If you’ve ever fallen directly onto your shoulder, you’ll understand they type of pain that comes with an AC joint injury. It feels like intense shoulder pain, but technically it is slightly different than shoulder joint pain. AC stands for acromioclavicular and it forms part of the shoulder joint as a whole. You might be reading this and might be wondering how you should know what you’ve hurt in your shoulder. But the pain you’re feeling is bad enough to feel like you can’t move your arm. Putting on a shirt, reaching for something in the cupboard or picking up your bag feels extremely painful and the only way for it to feel better is to hold your arm next to your body, moving it as little as possible.

Read on, to better understand AC joint injuries and how we can help you to manage it.

What’s the difference between my AC joint and my shoulder joint?

Your shoulder is formed by three bones namely: the humerus (upper arm bone), the scapula (shoulder blade) and the clavicle (collarbone). The AC (acromioclavicular) joint is formed by the collarbone (clavicle) that connects with the acromion, which is a bony point at the front of your shoulder blade. As a result, the name acromioclavicular (AC) comes from acromion and clavicle. These bones form an arch and underneath it is the place where your humerus (upper arm) connects. This is called the glenohumeral joint and it is the true ball-and-socket joint that people typically refer to when they talk about their shoulder joint.

AC joint anatomy

Inside the AC joint, the bones are covered in cartilage and there is a cartilage-like structure called a disc or meniscus. The AC joint is covered by a layer of tissue, called the joint capsule. Together with the ligaments, it helps to keep the joint stable.

There are two important ligaments around your AC joint:

  • Coracoclavicular ligament: This is the primary support ligament for the AC joint as it prevents the clavicle from moving upwards and out of place. It connects the coracoid process with the clavicle.
  • Acromioclavicular ligament: This ligament runs over and along the joint and reinforces the joint capsule. It connects the acromion and the clavicle.


The AC joint and acromioclavicular arch is what gives your shoulder its shape. Almost like a shoulder pad, that gives shape to a jacket. This arch serves as attachment point for several muscles. And from here muscles can connect your head, neck and shoulder.

  • Deltoid muscle: This muscle attaches directly from your acromioclavicular arch and onto your upper arm. It’s main function is to lift your arm up sideways.
  • Trapezius muscle: This muscle runs all the way from your neck, where it attaches onto your spine, and attaches onto the acromioclavicular arch. If it contracts, it can either shrug your shoulder upwards or move your neck sideways.
  • There are several other muscles, like your pectoralis major and rotator cuff, to take note of. They don’t attach directly onto the AC joint, but they assist with shoulder movement and will also be affected by an AC joint injury.

The shoulder and AC joint works together

Together, your glenohumeral and acromioclavicular joint form what we call your shoulder. And they always move in coordination with each other. There is a specific space underneath your AC joint, called the subacromial space, where your rotator cuff muscles and other soft tissue attach. This space needs to be maintained at all times, otherwise it leads to shoulder impingement. Thus, when you lift your arm up, it is not just your shoulder that’s moving, but your AC joint as well, creating enough space for the movement.

So, even though you might have an AC joint injury, your it’s your shoulder that will hurt and all your shoulder movements will be affected.

The function of your AC joint

Your shoulder is the one joint in your body with the biggest range of motion and your AC joint helps to improve that range. It doesn’t really move out of its own or in its own direction, but moves in coordination with your shoulder and arm.

Because it is such a mobile joint, you are able to move your arm in almost all directions. Such as:

  • Reaching forward and down to pick up a bag or your child
  • Lifting your arm to reach something high up in your cupboard, paint the ceiling or trim a tree in your garden
  • Reaching your own face and mouth to eat and drink
  • Reaching back to pick up your handbag from the backseat of your car, or even to scratch your own back
  • Doing a circular movement like swimming or bowling a cricket ball

However, for the shoulder to be mobile, it needs a stable base to move from. This is where the AC joint plays another important role, as it anchors your shoulder blade.

Causes of an AC joint injury

AC joint injuries are usually caused by a traumatic force that disturbs the joint position. Depending on the severity of injury, your AC joint can either be sprained, dislocated or fractured.

Initially, inflammation will cause swelling and pain in and around the joint. All shoulder movements, like lifting your arm, will be painful to do. Any pressure on your shoulder, like sleeping on your side, will be excruciating. You’ll want to cradle your arm and support your shoulder. Then, once the inflammation settles, your shoulder movement will be limited and stiff. Your AC joint might be a small joint, but an important one, nonetheless. That is why it is so important to manage an injury like this the right way from the start.

Examples of how you could injure your AC joint:

  • Falling directly onto your shoulder, without stretching your arm out
  • Taking a rugby tackle onto the side of your shoulder
  • Car accidents
  • Falling sideways off your bicycle
  • Bench press with weights that are too heavy
  • Getting hit on your shoulder while boxing or fighting
  • Strenuous exercises with your arms lifted up

Symptoms of an AC joint injury

Tests that you can do to see if you have an AC joint injury

  • Sit upright on a chair
  • Lift one arm up sideways as high as you can
  • Repeat the movement with your other arm
  • Compare what you feel in both arms
  • If you feel pain around the side of your shoulder that gets worse the higher you lift your arm, it could mean that you have an AC joint injury
  • Sit upright on a chair
  • Cross one arm over your chest, as if you want to touch your opposite shoulder
  • Repeat the movement with your other arm
  • Compare what you felt in both arms
  • If you feel pain around the side of your shoulder that gets worse as you move your arm across your chest, it could be a sign that you have an AC joint injury
  • Stand comfortably with your arms next to your sides
  • Take one arm and reach behind your back as if you want to tuck in your shirt or fasten your bra
  • Now, bring that arm back to your side
  • Repeat the same movement with your other arm
  • Compare what you feel in both shoulders and measure how high you can reach behind your back with each arm
  • If you have limited movement or shoulder pain while doing this, it can be a sign that you have an AC joint injury
  • Go down into a planking position on the floor
  • Push yourself up and down with your arms by bending and straightening your elbows
  • If you cannot do this test lying down on the ground, you can do the same movement by leaning against a wall
  • Push yourself away from the wall by bending and straightening your elbows
  • Compare what you felt in both shoulders
  • If you have pain while while pushing yourself up or even feel like you’re unable to do a pushing movement with your arm, it could be a sign that you have an AC joint injury

How severe is my AC joint injury?

The Rockwood classification system is used to determine the severity of an AC joint injury.

Grade 1: Acromioclavicular ligament sprain

This is the ligament that covers the AC joint. Thus, the stability of the joint will be compromised, but the coracoclavicular ligament will still be intact. Meaning that the collarbone is still anchored to the shoulder blade.

Grade 2: Rupture (tear) of the acromioclavicular ligaments

An injury like this is described as an AC joint subluxation because the ligament that covers the joint is torn. The clavicle can thus move out of its normal position, and this disturbs the joint position. The coracoclavicular ligament is still intact.

Grade 3: Both the acromioclavicular and coracoclavicular ligaments are torn

Both ligaments that anchor the AC joint are torn. It can also be called an AC joint dislocation. That means that the collarbone will be very unstable as nothing anchors it and it dislocates from its position. Usually, your shoulder will look deformed because your collarbone will seem higher than it should be.

Grade 4: AC joint dislocation with posterior collarbone displacement

The collarbone is dislocated from the AC joint and pushed backwards into the trapezius muscle tissue. There will be an obvious deformity of your shoulder as well as an injury to the trapezius muscle.

Grade 5: Complete tear of ligaments and fascia

The AC joint is completely dislocated with both the acromioclavicular and coracoclavicular ligaments torn. However, with a grade 5 injury, the surrounding fascia (connective tissue) is also torn. This is a more severe form of a grade 3 injury.

Grade 6: Dislocation and inferior displacement of the collarbone

This is the most severe type of dislocation. The collarbone is displaced downwards and quite a severe force was needed for the collarbone to be pushed so far out of position. Now, other structures like muscles, nerves and arteries can also be damaged, depending on how far down the collarbone has been displaced.

AC joint fractures

If the injury is severe enough, you can sustain an AC joint fracture. Out of the two bones that form the AC joint, it is the collarbone that usually gets fractured. It can break anywhere along the length of the bone or even in multiple places, depending on the injury.


Physiotherapy diagnosis

Our physiotherapists are experts in human anatomy and movement, with the necessary experience to diagnose an AC joint injury. We understand how your shoulder should move and how your AC joint works in coordination with it. We will be able to confidently identify if any other soft tissue, like muscles, have been injured as well. Doing a full clinical assessment and getting the necessary information about your pain is the starting point.

During your physiotherapy evaluation, we will stretch and stress your shoulder and AC joint, test the strength of your surrounding muscles and evaluate your shoulder movement patterns. Then we’ll know how your everyday movements have been affected. It is important that we evaluate movement of your neck as well. Thorough evaluation makes our physiotherapists the best at diagnosing this type of problem.


X-rays will only give us an image of the bones in your shoulder. None of the surrounding muscles, ligaments or signs of swelling will display on an x-ray. However, x-rays will be able to show the degree of AC joint separation or dislocation.

Your physiotherapist will refer you to get x-rays taken if necessary.

Diagnostic ultrasound

This can be a helpful test to confirm the diagnosis of an AC joint injury, especially a ligament sprain. It could show swelling and the degree of the ligament or muscle tear.

It is not compulsory that you get a sonar before you see your physiotherapist for the first time. However, if your physiotherapist feels it is necessary that you get one, you will be referred to the right place.


An MRI scan can image all of the structures in your shoulder, including bones, joints, muscles, ligaments and tendons. However, you need a referral from a specialist to get an MRI scan and it is an expensive test.

It isn’t necessary to get an MRI straight away, but if your physiotherapist feels it is necessary for you to get one, you will be referred to the right specialist.

Why is my shoulder not feeling better after an AC joint injury?

Initially, your pain is caused by inflammation and swelling around the AC joint. This causes pain when you lift your arm. Resting and cradling your arm seems to help, so you use your arm less than before. If you’re not moving your arm fully, your muscles become weaker, shoulder joints become stiff and you compensate by using the wrong muscles at the wrong time.

It isn’t that easy to avoid using your painful arm. Through the day you might quickly need to pick up your handbag and before you know it pain shoots into your shoulder. Putting on a shirt, combing your hair or even picking up your cup of coffee worsens your pain. These movements cause further irritation or leads to more inflammation and starts up the cycle of pain again. It’s easy to become stuck in a cycle of pain, not knowing if it is safe to move or not.

Effective treatment of an AC joint injury needs to address the real cause. A sprain will be managed differently than a dislocation. Certain treatments like medication might ease the pain, but your body still needs to work through the healing process. Swelling needs to settle and normal movement need to be encouraged. If you use your arm too soon or try to exercise, there is a big chance that your pain will simply return.

What NOT to do

  • Long-term use of anti-inflammatory medications

  • Manage the pain through medication alone

  • Stretch

  • Exercise through the pain

  • Do not ignore shoulder pain that gets worse

  • Leave it untreated

  • Sleep on your sore shoulder

  • Do sudden shoulder or arm movements

  • Repeated movement above your head

  • Carry your handbag or shoulder bag over your sore shoulder

What you SHOULD do

  • Rest as needed initially

  • Avoid movements that is flaring up your pain, like lifting your arm up too high, reaching for a heavy bag or bumping into something with your shoulder

  • Make an appointment to confirm the diagnosis and determine how severe the injury is

  • Finish your treatment and rehabilitation programme for better long-term results

  • Load your shoulder and neck muscles with appropriate exercise

  • Use ice to decrease swelling and numb the pain

Making it WORSE

  • Putting on a shirt or jacket

  • Picking up your child

  • Push-ups

  • Weight training at the gym

  • Bumping into someone with your shoulder

  • Turning your car’s steering wheel

  • Combing your hair

  • Pull-ups

  • Swimming

  • Painting the ceiling

  • Working on your computer or desk for long hours

  • Sleeping on your side

Problems we encounter when patients come to see us with an AC joint injury

Waiting too long and not getting a proper diagnosis

A common problem we see is that patients wait too long before they seek help. Often, they seek our help only after they have walked around with shoulder pain for weeks. Now, the problem has become more advanced and it will take a lot longer to get better. It wastes a lot of time if you don’t get a proper diagnosis.

Trying out, but not completing different forms of treatment

Patients try to get relief by taking medication or getting a cortisone injection in the hopes that it will ease their pain. Together with things like massages, foam-rolling, cupping or stretching might relieve some of your symptoms. However, these treatments will only be a temporary solution.

And then, a lot of people tend to feel better halfway through their physiotherapy treatment programme, so they stop. But you need to finish your rehabilitation and get your shoulder mobility and stability on the level that it should be. Otherwise, your pain could simply come back. Patience is key.

Resting too much or too little

Wearing a sling to support and rest your arm, can be helpful in the initial stages of an AC injury. However, once you take it off, you sit with a weak and sore arm. Wearing a sling long-term is a big problem; before long you will depend on the support it gives. You need to have an active rehabilitation plan to wean yourself off of the sling and to strengthen your shoulder.

On the other hand, overdoing it and pushing through your pain can make it even worse. Over time, you’ll start to worry about your shoulder more and more and think twice before doing things that you love like gardening or playing with your kids. Moving too much causes extra irritation, inflammation or pain that gets worse. Finding the balance between resting and doing safe movements is key. That is something we can help you with.

Physiotherapy treatment

We are confident that we can provide the best treatment for an AC joint injury. We understand that you want to have full use of your arm to be able to brush your teeth, pick up your child or lift weights at the gym. That is why we are here to guide you through the process, so that you understand your condition and which movements you can do safely. As physiotherapists, we will implement a very effective and structured plan of action that treats all the aspects of your AC joint injury. This way, you can put on a shirt or pick up a bag without fear of pain. Our physiotherapy treatment will help to decrease inflammation and swelling and get your shoulder movement and strength back to normal.

The basic structure of our treatments:

  1. Determine what is causing your subacromial impingement
  2. Which structures has been injured?
  3. Protect it from further injury
  4. Give it time to heal
  5. Improve range of movement and strength
  6. Re-evaluate to monitor progress

We will be looking at different aspects, like your shoulder range of motion, strength and stability. Treatment of an AC joint injury includes: soft tissue massage, joint mobilisations, dry needling, strapping, laser therapy, nerve mobilisations and guiding you through a rehabilitation program of gradual strengthening and conditioning. It’s important that you commit to the treatment plan, as this improves your chances of successful long-term recovery.

Phases of rehabilitation

1st Phase: Initial healing and range of motion

We will monitor the levels of inflammation and pain and encourage the healing process taking place in your AC joint. On a cellular level we’re able to accelerate healing using dry needling, laser and ultrasound. With time, the swelling should decrease and with it, the stiffness and pain in your shoulder as well.

Initially, you are safe to move in a pain-free range of movement, and our exercises will be targeted between these boundaries of your pain. With time, the pain-free range of movement will increase up to a point where you have the full range of your shoulder back.

You should be able to lift your arm up all the way and with more ease at the end of this phase.

2nd Phase: Posture and joint stability

Your posture and the positions you spend time in daily, will influence the position of your shoulder and AC joint as well. If you tend to sit hunched over and hold  your arm next to your body the whole time, it limits your shoulder movement. It is important to restore the normal, coordinated shoulder and acromioclavicular joint movement. Addressing your posture and making sure you get your shoulder and scapula in a neutral position is the first step to improve shoulder stability. Often, just getting used to your shoulder in a neutral position is hard work because you got used to wrong movement patterns.

From here on, you will have to be able to hold the stable position of your scapula while you move your arm.

3rd Phase: Strength and endurance

It’s common to feel pain when you start to work on getting your arm and shoulder stronger again. This could be due to abnormal tissue thickening in your surrounding muscles, which prevents the muscle from contracting smoothly. But it could also be due to poor endurance and muscle strength. By strengthening the muscles around your shoulder, your day to day activities will become easier. Picking up a heavy bag won’t be such a daunting task.

During this phase of rehabilitation we will progress your exercises more and more, adding resistance, doing more repetitions and building your overall strength.

4th Phase: Control of movement and power

It is one thing to feel stronger, but another thing to do movements with control and power. Holding your arm up while you type or paint needs control. Whereas, throwing a ball or doing a benchpress in the gym needs power. However, both of these things are important when you use your arm for day to day activities. The muscles around your shoulder need to adapt to different type of movements again, without putting too much pressure on your AC joint.

5th Phase: Getting back to your routine, training or sport

Gradually returning to your routine and getting used to the intensity of your usual daily activities is a big part of your recovery. We need to determine if you are ready to return to fully working and training without any painful flare-ups of AC joint pain. Even with repetitive movements throughout your day (like packing something in and out of a cupboard) or more load (like weightlifting at the gym), your AC joint should be able to adapt to the load. Your physiotherapist will guide you to re-engage in safe increments, and make adjustments where necessary.

Getting you back to swimming, throwing a ball, pull-ups or weightlifting is the ultimate goal.

6th Phase: Final clearance tests  

By now you should be able to exercise, throw a ball, swim or pick up something heavy, but there’s some specific stress tests that you should be able to do

This allows us to make sure the AC joint and surrounding muscles are able to handle stretching, stress, maximum load and compressive forces.

Now we can sign off on your recovery, knowing you’re safe.

Healing time

AC joint injuries can take anything from 6 weeks to 3 months to heal, depending on the severity of your injury. All people experience pain differently, so your treatment plan will be tailored to your individual goals. That way you’ll be able to get back to doing all the things you love. We can make a big difference in your pain and quality of life.

You will need physiotherapy treatment twice a week for the first two weeks to work through the first phases of treatment. The aim will be to improve inflammation and get your shoulder movement back to normal. After this, your treatment sessions can be spread out to once a week or once in two weeks. This is when you will start to work on shoulder stability and strength. Remember, you only spend an hour at a time with your physiotherapist. How fast you recover will greatly be up to you. When you complete your physiotherapy treatment protocol, you should feel like you have recovered fully and that you are ready to return to your sport.

Remember, that even if your doctor has suggested surgery, you don’t have to wait until after your procedure to start physiotherapy treatment. Prehabilitation ensures that you are strong before surgery and can dramatically shorten your recovery after surgery.

Other forms of treatment

  • Your doctor might prescribe anti-inflammatory medication or give you a cortisone injection to decrease the inflammation and pain in your shoulder. Both of these medications will give you temporary relief. However, it will not be the solution to your problem. Once the effect of the medication wears off and you try to get back to working or exercising, your pain could simply return.
  • Getting your shoulder or neck ‘aligned’ or ‘clicked’ in the hopes of improving the pain will not improve the condition of your AC joint. It could even worsen or trigger an increased inflammatory response.
  • A biokineticist will be able to help you in the final stages of your rehabilitation programme or to get you back to actively training for your sport.
  • Wearing a sling could be useful initially, if your pain is severe. However, the sling puts your arm in an awkward position that interferes with normal movements, so it won’t be a permanent solution. In fact, your shoulder muscles will become weaker when you wear a sling.
  • Stretching your arm and your shoulder might ease some of your pain, but forcing your shoulder into painful positions in the hopes of stretching the pain away, could actually worsen your inflammation and pain.

Is surgery an option after an AC joint injury?

The good news is that the majority of grade 1, 2 and 3 (separation) injuries do not need surgery. If you have an AC joint dislocation or fracture (grade 4 – 6 injuries), then you would have to be referred to an orthopaedic surgeon. Then, the surgeon can decide what needs to be done. Make sure you have the necessary information about the risks, expenses and recovery time associated with AC joint surgery.

Whilst recovering from surgery, you will probably have to wear a sling for 2-6 weeks (depending on the procedure that was done). During this time, it is extremely important to comply to your rehabilitation process. Physiotherapy after shoulder surgery is vital to get you back to top form.

Even if you don’t need surgery, you will need to address the associated muscle weakness and problematic movement patterns after an AC joint injury. This can be done through physiotherapeutic conservative treatment and exercise.

What else could it be?

  • Rotator Cuff Muscle Strain – An injury to the rotator cuff muscles around your shoulder that causes a tear in the muscle tissue. Usually due to overuse, lifting something too heavy or forceful throwing.
  • AC joint arthritis – You’ll experience pain and stiffness of your shoulder that feels especially worse with cold weather and when you get up in the mornings. Also known as AC joint osteoarthritis.
  • Shoulder labrum injuries – Pain in the shoulder that includes ‘clicking’ or ‘popping’ noises or your shoulder feeling stuck in one position.  Also known as SLAP lesions.
  • Bicep tendonitis or tear – Inflammation and injury of the bicep muscle or tendon attachment to the front of the shoulder. Pain when lifting your arm up in front of you.
  • Frozen shoulder – It can also be known as adhesive capsulitis and it leads to extremely limited shoulder movement, stiffness and pain.
  • Shoulder impingement – Sharp shoulder pain specifically when lifting your arm up sideways. Often feels better when you rest.

Also known as

  • AC joint injuries
  • Acromioclavicular joint pain
  • AC joint pain
  • Shoulder pain
  • Dislocation of AC joint
  • Fracture of AC joint