fbpx Skip to content

What is the Acromioclavicular Joint?

The Acromioclavicular joint (AC joint) is a common source of shoulder pain. The AC joint is located on the top of our shoulder, and joins the acromion process of the scapula (shoulder blade) to to the lateral clavicle (collar bone).

The AC joint is vital in movement of the shoulder, it is involved in rotation of the scapula as our arm moves through range. The AC joint is also important in absorbing forces placed onto the arm.

The AC joint is stabilised by two main ligaments, the Acromioclavicular ligament and the Coracoclavicular ligament.

Pain in the AC joint can be coming from degenerative changes within the joint, such as with osteoarthritis, but more commonly occurs as an acute injury after trauma, resulting in a dislocation or tear of the stabilising ligaments. This article will focus on more acute injuries of the AC joint.

Anatomy of the Shoulder and AC joint. Source

Signs and Symptoms


The mechanism can be a good indicator of whether there is an acute injury of the AC joint. There are two common ways that this happens:

  1. Direct Contact.
    • This might have happened when falling, where you have landed directly on the tip of your shoulder.
    • It also often occurs in contact sports such as Rugby League, when another player collides with directly with the AC joint.
  2. Indirect Contact.
    • This also often happens when falling, however it is when we fall on an outstretched hand or our elbow.
    • This happens because the AC joint absorbs a lot of the forces placed on the upper limb.

If there is no acute mechanism like this, it is possible the pain is not related to an acute injury of the AC joint, and could be coming from elsewhere.


Symptoms might include, but are not limited to:

  • Immediate onset of pain.
  • Pain over the tip of the shoulder.
  • Pain in the neck or side of the shoulder.
  • Tenderness over the tip of the shoulder.
  • Pain with movement, specifically lifting of the arm and moving the arm across the body.
  • Swelling surrounding the top of the shoulder.

Grading the Severity of Acute AC Joint Injuries

Diagnosis of the severity of the AC joint involves the use of a scale known as the Rockwood Grades. The Rockwood Grades diagnose an AC joint injury based on the severity of disruption to the AC joint, as well as the direction of dislocation.

It involves 6 different gradings. Grades I to III diagnose the severity of injury sequentially based on ligament and joint disruption. This means Grade I is the least severe, and Grade III is most severe.

Grades IV to VI diagnose injury based on the direction of clavicle displacement, but are not necessarily sequential in terms of severity.

Diagnosis is done through a physical assessment by a Physiotherapist, but can also be done through Xray and MRI. Imaging is usually only used when it may change the course of treatment. Imaging might be done if a Grade III, IV, V or VI injury is suspected, or if symptoms have not progressed as they are expected to.

The Rockwood Grades for acute AC joint injuries are as follows:

Grade DiagnosisSigns
IMinor Ligament Sprains:
Minor-moderate AC ligament sprain. No rupture.
Intact AC joint, CC ligament, surrounding muscles.
Pain, but no instability on physical stress tests.
IILigament Tears with joint intact:
Tear of AC ligament.
Possible sprain of CC ligament, AC joint disruption but not dislocation.
Instability of the clavicle on physical stress tests.
IIILigament Tears with Joint Dislocated Superiorly:
AC joint dislocated, clavicle sits superior to acromion.
Complete tear of AC ligament and partial tear of CC ligament.
Deltoid and trapezius muscles likely affected.
Instability of the clavicle, with visible deformity where the clavicle sits higher than usual.
IVLigament Tears with Joint Dislocated into Trapezius:
Complete tear of AC ligament, partial or complete tear of CC ligament.
AC joint dislocated, clavicle displaced posteriorly into or through trapezius muscles.
Visible deformity at the back of the shoulder.
VA More Severe Grade III:
Complete tears of AC and CC ligaments.
AC joint dislocated, clavicle sitting severely higher than acromion.
Obvious clavicle elevation relative to the acromion. Downward rotation of the shoulder blade.
VILigament Tears with Joint Dislocated Inferiorly:
Complete tears of AC ligament, but CC ligament intact.
AC joint dislocated, clavicle sitting inferiorly to acromion.
Clavicular instability, visible deformity with clavicle sitting lower than acromion.
Visible deformity of the AC joint, showing the clavicle sitting higher than usual. Likely a grade III or V injury. Source

How Do We Treat It?

This depends on the severity and grading of the AC joint injury. Many AC joint injuries will respond to nonoperative treatment options, however more severe injuries may require surgery.

Initial Management:

If you suspect you have an AC joint injury, make an appointment with your Physiotherapist.

As these injuries often result from acute trauma, it is necessary to rest for a period of time and allow the body to have time to heal. During this period, it can be useful to follow a protocol such as RICE, involving Rest, Ice, Compression and Elevation. If pain is high or the joint is unstable, supportive taping or a sling may be used initially to support the shoulder.

If your Physiotherapist suspects you may have a Grade III to VI injury, you may be referred for further imaging and a specialist opinion on whether surgical management is indicated in your case.

When to Operate:

Generally Grade I and Grade II injuries do not require surgery, and respond well to non-operative management options. Grade IV, V and VI injuries require surgery to stabilise the AC joint, however it is not always necessary to operate on Grade III injuries. Surgery in Grade III injuries can depend on how unstable to clavicle is, and whether the scapula is affected. It is necessary to have a specialist review to make a decision on whether surgery is required.

After surgery, post-operative management and rehabilitation will be similar to non-operative management of Grade I and II injuries, however can differ slightly depending on surgical guidelines. Initially the aim is to manage pain, protect the AC joint and surgical site, and begin early range of motion exercises.

Non-Operative Management:

Non-operative management aims to regain full range of motion (ROM), strengthen the shoulder and safely return to activity.

Range of motion is improved initially through passive range of motion exercises, which are then progressed to active assisted and finally active range of motion exercises. Once pain is decreased, exercises can focus on scapula control as well as strengthening the rotator cuff, deltoid and trapezius muscles.

Once strength has returned to normal levels and full range of motion has been achieved, plyometric exercises can be introduced before returning to activity. Plyometrics prepare the joint, muscles and tendons for the load it will experience during normal activities.

Return to Activity:

Return to activity is gradual and symptom dependent. The severity and type of injury will change the expected time-frames for return to normal activity.

Expected time-frames for return to activity are:

  • Grade I injuries: 2-4 weeks.
  • Grade II injuries: 4-6 weeks.
  • Non-operative Grade III injuries: 6-8 weeks.

Return to activity for surgical procedures will depend on the type of operation that is done, as well as the differing surgical guidelines. Generally it takes 6 months to return to normal activity after surgery.


Gorbaty, J. D., Hsu, J. E., & Gee, A. O. (2017). Classifications in brief: Rockwood classification of acromioclavicular joint separations. Clinical Orthopaedics and Related Research475(1), 283–287. https://doi.org/10.1007/s11999-016-5079-6

Matthew Tingle, MD, Heinz R. Hoenecke Jr., MD, Tim Wang. (2023). Current trends in surgical treatment of the acromioclavicular joint injuries in 2023: a review of the literature. https://doi.org/10.1016/j.jseint.2023.11.018

Reid, D., Polson, K., & Johnson, L. (2012). Acromioclavicular joint separations grades I–III: A review of the literature and development of best practice guidelines. Sports Medicine (Auckland, N.Z.)42(8), 681–696. https://doi.org/10.1007/bf03262288

Kiel J, Taqi M, Kaiser K. Acromioclavicular Joint Injury. [Updated 2022 Sep 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK493188/