Piriformis
Musculus piriformis
Also known as: pear-shaped muscle
A pear-shaped muscle from the anterior sacrum, through the greater sciatic foramen, to the greater trochanter. It is the key landmark of the gluteal region.
Overview
Piriformis arises from the anterior surface of the sacrum (between the S2–S4 anterior foramina) and the sacrotuberous ligament. It leaves the pelvis through the greater sciatic foramen and inserts on the superior border of the greater trochanter. It nearly fills the foramen, dividing it into two parts.
- Above piriformis (suprapiriform foramen): the superior gluteal nerve and vessels.
- Below piriformis (infrapiriform foramen): the sciatic nerve, the inferior gluteal nerve and vessels, the pudendal nerve and internal pudendal vessels, the nerve to obturator internus, the nerve to quadratus femoris and the posterior femoral cutaneous nerve.
It laterally rotates the extended thigh and abducts the flexed thigh, and it steadies the femoral head in the acetabulum. In about 10–15% of people, part of the sciatic nerve, usually the common fibular division, pierces piriformis or passes above it.
Anatomy
- Origin
Anterior surface of the sacrum (S2–S4) and the sacrotuberous ligament.
- Insertion
Superior border of the greater trochanter of the femur.
- Action
Lateral rotation of the extended hip; abduction of the flexed hip.
- Innervation
Nerve to piriformis (anterior rami of S1–S2).
- Nerve roots
S1–S2 (L5–S2)
- Arterial supply
Superior and inferior gluteal arteries; lateral sacral and internal pudendal branches.
- Relations
The superior gluteal neurovascular bundle passes above it. The sciatic nerve and the other structures listed pass below it.
Function
- Laterally rotates the extended thigh
- Abducts the flexed thigh
- Stabilises the hip joint
Clinical significance
Piriformis syndrome
A controversial cause of buttock pain and sciatica-like symptoms, attributed to compression of the sciatic nerve by a tight or hypertrophied piriformis or by an anatomical variant. Pain worsens on sitting and on flexion–adduction–internal rotation of the hip (FAIR test).
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.