AC Joint Dislocation: Grades & Treatment

In brief

Summarized and reviewed by Dr. Avi Chezar, shoulder surgery specialist, Assuta Haifa and RMC Afula.

What it is: Dislocation of the AC (acromioclavicular) joint, located between the collarbone and the acromion (part of the shoulder blade), usually caused by a fall on the shoulder. The trauma tears some or all of the ligaments, and this determines how severe the injury is.
Symptoms: Pain at the top of the shoulder with pinpoint tenderness, and a drooping shoulder with a prominent bump of the collarbone. Raising the arm is difficult and painful.
Diagnosis: An X-ray aimed at the AC joint; ideally also a standing X-ray of both shoulders, to compare them and grade the injury.
Treatment: Grades 1–2 (mild): a short rest in a sling and physiotherapy for rehabilitation. Grade 3 (moderate): conservative treatment first, surgery if there is no improvement. Grades 4–6 (severe): surgical repair.

How does it typically present?

The dislocation results from an injury: a fall or a blow to the shoulder, or breaking a fall with the hand. After the injury there is pain at the top of the shoulder; over the bone there is pinpoint local tenderness, and the shoulder can be seen to droop, with the collarbone sticking out. Raising the arm is difficult and painful.

It is common between the ages of 18 and 55 and in people who do sports such as skiing and cycling.

What is a dislocation of the acromioclavicular joint?

The joint connects the collarbone and the acromion, which is one of the parts of the shoulder blade (the scapula). The joint is held in place by several ligaments. The trauma tears some or all of the ligaments, and this determines how severe the injury is. The arm is connected to the body in two places: the shoulder blade is attached to the chest wall by muscles (without a true joint), and through the acromioclavicular joint. The injury disrupts the connection between the shoulder and the body, which shows itself mainly as pain and disturbed movement above shoulder height.

How is a dislocation of the acromioclavicular joint diagnosed?

The diagnosis is suspected from the description of the event, the patient's complaints and the physical examination findings, including a painful bump at the shoulder. Compared with the healthy side, the shoulder sits lower.

The diagnosis is confirmed with an X-ray aimed at the AC joint. It is advisable to also have a standing X-ray that includes both shoulders, for comparison.

How is a dislocation of the acromioclavicular joint treated?

Treatment depends on the severity of the injury and on the patient's level of activity:

In a severe injury (grades 4–6 in the injury classification), surgical repair is indicated.
In mild injuries (grades 1–2), surgery is usually not needed. Treatment is based on a short period of rest in a sling and physiotherapy to restore function. Only if, on follow-up over months, the pain continues and returning to function is difficult, should surgery be considered.
The common injury is of moderate severity (grade 3). For an injury of this grade it is standard to try a period of non-surgical treatment and to consider surgery if there is no improvement. In certain situations, immediate surgery can also be considered. For this grade, the option of surgery and how long to wait before deciding on treatment should be discussed with the treating physician.

How far does activity return after the injury?

The return to activity depends, of course, on the type of injury and the treatment chosen.

A return to normal activity can be expected, mainly in the mild grades; the process may take several months.
After a grade 3 injury a bump may remain at the injury site, which is usually not significant for function.
After surgical repair, a return to full function can be expected after a rehabilitation period of several months, 4–6. Even after surgery a bump may remain at the injury site, usually slight and without affecting function.
In high-grade injuries, 4–6, varying degrees of loss of function should be expected if no repair is done, so in these situations the preference is early surgery. The function mainly affected is use of the arm above shoulder height.

Frequently asked questions about AC joint dislocation

Why does the collarbone stick out after the injury, and does the bump stay forever?

The bump forms when the ligaments that stabilize the joint tear and the shoulder drops relative to the collarbone. After a grade 3 injury a bump may remain at the injury site, which is usually not significant for function. A bump may remain even after surgical repair, usually slight and without affecting function.

How long does recovery from an AC joint dislocation take?

Recovery time depends on the grade of the injury and the treatment chosen. In the mild grades a return to normal activity can be expected, and this process may take several months. After surgical repair, a return to full function can be expected after a rehabilitation period of 4 to 6 months.

Grade 3 AC joint dislocation: is surgery necessary?

Grade 3 is the most common injury, and it does not always require surgery. The standard approach is to try a period of non-surgical treatment first, and to consider surgery if there is no improvement. In certain situations, immediate surgery can be considered. For this grade, the option of surgery and how long to wait before deciding should be discussed with the treating physician.

What is the acromioclavicular (AC) joint, and why does it dislocate?

The joint connects the collarbone to the acromion, which is one of the parts of the shoulder blade, and is held in place by several ligaments. The dislocation results from an injury: a fall or a blow to the shoulder, or breaking a fall with the hand. The trauma tears some or all of the ligaments, and this determines how severe the injury is.

How is an AC joint dislocation diagnosed, and which X-ray is needed?

The diagnosis is suspected from the description of the event, the patient's complaints and the physical examination findings, which include a painful bump at the shoulder and a shoulder that sits lower than the healthy side. It is confirmed with an X-ray aimed at the AC joint, and it is advisable to also have a standing X-ray that includes both shoulders, for comparison.

When can I return to sport after an AC joint dislocation?

The injury is common between the ages of 18 and 55 and in people who do sports such as skiing and cycling. The return to activity depends on the type of injury and the treatment chosen. In grade 4 to 6 injuries that are not repaired, loss of function should be expected, mainly in movements above shoulder height, so in these situations the preference is early surgery.