The piriformis muscle () is a flat, pyramidally-shaped muscle in the gluteal region of the lower limbs. It is one of the six muscles in the lateral rotator group.

The piriformis muscle has its origin upon the front surface of the sacrum, and inserts onto the greater trochanter of the femur. Depending upon the given position of the leg, it acts either as external (lateral) rotator of the thigh or as abductor of the thigh. It is innervated by the piriformis nerve. It is the key muscle of the gluteal region.

Structure

left|thumb|Pelvis seen from behind (the piriformis and the rest of the [[lateral rotator group are visible).]]

The piriformis is a flat muscle, and is pyramidal in shape. by three fleshy digitations attached to the second, third, and fourth sacral vertebrae.

It also arises from the superior margin of the greater sciatic notch, the gluteal surface of the ilium (near the posterior inferior iliac spine), the sacroiliac joint capsule, and (sometimes) the sacrotuberous ligament (more specifically, the superior part of the pelvic surface of this ligament).

Innervation

The piriformis muscle is innervated by the piriformis nerve.

It may be united with the gluteus medius, send fibers to the gluteus minimus, or receive fibers from the superior gemellus.

It may have one or two sacral attachments; or it may be inserted into the capsule of the hip joint.

Function

The piriformis muscle is one of the lateral rotators of the hip, along with the quadratus femoris, gemellus inferior, gemellus superior, obturator externus, and obturator internus. The piriformis laterally rotates the femur with hip extension and abducts the femur with hip flexion.

Clinical significance

Piriformis syndrome

Piriformis syndrome occurs when the piriformis irritates the sciatic nerve, which enters the gluteal region beneath the muscle, causing pain in the buttocks and referred pain along the sciatic nerve. This referred pain is known as sciatica. The sciatic nerve runs through the piriformis muscle in seventeen percent of the population; this subgroup of the population is predisposed to developing sciatica.

Sciatica is characterized by pain, tingling, or numbness deep in the buttocks and along the sciatic nerve. Sitting down, stretching, climbing stairs, and performing squats usually increases the pain. Diagnosis of the syndrome is usually based on symptoms and on a physical exam. More testing, including MRIs, X-rays, and nerve conduction tests can be administered to exclude other possibilities pathologies.

History

The piriformis muscle was first named by Adriaan van den Spiegel, a professor from the University of Padua in the 16th century.

Additional images

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File:Piriformis muscle.PNG|Muscles of the gluteal and posterior femoral regions

File:Sobo 1909 296.png

File:Sobo 1909 300.png

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See also

  • Piriformis syndrome
  • Deep gluteal syndrome
  • Lateral rotators of the hip
  • Piriformis nerve
  • Greater sciatic foramen
  • Sacrum
  • Greater trochanter

References

  • "Piriformis" University of Washington
  • - "Gluteal Region: Muscles"
  • - "The Female Pelvis: The Posterolateral Pelvic Wall"