Acromioclavicular Joint Arthritis (AC Joint Arthritis)

Summary

Acromioclavicular arthritis (AC joint arthritis) happens when the small joint at the top of the shoulder (Figure 1) wears out. It causes pain, swelling, and trouble lifting the arm. It usually affects older people or those who use their shoulders a lot. Doctors diagnose it with an exam and X-rays. Treatment includes rest, medicine, and therapy. If pain doesn’t go away, surgery may be done to remove part of the collarbone. Most people improve with treatment and many return to normal activities with little or no pain.

Introduction

Acromioclavicular joint arthritis (AC joint arthritis) is a condition that affects the joint between the collarbone (clavicle) and the acromion (Figure 1), a part of the shoulder blade. This small joint helps with shoulder movement, especially when lifting the arm overhead. Over time, the cartilage that cushions the bones in the joint can wear down, leading to pain, stiffness, and swelling. People with AC joint arthritis often feel pain at the top of the shoulder, which can worsen with activities like reaching across the body, lifting, or doing pushups. This condition is more common in older adults and people who have had shoulder injuries or perform repetitive overhead activities, such as weightlifters, construction workers, or athletes.

How and When AC Joint Arthritis Develops

AC joint arthritis usually develops gradually over time due to wear and tear on the joint. As we age, the cartilage in our joints may break down if it is exposed to excessive repetitive loads, or there is a genetic predisposition to develop arthritis. In the AC joint a loss of cartilage can lead to pain and inflammation. The condition is a type of osteoarthritis, which means it involves the breakdown of joint cartilage. In some people, AC joint arthritis may develop earlier, especially if they have had past injuries, such as a shoulder separation, or if their job or sport involves frequent heavy lifting or overhead movement. These repeated stresses can cause the joint to wear out faster.

Diagnosing Acromioclavicular Joint Arthritis

To diagnose Acromioclavicular joint arthritis, a doctor will start by asking about your symptoms and examining your shoulder. They may press on the top of the shoulder to see if it is tender, and ask you to move your arm in different directions to check for pain or stiffness. A common test is asking you to reach across your chest, which often triggers pain in the AC joint if arthritis is present. To confirm the diagnosis, doctors may order X-rays, which can show narrowing of the joint space, bone spurs, or other signs of arthritis. In some cases, an MRI may be used to check for other causes of shoulder pain, such as rotator cuff problems.

Conservative Treatment for AC Joint Arthritis

In most cases, AC joint arthritis is first treated with conservative (non-surgical) methods. These include resting the shoulder, avoiding painful activities, and taking anti-inflammatory medications like ibuprofen. Ice packs can help reduce swelling and ease discomfort if there is a flare-up of symptoms. Physical therapy may be recommended to improve strength and flexibility around the shoulder. In some cases, a doctor may offer a corticosteroid injection into the joint to reduce inflammation and relieve pain. These treatments often help manage symptoms and delay or avoid the need for surgery.

When Surgery Is Needed to Treat AC Joint Arthritis

Surgery is usually considered only when conservative treatment of acromioclavicular arthritis does not provide enough relief and the pain starts to interfere with daily activities. The most common surgical option is called a distal clavicle excision, also known as the Mumford procedure. In this operation, a small portion of the end of the clavicle is removed to prevent the bones from rubbing against each other. This can be performed with an incision over the AC joint, or may be done using arthroscopy, a minimally invasive technique using a camera and small instruments. Most people can go home the same day and begin physical therapy soon after surgery.

Prognosis for AC Joint Arthritis

The long-term outlook for people with AC joint arthritis is usually very good. Many people manage their symptoms well with rest, medication, and physical therapy. Even those who need surgery often return to their regular activities with little or no pain once they recover. It’s important to follow through with rehab and avoid heavy lifting until the joint is healed. While arthritis cannot be completely reversed, proper treatment can greatly reduce pain and improve function for most people.

Edited by Stephen Pinney MD, August 3rd 2025.