What is the acromioclavicular joint?

The acromioclavicular joint (also called the AC joint) is where the collarbone (clavicle) meets the highest point of the shoulder blade (acromion).

What conditions can affect the acromioclavicular joint?

Arthritis and injury are the most common conditions that affect this joint.

Acromioclavicular joint arthritis is relatively common and causes pain on top of the shoulder region, and pain is often provoked by movement across the body or above shoulder level.

Injury can also affect the AC joint. A fall can injure the acromioclavicular ligament and capsule of this joint and cause instability and dislocation.  If the force is severe enough, the ligaments attaching to the undersurface of the collarbone are torn. This causes a separation (AC separation) of the collarbone and shoulder blade and creates a bump or bulge above the shoulder. The injury can range from a little change in configuration with mild AC joint pain, to be quite deforming and very painful.

AC separation and injury diagnosis

The injury is easy to identify when it causes deformity. When there is less deformity and changes have occurred slowly with ageing and “wear and tear” degeneration, the location of pain and X-rays will help make the diagnosis. Sometimes having the patient hold a weight in the hand can increase the deformity, which makes the injury more obvious on X-rays.

A CT scan or MRI scan can also assist in diagnosing problems with this joint.

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What are the treatment options for AC joint pain?

Most injuries to this joint can be effectively treated without an operation. Rest, ice, AC joint exercises, and physiotherapy are often helpful in reducing pain and helping to return to usual activities. Ongoing troubles with pain or inability to perform usual activities may warrant surgery to stabilise this joint.

In wear and tear (degenerative) arthritis, significant pain and dysfunction may necessitate surgery to alleviate symptoms.

This is usually in the form of keyhole surgery performed by a shoulder specialist to remove the end of the collar bone and decompress this painful joint. AC joint rehab and AC joint recovery from this type of surgery is normally quick.

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