Acromioclavicular (AC) Joint Arthritis: What to Know

AC arthritis is chronic inflammation of the acromioclavicular (AC) joint, one of the four joints that work together in the complex system that makes up the shoulder. Like most cases of osteoarthritis (OA), AC arthritis happens when the cartilage protecting certain bones within the joint wears thin.

Recognizing AC arthritis as the unique condition that it is is important when it comes to treatment. Though shoulder arthritis occurs in the same region, the conditions are not the same.

AC Joint vs. Shoulder Arthritis

To understand how AC joint arthritis and shoulder arthritis are different, you need to know a little about the shoulder joints.

The term shoulder arthritis means arthritis in the glenohumeral joint. That's the ball-and-socket joint most people think of when they think of the shoulder.

• The shoulder blade (scapula) forms the socket
• The ball is at the top of the upper arm bone (humerus)

The acromioclavicular joint is formed by:

• The acromion, which is a finger-like projection of the scapula
• An end of the collar bone (clavicle)

AC arthritis refers to inflammation and cartilage loss in this joint.

These two conditions cause different symptoms and complications, and they're treated differently as well. In both cases, however, an X-ray (along with a physical exam) is often enough to help diagnose the condition and reveal how severe it is.

AC Joint Arthritis Symptoms

If you have AC joint arthritis, you may feel tenderness and pain at the top of the shoulder early on. Other possible symptoms of AC joint arthritis include:

• More pain after sleeping on that side
• Lost range of motion in your shoulder
• More pain when the joint is compressed (like when crossing an arm across your chest)
• Visible inflammation and increased prominence around the AC joint

AC arthritis pain is most often tied to shoulder motion, but neck and arm pain may also play a part. That can complicate diagnosis, as several types of arthritis and some other conditions may cause similar symptoms.

Specific movements tend to exacerbate the symptoms. The typical test for AC joint pain is to bring the affected arm across your chest. That compresses the AC joint and usually recreates the pain.

Causes

AC arthritis is usually osteoarthritis, the result of repeated movements that wear away cartilage in the acromioclavicular joint. Because the shoulder is used so commonly, it is not surprising that joint surface may wear thin after years of use.

However, other problems may bring on symptoms:

• Inflammatory conditions: Autoimmune diseases like rheumatoid and psoriatic arthritis can attack the AC joint.
• Septic arthritis: This stems from an infection in the joint that can be transmitted via the bloodstream or by an injury delivering germs directly to the joint (a puncture, for example).
• Injuries: Shoulder trauma, such as shoulder separation, may contribute to the development of AC arthritis.

AC Joint Arthritis Treatment

AC joint arthritis treatment depends on the severity of symptoms and the presence of other shoulder problems, including:

• Impingement syndrome
• Glenohumeral arthritis
• Muscular injury (e.g., rotator cuff tear)

For Mild-to-Moderate Symptoms

If the symptoms of AC arthritis are mild to moderate, anti-inflammatory medications and physical therapy are the most common conservative measures.

Your healthcare provider may inject the AC joint with a local anesthetic or steroids to see if your symptoms improve.

For Severe or Unresponsive Symptoms

If the symptoms do not respond to conservative treatment, or if the pain is too severe, you may need surgery. Your healthcare provider may suggest an arthroscopic procedure called an isolated AC joint resection.

In this procedure, the surgeon removes the tip of the clavicle. This allows for normal movement of the AC joint (which is minimal even in healthy shoulders) while stopping the exposed bones from rubbing together.

Usually, the incision is about an inch long and they remove less than a centimeter of bone. Then, over time, the AC joint fills up with scar tissue.

Recovery

After an AC joint resection, you can usually go home the same day. You'll likely start shoulder motion right away, possibly with physical therapy.

While you recover, you may have pain and/or fatigue in your shoulder with heavy lifting or strenuous activity. Most people can return to full activity within the three months after surgery.