Origin

Sacrum

Insertion

Greater trochanter

Action(s)

Rotate laterally (outward) the thigh

Nerve Supply

Nerve to the Piriformis (L5, S1, and S2 nerve roots)

Arterial Supply

Inferior gluteal artery, lateral sacral artery, superior gluteal artery.

Physical Exam

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Clinical Importance

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Disease States

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Discussion

Shape and location:

The piriformis is a flat muscle, pyramidal in shape, lying almost parallel with the posterior margin of the gluteus medius.

It is situated partly within the pelvis against its posterior wall, and partly at the back of the hip-joint.

It arises from the front of the sacrum by three fleshy digitations, attached to the portions of bone between the first, second, third, and fourth anterior sacral foramina, and to the grooves leading from the foramina: a few fibers also arise from the margin of the greater sciatic foramen, and from the anterior surface of the sacrotuberous ligament.

The muscle passes out of the pelvis through the greater sciatic foramen, the upper part of which it fills, and is inserted by a rounded tendon into the upper border of the greater trochanter behind, but often partly blended with, the common tendon of the obturator internus and gemelli.

Variations:

It is frequently pierced by the common peroneal nerve (fibular) when the sciatic nerve bifurcates prior to exiting the greater sciatic foramen. Thus, the piriformis is divided more or less into two parts.

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 in to the capsule of the hip joint.

Clinicals:

This syndrome occurs when the piriformis irritates the sciatic nerve, which comes into 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.” Fifteen percent of the population has their sciatic nerve coursing through the piriformis muscle. This subgroup of the population is predisposed to developing sciatica.

Figures

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Credits:

From Wikipedia:
Piriformis

Attachments:


Piriformis.png (image/png)