When leg pain does not come from a disc, it has to come from somewhere. That is the part of the sciatica
conversation that usually gets skipped: the lumbar MRI is read, a degenerative finding is offered as the
explanation, and if treatment aimed at the spine does not work, the case is filed as difficult rather than
reopened.
There is a defined list of structures that generate sciatica-like leg pain without a disc being involved, and
most of them live in the buttock. “Piriformis syndrome” is a satisfying label. It names a specific muscle, it explains why the buttock hurts and
the leg tingles, and it arrives with a stretch you can start that afternoon. The difficulty is that the deep
gluteal space contains several structures capable of producing an almost identical complaint, and the piriformis
is simply the one with the best-known name.
The umbrella term for the group is deep gluteal syndrome — compression of the sciatic or
pudendal nerve by non-discogenic pelvic causes. It includes piriformis syndrome, gemelli-obturator internus
syndrome, ischiofemoral impingement syndrome, and proximal hamstring syndrome, and the concept exists precisely
because the traditional piriformis-only model was too narrow to explain what clinicians were seeing.1
The four conditions inside the deep gluteal space
- Piriformis syndrome — the sciatic nerve irritated by the piriformis where the two cross
at the greater sciatic notch. - Gemelli–obturator internus syndrome — the same nerve, one layer lower, irritated by
the smaller external rotators sitting beneath the piriformis. - Ischiofemoral impingement — narrowing of the space between the ischium and the lesser
trochanter, with the quadratus femoris caught between them. - Proximal hamstring syndrome — tendinopathy or scarring at the ischial tuberosity, right
where the sciatic nerve passes.
All four produce posterior hip pain that radiates, all four are worse with sitting, and the review that
consolidated them notes that deep gluteal syndrome has often been undiagnosed or mistaken for other
conditions.1 Careful history, physical examination including provocation tests, electrodiagnostic study
where indicated, and imaging are what separate them — not the symptom description.
And then there is the hip joint
Before any of the deep gluteal diagnoses is entertained, the hip joint itself has to be accounted for, because
it is both more common and more treatable.
This is not a hypothetical failure mode. Hip osteoarthritis, femoroacetabular impingement, and avascular
necrosis all sit on the differential for posterior hip pain, and all of them are missed when the examination
begins and ends with palpating the buttock. The practical test is unglamorous: check hip range of motion, and
compare internal rotation side to side.
Why the spine gets the credit it does not always deserve
The reflex when leg pain appears is to image the lumbar spine, and that reflex is not wrong — a disc
herniation or foraminal stenosis is a more common cause of true radicular pain than anything in the buttock. The
problem is what happens next.
A lumbar MRI in an adult over forty will almost always find degenerative change. That finding is offered as the
explanation, the patient is routed toward the spine, and the deep gluteal space is never examined. When the epidural
does not help, the conclusion drawn is usually that the pain is difficult rather than that the target was
wrong.
The way out of that loop is to test the level the scan nominated rather than treat it on faith. A
selective nerve root block places
anesthetic at one specific root with contrast documenting containment, and answers whether that root is
carrying your pain. If it is, you have a target; if it is not, the
disc finding on the report was incidental and the buttock still
needs examining.
Electrodiagnostic testing is useful here, though for a narrower reason than most people expect. It can help
exclude other causes of the symptoms — a lumbar root lesion in particular — but there is no
well-accepted electrodiagnostic test that confirms piriformis syndrome.2 It rules out. It does not rule
in.
What is actually left to make the diagnosis with
Once the spine and the hip joint have been addressed, the diagnosis of piriformis syndrome rests on a
combination of history, tenderness over the muscle belly and the greater sciatic notch, provocative maneuvers
that load or stretch the piriformis, and the exclusion of everything else. The most current review states the
limitation directly: many clinical signs are reported for piriformis syndrome, but their sensitivity and
specificity are unclear, in part because there is no uniformly accepted case definition.2
That is an uncomfortable position to build a treatment plan on, and it is why a targeted, image-confirmed
injection carries diagnostic weight here that it would not carry in a joint where the diagnosis was already
secure. The response to a correctly placed injection is one of the few pieces of objective information available.
The question worth asking before an injection is scheduled
Not “will this injection help?” but “if this injection does nothing, what will we have learned, and what is
next on the list?” If there is no answer to the second half, the differential has not been worked through yet.
Frequently asked questions
Why does piriformis pain hurt so badly when I sit?
Sitting loads the deep gluteal space directly. Body weight compresses the muscle and everything running beneath it against the ischial tuberosity and the back edge of the pelvis, and a nerve that is already irritated does not tolerate sustained compression well. External tenderness over the greater sciatic notch and aggravation of pain through sitting are among the most consistently reported features of the condition. Worth noting: the same posture provokes proximal hamstring problems and pudendal nerve irritation, so sitting intolerance alone does not identify which structure is at fault. Learn more: pelvic pain that is worse when you sit.
Can you permanently get rid of piriformis syndrome?
Many people do settle permanently, and most of them get there without a procedure — by changing the loading pattern, the seating, or the training error that provoked it, and giving the tissue time. What recurs reliably is a case where the driver was never identified, because the muscle was treated and the reason it was overloaded was not. That is also true when the original diagnosis was wrong, which in this region is common. Learn more: when a piriformis injection does not work.
How do I know it is not my hip joint?
You often cannot tell from symptoms alone, which is the point. Hip osteoarthritis classically produces groin pain, but a meaningful number of people with an arthritic hip report their pain in the buttock and describe it running down the leg. Examination separates them better than description does: hip range of motion, particularly internal rotation, tends to be restricted and painful when the joint is the source, and an image-guided diagnostic injection into the joint settles it when the exam is equivocal. Learn more: lateral hip pain that is rarely just bursitis.
Does an MRI diagnose piriformis syndrome?
No. An MRI of the pelvis is used to exclude the things that do show up on imaging — a mass compressing the sciatic nerve, ischiofemoral impingement, a proximal hamstring tear, hip pathology — and that is a genuinely useful job. What it does not do is confirm piriformis syndrome, because there is no imaging finding that establishes the diagnosis. Ultrasound may show thickening of the muscle, but whether that correlates with the clinical diagnosis has not been established. Learn more: what fluoroscopy images can and cannot prove.
Should I have a lumbar MRI first if the pain runs down my leg?
Usually yes, and then read it carefully. Excluding a spinal cause is a reasonable first move when pain radiates below the knee or there is any neurologic deficit. The trap is that a lumbar MRI in anyone past forty will nearly always show some disc degeneration, and a plausible-looking finding then closes the investigation before the buttock is ever examined. A scan that shows something is not the same as a scan that explains something. Learn more: sciatica is not a diagnosis.
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
- Park JW, Lee YK, Lee YJ, Shin S, Kang Y, Koo KH. “Deep gluteal syndrome as a cause of posterior hip pain and sciatica-like pain.” The Bone & Joint Journal. 2020;102-B(5):556–567. doi:10.1302/0301-620X.102B5.BJJ-2019-1212.R1
- Lo JK, Robinson LR. “Piriformis syndrome.” Handbook of Clinical Neurology. 2024;201:203–226. doi:10.1016/B978-0-323-90108-6.00002-8
Dr. Gurpreet Singh Padda, MD, MBA, MHP
