Acromio-Clavicular Joint

The acromio-clavicular joint (ACJ) is the lumpy bit you can feel on the top of your shoulder. In some people it can be very prominent but in others it may be pretty flat. This is the point where the clavicle (collarbone) links with the acromion (the top part of the shoulder blade). It is quite a small joint but an awful lot of force has to go across it every time you load up your arm/shoulder and especially when you are doing something like pushing all your weight through it whether that is doing a press-up or pushing yourself out of a bath.

In fact it is probably too small for what it is expected to do and therefore it does have a tendency to wear out. It can become inflamed and eventually arthritic and those are causes of shoulder pain.

It is also prone to give way when a more acute force goes through it – such as a fall from a bicycle or on a ski-slope or playing collision sports like rugby.

Let’s start with the acute ACJ injuries.


I fell a few days ago and the casualty doctor said I had a ‘sprung’ shoulder. Is that the ACJ?

Yes it is. When the ‘A’ bit comes away from the ‘C’ bit that can be called a sprung shoulder or an ACJ disruption or an ACJ dislocation – all meaning the same thing.

The right ACJ has dislocated in a fall – see the step?

They said I had a grade 5 and I am booked into the fracture clinic because I might need an operation. How bad is a 5?

A 5 is pretty bad and, yes, you almost certain need an operation because the shoulder can’t heal itself when there is that amount of damage.

X-ray of a grade V ACJ dislocation – see the gap?

What has been damaged? I can see the collarbone sticking up a mile. Is there other damage?

Afraid so and, oddly enough, the bit you can see is the bit we worry about the least. What you see is actually the arm dropping down rather than the collarbone sticking up and this tells me that some pretty important ligaments have been torn. The main strength of the ACJ comes from 2 very strong ligaments that run from the underside of the clavicle and attach to the top of the scapula. Where the acromion joins the clavicle is not strong at all and, as you will read later, I frequently remove that joint for painful arthritis. So it’s those ligaments that are the key.

The ligaments between the clavicle and the scapula have torn as the ACJ dislocated.

So you will fix those ligaments and line up the ACJ again?

No. They are very difficult and very dangerous to get to with a lot of important plumbing and wiring running close to them. So I don’t repair them directly. Instead I do an operation that indirectly brings them together and holds the ACJ in a stable position while those ligaments bond back together by natural means.

Hook Plate used to ‘hook’ under the acromion and stabilse the ACJ

I was told I just had a sprain of my ACJ. Will that get better?

There are 6 grades of ACJ disruption and grades 1 and 2 are ‘sprains’. Those important ligaments are intact and not even stretched but the capsule (the lining) around the ACJ itself has been damaged. So there may be no movement at the ACJ or just a little bit and it will get better.

Is there any treatment?

You may be more comfortable in a sling for a week or two and you should be careful what you do with the arm. Take anti-inflamatories regularly and adapt around the painful shoulder; sleep on your back rather than your side and cuddle your partner with the good arm. It is worth getting some therapy on the shoulder after a couple of weeks as this can help with pain relief and help you recover movement, control and strength.

How long will that take?

It could be as short as 6 weeks for minor injuries but 3 months and longer for the worst of the grade 2s. You can increase your activities as pain allows but you do need to be patient.

You’ve covered grades 1, 2 and 5. What about 3, 4 and 6?

You don’t need to worry about 4 and 6 because they are as rare as hens teeth. The grade 3 though, that’s a controversial one.

Why? Surely it either needs an operation or not?

That is true but the problem is that, at the time, it isn’t always clear which ones do and which ones don’t and that can be a hard decision to make. If I think you have a grade 3 there will be a few factors to think about including how active you are, how active you want to be and what the shoulder is like by the time I see you.

Is there a time limit on operating then?

There are two time relevant factors. Yes – if I don’t see you until 3 weeks after your injury then we have missed the boat for doing the Hook Plate and would have to treat it as a chronic case with a different operation.

But many grade 3 shoulders are starting to feel much better after 2 weeks and you may be out of the sling and starting to move the arm quite well. So it might seem a bit odd if I tell you that you need an operation on it.

What happens if, after going thought the options, I decide not to have an operation because my shoulder is getting better?

With any luck you will be fine. Your shoulder will make a complete recovery over 3 to 6 months and you will get back to doing all the things you wanted to.

And if it doesn’t go on getting better? You said after 3 weeks I’d missed the Hook Plate boat?

Thankfully there is a different boat that is an excellent option in the chronic case. So we haven’t blown your chances of a great shoulders if we made the wrong decision early on believing that it was going to go on getting better.

So sometimes you can’t tell?

That’s right. Sometimes we make the wrong call. That could mean we decide to operate on a shoulder that would have got better by itself over time or we leave one alone because it seems to be getting better but doesn’t recover or gets worse again.

I believe that the grade 3s that don’t fully recover were probably really grade 5s originally but had started to heal up quickly so appeared less severe than they actually were

I did my ACJ 2 years ago! I wasn’t offered an operation then and my shoulder is wobbly and painful and limiting what I can do.  Have you got an answer for that?

Yes I do. Your shoulder is definitely a chronic case (remember we said after about 3 weeks it becomes chronic) so I can’t use the Hook Plate alone. Even if I was able to get the tendon ends together they will have become so scarred up and healed over that they won’t join back up with each other anyway.

So in this situation I have to use an artificial ligament plus the Hook Plate. The ligament is a loop of material that is inserted around the coracoid process (part of the shoulder blade), then tensioned to bring the A and C parts back into alignement  and finally the ligament ends are attached to the clavicle with screws. As ‘belt and braces’ I also put in a Hook Plate to give primary rigidity to the re-aligned joint while the ligament bonds in over 3 months or so and then the plate can come out.

It’s  much the same rehab programme as for the Hook Plate but the artificial ligament stays in for good

So, if you fall on the shoulder the poor old ACJ may well be damaged and depending on how much damage has been done you may need an operation to stabilise the joint again.

I haven’t fallen on my shoulder but that lumpy bit on the top is very painful. What’s going on there?

This is the second way in which the ACJ can cause problems. It gets irritated and inflamed and eventually becomes arthritic with overuse or abuse and sometimes as a long-term complication after a grade 1 or 2 injury years before.

X-ray showing arthritis of the ACJ – no gap between the bones and osteophytes under the clavicle.

I think this might have started in the gym when I was doing weights.

That is very common. That and other overhead activities or sports. It can seem like it comes in very quickly but the damage has probably been going on for a lot longer than you’ve been aware of it. Quite often we will find some arthritis on an x-ray of your ACJ and that didn’t just suddenly appear. It will have been building up for years and then something tips it over the edge and it becomes painful.

I’ve done the usual stuff – rested it, taken Nurofen and had a few sessions with my physio but it is getting worse. I can’t sleep on that side and it’s a real pain. Can you help?

Of course. An inflamed ACJ is very common and I can make it better. Once I’ve heard your story and had a chance to examine you I should come up with a diagnosis. The ACJ causes pain in two ways. When it is compressed the two red raw sides of the joint rub against each other (pain sleeping on it, pushing open a heavy door or pushing out of a bath for example) and that’s the first type of pain. Any joint that is inflamed or arthritic also swells and expands. Now, it doesn’t matter too much if it expands upwards because that doesn’t interfere with anything. But as it expands downwards, into the shoulder, so the rotator cuff tendons can catch and rub on it giving you classic Impingement type pain. But without having a hook or spur like discussed in the rotator cuff section.

I will probably do an x-ray to look at the state of the joint and see if there is any arthritis and I may do a scan as well particularly if there is any weakness in it (especially if you had a fall) just to make sure the rotator cuff is intact.

Now I have the diagnosis – an inflamed and/or arthritic ACJ – I can discuss the treatment options. If you’ve tried rest and Nurofen then the next stage is a steroid injection into the joint to reduce the inflammation and get rid of your pain.

Steroid injections – not so sure about that.

Go to the steroid injection section and see what I have to say about that and I think you will probably decide to go ahead with it.

Okay, I’m back and you’ve convinced me. Let’s do the injection.

Good call. I have had this done myself about 4 years ago and my shoulder has been fine since then so I know what it’s like!

About a week after the injection you need to get back to your usual activities and see if it holds up to them.

I guess it’s an operation if the pain comes back then?

It is if it comes back within a few weeks. If you get 6 months or more from it then it’s worth one more before we go for the surgery unless you have an arthritic ACJ in which case it is surgery.

And what’s the operation?

I need to remove the ACJ! That is done as an open operation under general anaesthetic. I make an incision about 4 cms long over the ACJ, move the muscle out of the way and saw off the lateral 4/5mm of the clavicle creating a gap. That gap fills up with scar tissue which acts like a shock absorber between the two bone ends. The cut is stitched closed and you wear a sling for a couple of days.

What happens to that big gap?

It fills up with scar tissue. Initially that is quite soft and spongy so that when you lean or sleep on the shoulder, the two raw ends of the joint will push against each other. As the weeks and months go by the scar matures and becomes solid so it prevents the two surfaces coming into contact and so all your pain goes away.

What’s the recovery like?

Very much the same as for the decompression operation but sleeping all through the night comfortably could take 4 months or so.

The ACJ takes a bit of a hammering through it’s life and often isn’t really up to the job so it gets inflamed and can become arthritic. It is a common problem but I do have very good ways of getting rid of the pain. And if the injection doesn’t do the trick then the operation will.