Shoulder Impingement or Instability? The Real Cause of Rotator Cuff Pain
THE PHYSIO CREW · SHOULDER SERIES: PART 2 OF 5
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Why impingement and rotator cuff tendinopathy so often turn out to be symptoms of shoulder instability, not standalone problems.
In part one of this series, we looked at shoulder instability and how it hides behind rehab that helps briefly, then stalls. This time we're looking at what happens next: the diagnoses that instability so often gets mistaken for.
If you've been told you have shoulder impingement, rotator cuff tendinopathy, or a labral irritation, and treatment has chipped away at the pain without ever really finishing the job, this article is for you. These diagnoses are real and common. But very often, they're the downstream result of instability that nobody looked for.
Two Diagnoses, One Root Cause: Impingement, Tendinopathy and Shoulder Instability
Impingement and rotator cuff tendinopathy are two of the most commonly given shoulder diagnoses in general practice and physio clinics alike. Both describe the same basic picture: soft tissue in the shoulder getting compressed, irritated, or overloaded, usually somewhere near the top or front of the joint.
What often gets left out of the conversation is why that tissue is getting compressed or overloaded in the first place. In a genuinely stable shoulder, the ball of the joint stays well centred in the socket through movement. In a shoulder with underlying instability, the ball drifts more than it should, especially overhead or under load. That extra movement narrows the space available for the rotator cuff tendons and surrounding structures, and something has to give.
Treat the tendon without addressing the drift causing the compression, and you're treating the smoke while the fire keeps burning underneath it.
How Shoulder Instability Shows Up in the Clinic
This pattern is common enough that we see a fairly consistent story from people coming in with a prior impingement or cuff diagnosis:
Pain settles with rest, anti-inflammatories, or a cortisone injection, then returns once training resumes
A round of rotator cuff strengthening helps for a few weeks, then plateaus at the same point every time
Pain location shifts slightly over time: front of the shoulder, then the side, then deep inside the joint
Symptoms are worse in specific positions, usually overhead, behind the back, or at end range, rather than being constant
There's a history of a previous dislocation, subluxation, or a shoulder that was always "a bit loose," even if it was never flagged as relevant
None of these on their own confirm instability is the real driver. Together, especially the plateau pattern, they're a strong signal that the tendon or bursa is reacting to a control problem rather than being the primary issue.
Why Imaging Doesn't Settle Rotator Cuff Tendinopathy or Impingement
A scan showing tendinopathy, bursitis, or mild impingement changes is often taken as the full explanation, and treatment stops there. But imaging tells you what's irritated, not why it's irritated. Two shoulders can have near identical scan findings, one from years of poor scapular control and joint laxity, the other from a single overuse spike in an otherwise well controlled shoulder. They need different treatment plans, and a scan alone won't tell you which one you're looking at.
This is exactly why our assessment doesn't stop at confirming a tendon is irritated. We test how the joint behaves through movement, how well the shoulder blade controls the humeral head, and whether there's underlying laxity that's setting the tendon up to keep getting compressed.
What Changes When Instability Is the Real Driver of Your Shoulder Pain
Once instability is identified as the underlying cause, the treatment plan shifts in a few important ways:
Rotator cuff and scapular strengthening is sequenced around control and positioning, not just loaded for strength alone
Anti-inflammatory strategies (rest, load management, injections where appropriate) are used to calm the tissue down, not as the finishing move
Movement retraining targets the specific positions where the joint drifts, rather than generic range of motion work
Return to sport or training is staged around demonstrated control, not just pain levels settling
This is usually a longer process than a standard tendinopathy protocol. It's also the difference between a shoulder that feels fine for a few months and one that actually holds up.
A Few Things Worth Unlearning About Rotator Cuff Weakness and Wear and Tear
“I had a cortisone injection and it worked, so it must have been inflammation.”
Cortisone reduces inflammation regardless of what's causing it. Relief confirms there was inflammation present, not that inflammation was the whole story.
“My rotator cuff is just weak.”
Weakness and poor control often look identical on the outside. A shoulder can test reasonably strong in isolation and still lack the control to keep the joint centred under real load.
“It's just wear and tear from age or training volume.”
Volume and age can certainly contribute, but they're rarely the full picture on their own. Two people with similar training histories can have very different outcomes depending on how well their shoulder controls itself.
A Quick Self-Check for Shoulder Instability (Not a Diagnosis)
If you've been treated for impingement or tendinopathy before and it hasn't fully stuck, ask yourself:
Has treatment ever helped for a few weeks, then stopped making a difference at the same point?
Does the pain move around slightly rather than staying in one fixed spot?
Have you ever had a shoulder dislocation or subluxation, even one that felt unrelated at the time?
Does the pain show up mainly in specific positions rather than all the time?
Two or more of these, and it's worth having the underlying control of the joint properly assessed rather than repeating the same tendon-focused program.
Frequently Asked Questions About Shoulder Impingement and Instability
What is the difference between shoulder impingement and shoulder instability?
Impingement describes soft tissue being compressed within the shoulder joint, most often the rotator cuff tendons or the bursa. Instability describes a joint that doesn't stay well centred in its socket during movement. The two often occur together, since instability lets the joint drift into positions that compress the tendons.
Can rotator cuff tendinopathy be caused by instability?
Yes. Poor joint control can let the humeral head move more than it should, especially overhead or under load. This narrows the space available to the rotator cuff tendons, causing them to become irritated or overloaded, which is diagnosed as tendinopathy.
Why does my shoulder pain keep returning after treatment?
If treatment addresses only the irritated tendon and not the underlying control problem, relief is usually temporary. Once training or loading resumes, the same compression returns, and so does the pain.
Can imaging show whether instability is the cause of my shoulder pain?
Imaging shows what tissue is irritated, not why. Two shoulders with identical scan results can have different underlying causes, so instability needs to be assessed through movement testing rather than imaging alone.
How is shoulder instability assessed at The Physio Crew?
Assessment goes beyond confirming a tendon is irritated. It includes testing how the joint moves, how well the shoulder blade controls the humeral head, and whether underlying laxity is present that continues to set the tendon up for compression.
Where to From Here
If you've been treated for shoulder impingement or rotator cuff tendinopathy before and it never quite held, the tendon may not be where the story starts. It's worth getting the actual driver identified rather than going through another round of the same exercises.
In the next part of this series, we'll look at how the shoulder blade itself, not just the ball and socket, plays a bigger role in shoulder pain than most rehab programs give it credit for.
Shoulder Pain That Keeps Coming Back?
Book a proper assessment at our Tullamarine, Carlton, or Keilor Downs clinic and get a clear answer, not another generic exercise sheet.