The piriformis is a flat, pear-shaped muscle occupying the greater sciatic foramen and running from the anterior sacrum to the greater trochanter, serving as the anatomical centrepiece of the deep gluteal region. The sciatic nerve typically exits below it through the infrapiriform foramen, multiple other neurovascular structures exit above it, and its relationship to these structures makes it the focus of piriformis syndrome, one of the most debated diagnoses in musculoskeletal medicine.
| Origin | Anterior surface of the sacrum between the first and fourth sacral foramina; Superior margin of the greater sciatic notch and sacrotuberous ligament |
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| Insertion | Superior border of the greater trochanter of the femur |
| Nerve Supply | Nerve to piriformis from L5, S1, and S2 |
| Blood Supply | Superior and inferior gluteal arteries |
| Actions | External rotation of the hip when the hip is extended; Abduction of the hip when the hip is flexed beyond 60 degrees; Stabilisation of the sacroiliac joint |
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Its action reverses depending on hip position. It externally rotates when the hip is extended or slightly flexed but becomes an abductor when the hip is flexed beyond 60 degrees, a biomechanical shift that has direct clinical implications for how it is tested and treated.
Piriformis syndrome describes buttock pain and posterior leg symptoms attributed to sciatic nerve irritation at the piriformis, diagnosed by exclusion of lumbar disc pathology. In approximately 17 percent of people the sciatic nerve pierces directly through the piriformis belly, increasing entrapment vulnerability. The FAIR test (hip flexion, adduction, internal rotation) and Pace sign (resisted abduction in the seated position) are the specific clinical provocations. Sacroiliac joint dysfunction almost always co-presents with piriformis overactivity.
The piriformis is palpable with firm deep pressure applied halfway between the posterior superior iliac spine and the greater trochanter, becoming tender and firm in pronation to internal rotation and taut during resisted external rotation.
Deep gluteal pain and posterior leg paraesthesia from piriformis compression of the sciatic nerve, reproduced by the FAIR test and managed with stretching, dry needling, and correction of underlying hip biomechanics.
Acute tear from sudden external rotation or torsional hip loading, producing deep gluteal pain that worsens with sitting, walking, and resisted hip external rotation.
