The Piriformis muscle is situated between the anterior surface of the sacrum (the upside down triangular bone at the base of the spine)and the top lip of the femur (greater trochanter).

Piriformis plays a large role in sciatica and derivatives of this painful disorder. This is to do with the fact that the sciatic nerve travels in very close proximity to this muscle. Several variations occur, but the most common type of anomaly (81% of anomalies) is the Beaton's type B which is when the common peroneal nerve pierces the piriformis muscle.

Piriformis Syndrome occurs when the piriformis muscle irritates the sciatic nerve, causing pain in the buttocks and referred pain along the sciatic nerve (posterior thigh, leg and foot).

This referred pain is known as sciatica.In 15% of the population the sciatic nerve courses through the piriformis muscle making this subgroup of the population predisposed to developing sciatica. Sciatica can be described by pain, tingling, or numbness deep in the buttocks and along the sciatic nerve. Sitting down, stretching, climbing stairs usually increases pain.