Muscle
Piriformis
Hip rotator marking routes through the greater sciatic foramen
High-yield
Superior gluteal vessels and nerve pass above it; the inferior gluteal bundle and usually the sciatic nerve pass below. Sciatic branches can take different routes, including through the muscle.
Overview
Piriformis passes from the pelvic surface of the sacrum into the buttock through the greater sciatic foramen. It reaches the upper greater trochanter and helps rotate and stabilize the hip.
Reference facts
- Origin
- Mainly the anterior sacrum, with variable adjacent iliac, sacroiliac capsular and ligamentous attachments
- Insertion
- Upper border of the greater trochanter, with variable connections to neighboring rotator tendons
- Action
- Externally rotates the extended hip, assists abduction in flexion and contributes to hip stability
- Innervation
- Nerve branches to piriformis, chiefly S1-S2; L5 contribution and other variations are reported
- Blood supply
- Superior and inferior gluteal branches, with internal pudendal contribution
Mnemonic
Picture piriformis as a divider in the greater sciatic opening: the superior gluteal bundle takes the upper route, while the usual sciatic route lies underneath.
Clinical correlation
Sciatic irritation in the deep gluteal region can produce buttock and radiating leg pain. Piriformis syndrome requires assessment of competing causes; a variant nerve route on a scan does not by itself establish the diagnosis.
Frequently asked questions
What does the piriformis do?
The piriformis externally rotates the extended hip, assists abduction in flexion and contributes to hip stability.
What nerve innervates the piriformis?
Nerve branches to piriformis, chiefly S1-S2; L5 contribution and other variations are reported.
Where does the piriformis attach?
Origin: Mainly the anterior sacrum, with variable adjacent iliac, sacroiliac capsular and ligamentous attachments. Insertion: Upper border of the greater trochanter, with variable connections to neighboring rotator tendons.
What is the blood supply of the piriformis?
Superior and inferior gluteal branches, with internal pudendal contribution.