Acromioclavicular joint (ACJ) injuries

What is an acromioclavicular joint injury?

The acromioclavicular joint, usually called the AC joint or ACJ, is where your collarbone (clavicular) meets the top of your shoulder blade (acromion), at the very point of your shoulder. An AC joint injury happens when the ligaments holding this joint together are sprained or torn, most often after a fall or a blow to the shoulder.

What are the symptoms of an AC joint injury?

Symptoms usually start straight after the injury and can include:

• pain at the top of the shoulder, which may spread to your neck or down your arm
• swelling and bruising around the joint
• tenderness when the area is touched
• a visible bump, or your collarbone looking more prominent than usual
• reduced or painful shoulder movement, particularly reaching overhead or across your body.

Because pain from the AC joint can spread into the neck, chest or back, it isn't always easy to tell straight away that the AC joint is the cause, which is why a proper examination is useful.

What causes AC joint injuries, and who is at risk?

The most common cause is a direct fall onto the point of the shoulder, which forces the shoulder blade downward while the collarbone stays in place. A fall onto an outstretched hand, a direct blow to the shoulder, or a car accident can also injure the joint.

AC joint injuries are particularly common in:

• contact and collision sports, such as rugby, football and hockey
• horse riding and motorsports
• overhead sports, boxing and weightlifting, which tend to cause more gradual, repetitive strain rather than a single injury.

AC joint injuries are common, accounting for more than 40% of all shoulder injuries, and a sprain is the most frequent pattern.

Are there different types of AC joint injury?

AC joint injuries are traditionally graded from 1 to 6, based on how much the joint has moved out of place and how much ligament damage there is:

• grades 1 and 2 are sprains, with no or minimal displacement of the joint
• grade 3 is a complete tear of the main joint ligament, with minimal displacement
• grades 4 to 6 are more complex injuries, where the collarbone is displaced further out of position.

In practice, the grade doesn't always determine your treatment, since the evidence linking grade to the best treatment is weak. Increasingly, treatment is guided by your symptoms, particularly pain and how much the injury limits you, rather than by the grade alone.

How is an AC joint injury diagnosed?

A doctor will examine your shoulder for swelling, bruising, tenderness and any visible deformity, and will check the movement and strength of your arm, hand and neck to rule out any wider injury. Moving your arm across your body often reproduces the pain, which helps confirm the joint involved.

X-rays are the standard first test, sometimes including a specially angled view to show the joint more clearly. If there's still uncertainty about the extent of the injury, an ultrasound or MRI scan may be used.

How is an AC joint injury treated?

Most AC joint injuries, including all grade 1 to 3 sprains, are treated without surgery, and even some more severe injuries do well with non-surgical treatment.

Non-surgical treatment

• a sling for comfort for around 3 weeks, which you can come out of sooner if your pain settles
• ice applied for 10–15 minutes every 2–3 hours in the first 72 hours, to help with pain and swelling
• over-the-counter pain relief or anti-inflammatory medicine
• gentle movement of your hand, wrist, elbow and neck from day one to prevent stiffness, progressing to shoulder exercises from around 2 weeks
• physiotherapy focused on stabilising the shoulder blade and a gradual, structured return to activity.

The injury usually takes around 6 weeks to heal, though soft-tissue discomfort can linger for 3 to 6 months. Many people find the joint looks slightly more prominent than before on a lasting basis, but this doesn't affect how the shoulder moves.

Contact sport and heavy lifting can usually be considered again from around 6 to 12 weeks after injury, once you have good movement and strength. At a year, there's around a 17% chance of some reduced bench-press strength, though most people who have this don't find it a practical problem.

You're not insured to drive while wearing a sling. Once you're out of the sling, check with your insurer, but you're generally considered safe to drive again once you can grip the wheel, change gear, use the handbrake and indicators, and perform an emergency stop comfortably.

Surgical treatment

Surgery is more often needed for the more severe grade 4 to 6 injuries, because of the greater instability involved. For grade 3 injuries, the decision is more individual, and will depend on your occupation, activity goals and a specialist's assessment, since the evidence doesn't clearly favour surgery over non-surgical treatment for this group.

Surgery may also be considered if pain persists, often after 3 to 6 months, or if the deformity is significant. Depending on your situation, this might involve trimming back the end of the collarbone so it no longer rubs against the shoulder blade, or reconstructing the ligaments if there's significant displacement. This can be done as open surgery or through keyhole (arthroscopic) techniques, and works well even if carried out some time after the original injury.

Long-term outcomes tend to be similar whether or not you have surgery, so non-surgical treatment remains the first choice for most people. After surgery, you won't be able to drive for at least 6 weeks, and your return to work will depend on your job: often around 3 to 6 weeks for desk-based work, but up to around 3 months for manual or heavy work.

A notable proportion of people have some ongoing discomfort after an AC joint injury, though for most this is manageable. Occasionally, lasting pain is caused by damage to the small disc of cartilage inside the joint, and a steroid injection can help speed up recovery in this situation. Osteoarthritis can also develop in the joint over time, particularly as you get older.

When should you see a doctor?

Seek medical assessment for any fall or blow to the shoulder that causes pain, swelling, visible deformity or difficulty moving your arm, so it can be examined and X-rayed if needed.

If you're already being treated for an AC joint injury, contact your physiotherapy or medical team if:

• your pain isn't improving as expected
• you still have reduced movement, strength or function after several weeks
• you have any new concerns about the injury.