An acromioclavicular joint dislocation, commonly known as an AC joint dislocation or AC joint separation, is an injury to the small joint at the top of the shoulder where the collarbone (clavicle) meets the shoulder blade (acromion).
AC joint injuries are particularly common following a fall directly onto the shoulder and are frequently seen in people who participate in contact sports, cycling and other activities where falls or collisions can occur.
The severity of an AC joint injury can vary considerably. A mild injury may involve stretching or partial damage to the supporting ligaments, while a more significant injury can cause complete ligament rupture and separation of the joint.
Although the appearance of an AC joint dislocation can sometimes be quite dramatic, not every AC joint injury requires surgery.
Many people recover successfully with appropriate rehabilitation.
The decision about treatment depends on the severity and stability of the injury, your symptoms and the demands you place on your shoulder.
What is the AC joint?
The acromioclavicular joint (ACJ) is located at the top of the shoulder. It is formed where the outer end of the clavicle meets part of the shoulder blade called the acromion.
A number of important ligaments help stabilise this area, including the acromioclavicular and coracoclavicular ligaments.
When these ligaments are injured, the normal relationship between the clavicle and shoulder blade can be disrupted. In more significant injuries, the end of the collarbone can become noticeably prominent, producing the characteristic bump on top of the shoulder associated with an AC joint separation.
What causes an AC joint dislocation?
Most AC joint dislocations occur following a direct impact onto the outside or top of the shoulder.
This may happen during:
- rugby, football and other contact sports
- cycling accidents
- skiing or snowboarding
- martial arts
- falls from a bike or horse
- falls directly onto the shoulder
- road traffic accidents.
The force of the impact pushes the shoulder downwards while the collarbone remains relatively fixed, potentially damaging or rupturing the ligaments stabilising the AC joint.
What are the symptoms of an AC joint dislocation?
Symptoms usually begin immediately after the injury and can include:
- pain over the top of the shoulder
- tenderness directly over the AC joint
- swelling and bruising
- pain when lifting the arm
- pain when bringing the arm across the body
- difficulty sleeping on the affected shoulder
- weakness or discomfort when lifting or carrying
- a feeling that the shoulder is unstable
- a visible bump or prominence at the end of the collarbone.
With higher-grade injuries, the change in the shape of the shoulder can be very noticeable.
Importantly, the size of the bump does not necessarily tell us how well your shoulder will function in the longer term. Some people are left with a visible prominence but have very little pain and return fully to sport and everyday activities.
How are AC joint injuries graded?
AC joint injuries are commonly described using the Rockwood classification, which divides them into six types according to the amount and direction of displacement and the extent of ligament damage.
Rockwood Type I
The AC ligaments are sprained but the joint remains stable. There may be significant pain initially, but there is usually no obvious deformity.
Rockwood Type II
There is greater ligament damage and some separation of the AC joint, although the injury remains relatively stable.
Rockwood Type III
Both the AC and coracoclavicular ligament complexes are disrupted, resulting in more obvious separation of the joint.
Treatment of Type III injuries is more individualised. Many can be successfully treated without surgery, but persistent instability, symptoms and the patient’s sporting or occupational requirements may influence whether surgical treatment is considered.
Rockwood Types IV–VI
These are more severe injuries involving significant displacement of the clavicle. Specialist orthopaedic assessment is important, and surgical stabilisation may be considered more frequently.
The Rockwood grade is useful, but it is only one part of the decision-making process. Your consultant will also consider how stable the shoulder is, your symptoms, occupation, sporting requirements, age and expectations.
How is an AC joint dislocation diagnosed?
Diagnosis begins with understanding how the injury occurred and examining the shoulder.
Your consultant will assess the AC joint itself as well as the movement, strength and overall stability of the shoulder. It is also important to look for other injuries that may have occurred at the same time.
X-rays are usually the main imaging investigation following an acute AC joint injury. They can show the position of the clavicle relative to the acromion and help determine the severity of the injury.
Additional imaging may occasionally be recommended if there is concern about an associated injury or if symptoms do not follow the expected pattern.
Does an AC joint dislocation need surgery?
Not necessarily.
This is an important point because a visible AC joint dislocation can understandably make patients assume that the joint needs to be surgically put back into position.
For many AC joint injuries, particularly lower-grade injuries, non-surgical treatment can provide excellent functional results.
Initial treatment for ACJ dislocation may include:
- a sling for comfort – short term only
- pain relief
- ice during the early stages
- temporarily modifying activity
- physiotherapy and rehabilitation.
As pain settles, rehabilitation focuses on restoring comfortable shoulder movement before progressively rebuilding strength and control around the shoulder blade and shoulder joint.
The aim is ultimately to return you to your normal work, exercise or sport rather than simply concentrating on the appearance of the joint.
When might surgery be considered?
Surgery is more likely to be discussed for higher-grade AC joint dislocations, particularly where there is significant instability or displacement.
It may also be considered in selected patients with intermediate injuries where non-surgical management has not provided a satisfactory outcome.
Factors your consultant may consider include:
- the grade and stability of the injury
- persistent pain
- ongoing instability
- difficulty returning to sport
- physically demanding or overhead occupations
- functional limitations despite appropriate rehabilitation
- the time since the original injury.
Type III AC joint injuries require particularly careful consideration. Current research has not demonstrated a clear overall functional advantage of surgery for every acute Type III injury, so treatment should be tailored to the individual rather than based on the X-ray appearance alone.
What surgery is used for an AC joint dislocation?
The aim of surgery is to restore stability to the AC joint and reconstruct or support the damaged ligaments.
There are a number of surgical techniques available. The appropriate procedure depends on factors including the severity of the injury, whether it is an acute or longstanding dislocation, the direction of instability and the patient’s individual requirements.
Surgery may involve stabilising the relationship between the clavicle and the coracoid while the injured ligaments heal.
In chronic injuries, where the original ligaments are no longer expected to heal effectively, ligament reconstruction may be required.
Your shoulder surgeon will explain which technique is most appropriate for your injury, together with the potential benefits, limitations and rehabilitation involved.
What happens after AC joint surgery?
Rehabilitation is an important part of recovery following AC joint stabilisation.
The shoulder will usually need to be protected initially to allow the repaired or reconstructed tissues to heal. Physiotherapy then progresses gradually through restoring movement, rebuilding shoulder and shoulder-blade strength and eventually returning to heavier activities and sport.
Recovery times vary according to the injury, surgical procedure and activities you are hoping to return to.
Contact and collision sports place significant forces through the AC joint, so return to these activities usually occurs later in rehabilitation once sufficient healing, strength and shoulder control have been achieved.
Can an old AC joint dislocation still be treated?
Yes. Some people seek specialist advice months or even years after their original injury.
You may have been treated without surgery initially but continue to experience pain, weakness, instability or difficulty with certain activities. In other cases, the shoulder may function well but the prominence over the AC joint remains visible.
A longstanding bump does not automatically require treatment if the shoulder is comfortable and functioning normally.
However, persistent symptoms can be assessed to determine whether they are coming from chronic AC joint instability, post-traumatic changes within the joint or another shoulder problem.
Surgical reconstruction can be considered for selected patients with symptomatic chronic AC joint instability.
AC joint dislocation or AC joint arthritis?
Although both conditions affect the same joint, they are quite different.
An AC joint dislocation is usually caused by trauma and involves damage to the ligaments that stabilise the joint.
AC joint osteoarthritis is a degenerative condition in which the surfaces of the joint change over time. It tends to cause more gradual pain over the top of the shoulder, often aggravated by overhead movements, weight training or bringing the arm across the body.
Occasionally, a previous AC joint injury can contribute to problems within the joint later in life.
When should I see a shoulder specialist?
You should consider specialist assessment following a significant AC joint injury if you have an obvious deformity, substantial pain or loss of shoulder function, or if you have been diagnosed with a higher-grade AC joint separation.
Assessment can also be helpful if an apparently minor AC joint injury is not improving as expected, or if pain, instability or difficulty returning to work or sport persists despite rehabilitation.
At London Bridge Orthopaedics, our specialist shoulder and elbow surgeons can assess your injury, arrange appropriate imaging and explain whether rehabilitation or surgical treatment is most appropriate for you.
The aim is to help you regain a strong, comfortable and functional shoulder – whether that involves surgery or not.
Frequently Asked Questions
Is an AC joint separation the same as a dislocated shoulder?
No. An AC joint separation affects the joint between the collarbone and the acromion at the top of the shoulder. A shoulder dislocation occurs when the ball of the upper arm bone comes out of the main shoulder socket (glenohumeral joint). They are different injuries and are treated differently.
Will the bump from an AC joint dislocation go away?
Not always. More significant AC joint injuries can leave a permanent prominence at the end of the collarbone. This does not necessarily mean the shoulder will remain painful or function poorly, and many patients regain excellent function despite the visible bump.
Can an AC joint dislocation heal without surgery?
Yes. Many AC joint injuries are successfully managed without surgery. Lower-grade injuries are routinely treated conservatively, while the management of more significant injuries depends on the degree of instability, symptoms and the patient’s individual requirements.
Does a Grade 3 AC joint separation need surgery?
Not automatically. Treatment of Rockwood Type III injuries remains an area of debate, and research has not shown surgery to provide superior functional outcomes for every patient. Your activity levels, occupation, degree of instability, symptoms and response to rehabilitation should all be considered.
Can I return to sport after an AC joint dislocation?
Yes. Many patients return to their previous sport following either non-surgical or surgical treatment. The timing will depend on the severity of the injury, the sport involved and your recovery of movement, strength and shoulder stability.
What happens if an AC joint dislocation is left untreated?
Many AC joint dislocations do very well with non-surgical treatment, so choosing not to operate does not mean the injury is being left untreated. A small proportion of patients may develop persistent pain, instability or difficulty with demanding activities, in which case further assessment and treatment can be considered.
