risk for an AC joint sprain? About 9% of all shoulder injuries are AC joint sprains or separations. Nearly half of AC joint sprains happen in patients in their twenties. This type of sprain most commonly affects men. 

A major risk factor for an AC joint sprain is playing a high-contact sport like hockey or football. AC joint sprains account for about 15% of shoulder injuries in hockey players and over 40% in football players.

AC joint sprains happen when the ligaments holding the joint in place become damaged. 

Common causes of AC joint sprains include:

  • A hard, direct hit to the shoulder
  • Falling onto the shoulder
  • Falling and landing on an arm or hand that was outstretched to break the fall 

AC joint sprains typically cause shoulder pain and soreness and may reduce movement in the shoulder. Symptoms can vary depending on how bad the sprain is but may include:

  • Pain and soreness in the shoulder
  • Swelling or bruising of the shoulder
  • Reduced shoulder movement
  • A bulge in the shoulder or a general change in its shape
  • A shift in the collarbone’s position

AC joint sprain diagnosis. AC joint sprains can typically be diagnosed following a physical exam with a doctor. Your doctor may also want to perform X-rays to confirm that the AC joint is sprained and to see how bad the injury is. 

AC joint sprains are classified by a grading system. Your doctor may also assign a grade to the injury. AC joint sprain grades refer to how severe the damage is.

Depending on how bad the injury is, AC joint sprains can be classified as:

  • Type I. In Type I injuries, the acromioclavicular (AC) ligament, one of the ligaments supporting the AC joint, is sprained. The AC joint, other supporting ligaments, and surrounding muscles aren’t affected.
  • Type II. Type II injuries have a completely torn AC ligament. Because the ligament is torn, the joint is wider than normal and surrounding ligaments are sprained. Supporting muscles might start to detach from the joint. 
  • Type III. Type III injuries also have a completely torn AC ligament and the AC joint is out of place. The collarbone may shift to a different position and the surrounding muscles are likely to detach. 
  • Type IV, V, and VI. Types IV-VI are subtypes of Type III. All of these types include torn AC ligaments and displaced AC joints. Type IV, V, and VI describe the direction that the collarbone has shifted compared to the shoulder, whether above the shoulder, below it, or behind it. 

AC joint sprain treatment. AC joint sprains generally respond well to treatment, and most injuries don’t require surgery. 

Typical treatment for an AC joint sprain includes:

  • Resting the shoulder. Give the shoulder time to rest and heal. Avoid any activities that further aggravate the injury, including sports, sleeping on the shoulder, and using the injured arm to reach above your head. 
  • Keeping the shoulder in a sling. A sling can help protect the shoulder from another injury and helps position the joint to heal correctly.
  • Using cold packs and pain medicine if necessary. Both cold packs and over-the-counter or prescribed pain medications can help alleviate pain and reduce swelling near the shoulder.
  • Sticking to a rehabilitation plan. As the shoulder starts to heal, it’s important to move the shoulder joint to heal properly. Please consult with your doctor or a physical therapist before beginning any shoulder exercises to make sure that your shoulder is ready for them.

AC joint sprain recovery time. AC joint sprain recovery time varies depending how bad the sprain is. Type I sprains are pretty mild, while type IV, V, and VI sprains can be very severe and may require treatment from a specialist. 

With a mild sprain, you can expect it to start to feel better and move more normally after six weeks. By three months, the shoulder should be mostly back to normal. 

More severe injuries take longer to heal, especially if the joint needed to be fixed with surgery. After surgery, the shoulder typically has to be in a sling or cast for six weeks. It will take at least six months for the shoulder to fully return to normal. 

Some patients may still experience joint pain even after the joint has recovered. Some patients, especially those who had surgery on the joint, may also be at risk for AC joint arthritis.

AC joint sprains are a fairly common cause of shoulder injury, especially in younger people and athletes. These sprains vary in severity but can typically be treated without surgery. After an AC joint sprain, it’s important to talk with your doctor about a treatment plan and to rest your shoulder so that the joint has time to heal.