AC Joint Separation

The AC joint sits at the very top of your shoulder. It is where the outer end of your collarbone (the clavicle) meets a bony shelf on top of your shoulder blade (the acromion). What holds those two bones together is a small set of ligaments that wrap the joint and tether the underside of the collarbone down to the shoulder blade. Those ligaments are the main thing keeping the collarbone from riding up.

An AC separation happens when you fall directly onto the point of your shoulder: a tackle, a bike crash, a fall onto an outstretched hand that loads the shoulder from the side. The blow drives the shoulder down while the collarbone cannot follow, and the ligaments tear. How many of them tear, and how far the collarbone shifts out of place, is what sets the grade of the injury. The grade is what determines whether your shoulder can heal on its own or needs surgical reconstruction.

Surgeons sort these injuries into grades from mild to severe. The mildest are sprains: the ligaments are stretched or partly torn, the bone has not moved on X-ray, and they heal with rest. The middle grade is a complete tear with the collarbone visibly riding up; here the surgical-vs-non-surgical decision is genuinely debated and depends on what you do for a living and how active you are. The most severe grades involve the collarbone shifting far out of place and almost always need surgery.

You will know something happened the moment it happens: a sharp, well-localized pain right on top of your shoulder after the fall or hit. Higher-grade separations come with a visible bump: the outer end of the collarbone sits higher than the acromion, creating a step you can see and feel. Lifting the arm overhead is sharply painful, and reaching across your chest to the opposite shoulder reproduces the pain. Lying on that side at night is uncomfortable for weeks.

What is not typical: numbness, tingling, or weakness running down the arm. Those point to a different injury (a brachial plexus stretch, a clavicle fracture pinching a nerve, or a separate shoulder dislocation) and need to be sorted out separately. AC separations are mechanical pain at a single point on top of the shoulder; that focality is the giveaway.

The diagnosis is mostly made on exam and X-ray. Your provider will look for a step deformity (the bump on top of the shoulder), tenderness right on the joint, and pain when your arm is pulled across your chest. Standard shoulder X-rays show the joint clearly; sometimes a special view with a small weight in your hand (a weighted view) is used to unmask the displacement that closes up when the arm hangs free; that is how a borderline grade II/III gets sorted out. MRI is not routine for low grades but is useful for high-grade or atypical injuries to confirm exactly which ligaments are torn and rule out an associated rotator cuff or labral problem.

For milder separations, and for many complete tears, the ligaments calm down and the shoulder recovers without surgery.

1. Sling Immobilization

   The first job is to let the torn ligaments calm down. A sling for one to three weeks unloads the shoulder, and ice and over-the-counter pain medicine handle the acute soreness. The sling is not holding anything in place; it is just letting you move through a day without yanking on the joint.

2. Physical Therapy

   Once the acute pain settles, gentle range-of-motion work begins, followed by progressive strengthening of the shoulder blade stabilizers and rotator cuff. The goal is to restore full motion and rebuild the muscular control that compensates for any residual stretch in the ligaments.

3. NSAIDs

   Anti-inflammatories like ibuprofen or naproxen take the edge off the pain and the inflammation in the first few weeks. Used short-term for pain control, not for healing the ligaments themselves.

4. AC Joint Injection

   A small cortisone injection placed directly into the AC joint quiets the inflammation when low-grade sprains leave you with lasting joint pain, usually because the cartilage took a small hit at the time of injury and the joint is now mildly arthritic. For patients in this situation, repeating the injection every several months is a routine, reliable way to stay ahead of the pain without surgery.

A complete tear with the collarbone riding up sits in a genuine gray zone. Current evidence does not clearly favor surgery over non-operative care for the average patient, and many of these do well with rehab alone. Heavy laborers, throwing athletes, or patients whose visible bump bothers them may still elect surgical reconstruction. The most severe grades almost always need it: the collarbone is displaced too far for the ligaments to ever heal back into place, and the surgical answer is to rebuild the torn ligaments, usually with a graft that pulls the bone back down where it belongs.

If non-operative care is not enough, this procedure can address this condition:

• AC joint reconstructionShoulder

Providers Who Treat AC Joint Separations

Michael S. Vrana, M.D.

David B. Templin, M.D.

Trent Twitero, M.D.

External patient-education references and related OSI pages for additional background:

• AAOS OrthoInfo, patient education library
• OSI glossary, orthopedic terminology in plain language