Anatomy
Origin
- Anterior aspect of the sacrum at the level of about S2 through S4
- Sacrotuberous ligament
- Periphery of the greater sciatic notch
Insertion
- Superior and medial aspects of the greater trochanter.
Nerve
- Sacral plexus,5 and S1,2
Artery
- The arterial supply is from the inferior gluteal, superior gluteal and internal pudendal arteries, all branches of the internal iliac artery.
Function
- Lateral Rotation of the hip when it is extended (that is when in standing).
- Abduction of the hip when it is flexed.
- Aids slightly in tilting pelvis laterally.
- Also aids in tilting pelvis posteriorly by pulling the sacrum down towards the thigh.
Clinical relevance
The piriformis muscle can be used to locate the sciatic nerve. This nerve enters the gluteal region inferiorly to the piriformis. If the lateral rotators of the hip are tight they may exert pressure on the sciatic nerve, producing pain radiating into the lower extremity.This is known as Piriformis Syndrome.
Another importance of this muscle is that it divides the gluteal region into a superior and inferior part. Therefore, it determines the name of the vessels and nerves that supply the area (e.g. the superior gluteal nerve and vessels emerge superiorly to the piriformis, and the inferior gluteal nerve and vessels emerge inferiorly to the piriformis).
