The piriformis is the key muscle of the greater sciatic notch — it divides the notch into the suprapiriform and infrapiriform foramina, through which the gluteal and sciatic vessels and nerves pass. The sciatic nerve usually emerges below the piriformis (infrapiriform foramen).
| Origin | Anterior surface of the sacrum — S2, S3, S4 segments and the sacrotuberous ligament |
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| Insertion | Greater trochanter — superior aspect, via a tendon passing through the greater sciatic foramen |
| Nerve Supply | Nerve to piriformis — direct branches from S1, S2 |
| Blood Supply | Superior gluteal artery |
| Actions | Externally rotates the hip — primary action when hip is extended; Abducts the hip when the hip is flexed beyond 60 degrees; Stabilises the sacroiliac joint |
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Piriformis syndrome (disputed) involves sciatic nerve compression by the piriformis — the sciatic nerve in 15% of individuals passes through the piriformis muscle (anatomical variant), increasing compression risk. The pace sign (pain on resisted hip abduction-external rotation in seated position) and Freiberg test help diagnose piriformis syndrome. Botulinum injection into piriformis under EMG or imaging guidance is diagnostic and therapeutic.
Palpated in the gluteal region midway between the posterior superior iliac spine and the greater trochanter during resisted hip external rotation.
Piriformis muscle irritation or spasm compressing the sciatic nerve — especially in the anatomical variant where the nerve pierces the muscle — producing buttock pain and sciatica, managed by piriformis stretching and botulinum injection.
