Sometimes There's Physically Not Enough Room In The Shoulder
You've probably done the physio. You've done the exercises, and your shoulder is exactly the same. If that's you, this article might be your answer — because sometimes there is physically not enough room in the shoulder, an actual bit of bone causing all your problems. And you cannot exercise a bone out of the way.
This is the smaller group. Most shoulders aren't like this. But if you've done everything right and got absolutely nowhere, this is the one you need.
My name is Joe, an ex-professional football head physio and multi-clinic owner here in the UK. As always, this is a guide to help you understand what's going on — it's not a diagnosis.
There are two ways impingement happens. Structural, where something is physically taking up room within the subacromial space. And functional, where the shoulder isn't working properly, and that closes the space down itself. This article is about the structural side.
The Shape Of Your Acromion
Let's start with the acromion. It's the bit of bone that sits over the top of the shoulder like a roof, and your tendons run straight underneath it.
Here's the thing: that bone isn't the same shape in everybody. In some people it's flat, in some it's gently curved, and in some it hooks down at the front. If yours hooks down, there's simply less room underneath for the tendons to run through. You're starting with a much tighter space than the next person, before anything else has even gone wrong. That's why two people can do exactly the same training for exactly the same number of years, and one gets an impingement and the other doesn't.
One thing worth saying: there's a fair bit of debate about whether people are born with that hook shape, or whether it develops over time from years of pulling and loading. Honestly, for you, it doesn't matter. What matters is whether it's there now.
Bone Spurs
The second is bone spurs, or osteophytes — little extra bits of bone that grow over time, usually where there's been wear and tear or repeated stress over a prolonged period. They can form on the underside of the acromion, growing directly down into the space where the tendons are trying to run.
This is generally an age thing — a gradual, degenerative change, not something that happens overnight. It means the space slowly gets tighter over the years, and eventually the tendons start complaining. That's exactly why some people tell me their shoulder was fine for fifty-plus years, and then it just started out of nowhere, with no injury and no change in what they were doing. Nothing changed in what they were doing — something changed in that space.
The AC Joint
The third is the AC joint — the acromioclavicular joint, at the end of your collarbone, right on top of the shoulder. You can feel it; it's that little lump on top of the shoulder.
That joint sits directly above the subacromial space, directly above where the tendons run, and it's a joint that takes a lot of load over a lifetime. So it commonly gets arthritic, especially in people who've done heavy manual work, lifted a lot of weights, had a knock to it years ago, or played sports like rugby. When it wears, it can form bone around the edges, same as any arthritic joint — and the problem is the direction some of those bony spurs grow, which tends to be downwards into the space underneath. So if you've got an arthritic joint above, you can end up with extra bits of bone dropping down into the gap the tendons need. You get two problems at once: a sore AC joint, and less space for the rotator cuff. That's a really common combination for people over about the age of 50, particularly if they've done a lot of physical work in their lifetime.
Calcific Tendinitis (And Two Rarer Causes)
The fourth is calcific tendinitis. This is a bit different, because the problem isn't in the bone — it's in the tendon itself. Calcium deposits form in the cuff tendon, an actual gritty calcium sitting inside the tendon, and that does two things: it takes up space, making the gap effectively smaller, and when it's in an active phase, it's incredibly painful. I'll be honest with you — this is one of the most painful shoulder presentations I see in clinic, alongside frozen shoulder. People can be in genuine agony with it, unable to sleep and unable to move.
The reassuring bit is these deposits often break down and reabsorb on their own over time, and there are a lot of things that can be done to help it along if it's really severe — they respond really, really well to radial shockwave. It's worth knowing about, because if you've got sudden, severe shoulder pain that's out of proportion to anything you've done, that's one to get looked at as soon as possible — it often shows up clearly on a simple X-ray.
Two rarer causes are worth a quick mention too. If you've broken your shoulder or collarbone in the past and it's healed slightly out of position, that can change the shape of the space or how much room there is. And a smaller number of people have an acromion that never quite fused properly when they were growing, leaving a bit of movement in that joint that shouldn't be there. Both are less common, but they do exist.
Why Structural Findings Don't Automatically Explain Your Pain
Here's the real balance I want to give you on all this, because it matters: structural findings don't automatically explain your pain. You can scan loads of people with hooked acromions, bony spurs, and arthritic AC joints who have no shoulder pain whatsoever. They're walking around fine, with no idea any of it is there. So finding a spur on a scan doesn't mean the spur is the problem, or that it needs to be dealt with.
What you tend to find is it's the combination. The space was already a bit tight structurally, then the functional stuff piled on top — tight muscles, a weak cuff, a shoulder blade that's not doing its job — and it's that combination that tips things over into pain.
Which is why, even when there's something structural, I'd still do the work on the mechanics first. You can't exercise a bone spur away, but you can absolutely change how much room the shoulder has to work with, and often that's enough to get people out of pain. If it isn't — if you've had a genuine go at rehab and nothing's shifted — that's when the structural side becomes relevant, and an operation to open that space up might have a place. But that's the order: deal with the mechanics first, and surgery only if everything else hasn't worked.
This article is a guide to help you understand what's going on with your shoulder. It's not a diagnosis. If you have sudden, severe shoulder pain out of proportion to any injury, or you've had a proper course of rehab with no improvement, get it properly assessed and imaged by a professional.
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