Acromioclavicular Joint (ACJ) arthritis
The AC joint is located at the top of the shoulder and is the joint that connects the outer end of your collarbone (clavicle) to the shoulder blade (acromion). The joint surfaces are covered by articular cartilage and the joint has a small amount of lubricating fluid. This allows the joint to move effortlessly with over 100 times less friction than ice sliding on ice.
As we get older we can wear out the cartilage which causes pain, swelling and stiffness. This is known as arthritis or osteoarthritis.
ACJ arthritis is when the AC joint wears out. It is important to remember that this is not the shoulder joint but a small joint near the shoulder.
What are the causes?
ACJ arthritis most commonly occurs because you have used your shoulder enough to cause the cartilage to wear out. The more stress that you have put through the AC joint the more likely you are to develop arthritis. For example, regularly using your arms above shoulder height or across your body can lead to ACJ arthritis. Therefore, plasterers and builders are commonly affected.
Occasionally ACJ athritis will occur following an injury to the ACJ, such as a sprain or dislocation.
What are the symptoms?
ACJ arthritis affects middle aged people and commonly causes pain over the ACJ itself. This can be felt on the top of your shoulder at the outer end of your collarbone.
Moving your arm across your body or lifting your arm high can bring on the pain. It can also be painful at night and when lying on the affected shoulder. Symptoms can be similar to those caused by subacromial impingement and both these conditions can occur at the same time.
How is it diagnosed?
Your surgeon can usually make the diagnosis by asking about the symptoms you have and examining your shoulder. X-rays are useful at confirming the diagnosis.
Occasionally, it is not completely clear if ACJ arthritis is the cause of your symptoms. If there is doubt, your surgeon will organise a diagnostic injection to the AC joint to see if your symptoms get better. Sometimes an injection will resolve your symptoms but usually this is short lived.
An ultrasound or MRI can be useful to rule out other causes of your pain.
How is it treated?
Simple painkillers and physiotherapy can help relieve symptoms, particularly in the early stages of the condition. An injection can help with diagnosing ACJ arthritis as the source of pain but relief is usually short lived. If your symptoms do return then a surgical excision of your AC joint is advised. This can be done as a keyhole procedure or through a small open incision.