AC Joint Osteoarthritis: Causes, Symptoms & Treatment
If reaching for a high shelf or putting on a jacket causes a sharp ache at the top of your shoulder, you may be dealing with AC joint osteoarthritis. This guide explores what causes this joint degeneration, how to recognise the symptoms, and the treatments available to help you regain mobility.
What Is AC Joint Osteoarthritis?
The acromioclavicular (AC) joint sits at the very top of your shoulder — the point where your collarbone (clavicle) meets the highest part of your shoulder blade (acromion).
In a healthy shoulder, a smooth layer of cartilage covers the ends of these bones, acting as a shock absorber. Over time, or following an injury, this cartilage can wear down. When it deteriorates, the bones begin to rub directly against one another, causing friction, inflammation, swelling, and pain.
Common Symptoms
Symptoms typically develop gradually and worsen over time.
- —Pain at the top of the shoulder — A deep, aching pain located where the collarbone ends, at the very top of the shoulder.
- —Pain when lifting the arm — Reaching across the body or lifting the arm overhead often triggers a sharp pinch or ache.
- —Clicking or grinding — A popping, snapping, or grinding sensation (crepitus) when moving the shoulder.
- —Reduced range of motion — The shoulder may feel stiff, limiting your ability to move freely.
- —Night pain — Aching that disrupts sleep, particularly when lying directly on the affected shoulder.
Mild vs Moderate AC Joint Osteoarthritis
—Mild
In the early stages, cartilage shows signs of fraying or thinning but the joint space remains relatively open. Symptoms are typically intermittent — mild discomfort that flares after heavy physical activity or direct stress on the shoulder. Many people manage this stage effectively with rest and minor lifestyle adjustments.
—Moderate
As the condition progresses, cartilage wears away more significantly and X-rays reveal greater joint space narrowing. The body may begin forming bone spurs around the joint. Pain during daily activities increases, stiffness becomes more pronounced, and shoulder flexibility noticeably decreases.
Causes and Risk Factors
- —Ageing — Natural wear and tear over decades is the leading cause of joint degeneration.
- —Previous shoulder injury — A past shoulder separation, dislocation, or direct trauma can accelerate cartilage breakdown years later.
- —Repetitive overhead motion — Jobs or hobbies requiring constant overhead reaching place excessive stress on the joint.
- —Weightlifting — Heavy resistance training, particularly bench presses and overhead presses, can significantly load the AC joint and accelerate cartilage wear.
- —Arthritis progression — Inflammatory conditions or advancing osteoarthritis elsewhere in the body can also affect the shoulder.
How It Is Diagnosed
- —Physical examination — Your doctor will assess tenderness, swelling, and range of motion. Bringing your arm across your chest compresses the AC joint and typically reproduces the pain if arthritis is present.
- —X-rays — Reveals narrowed joint spaces, bone spurs, and other signs of structural damage.
- —MRI — If damage to surrounding soft tissues such as a rotator cuff tear is suspected, an MRI provides detailed images of the muscles and ligaments.
- —Differential diagnosis — Your specialist will rule out other conditions such as frozen shoulder, cervical spine issues, or rotator cuff tendinitis to ensure an accurate diagnosis.
Treatment Options
Your orthopaedic specialist will typically begin with conservative approaches before considering surgery.
—Non-Surgical Treatments
- —Rest — Reducing or avoiding activities that aggravate the joint allows inflammation to settle.
- —Activity modification — Adjusting how you lift or exercise to avoid placing direct stress on the top of the shoulder.
- —Anti-inflammatory medication — Over-the-counter NSAIDs such as ibuprofen or naproxen can reduce both pain and joint swelling.
- —Physical therapy — Targeted exercises strengthen the muscles surrounding the shoulder blade and rotator cuff, reducing the mechanical load on the AC joint.
- —Cortisone injection — A corticosteroid injection delivered directly into the AC joint can provide significant, longer-lasting relief from severe inflammation and pain.
—Surgical Treatment
- —Distal clavicle excision — The most common procedure. A small section of the end of the collarbone is removed, eliminating bone-on-bone contact and relieving friction.
- —Arthroscopic approach — The procedure is typically performed using small incisions and a camera to minimise tissue damage and support faster recovery.
- —Recovery — Most patients wear a sling for a few days to a week following surgery. Physical therapy begins shortly after, and the majority return to full normal activity within a few months.
When to See a Specialist
Schedule an evaluation with an orthopaedic specialist if you experience any of the following.
- —Persistent pain lasting more than a few weeks
- —Weakness in the arm or shoulder
- —Limited function that prevents you from performing basic daily tasks such as getting dressed or sleeping comfortably
- —No improvement with rest and over-the-counter pain relief
Frequently Asked Questions
Find Relief from Shoulder Pain
If persistent shoulder pain is affecting your daily life, schedule a consultation with an orthopaedic specialist to discuss the most effective treatment options for your condition.
