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The acromioclavicular (AC) joint
What are the causes of acromioclavicular joint pain?

The acromioclavicular (AC) joint

The acromioclavicular joint articulates the clavicle (collar bone) and the acromion (part of the shoulder blade). It is a small joint at the top of the shoulder but undergoes considerable stress during daily activities and when exercising. As a result, it is often an underappreciated cause of shoulder pain. The joint can also become painful secondary to injuries or wear and tear changes that increase with age. It differs from the main ball and socket shoulder joint, formed by the humeral head (the upper end of the arm bone) and the glenoid (part of the shoulder blade).

What are the causes of acromioclavicular joint pain?

- Trauma/injury. AC joint injuries can happen after a fall to the corner of the shoulder joint. The AC joint is supported by a joint capsule and internal and external ligaments, and the degree of injury depends on the damage to these structures.

 

- ACJ osteoarthritis - Refers to wear and tear changes that can affect the joint and increase with age. Most of these are seen in patients older than 50 unless there has been a previous injury to the joint.

 

- Overhead sports like tennis, throwing sports like cricket and weight training can be associated with ACJ osteoarthritis.

 

- Other factors like occupations that involve repetitive shoulder movements or heavy lifting.

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What are the clinical features of Acromioclavicular joint problems?

- The main symptom of AC joint problems is pain at the site of the joint (at the top of the shoulder). The pain is usually worse when lifting the arm above the shoulder joint level and moving the arm across towards the other shoulder (like in the picture below). In addition, pressing over the joint is usually uncomfortable. In severe cases, lying on the affected side worsens the pain and interferes with sleep.

- Joint deformity. In case of previous injury and disruption of the AC joint, a bump can be felt at the top of the shoulder, close to the end of the collar bone.

 

- Joint clicking on shoulder movements.

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What other shoulder conditions can mimic acromioclavicular (AC) joint problems?

Other shoulder conditions that can have similar symptoms include:


Less likely AC joint problems can be confused with a frozen shoulder or calcific tendonitis.

Acromioclavicular (AC) joint pain vs shoulder (glenohumeral) joint arthritis?

AC joint pain is different as it is located at the top of the shoulder and is usually associated with superficial tenderness. The ball and socket (glenohumeral) shoulder joint arthritis pain is more generalised and usually felt deep inside the shoulder. It can radiate down the arm as well. The pain in both conditions can increase by over-the-head movements, but AC joint pain is typically exacerbated when the arm is moved across towards the other shoulder (like the movement you do to put a scarf around your neck).

How to diagnose acromioclavicular joint pain?

The diagnosis is usually suspected clinically after performing a clinical assessment by a shoulder specialist. Imaging is beneficial in confirming the diagnosis. A shoulder x-ray is very useful in assessing the joint alignment and if there is any evidence of bony injury or joint disruption. Sometimes, you may be asked to hold a weight in your hand while the x-ray is taken to assess the joint alignment when applying force or stress upon the joint (referred to as stress view). The right shoulder x-ray below shows widening and loss of the normal alignment of the right AC joint (arrow). Compare this to the normal appearance on the left side. A shoulder MRI scan is also very useful for a general assessment of the shoulder, including the acromioclavicular joint. It will accurately assess for the presence of any active arthritis changes within the joint. A shoulder ultrasound examination is equally beneficial for the diagnosis. It can assess for any arthritic changes within the joint and perform a dynamic assessment of the joint during arm movement while putting stress upon the joint. Furthermore, ultrasound is extremely useful in guiding injection therapy.

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How to treat acromioclavicular joint pain?

The treatment usually consists of physiotherapy, which involves strengthening, stretching, and postural exercises. It may also include using anti-inflammatory tablets and avoiding activities that could exacerbate the pain.

What if conservative management does not help?

Suppose the above treatment does not result in a satisfactory outcome, and your severe pain interferes with your sleep, daily activities or exercise. In that case, an ultrasound-guided acromioclavicular joint steroid injection can be considered.

Will a steroid injection help with acromioclavicular (AC) joint pain?

Corticosteroid (cortisone) injections are usually very effective in managing inflammatory conditions (like arthritis). They are potent anti-inflammatory medicines that aim to reduce the inflammation in the joint. Current evidence suggests that cortisone can improve pain and function for up to 3 months, but in some cases, it can last longer. The injections usually also contain a local anaesthetic that provides immediate pain relief lasting a few hours. To learn more, please read our article about ultrasound-guided shoulder steroid injections.

Do acromioclavicular (AC) joint injections need to be done under ultrasound guidance?

The AC joint is small, and using ultrasound guidance will ensure accurate delivery of the injection into the site of pain and reduce the risk of complications. In addition, performing these injections under ultrasound guidance allows direct visualisation of the needle. There is plenty of evidence that ultrasound guidance results in a more accurate, less painful, and faster procedure.

What are the side effects of acromioclavicular (AC) joint steroid injection?

The procedure is generally very safe, with minimal reported side effects. These include possible skin colour changes at the injection site, pain for a few days following the injection (referred to as steroid flare), and a very small risk of infection. To learn more about general steroid injection side effects, please see our FAQs.

Will a steroid injection help with acromioclavicular (AC) joint problems after an injury?

If your AC joint pain is due to instability or injury following a fall, we prefer to delay the choice of ultrasound-guided steroid injection into the joint and get an opinion from a shoulder specialist. A steroid can reduce or delay the normal healing process after injury.

How many steroid injections can I have for my AC joint?

We aim to reduce the number of steroid injections administered into a specific body area. The injection will provide a beneficial window for you to undergo effective rehabilitation and reduce the need for a repeat injection. However, in cases of significant arthritis or joint inflammation, you might need a repeat joint injection.

Ultrasound guided acromioclavicular (AC) joint steroid injection
What are the clinical features of AC joint problems?
AC joint pain vs shoulder joint arthritis?
How to diagnose acromioclavicular joint pain?
How to treat acromioclavicular joint pain?
When is conservative management does not help?
Will a steroid injection help with ACJ pain?
Do AC joint injections need ultrasound guidance?
What are the side effects of AC joint steroid injection?
How many steroid injections can I have for AC joint?

Specialist Consultant Musculoskeletal Radiologist Doctor with extensive experience in image-guided intervention

To book a consultation:

Call us on 020 3442 1259 or Book online

The Musculoskeletal Ultrasound & Injections clinic
Unit 3, Brentside Executive Park

Brentford, TW8 9DR

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