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Piriformis Muscle Anatomy

The pear-shaped piriformis muscle (L. pirum, a pear) is located partly on the posterior wall of the lesser pelvis and partly posterior to the hip joint. The piriformis leaves the pelvis through the greater sciatic foramen, almost filling it, to reach its attachment to the superior border of the greater trochanter.

Because of its key position in the buttocks, the piriformis muscle is the landmark of the gluteal region. The piriformis provides the key to understanding relationships in the gluteal region because it determines the names of the blood vessels and nerves:

  • The superior gluteal vessels and nerve emerge superior to it.
  • The inferior gluteal vessels and nerve emerge inferior to it.

Piriformis Muscle Anatomy

The piriformis muscle lies in the deep layer of muscles of the gluteal region that consists of smaller muscles (piriformis, obturator internus, superior and inferior gemelli, and quadratus femoris) covered by the inferior half of the gluteus maximus. These muscles all have distal attachments on or adjacent to the intertrochanteric crest of the femur. These muscles are external rotators of the thigh, but they also stabilize the hip joint, working with the strong ligaments of the hip joint to steady the femoral head in the acetabulum.

The piriformis muscle arises from the superior sacrum, lateral to its pelvic foramina and from gluteal surface of ilium at the margin of the greater sciatic notch. The muscles pass laterally, leaving the lesser pelvis through the greater sciatic foramen to attach to the superior border of the greater trochanter of the femur. The piriformis muscles occupy much of the greater sciatic foramen, forming the posterolateral walls of the pelvic cavity.

A gap at the inferior border of each piriformis muscle allows passage of neurovascular structures between the pelvis and the perineum and lower limb (gluteal region).

The piriformis muscle is innervated by the nerve to the piriformis, which is formed by the ventral rami of the sacral plexus’s S1 and S2 spinal nerves, it gets its blood supply from the superior and inferior gluteal and internal pudendal arteries.

The action of this muscle is to externally rotate the hip joint and also helps abduct the hip if it is flexed.

Piriformis Muscle
OriginAnterior surface of lateral process of sacrum and gluteal surface of ilium at the margin of the greater sciatic notch
InsertionSuperior border of greater trochanter
InnervationNerve to the piriformis, which is formed by the ventral rami of the sacral plexus’s S1 and S2 spinal nerves
Blood SupplySuperior and inferior gluteal and internal pudendal arteries
ActionLateral rotator of the hip joint
Also helps abduct the hip if it is flexed
Piriformis anatomy

The sciatic nerve generally exits the pelvis inferior to the piriformis muscle. However, variations occur, and the entire nerve may pass superior to or through the muscle. In other variations, the sciatic nerve may split into its major divisions as high up as the level of the piriformis instead of in the popliteal fossa. The tibial and common peroneal nerves may descend toward the thigh together or separately from either side of the piriformis. 

In around 80% of cases, the sciatic nerve travels below the piriformis muscle. While in 17% of people, the piriformis muscle is pierced by parts or all of the sciatic nerve.

Piriformis muscle variations

Piriformis syndrome is a disorder affecting the proximal sciatic nerve, usually presenting with hip and buttock pain due to inflammation. The syndrome is often misdiagnosed and inappropriately treated. Surgical release is only considered in refractory conditions after nonoperative modalities have been exhausted.

See Also: Piriformis syndrome
See Also: Piriformis Syndrome Test

References & More

  1. Gray’s Anatomy: The Anatomical Basis of Clinical Practice
  2. Clinically Oriented Anatomy – 8th Edition
  3. Chang C, Jeno SH, Varacallo M. Anatomy, Bony Pelvis and Lower Limb: Piriformis Muscle. [Updated 2023 Nov 13]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: Pubmed
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