Why an MRI of the lumbar spine is rarely the whole answer
For decades, buttock pain radiating down the leg was assumed to be a lumbar disc problem. Yet up to 25% of patients carrying a 'sciatica' diagnosis have a normal spine on MRI. Modern anatomical and imaging research has shown that the true culprit often lies below the pelvis — inside the deep gluteal space, a small anatomical corridor bordered by the piriformis, obturator internus and hamstring origins.
The anatomy in one paragraph
The deep gluteal space sits between the greater trochanter and the ischial tuberosity. It houses the sciatic nerve, the pudendal nerve, the posterior femoral cutaneous nerve, and the inferior gluteal vessels. Any of these structures can be compressed by a hypertrophic piriformis, a fibrous band, an ischiofemoral impingement, or a scarred hamstring origin — producing symptoms indistinguishable from a herniated lumbar disc.
Clinical clues that point away from the spine
Pain that worsens with sitting rather than with lumbar extension, tenderness to deep palpation over the sciatic notch, a positive seated piriformis test, and pain triggered by hip rotation all point to extra-spinal entrapment. Neurological deficits are usually absent, and reflexes remain intact — a helpful contrast with true radiculopathy.
Diagnostic pathway used at the Pelvic Institute
The 2026 protocol relies on three converging tests. First, high-resolution MR neurography visualises the sciatic and pudendal nerves along their entire deep gluteal course. Second, a diagnostic image-guided injection into the deep gluteal space distinguishes muscular from neural pain generators. Third, dynamic ultrasound reproduces the entrapment during hip rotation and adduction — something a static MRI cannot do.
From conservative care to endoscopic decompression
First-line management is always non-surgical: targeted pelvic floor and hip physiotherapy, image-guided injections, and activity modification. Roughly 60–70% of patients improve substantially within six months.
For the remaining group, endoscopic deep gluteal decompression is the current gold standard. Performed through two or three small posterior incisions, the technique releases the entrapping bands, decompresses the sciatic and pudendal nerves, and preserves the surrounding muscles. Published series from 2024–2026 report meaningful pain reduction in 75–85% of correctly selected patients at 12 months.
The key to good outcomes is patient selection: imaging, diagnostic injections and clinical pattern must all agree before proceeding to surgery.