AC Joint Osteoarthritis Info

AC joint osteoarthritis causes localized shoulder pain with cross-body movements; treatment ranges from activity modification to surgery.

What you're feeling

You likely notice a dull, aching pain right on top of your shoulder, where your collarbone meets the highest point of your shoulder blade. This pain often flares up when you reach across your body, such as when fastening a bra, tucking in a shirt, or reaching for a seatbelt. You might also feel a grinding sensation or hear a clicking sound when you move your arm overhead.

Unlike the deep ache of a rotator cuff tear, this pain is usually very localized to the top of the shoulder. It tends to worsen with repetitive overhead activities or heavy lifting. Many patients find that the pain is most noticeable at night, especially if you sleep on the affected side. The discomfort can come and go for months or even years, often worsening during periods of increased activity.

What's actually happening

Your shoulder has two main joints. The large, ball-and-socket joint allows for most of your arm’s movement. The smaller joint at the very top, where the collarbone (clavicle) meets the shoulder blade (acromion), is the acromioclavicular (AC) joint. This small joint helps stabilize your shoulder and allows it to rotate smoothly.

Over time, the protective cartilage cushioning the ends of these bones can wear down. This is osteoarthritis, or "wear-and-tear" arthritis. As the cartilage thins, the bones may rub against each other. In response, your body may form extra bone, known as bone spurs or osteophytes, around the joint edges. These spurs can narrow the space in the joint and irritate the surrounding tissues.

This condition is common in people who have done repetitive overhead work or sports, such as weightlifting, swimming, or painting. It can also follow a direct injury to the shoulder, like a fall onto the point of the shoulder. While age is a factor, AC joint osteoarthritis often affects active individuals in their 30s to 50s. The inflammation and bone changes cause the pain and stiffness you experience during movement.

What we can do about it

Treatment usually starts with non-surgical options, which help most people manage their symptoms effectively.

Activity Modification and Physical Therapy Your therapist will teach you exercises to strengthen the muscles around your shoulder blade. This helps stabilize the joint and takes pressure off the AC joint. You will also learn to avoid movements that trigger pain, such as heavy bench pressing or cross-body reaching.

Medications and Injections Over-the-counter anti-inflammatory drugs, like ibuprofen or naproxen, can reduce pain and swelling. If these are not enough, your doctor may suggest a corticosteroid injection directly into the AC joint. This powerful anti-inflammatory can provide significant relief for several months, helping you participate more fully in physical therapy.

Surgery: Distal Clavicle Excision If conservative treatments fail to relieve your pain after several months, surgery may be considered. The standard procedure is a distal clavicle excision. In this operation, your surgeon removes a small portion of the end of the collarbone. This creates more space in the joint, preventing the bones from rubbing together.

The surgery is typically done arthroscopically, using small incisions and a camera. Most patients go home the same day. Recovery involves wearing a sling for comfort for a few weeks, followed by physical therapy to restore range of motion. Full recovery and return to heavy lifting usually take three to six months. Success rates are high, with most patients experiencing lasting pain relief.

For step-by-step detail about the operation, recovery, and what to expect on the day of surgery, see the distal clavicle excision page.

When to see someone

You should schedule an appointment with an orthopaedic specialist if:

• Pain persists despite rest, ice, and over-the-counter anti-inflammatory medications.
• You notice visible swelling or a bump on top of your shoulder that is growing or becoming tender.
• You experience significant weakness or inability to lift your arm.
• The pain disrupts your sleep or daily activities, such as dressing or driving.
• You have had a recent fall or injury to the shoulder that caused immediate pain and swelling.

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