Acromion: Shoulder Anatomy, Injuries, Pain, and How to Fix It

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The shoulder is an amazing and complicated part of the body that is made up of many different parts. In fact, some health professionals argue that the shoulder is the most complicated joint of the body.

So, instead of trying to understand everything at once, we’re going to focus on one part of this elaborate puzzle: the acromion.

The acromion, AKA the acromion process, is a part of the shoulder blade, which meets with your clavicle, or “collar-bone.”

At first glance, it doesn’t seem so important — why does a small projection of bone even matter in a joint that is already so complicated? 

Well, it turns out that the acromion not only acts as the connecting point of your shoulder to the rest of your body, but it also hosts the attachment sites of many different ligaments and tendons — which your shoulder would essentially fall off without.

Let’s explore what the acromion exactly is, how it may relate to your shoulder pain, and how to treat any injuries surrounding it.

Anatomy 101

As I mentioned, the acromion comes from the shoulder blade. It begins at the upper-back side and works its way upwards and to the outside of your shoulder. 

Essentially, it’s a continuation of the scapular spine, which is the ridge at the back of your shoulder blade. If you look at the acromion closely, it resembles a hook that reaches over the front of your shoulder.
Some people call it the cap of the shoulder, because it sits on top of it like a hat.

Acromioclavicular Joint

If you follow your clavicle outwards, you can feel where it connects to your acromion to create the acromioclavicular joint (AKA the AC joint).  

This joint acts as a bony bridge from your arm to the rest of your body.

The AC joint allows your shoulder blade to move more freely, as the connection between the clavicle and acromion has a degree of movement through gliding. 

This gliding of the joint is minimal, since it also needs to be strong and stable to fulfill its other role: transmitting forces from the arm to the collar bone. 

If you injure your acromion, this is usually where it happens. The joint is more susceptible to injury than the actual bone itself, but we’ll get into that later.

Ligament Attachments

Ligaments differ from tendons because they connect bone-to-bone, whereas tendons connect muscle-to-bone. 

The acromion has a couple of different ligament attachments, all serving an important purpose in:

• keeping your shoulder held together
• joint structure
• preventing injuries

They come in two different sets: the acromioclavicular ligament and the coracoacromial ligament — with one additional ligament!

Let’s take a look.

Acromioclavicular Ligament

This short ligament attaches from the clavicle to the acromion, reinforcing the joint capsule of the AC joint. Its main purpose is to prevent the acromion from sliding backwards and to resist twisting.

Coracoacromial Ligament

The coracoacromial ligament is shaped triangularly, and attaches from the acromion to the coracoid process, which is another part of the shoulder blade. 

Its main purpose is to protect the humeral head, working together with the acromion and the coracoid process to create an arch over it.

Coracoclavicular Ligament

Although this ligament doesn’t attach directly to the acromion, it’s still really important to the AC joint. 

The coracoclavicular ligament attaches from the coracoid process up to the clavicle, and resists upward forces where the collar bone tries to separate from the shoulder in a vertical direction. 

As you can tell, if this ligament is compromised and the clavicle can separate upwards, the acromion is at risk of injury as well — this is one of the reasons that makes the shoulder so complicated, everything is connected either directly or indirectly.

Muscle/Tendon Attachments

There are two major muscles that attach to the acromion: the deltoid and the trapezius (AKA traps). 

These are two big players when it comes to upper-body musculature, both from aesthetic and functional perspectives — think of broad-shouldered athletes who have highly developed shoulders and traps. Those muscles are usually for more than just show. 

Your deltoid muscles start across the acromion, clavicle, and the spine of the scapula, and then attach to the deltoid tuberosity of the humerus. They mainly raise your arm forwards, backwards, and sideways.
Your traps start at the cervical and thoracic spine, with your upper traps attaching to the acromion, spine of scapula, and the last third of the clavicle. It mainly acts to “shrug” up your shoulders and stabilize your shoulder blade.

Other Important Structures

Now, there are a couple of muscles and tendons that don’t attach to the acromion, but we still want to be aware of them when understanding why pain and injuries may happen in the area. 

• The supraspinatus — this is one of your four rotator cuff muscles, and sits at the top of your shoulder blade. Its tendon runs underneath the acromion and the coracoacromial ligament, through a small space called the subacromial space
• The long-head biceps tendon — this tendon comes from one of the two heads of the biceps muscle and attaches to the front of the shoulder
• The subacromial bursa — a bursa is a fluid-filled sac that lies between bone and tendon, helping to reduce the friction when your tendons rub over bone
• The joint capsule — this is essentially a tissue that helps keep the AC joint together, but isn’t the strongest — which is where the ligaments come in to help strengthen it

Our article on shoulder injury prevention talks more about some of these structures and how to strengthen them, in order to minimize the risk of injury.

Injuries and Symptoms of Acromion Pain

Now that we understand the shoulder a bit better and see how different structures relate to the acromion, we can get a better grasp of how injuries happen. 

An injury to the acromion may happen when you fall on your outstretched hand or elbow, or through a direct impact to your shoulder.

You’d be correct in assuming that based on these mechanisms of injury, athletes are often at high risk — in fact, AC joint separation accounts for over 40% of all shoulder injuries in athletes!

However, that doesn’t mean that people who don’t play sports are completely safe— think of people slipping, falling down stairs, etc. 

Let’s dive into the different types of injuries that affect the acromion, and see if that pain you may be experiencing is related.

Sprains and Strains

The difference between a sprain and a strain is that sprains affect ligaments, and strains affect tendons/muscles. 

The tendons and ligaments around the acromion are small, so there’s not a ton of stretch to them. 

This means that a relatively small “forced stretch” could prove to be too much for these structures — think of it like pulling a rubber band too far. You might not completely snap it, but it definitely doesn’t like it.

This can happen in many different ways — like directly falling on your shoulder while skiing or getting bodychecked during a hockey game. 

If this stretch/force is strong enough, it can cause separation between the acromion and the clavicle. 

There are 5 different grades of separation (there are different models of grades out there, FYI):

• Grade 1: over-stretching of the joint capsule, with irritation to the surrounding ligaments. May show some swelling over the area.
• Grade 2: the joint capsule shows some tearing, and the ligaments are overstretched. Often creates a bump on the top of your shoulder.
• Grade 3: the joint capsule and the ligaments tear
• Grade 4: tearing, and the clavicle is pushed backwards due to the tears and impact of injury
• Grade 5: your clavicle tears through some of the muscle-covering (fascia) around it, leaving you with a large bump over the top of the AC joint.

Impingement

Impingement (in this case) happens when a structure in the subacromial space becomes compressed. 

The subacromial space shrinks as you lift your arm, and that can cause closing-down on the structures in there, resulting in irritation. 

Now, it’s agreed that this is a mechanism, and not necessarily a diagnosis — just because there is impingement going on doesn’t mean that’s the sole reason for why you’re feeling pain. 

Like I said, the shoulder is a complicated structure, and not everything is black-and-white. 

Regardless, this type of injury usually causes pain around the acromion, with swelling a possibility, and usually increases in pain as you lift your arm higher up.

Arthritis

Arthritis, more specifically osteoarthritis, is a condition where the cartilage in your joint wears down, and your bones become exposed and rub against one-another, causing inflammation. 

Yes, it’s as irritating as it sounds. 

Usually, this happens later on in life after 60 years, but there are cases where even 20-30 year-olds develop arthritis. 

Arthritis in the AC joint often happens with wear-and-tear — think of baseball and tennis players, or people that bench press often. 

You’ll usually struggle with stiffness, aching pain and soreness — especially after a long rest or longer periods of activity — and joint swelling.

Bursitis

Bursitis happens when a bursa becomes inflamed and irritated. In this case, we’re looking at the subacromial bursa. 

This bursa sits under the acromion process, and may get irritated with repetitive overhead movements, during which it tends to be the most compressed. It can also happen with direct impact, like when tripping and landing on your shoulder. 

Subacromial bursitis usually presents with pain in the shoulder — especially with movement — swelling, and tenderness to the touch.

Breaks and Fractures

This one usually happens less frequently than a separation would, and you’ll most likely know when you break a bone — it happens with a traumatic force, you have immediate sharp pain, you may hear a snap, and you have swelling and redness that doesn’t get better with time.

How To Fix Issues Surrounding the Acromion

Treating pain comes in many different forms, which means you may have several different options!

Splinting and Casting

Splinting or casting is usually only required if you have a fracture or a high-grade tear. The point of this is to immobilize and decrease the movement around the shoulder so that your bones, ligaments and/or tendons can heal properly.

Surgery

Surgery usually goes hand-in-hand with casting/splinting, where the injury has to be more severe to warrant going under the knife. 

Your doctor may recommend this route if you have a high-grade sprain, muscle tear, or bone fracture. 

Massage

Muscles can tighten around an injured joint or bone, and getting a massage can help loosen everything up and help relieve some pain. Alternatively, using a massage gun can do the trick, and is something you can do yourself!

Corticosteroid Injections

This is when your doctor injects your pain site with a steroid-medicine (AKA cortisone shots) that is designed to help relieve inflammation and pain. 
The cool thing about these is that they may provide relief for several months. That being said, abusing these can cause long-term issues such as degenerative changes and infections — that’s why these shots are limited to 3 to 4 times a year, max.

Exercises for the Acromion

Ah, the ever-proven and age-old method of dealing with pain.

Exercises can be used for all of the causes we talked about today, from minor irritations to full-blown ligament tears. 

Now, this may have to be used in conjunction with surgery, but you can never go wrong getting stronger and more mobile when dealing with injuries and pain. 

If you do have surgery around your acromion, your doctor will give you a protocol that they want you to follow. This may include a progression from isometric exercises all the way to sport-specific movements. 

If you’re struggling with low grade sprains, impingement, or arthritis, there are different ways you can go about this. 

You’ll want to start with upper body exercises that feel comfortable to do. That may mean that you need to start with a smaller range of motion or lighter weight than what you’re used to. 

For example, if you love bench pressing, but are getting a ton of pain from your AC joint sprain, begin with lighter weight and a smaller range of motion. Then, slowly increase your range until you are back to normal, followed by a gradual progression of weight.

In our Upper Body Workout with the Redge Fit article, you’ll learn a couple of exercises that you could start with.

The main principle is that you shouldn’t reproduce your symptoms — some discomfort may be okay, but once you push into pain you’re asking for trouble. 

It’s kind-of like scratching a scab open over-and-over — it won’t heal as fast, and you may re-injure yourself. Work within tolerance, and progress as able.

If you haven’t worked out before, check out our article on starting calisthenics, which uses bodyweight exercises that can be done anywhere, even as a beginner!

Recap

Let’s take a look at what we learned today:

• Acromion pain can come from many different things, including sprains, strains, fractures, impingement, bursitis, and arthritis
• There are many ways of dealing with pain, and they’re usually specific to the injury — for non-traumatic injuries, starting with a light upper-body exercise program that progressively gets harder is a great method
• The shoulder is a complex area of the body — don’t overthink it, just do what you can without aggravating your symptoms, and slowly take control of your body again

Understanding where to start, especially with exercise, can be a daunting task. The fact is, we’ve been in that position before, and we’d love to help you out. Book a free consultation session with us and we can discuss how to get you going, and provide you with a detailed plan to help you manage your pain and become stronger for good!