An AC joint sprain is an injury to the ligaments that hold the collarbone and shoulder blade together at the top of the shoulder. It often happens after a fall or direct hit to the shoulder, and it can range from a mild stretch to a complete tear.

Quick Scoop

The AC joint is the small joint at the top of your shoulder where the clavicle meets the acromion, and it helps with shoulder motion and stability. When those ligaments are stretched or torn, you may hear it called a “shoulder separation,” though that term can cover different severities of injury.

Common signs

  • Pain at the top of the shoulder, especially when lifting the arm or reaching across the body.
  • Swelling, bruising, or tenderness around the joint.
  • A visible bump or deformity near the top of the shoulder in more serious cases.
  • Weakness, limited motion, or pain when lying on the injured shoulder.

Usual causes

Most AC joint sprains happen from trauma, especially falling onto the shoulder, landing on an outstretched hand, or taking a direct blow to the shoulder. They are also common in contact sports and other activities with falls or collisions.

Severity

Mild sprains involve stretching or small tears, while more serious injuries can fully tear the ligaments and make the shoulder look visibly separated or unstable. Many mild cases improve without surgery, but severe injuries may need more advanced treatment.

When to get checked

If you have strong pain, a noticeable bump, trouble lifting the arm, or worsening swelling after a shoulder injury, it’s a good idea to get medical evaluation.