The AC Joint Compression Test

Do you have a separated acromio-clavicular joint?

The acromioclavicular (AC) joint is a part of your shoulder joint that's comprised of the meeting of your collar bone (clavicle) with the acromion process of your shoulder blade. Problems here can lead to loss of shoulder motion, pain, and difficulty performing tasks that require the use of your arm.

If you have shoulder pain, your physical therapist (PT) can assess your condition and determine the best treatment. During the examination, your PT may perform the AC joint compression test.

Woman with hand on bare shoulder
PhotoAlto / Frederic Cirou / Getty Images

The AC joint is a very stable joint, and only slight motions occur there. Still, you can suffer a sprain of the ligaments that hold your AC joint together. When this occurs, it's called an AC joint separation. This will likely cause significant shoulder pain and you may have difficulty moving your arm normally.

An AC joint separation should not be confused with a shoulder dislocation. A shoulder dislocation occurs where the ball and socket of your shoulder joint meet. An AC joint separation occurs on the upper part of your shoulder where your collar bone and acromion process of your scapula meet.


Click Play to Learn All About AC Joint Sprains

This video has been medically reviewed by Oluseun Olufade, MD.

AC Joint Separation Causes

Since your AC joint is such a stable joint, usually significant trauma is required to cause an injury here. An AC joint separation typically occurs after a fall onto the side of your shoulder or during a fall on your outstretched hand (also known as a FOOSH injury).

Impact or forces during athletic competition that come from the side or directly in front of your shoulder may also cause an AC joint separation.

Symptoms of an AC joint separation:

  • Pain in your shoulder on the top or side of your upper arm
  • Difficulty moving your shoulder joint
  • Feeling of heat coming from your shoulder joint (a sign of inflammation)
  • A large lump or bump on the top of your shoulder joint
  • A feeling of weakness with lifting or using your arm

If you suspect you've separated your shoulder, you should go to your healthcare provider right away. Your healthcare provider may perform the AC joint compression test as part of a clinical examination. Usually, a simple X-ray can be done to confirm a diagnosis of AC joint separation.

Test for an AC Joint Separation

The shoulder special test for an AC joint separation is called the AC joint compression test. It's a simple test to perform, and your PT or healthcare provider may do this as part of your evaluation for shoulder pain or problems. Here's how you do it:

  1. Sit comfortably in a chair.
  2. Have a friend or family member stand to your side where your painful shoulder is.
  3. Your friend should place one hand on the front of your shoulder joint and one hand behind your shoulder joint.
  4. Your friend should slowly but firmly press on both sides of your shoulder to compress your AC joint. This compression should be held for a few seconds.

A positive test indicating a possible AC joint separation is when extreme pain is elicited in your shoulder during the compression. If your AC joint compression test is positive, you should visit your healthcare provider right away to confirm your suspicions and get you started on the correct treatment right away.


If you have an AC joint separation, you'll likely need to wear a sling on your shoulder while things are healing.

After a few weeks of healing of your AC joint, your healthcare provider may recommend physical therapy to help you improve your shoulder range of motion (ROM) and strength. Your PT can prescribe specific exercises to get your shoulder (and shoulder blade) moving properly.

Occasionally, surgery is recommended to repair an AC joint separation. If you have surgery to repair your AC joint, you may also benefit from physical therapy after your surgery to help improve your overall mobility and restore normal shoulder motion and strength. Your PT can also help you manage your shoulder pain after surgery.

A Word From Verywell

If you have shoulder pain and suspect you have injured your AC joint, the AC joint compression test can help confirm your suspicions. If you try the test and feel you have separated your AC joint, visit your healthcare provider to confirm your diagnosis and start the process of healing and recovery.

Shoulder pain can limit your ability to do normal activities, but when treated correctly, you can quickly get back to normal activity. Almost 95% of people can resume their pre-injury activity level—however, this figure applies to surgical treatment.

If your shoulder hurts, see your healthcare provider and your physical therapist, and get started on treatment right away. That way you can quickly get back to your day-to-day activity.

3 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Gallagher CA, Blakeney W, Zellweger R. Acromioclavicular joint dislocation with associated brachial plexus injury. BMJ Case Rep. 2014;2014. doi:10.1136/bcr-2013-203299

  2. Johns Hopkins Medicine. AC joint problems.

  3. Kiel J, Kaiser K. Acromioclavicular joint injury. StatPearls Publishing. 2019.

By Brett Sears, PT
Brett Sears, PT, MDT, is a physical therapist with over 20 years of experience in orthopedic and hospital-based therapy.