AC Joint Pain: Causes, Symptoms, and Treatment Options

AC joint pain can be stubborn and limit your shoulder movement. Discover how physiotherapy and guided treatment can relieve pain, restore function, and help you return to daily activity.

What Is the AC Joint?

The acromioclavicular joint (AC joint) connects the acromion — part of the shoulder blade — to the end of the collarbone (clavicle). It is stabilized by several ligaments and plays a key role in shoulder and scapular movement. Multiple muscles attach around this joint, supporting shoulder stability and mobility.

Causes of AC Joint Pain

Non-Traumatic AC Joint Pain

These complaints usually develop gradually and can occur at any age. Common causes include overuse, poor posture, and repetitive shoulder movements during work or sports.

People over 40 are more prone to AC joint degeneration due to normal age-related wear. Even well-trained athletes can develop symptoms due to incorrect technique or training overload. In younger individuals, hypermobility (excess joint flexibility) and inactivity are also frequent contributing factors.

Traumatic AC Joint Injuries

Traumatic injuries usually follow a direct impact — for example, a fall onto the side of the shoulder. These are common among cyclists and ice hockey players. The ligaments stabilizing the AC joint can stretch or tear, leading to a dislocation (luxation) of the clavicle.

This can appear as a visible bump on the shoulder, known as the “piano key sign,” where the collarbone can be pressed down like a piano key.

Traumatic AC injuries are classified into six grades, according to Rockwood, ranging from mild to severe.

AC Joint Osteoarthritis

AC joint osteoarthritis (wear and tear) mainly affects older adults. As cartilage wears down, the joint space narrows, often causing persistent shoulder pain. When symptoms do not improve with conservative care, surgery may be considered.

Symptoms of an AC Joint Injury

• Pain at the top of the shoulder
• Increased pain when raising the arm or bringing it across the body
• Local swelling after trauma
• Visible elevation of the collarbone (in dislocations)

Diagnosis and Examination

Assessment may include X-ray or ultrasound imaging to evaluate joint condition. However, findings like mild osteoarthritis do not always explain pain — especially in older age, where such changes are as normal as wrinkles or grey.

Ultrasound assessment of the AC joint

Your physiotherapist or doctor will first take a detailed history: When did the pain start? What movements make it worse? A physical examination follows, focusing on shoulder movement, joint function, and provocation tests that load the AC joint.

Pain often increases when the arm is lifted or brought across the chest.  Finger pressure on the joint usually reproduces the familiar pain. If the source of pain is unclear, a diagnostic injection may be used. A small amount of local anaesthetic is injected into the AC joint — if the pain subsides, the diagnosis is confirmed.

Treatment Options for AC Joint Pain

Physiotherapy for AC Joint Pain

Most AC joint problems, especially non-traumatic ones, can be successfully treated without surgery. The key is to identify the underlying causes and correct them through:

• 👉 Lifestyle advice to reduce strain
• 👉 Targeted exercises to restore shoulder function
• 👉 Postural correction and muscle control training

In acute cases, supportive taping may provide relief. Painful movements should be temporarily avoided to allow proper healing. The physiotherapist may also assess your overall health profile, as factors such as stress, poor sleep, and inactivity can slow recovery.

Injections for AC Joint Pain

If pain persists, an ultrasound-guided corticosteroid injection may help reduce inflammation and improve mobility by accurately targeting the small joint space.

Surgery for AC Joint Pain

When severe osteoarthritis causes ongoing pain despite conservative treatment, surgery may be indicated. This typically involves removal of a small section of the clavicle (lateral clavicle resection) to create more space and reduce friction. In cases of dislocation, surgery is often unnecessary — most patients recover well with physiotherapy and time.

Can You Keep Exercising with an AC Joint Injury?

This depends on the severity of the injury. In mild cases, rest followed by gradual return to sport under physiotherapy guidance is often possible. Avoid activities that cause pain until symptoms subside.

Summary

The AC joint connects the collarbone and the shoulder blade. Pain can result from overuse, poor posture, or trauma. Diagnosis involves physical examination and imaging if needed.

Most people recover with physiotherapy and guided exercise, sometimes supported by an injection. Surgery is reserved for advanced osteoarthritis when other treatments fail. Even in dislocations, shoulder function often returns without surgery.