Shoulder pain has a talent for showing up at the worst times. You reach for something overhead, roll onto the wrong side at night, and there it is. One of the most common culprits is shoulder impingement, which is roughly what it sounds like: something in your shoulder is getting pinched.
What's actually getting pinched
Your shoulder has a narrow channel at the top called the subacromial space. The roof is the acromion, a bony projection off your shoulder blade. The floor is the head of your upper arm bone. Running through this channel are the tendons of your rotator cuff (mainly the supraspinatus tendon) and the subacromial bursa, a small fluid-filled sac that reduces friction between the tendon and bone.
When you lift your arm overhead, these structures slide through that space. If the space is too narrow, the tendon and bursa get compressed against the acromion. Enough repetition of that, and you get irritation, inflammation, and pain.
The shape of your acromion matters more than most people expect. Surgeons classify them as Type I (flat), Type II (curved), or Type III (hooked). A Type III creates a naturally tight space, which means some people are predisposed to impingement before they've even done anything particularly stressful. Bone spurs on the underside of the acromion accumulate over time and narrow things further.
Rotator cuff, bursitis, and the AC joint
"Impingement" tends to get used as a catch-all term, but it usually coexists with other things going on.
The supraspinatus tendon is particularly vulnerable. Chronic compression leads to tendinopathy, and if that's left unaddressed long enough, the tendon frays. Some of those partial tears progress to full tears. Impingement is often the mechanism that starts the chain.
The bursa has its own problem. When it gets repeatedly compressed, it becomes inflamed and swollen, which takes up more of an already tight space. Bursitis worsens the impingement, impingement worsens the bursitis. Once that cycle starts, it can be hard to break with rest alone.
The AC joint, where the acromion meets the collarbone, is technically a separate structure, but arthritis there can grow bone spurs that reach into the subacromial space from above. AC joint pain also tends to radiate to similar spots as subacromial impingement, which can muddy the initial diagnosis.
Who gets it
Most commonly people in their 40s through 60s, partly because tendons and bone structures change over decades in ways that shrink available space.
Overhead work is the other driver. Painters, electricians, carpenters, and plumbers spend careers in exactly the positions that stress this anatomy. Swimmers, baseball pitchers, volleyball players, and anyone who overhead presses regularly are also frequent visitors to orthopedic offices with this complaint. The damage usually accumulates long before symptoms appear, which is part of why it feels sudden when it arrives.
Born with a Type II or Type III acromion? You carry some baseline risk regardless of activity level.
Posture is a real factor too. Rounded shoulders push the acromion forward, shrinking the available space. Weak rotator cuff muscles or poor shoulder blade control means the arm doesn't track cleanly during elevation, and the tendon ends up rubbing the acromion on every rep.
What it feels like
The signature symptom is the painful arc. Lift your arm out to the side and somewhere between 60 and 120 degrees of elevation you hit pain. Keep going past 120 and it often eases off, because the compressed structures have passed through the narrowest point.
Overhead activities are reliably painful. Reaching for a high shelf, putting on a jacket, raising your arm to brush your hair. There's usually a deep ache in the front or side of the shoulder that radiates down the outer arm, present even at rest but sharper with movement.
Night pain is what tends to finally push people to see someone. Lying on the affected shoulder compresses the irritated tissue, and many people describe waking up multiple times because of it.
Diagnosis
A doctor will take your history, test range of motion and rotator cuff strength, and use specific provocative tests. The Hawkins-Kennedy and Neer's tests move your arm into positions that compress the subacromial space. If they reproduce your pain, that's a reasonable indicator of where the problem is.
X-rays show bone, not soft tissue, but they're still useful for seeing acromion shape, bone spur formation, and AC joint arthritis. Ultrasound can show tendon changes and bursal swelling in real time, though the quality is operator-dependent. MRI gives the clearest picture of the tendons, bursa, and cartilage, and it's what surgeons want before recommending an operation.
Sometimes a diagnostic injection of local anesthetic into the subacromial space is used to confirm the pain location. Significant relief from the injection points toward the subacromial space as the source.
Treatment
Most cases resolve without surgery, though it takes genuine commitment to the process.
Start by modifying activity. Not stopping everything, but identifying and reducing whatever is most aggravating, usually repetitive overhead movement. Ibuprofen or naproxen help with acute pain but don't address the underlying problem.
Physical therapy is where the actual improvement happens. A therapist will start with range of motion work, typically pendulum exercises and posterior capsule stretches, before adding rotator cuff strengthening. External rotation with a resistance band targets the infraspinatus and teres minor. Scapular stabilization work, things like wall slides, prone "Y" and "T" raises, and scapular retractions, gets overlooked but matters a lot. The shoulder blade needs to move correctly for the subacromial space to open up during arm elevation. If that movement is off, you can strengthen your rotator cuff endlessly and still pinch the tendon on every rep.
A standard PT course runs 6 to 12 weeks with a consistent home program between sessions. The people who get better fastest are the ones who treat the home exercises as non-negotiable rather than optional.
If pain is too severe to engage meaningfully with PT, a subacromial corticosteroid injection can break the cycle. It reduces inflammation quickly and gives you a window to do the rehab work. The effects are temporary, lasting weeks to a few months, so it works best as a bridge to therapy rather than a solution on its own. Most surgeons cap it at 2 to 3 injections per year because repeated cortisone can degrade tendon tissue.
Surgery
Surgery is for the minority who've done genuine PT for 3 to 6 months, tried injections, and are still in significant pain that limits daily function.
The standard procedure is arthroscopic subacromial decompression. Through small incisions, the surgeon removes the inflamed bursa, shaves the underside of the acromion to widen the space, and cleans up any tendon fraying. It takes about an hour and is done outpatient.
Something worth knowing before agreeing to this: a Finnish randomized controlled trial published in the BMJ in 2018 found that sham surgery (a diagnostic arthroscopy with no actual decompression) produced outcomes similar to real decompression at both two and five years. The study generated real controversy, and plenty of orthopedic surgeons dispute its conclusions. But it does mean this surgery deserves harder questions than it sometimes gets. If imaging clearly shows bone spurs impinging the tendon, the mechanical case for decompression is stronger. If the structural findings are subtle or absent, a second opinion before scheduling surgery is a reasonable idea.
Recovery involves a sling for comfort for a few weeks, then PT starting almost immediately. Getting back to overhead sports or physical labor typically takes 3 to 6 months.
When to get evaluated
If your shoulder has been bothering you for more than a few weeks, especially with night pain or significant limits on what you can do, it's worth getting looked at. Starting PT before tendons start breaking down gives you the best shot at avoiding surgery entirely. Most people who are diligent with a structured PT program avoid the operating room. For those who don't get there with conservative care alone, decompression has a reasonable track record, as long as the structural findings justify it.
