AC Joint Arthritis Symptoms and Treatment

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 arthritis, 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 one and the same.

Your Shoulder Joints

The ball-and-socket shoulder joint, the glenohumeral joint, is the junction of two bones: the shoulder blade (scapula) and the upper arm bone (humerus). The scapula forms the socket of the joint, and the humerus has a round head that fits within this socket.

Shoulder arthritis is actually a lay term for glenohumeral arthritis. Here, the humerus ball and its cartilage cover wear away at the socket of the shoulder joint.

A finger-like projection of the scapula is called the acromion, which meets with the lateral end of the clavicle to form the acromioclavicular/AC joint. Loss of cartilage between these bones is what causes AC arthritis.

Not only are these two conditions different in anatomic terms, but the implications for treatment, recovery, and complications are also different.

The other two joints of the shoulder are the sternoclavicular (SC) joint, which joins the clavicle to the sternum, and the scapulothoracic joint, which connects the scapula to the back ribs.

Symptoms

Patients with AC arthritis usually complain of pain associated with shoulder motion, but neck and arm pain may also play a part, which can complicate diagnosis.

Specific movements tend to exacerbate the symptoms. A common test performed by your healthcare provider would be to bring the affected arm across your chest. This movement compresses the AC joint and will most often recreate pain symptoms.

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.

Treatment

Treatment of AC arthritis depends on the severity of symptoms and the presence of other shoulder problems including impingement syndrome, glenohumeral arthritis, and muscular injury such as a rotator cuff tear.

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 local anesthetic or steroids to see if your symptoms improve.

If the symptoms do not respond to conservative treatment, or if the pain is too severe, surgery may be necessary. An arthroscopic procedure can remove the end of the clavicle (collarbone) and allow the AC joint to fill with scar tissue.

Usually less than a centimeter of bone is removed. This allows for normal movement of the AC joint (which is minimal even in healthy shoulders) while stopping the exposed bones from rubbing together.

For an isolated AC joint resection, treatment usually lasts about eight weeks and often involves working with a physical therapist.