The piriformis is the key external hip rotator and the primary landmark of the greater sciatic foramen, dividing it into the suprapiriform (superior gluteal vessels and nerve) and infrapiriform (sciatic nerve, inferior gluteal, pudendal) compartments. Piriformis syndrome is a diagnosis of exclusion — sciatic nerve irritation from piriformis compression or anatomical variants where the sciatic nerve passes through the piriformis rather than below it.
| Origin | Anterior sacrum (S2-S4 sacral foramina levels) and greater sciatic notch margin |
|---|---|
| Insertion | Superior surface of the greater trochanter medial to the gluteus medius insertion |
| Nerve Supply | Branches from S1, S2 (variable — sometimes the nerve to piriformis, sometimes direct sacral plexus branches) |
| Blood Supply | Superior and inferior gluteal arteries |
| Actions | Hip external rotation (primary action in any hip position); Hip abduction when hip is flexed beyond 60 degrees (paradoxical — the line of pull shifts above the hip centre) |
|---|
In the anatomical piriformis variant (sciatic nerve piercing the piriformis), the Freiberg sign (passive hip internal rotation in extension) provokes sciatic symptoms by mechanically compressing the nerve. In the normal relationship, the sciatic nerve is adjacent to the piriformis inferior border and can be compressed by piriformis spasm or hypertrophy.
The FAIR test (hip Flexion, Adduction, Internal Rotation) compresses the sciatic nerve between the piriformis and the ischium, reproducing symptoms in piriformis syndrome. Diagnostic injection into the piriformis muscle with ultrasound or CT guidance provides temporary relief and confirms the diagnosis. Botulinum toxin injection into the piriformis reduces spasm for 3-4 months.
Deep gluteal palpation medial to the greater trochanter midpoint reproduces piriformis tenderness. The tendinous insertion is palpable at the superior trochanter with the hip in flexion-external rotation.
Sciatic nerve irritation from piriformis spasm or anatomical variation producing buttock and posterior thigh pain managed with FAIR stretching, injection, and botulinum toxin.
