Most leg pain called sciatica gets attributed to a bulging disc, and a good deal of the time that is
wrong. When the spine has been imaged and treated and the leg still hurts, the piriformis is one of the
structures that has to be tested rather than assumed — and testing it means placing medication
inside a muscle nobody can feel from the outside.
Piriformis syndrome is estimated to account for somewhere between 0.3% and 6% of all causes of low back and
upper posterior thigh pain, which on a base of roughly 40 million new sciatic-type back pain cases a year in the
United States still works out to about 2.4 million new cases annually.1 It is a small slice of a very large
problem. The trouble is that the muscle sits four to eight centimeters deep in the buttock, directly against the
sciatic nerve, and there is no reliable way to know where a needle is once it disappears under the skin.
So we look. What follows is an actual fluoroscopic sequence from a left piriformis injection performed at the
Woodson Road office, in the order the frames were taken. Nothing here is a diagram or a stock illustration.
Why this muscle cannot be injected by feel
Two facts make landmark-only injection of the piriformis a poor idea. The first is depth: unlike a trigger point
in the trapezius, you cannot palpate the piriformis belly through the gluteus maximus with any precision. The
second is what it is lying against. The sciatic nerve exits the pelvis through the greater sciatic notch immediately
adjacent to the muscle, and in a substantial minority of people it runs through the muscle rather than under it.
The StatPearls review of piriformis injection puts the consequence plainly: inadvertent nerve irritation or
injury remains an important procedural risk, particularly when needle localization is inaccurate, and
fluoroscopic or ultrasound guidance improves needle placement and may reduce the risk of injury to adjacent
structures.1 That is the entire argument for imaging, and it is not a marketing argument.
Both fluoroscopy and ultrasound are used here for this injection. Where fluoroscopy is available we
prefer it, for one specific reason that the images below make obvious: contrast shows it better. Ultrasound
shows you a needle. Contrast under fluoroscopy shows you where the medication is going to go.
The sequence, frame by frame
1. The baseline view
This frame does no clinical work by itself. Its job is to establish the view that every subsequent image will be
read against, and to confirm the bony landmarks are where the anatomy says they should be before a needle is
introduced.
2. The needle advancing
3. The tip at target
Here is where a landmark-only technique would stop, because there is nothing further to check. The needle is
where the operator believes the muscle is. Whether that belief is correct is still unknown.
4. Contrast — the frame that actually proves something
Whether contrast is paired with fluoroscopy alone, with ultrasound, or with both is still an open
comparative question. The largest published look at it, a retrospective cohort of 78 patients and 109
procedures, found the greatest reduction in pain scores in the group done with fluoroscopy and ultrasound
together, with median procedure times of eight to eleven minutes across all three approaches.3 The
authors were careful to call for prospective trials before treating that as settled.
This is the difference between a needle that looks correctly placed and an injection that is correctly placed.
Contrast follows the path the drug will follow. If it had tracked into a fascial plane, run toward the sciatic
notch, or refused to spread at all, the needle would have been repositioned and a second contrast injection taken
— before a milligram of steroid or anesthetic went anywhere.
5. After the injection
What contrast adds that needle position does not
It is worth being precise about this, because “image-guided” gets used loosely. There are three distinct
questions during a piriformis injection, and they are not the same question:
- Where is the needle? Fluoroscopy answers this, continuously, in two dimensions.
- Where will the fluid go? Only contrast answers this. Needle position is a proxy, and a
mediocre one, because the tip can sit millimeters from the muscle and look identical on screen. - Is this muscle the pain generator? Neither one answers this. Only the patient’s response
over the following hours and days does.
What these images cannot tell you
A clean contrast pattern is a technical success, not a diagnostic one. The most current review of piriformis
syndrome is blunt about the underlying problem: there is no well-accepted test to confirm the presence of
piriformis syndrome, the sensitivity and specificity of the reported clinical signs are unclear, and in most cases
in the literature the diagnosis appears to describe a myofascial condition rather than a focal
neuropathy.2
The same review dispatches a piece of folklore worth retiring. It is often said that piriformis syndrome happens
in the people whose sciatic nerve pierces the muscle. The nerve does pierce the piriformis in roughly 16% of
healthy individuals — but that frequency is no different in people who have the syndrome, so the
relationship to that anatomic finding is unclear.2 An anatomic variant that is equally common in people with
and without the problem does not explain the problem.
Which is why the injection is deliberately positioned as a test as much as a treatment. It answers a question the
imaging cannot.
Radiation, stated plainly
The dose numbers are visible in the frames above because the C-arm displays them and we did not crop them out.
Across this sequence the cumulative readout moved from 26.4 mGy to 28.8 mGy. Fluoroscopy is used in short pulses to
verify position between movements, not held on continuously, and the total exposure for a case like this is modest.
It is a real exposure and it should be accounted for, not waved away — and it is also the reason the procedure
is done once, correctly, rather than repeated because nobody could confirm where the first one went.
Frequently asked questions
Does a piriformis injection hurt?
The skin and the track down to the muscle are numbed first with local anesthetic, so the part most people expect to be worst is brief. What patients tend to notice more is a deep pressure or a cramping ache as the injectate enters the muscle belly, which fades within a minute or two. No sedation is used, which means you are awake and able to tell us what you feel while the needle is being positioned. That feedback is useful, not incidental. Learn more: what actually happens during a piriformis injection.
Why is contrast used for a piriformis injection?
Contrast is the only thing in the room that shows where the fluid will actually go. A needle tip in the right place on an X-ray still tells you nothing about spread — the tip could sit in fat, in a fascial plane, or just outside the muscle, and the image would look identical. When contrast is injected first, it either takes the shape of the muscle belly or it does not, and that answer arrives before any medication is given. Learn more: the contrast frame in this image sequence.
Is fluoroscopy or ultrasound better for a piriformis injection?
We use both, and we prefer fluoroscopy when it is available, because the contrast shows it better. Under fluoroscopy a small volume of contrast is injected before any medication, and it takes the shape of the muscle belly — so you are looking at where the drug will actually spread, not just at where the needle tip appears to sit. Ultrasound shows the needle and the soft tissue in real time and adds no radiation, which makes it the right tool in some situations, but it does not produce that spread document. Published comparative data is thin: a 2022 retrospective cohort in Pain Physician of 78 patients and 109 procedures found the largest drop in pain scores in the group done with fluoroscopy and ultrasound together, and the authors called for prospective trials before treating that as settled. What the evidence supports consistently is that image guidance of some kind beats none. Learn more: how image-guided procedures are performed here.
If the images look perfect, does that mean the injection will work?
No, and this is the most important limit to understand. A textbook contrast pattern proves the medication reached the piriformis muscle. It does not prove the piriformis muscle is what is generating your pain. There is no imaging test and no blood test that confirms piriformis syndrome; the diagnosis is clinical, and the injection is part of how it gets tested rather than proof that it was right. Learn more: what a failed piriformis injection tells you.
To discuss your own case, request an appointment through the appointment request form, call (314) 481-5000, or text (314) 886-5902. You can review the full range of pain treatments, read about the pain management doctors in St. Louis, or find both offices on the locations page.
Sources
- Chang A, Ly N, Varacallo MA. “Piriformis Injection.” StatPearls. Treasure Island (FL): StatPearls Publishing; 2023. NCBI Bookshelf NBK448193
- Lo JK, Robinson LR. “Piriformis syndrome.” Handbook of Clinical Neurology. 2024;201:203–226. doi:10.1016/B978-0-323-90108-6.00002-8
- Martiszus B, Hua S, Christiansen S, Ramsey K, Zusmer E. “A Novel Piriformis Injection Technique Utilizing Combined Fluoroscopy and Ultrasound — A Pilot Study.” Pain Physician. 2022;25(2):E365–E374. PMID 35322992
Dr. Gurpreet Singh Padda, MD, MBA, MHP
