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Piriformis Muscle

Q: Into what two openings does the piriformis muscle divide the greater sciatic foramen?

The piriformis muscle (m. piriformis) divides the greater sciatic foramen (foramen ischiadicum majus) into two compartments: the suprapyriform and infrapyriform foramina. The muscle originates from the anterior surface of the sacrum and passes into the gluteal region, but it does not completely fill the foramen. This leaves two gaps through which major vessels and nerves exit the pelvic cavity.

Q: Which major nerve runs directly inferior to the piriformis muscle and can be compressed during muscle spasm?

The sciatic nerve (n. ischiadicus) runs directly inferior to the piriformis muscle through the infrapyriform foramen. It is the largest nerve in the body and serves as an important internal landmark. Spasm or hypertrophy of the piriformis muscle (m. piriformis) can compress this nerve, causing a clinical condition known as piriformis syndrome, which mimics sciatica.

Musculus piriformis

For medical students2 min readUpdated 2026-10-10

The piriformis muscle is a key pelvic girdle muscle and a crucial topographical landmark. It exits the pelvic cavity to enter the gluteal region, playing a primary role in lateral rotation and abduction of the thigh.

Origin (Origo)Anterior surface of the sacrum

Insertion (Insertio)Apex of the greater trochanter

FunctionLateral rotation and abduction of the thigh (when flexed)

Blood SupplySuperior and inferior gluteal arteries, internal pudendal artery

Topography and Attachment Points

The piriformis muscle originates within the pelvic cavity from the anterior surface of the sacrum. From its origin, the muscle fibers pass laterally, exiting the pelvis through the greater sciatic foramen (foramen ischiadicum majus).

After passing through this foramen, the muscle crosses the posterior aspect of the hip joint and firmly inserts onto the apex of the greater trochanter of the femur. This specific orientation determines its primary role in lower extremity biomechanics.

Biomechanics and Functions

The primary function of the piriformis muscle is to control the positioning of the femur. Depending on the current position of the hip joint, it performs the following actions:

Lateral Rotation (Supination): When the hip is extended, the muscle actively rotates the thigh laterally.
Abduction: When the hip is flexed, contraction of the piriformis leads to abduction of the thigh away from the midline.

Innervation and Blood Supply

Nerve supply is provided by branches of the sacral plexus (plexus sacralis), specifically from the S₁–S₂ nerve roots.

Blood supply is supplied by several major vascular trunks in this region:

Superior gluteal artery (a. glutea superior).
Inferior gluteal artery (a. glutea inferior).
Internal pudendal artery (a. pudenda interna).

Adjacent Structures and Thigh Muscles

When studying the muscles of the pelvis and thigh, it is essential to understand their topographical relationships. Other significant muscle groups and structures in this region include:

Vastus Medialis Muscle (m. vastus medialis) Originates from the medial lip of the linea aspera. Its fibers blend into the common tendon, forming the medial patellar retinaculum. Its main function is knee extension and prevention of lateral patellar subluxation. Innervated by the femoral nerve (n. femoralis), with blood supply from branches of the femoral artery and profunda femoris artery.

Pectineus Muscle (m. pectineus) Originates from the pectineal line of the pubis and inserts onto the pectineal line on the posterior aspect of the proximal femur. Performs adduction, flexion, and weak lateral rotation of the thigh. It frequently receives dual innervation from both the femoral nerve (n. femoralis) and the obturator nerve (n. obturatorius).

Clinically Significant Zones of the Lower Extremity

In addition to the piriformis muscle itself, several other anatomical landmarks are clinically relevant:

Pes Anserinus: The common tendinous insertion site of the sartorius (m. sartorius), gracilis (m. gracilis), and semitendinosus (m. semitendinosus) muscles on the proximal tibia. The adjacent bursa anserina is a common source of medial knee pain.
Adductor Canal (Hunter's Canal): Bordered by the vastus medialis laterally and adductor muscles medially/posteriorly. The roof is formed by the m. sartorius. It transmits the femoral artery and vein, along with the saphenous nerve (n. saphenus).
Clinical Patterns: Athletes frequently experience adductor strains (acute groin pain). Injury to the obturator nerve leads to weakness in thigh adduction, and avulsion fractures of the anterior inferior iliac spine (origin of the rectus femoris muscle) can occur in adolescents.

Frequently asked questions

Into what two openings does the piriformis muscle divide the greater sciatic foramen?

The piriformis muscle (m. piriformis) divides the greater sciatic foramen (foramen ischiadicum majus) into two compartments: the suprapyriform and infrapyriform foramina. The muscle originates from the anterior surface of the sacrum and passes into the gluteal region, but it does not completely fill the foramen. This leaves two gaps through which major vessels and nerves exit the pelvic cavity.

What vessels and nerves pass through the suprapyriform foramen?

The superior gluteal neurovascular bundle passes through the suprapyriform foramen (foramen suprapiriforme). It consists of the following anatomical structures:

Superior gluteal artery (a. glutea superior) — branches from the posterior division of the internal iliac artery inside the pelvis and divides into superficial and deep branches.
Superior gluteal veins (vv. gluteae superiores) — form a network covering the corresponding artery.
Superior gluteal nerve (n. gluteus superior) — located inferior and lateral to the vessels.

What anatomical structures exit the pelvis through the infrapyriform foramen?

The following structures exit into the subgluteal space through the infrapyriform foramen (foramen infrapiriforme):

Sciatic nerve (n. ischiadicus) — the largest nerve in the body, located most laterally.
Posterior cutaneous nerve of the thigh (n. cutaneus femoris posterior) — lies medial to the sciatic nerve.
Artery accompanying the sciatic nerve (a. comitans n. ischiadici).
Inferior gluteal neurovascular bundle — includes the inferior gluteal artery (a. glutea inferior), accompanying veins, and branches of the inferior gluteal nerve (n. gluteus inferior).
Pudendal neurovascular bundle — positioned most medially, containing the internal pudendal vessels (a. et vv. pudendae internae) and the pudendal nerve (n. pudendus).

Which major nerve runs directly inferior to the piriformis muscle and can be compressed during muscle spasm?

The sciatic nerve (n. ischiadicus) runs directly inferior to the piriformis muscle through the infrapyriform foramen. It is the largest nerve in the body and serves as an important internal landmark. Spasm or hypertrophy of the piriformis muscle (m. piriformis) can compress this nerve, causing a clinical condition known as piriformis syndrome, which mimics sciatica.

Through which foramen does the piriformis muscle exit the pelvis?

The muscle leaves the lesser pelvis through the greater sciatic foramen (foramen ischiadicum majus).

How does the function of the piriformis change with hip flexion?

In the neutral (extended) position, it laterally rotates the thigh, but when the hip is flexed, its primary action shifts to abduction.

What is the nerve supply of the piriformis muscle?

It is innervated by short branches of the sacral plexus originating from the S1 and S2 spinal nerves.

Go deeper

Topography of the greater sciatic foramen (supra- and infrapyriform spaces)
Vastus medialis muscle and patellar stabilization
Pectineus muscle and variants of its dual innervation
Anatomy and contents of the adductor (Hunter's) canal
Pes anserinus and clinical features of bursitis