Pain in the buttocks that radiates down the leg is referred to as sciatica. The most common cause of sciatica is irritation of the spinal nerves in or close to the spine. Sometimes the source of sciatic pain can be further down the leg in the buttocks. Before the sciatic nerve begins its path down the back of the leg, it runs under or through a deep pelvic muscle called the piriformis. When the piriformis squeezes or irritates the sciatic nerve, this can cause symptoms of sciatica. It has not been definitively proven why the piriformis sometimes starts to irritate the sciatic nerve. Most physicians feel it is from the muscle spasming and tightening to squeeze the sciatic nerve against the pelvic bone. It can also occur from a fall onto the buttocks that bruises the piriformis causing swelling and pressure against the sciatic nerve. As the muscle heals, scar tissue forms which is not as elastic as normal, healthy tissue. This can continue to put constant pressure on the sciatic nerve.