AC Joint Injuries & Arthritis
The AC joint sits on top of the shoulder where the collarbone meets the shoulder blade. It can be separated by a fall or wear down with arthritis — both causing pain right at the top of the shoulder.
What is the AC joint?
The acromioclavicular (AC) joint is the small joint at the very top of the shoulder where the collarbone meets the tip of the shoulder blade. A fall onto the shoulder can sprain or tear its ligaments — a "separated shoulder" — which is graded by severity. Over time, this joint can also simply wear out, causing AC joint arthritis.
Symptoms to watch for
- Pain and tenderness right on top of the shoulder
- A visible bump or step-off after a separation
- Pain reaching across the body, lifting, or pressing (such as bench press or push-ups)
- With arthritis, a dull ache localized to the top of the shoulder
How it is diagnosed
A physical exam pinpoints tenderness directly over the joint, and a cross-body test reproduces the pain. X-rays confirm the grade of a separation or the presence of arthritis.
Treatment
Most low-grade separations and AC arthritis improve without surgery — a sling for comfort, ice, anti-inflammatories, therapy, and sometimes a targeted injection. Surgery is reserved for high-grade separations or arthritis that stays painful despite good treatment, using ligament reconstruction for severe separations or removing the worn end of the collarbone for arthritis.
Pain or a bump on top of your shoulder?
An evaluation can grade the injury and guide treatment.
Common questions
After a higher-grade separation, a bump from the collarbone often remains even once it is comfortable and functional. It is usually cosmetic rather than a problem.
Most lower-grade separations do not. Higher-grade injuries, or those in people with high physical demands, are where surgery is considered.
A procedure that removes the small worn end of the collarbone to relieve AC joint arthritis pain, often done arthroscopically.
Lower-grade injuries often allow return within weeks once strength and comfort return; higher-grade or surgical cases take longer. Your plan will be individualized.
This page is for general education and is not a substitute for an in-person evaluation. Your specific diagnosis and treatment plan should come from Dr. Hachadorian based on your exam and imaging.