What is an AC Joint injury?

An AC joint injury, also known as AC joint separation, occurs at the acromioclavicular (AC) joint at the top of the shoulder where the acromion (a part of the shoulder blade) meets the clavicle (collar bone). This type of injury is common in contact sports and results from a fall directly onto the shoulder or from a direct blow received in sports like football or hockey.

Understanding AC joint pathology is crucial for diagnosing AC joint injuries. This joint is vital for allowing the shoulder a wide range of motion. When it's injured, it can lead to pain, swelling, and difficulty moving the shoulder.

AC joint separation is classified into different grades, ranging from mild (Grade 1) to severe (Grade 3), depending on the extent of the injury to the ligaments that support the joint. Grade 1 involves a slight displacement and minimal damage to the ligaments. Grade 2 involves a partial dislocation with more significant ligament damage. Grade 3 and above involve complete dislocation of the joint with severe ligament damage.

Check out our separated shoulder test for a comprehensive guide on conducting this simple AC Joint Test, which includes a detailed template to document findings.


Diagnosing an AC joint injury involves a combination of medical history, physical examination, and imaging tests. During the physical exam, a doctor will look for tenderness over the AC joint, visible deformity or bump over the shoulder, and assess its range of motion and strength.

Imaging tests play a crucial role in diagnosing the severity of an AC joint separation. X-rays are typically used to visualize the joint's displacement and assess for fractures. Sometimes, a doctor might request a weight-bearing X-ray, where the patient holds a weight in the affected arm to stress the AC joint, making any separation more apparent.

Advanced imaging techniques such as MRI or ultrasound may also be used to evaluate the condition of the ligaments and surrounding soft tissues. However, they are less effective tests commonly needed for initial diagnosis.

Printable AC Joint Test

Download this AC Joint Test to assist in diagnosing acromioclavicular joint injuries, facilitating targeted treatment approaches and improved patient outcomes in orthopedic care.

How to do the AC Joint Test?

The AC Joint Test is a physical examination technique used to diagnose injuries or disorders of the AC joint, such as AC joint separation or arthritis. Here's how to perform the physical tests:

Step 1: Patient positioning

The patient should be seated or standing, with the examiner positioned in front of them. This setup gives the examiner a good view and access to the shoulder area.

Step 2: Identification of the AC joint

The acromioclavicular joint is located at the top of the shoulder, where the clavicle (collarbone) meets the highest point of the scapula (shoulder blade), known as the acromion. The examiner should locate this joint as the first step before proceeding with the test.

Step 3: Test proper

The AC joint test can be administered in two ways to diagnose potential issues in the acromioclavicular joint. Below are the methods explained in bullet points for clarity:

  • Passive test: The examiner lifts the patient's arm across the chest. This is done by holding the patient's elbow with one hand and the opposite shoulder with the other hand. The examiner then gently moves the patient's arm across the body toward the chest at about 90 degrees of elbow flexion, compressing the AC joint.
  • Active test: The patient moves their arm across the chest to the opposite shoulder as far as possible without causing excessive pain. This method allows the patient to control the movement based on their comfort level, potentially making identifying the point of discomfort easier.

Step 4: Evaluation of results

A positive test is indicated by pain or discomfort in the region of the AC joint. This suggests a potential injury or disorder in the acromioclavicular joint, such as AC joint separation or arthritis. The severity of pain and specific location can help diagnose the condition more accurately.

AC Joint Test example (sample)

By providing sample documentation, practitioners can gain insight into effectively recording the execution and results of the AC Joint Test within their practice. This approach demonstrates the distinction between normal findings from special tests and those indicative of an AC joint disorder, leveraging a template to ensure comprehensive and consistent documentation of clinical tests.

The example illustrates not just the method of conducting the test but also emphasizes the importance of precise recording—highlighting pain levels, the exact location of discomfort, and any observed abnormalities, thereby enhancing understanding and usage of the test in clinical settings.

Download this free AC Joint Test example here: 

AC Joint Test example (sample)

Results and interpretation

When conducting the AC Joint Test, understanding the outcomes and their significance is crucial for effectively diagnosing and managing shoulder conditions. Here’s a brief overview of what positive and negative test results might indicate.

Positive test

The positive likelihood ratio of the AC Joint Test can help clinicians assess the probability of injuries. A positive test means that the patient is experiencing AC joint pain or discomfort. The intensity of the pain and the exact location where it is felt can provide valuable clues about the nature of the injury or condition.

  • AC joint separation: If the sharp pain occurs directly over the joint, it may indicate an acromioclavicular joint separation. This condition often results from a direct blow to the shoulder or a fall on an outstretched arm. The severity of separation may vary, and this test alone cannot determine the separation grade.
  • AC joint arthritis: A more chronic, achy pain felt during this test might suggest arthritis of the AC joint. This condition is usually due to wear and tear over time and might be accompanied by a reduced range of motion and crepitus (a crackling or grating sound).
  • Other conditions: While less common, pain elicited by this test might also be related to other shoulder conditions that do not directly involve the AC joint but cause pain in its vicinity.

Negative test

A negative test indicates no pain or discomfort during the maneuver compression test. This result suggests that the AC joint is likely not the source of the shoulder pain. However, it does not rule out other shoulder pathologies. Further examination with different tests and imaging studies may be required to accurately diagnose the cause of shoulder pain.

Next steps

If the AC Joint Test results in a positive finding, indicating pain or discomfort at the acromioclavicular joint, the following steps are recommended to evaluate further and manage the condition:

1. Detailed medical history and physical examination

A thorough medical history and comprehensive shoulder physical examination should be conducted to make an accurate diagnosis and gather more information about the injury or condition. This includes understanding the mechanism of injury, duration of symptoms, and any previous shoulder issues.

2. Imaging studies

To further make an accurate diagnosis, the following tests can be conducted:

  • X-rays: These are typically the first-line imaging studies to assess bone alignment, joint space, and any potential fractures or dislocations in the shoulder region.
  • MRI (magnetic resonance imaging): An MRI may be recommended if there's a need to evaluate soft tissues around the AC joint, including ligaments and the capsule, or to assess for other potential shoulder injuries.
  • Ultrasound: This imaging modality can help assess soft tissue structures and the degree of any ligamentous injury around the AC joint.

3. Referral to a specialist

Depending on the findings of physical tests and if the condition is severe or complex, referral to an orthopedic surgeon or a sports medicine specialist may be necessary for further evaluation and treatment planning.

4. Conservative management

For less severe injuries or conditions:

  • Rest and ice: To reduce inflammation and pain.
  • Pain management: Through over-the-counter pain relievers or anti-inflammatory medications.
  • Physical therapy: To strengthen the muscles around the shoulder and improve the range of motion.

5. Surgical intervention

In cases of severe AC joint separation or when conservative management does not alleviate symptoms, surgical intervention may be considered to repair or reconstruct the damaged ligaments and stabilize the joint.

6. Monitoring and follow-up

Regular follow-up appointments should be scheduled to monitor recovery progress and adjust treatment plans as necessary. The patient's activity level and return to sports or other activities should be guided by symptom resolution and functional improvement.

How long does it take for the AC joint to heal?
How long does it take for the AC joint to heal?

Commonly asked questions

How long does it take for the AC joint to heal?

Healing time for an AC joint injury can vary, typically ranging from a few weeks for minor injuries to several months for more severe injuries, depending on the extent of damage and treatment approach.

What are the common treatments for an AC joint injury?

Common treatments for an AC joint injury include rest, ice, physical therapy, and, in severe cases, surgery to repair the joint and stabilize the shoulder.

What are the causes of an AC joint injury?

AC joint injuries are commonly caused by direct falls onto the shoulder, sports injuries, or car accidents, leading to strains, sprains, or tears in the ligaments that support the joint.

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