AC Joint (Acromioclavicular Joint)

What is the AC joint?

The AC joint is one of two joints that make up your shoulder. It’s where the acromion (the top part of your shoulder blade) meets your clavicle (collarbone). That’s where the AC joint gets its full name — the acromioclavicular joint.

What does the AC joint do?

The AC joint’s main job is supporting your shoulder and acting as a connection point for ligaments around your shoulder.

Your acromioclavicular joint is a passive joint. That means all its movements are controlled by other muscles and joints. In this case, your shoulder muscles move the rest of your shoulder, which then moves your AC joint. It’s a planar joint — a type of joint that lets two bones glide smoothly past each other.

When your shoulder muscles move your shoulder, the AC joint helps your shoulder move from back to front (anteroposterior). Picture using your shoulder to do a rowing motion, pushing your arms out away from the front of your body, then pulling them back in so your elbows move behind you.

Where is the AC joint?

The AC joint is at the top of your shoulder. It’s where the outermost point of your collarbone connects to the front of your shoulder blade.

What are the parts of the acromioclavicular joint?

The acromioclavicular Joint includes:

• Bones: Your collarbone (clavicle) and shoulder blade (scapula).
• Cartilage: Tough, thick cartilage cushions the AC joint and helps your bones move smoothly past each other.
• Ligaments: Three ligaments in the AC joint connect the bones together and help the joint hold its shape.
• Nerves: The AC joint gets its sensation of feeling from nerves in your neck that branch out into your shoulder.
• Blood vessels: The suprascapular and thoracoacromial arteries supply blood to the AC joint.

What are common conditions and disorders that affect the acromioclavicular joint?

AC joint injuries are very common. Experts estimate that around 40% of shoulder injuries affect the AC joint, including:

• Shoulder sprains
• Separated shoulders
• Dislocated shoulders
• Shoulder fractures (broken shoulders)

Anything that puts a lot of sudden force on your shoulder can damage your AC joint. Sports injuries and trauma like car accidents and falls are the most common causes.

Arthritis can develop in your acromioclavicular joint. But many people never feel pain or other symptoms. You might not need treatment or ever know you have AC joint arthritis.

What does AC joint pain feel like?

When you’re experiencing shoulder pain, it might be tough to say for sure it’s in your AC joint.

Even if you know what the acromioclavicular joint is and exactly where it is, when your shoulder hurts, it’s not easy to pinpoint the exact place it’s coming from (where the pain originates).

You might feel pain right in your AC joint, but it may spread (radiate) to your neck, lower in your shoulder or to muscles in your chest or back.

What AC joint pain feels like will depend on what’s causing it. The pay may feel:

• Sharp and stabbing (especially when you move or use your shoulder)
• Dull and achy (like a constant hum in the background)
• Sore (the way you sometimes feel the day after a big workout or after helping a friend move a bunch of heavy furniture

What causes the AC joint to pop?

It’s perfectly normal for your joints to pop or crack sometimes. These noises are usually nothing more than gas trapped in the synovial membrane getting squeezed out. You don’t need to worry if you feel or hear a joint pop when you’re stretching or moving.

But if you hear or feel a pop when you fall or take a hard hit during a sport, you should see a healthcare provider — especially if your shoulder hurts or you can’t move it after the pop. Those kinds of pops can be from dislocations or separations. Visit a provider if your shoulder pops in exactly the same way every time, or if you can feel a grinding when you move.

Don’t let anyone other than a trained healthcare provider touch or push on your shoulder if you think it’s injured. Never try to force your shoulder back into place if you think it’s dislocated or separated. Try to hold it steady and as still as possible and go to the emergency room right away.

What are common treatments for AC joint issues?

Which treatments you may need will depend on the injury or issue you have. Your healthcare provider will suggest treatments to manage any symptoms you’re experiencing and help your AC joint heal. Some of the most common treatments include:

• Rest and avoiding intense physical activities.
• Over-the-counter medicine like NSAIDs (nonsteroidal anti-inflammatory drugs) or acetaminophen to relieve pain and reduce inflammation.
• Prescription corticosteroids (including cortisone shots).
• Physical therapy.
• Immobilization (wearing a sling or brace).
• Surgery to repair bone fractures or other serious injuries.

How can I take care of my AC joint?

The best way to take care of your AC joint is to maintain good overall health, including:

• Following an eating and physical activity plan that’s healthy for you
• Stretching, warming up and cooling down before and after physical activities
• Never “playing through the pain” if your shoulder hurts during or after physical activity
• Wearing proper protective equipment for any activity, sport or work you’re doing
• Visiting a healthcare provider for regular checkups and as soon as you notice any changes or symptoms in your shoulders