Piriformis muscle lies partly within the pelvis and partly in the gluteal region. The origin of the muscle is within the pelvis while its insertion is in the gluteal region outside pelvis. It emerges through the greater sciatic foramen to enter the gluteal region. It has an important position in the gluteal region because it serves to separate the superior gluteal vessels and nerves from the inferior ones.
Origin of piriformis:
It originates within the pelvis from the anterior surface of the second, third and fourth sacral vertebrae.
Insertion of piriformis:
The fibers of the muscle pass downward and laterally through the greater sciatic foramen and are attached to the upper border of the greater trochanter.
Nerve supply of piriformis:
It is supplied by anterior rami of the first and second sacral nerves.
Action of piriformis:
It serves as a lateral rotator of thigh at hip joint.