AC Joint Separation (Shoulder Separation)

Overview

An AC joint separation, often called a shoulder separation, is an injury to the acromioclavicular (AC) joint. This small joint sits at the top of the shoulder where the end of the collarbone meets a part of the shoulder blade called the acromion. Strong ligaments normally hold the two bones together.

When these ligaments are stretched or torn, the collarbone can shift out of its normal position, sometimes producing a visible bump on top of the shoulder. A shoulder separation is different from a shoulder dislocation, which involves the main ball-and-socket joint. Injuries are graded by severity, and most milder separations heal well without surgery.

Symptoms

Symptoms appear right after the injury and vary with severity:

• Pain at the top of the shoulder, especially when reaching across the body or overhead
• Swelling and tenderness over the AC joint
• A bump or step-off where the collarbone is raised
• Bruising and limited shoulder movement
• A sense of the shoulder being weak or unstable

Mild separations cause tenderness without an obvious bump, while more severe ones produce a clear deformity and greater loss of motion.

Causes

AC joint separations are caused by force applied to the top or point of the shoulder:

• Falls onto the shoulder: The most common cause, often in cycling, skiing, football, and other sports.
• Direct blows to the top of the shoulder during contact sports or collisions.
• Falls onto an outstretched hand that drive force into the joint.

The severity depends on how much force is involved and how many of the supporting ligaments are torn.

Risk Factors

• Participation in contact and high-speed sports
• Activities with a high risk of falling onto the shoulder
• Cycling, skiing, and snowboarding
• Younger, active individuals are most often affected

Diagnosis

Diagnosis is usually clear from the examination and imaging:

• Physical examination: Checking for tenderness, swelling, a bump, and pain when moving the arm across the body.
• X-rays: Show the position of the collarbone relative to the acromion and help grade the injury; sometimes taken while holding a weight to reveal subtle separations.
• MRI: Occasionally used to assess soft-tissue damage in complex cases.

Injuries are commonly graded from mild (ligament sprain) to severe (complete tear with marked displacement), which guides treatment.

Treatment

Most AC joint separations heal with non-surgical care:

• Rest and a sling: Supporting the arm reduces pain and protects the joint early on.
• Ice and pain relief: To ease swelling and discomfort in the first days.
• Physical therapy: Gradual exercises restore motion and strength once pain settles.
• Surgery: Reserved for severe separations with major displacement or persistent pain and weakness, especially in active people who need full overhead strength.

Many people return to normal activity within weeks, though a painless bump may remain. Severe injuries take longer to recover.

Prevention

• Wear protective padding for contact sports
• Use proper technique and protective gear when cycling or skiing
• Build shoulder strength and flexibility
• Reduce fall risks during activities and around the home

When to See a Doctor

See a doctor after a shoulder injury if you have significant pain, swelling, a visible bump, or trouble moving the arm. Seek prompt care if the skin over the bump looks stretched or about to break, if there is numbness or tingling in the arm, or if the pain is severe and not improving, as these may indicate a more serious injury.

Related Topics

Frequently Asked Questions

References

1. American Academy of Orthopaedic Surgeons (OrthoInfo). Shoulder Separation.
2. Mayo Clinic. Separated shoulder.
3. MedlinePlus, U.S. National Library of Medicine. Shoulder injuries and disorders.