Piriformis muscle is located in your buttock. More specifically, the muscle starts in your lower spine and passes through your greater sciatic notch. Spine and back specialist says piriformis muscle attaches to the upper part of each of your femurs. You have a piriformis muscle on either side of your body and it runs diagonally. Spine specialist says piriformis muscle performs two major functions: first, it helps enable your hip to rotate. Second, your piriformis muscle allows your leg and foot to turn outward. Piriformis syndrome is defined as a condition in which your piriformis muscle spasms and causes pain in your buttock. These spasms may also aggravate a nearby sciatic nerve root, which in turn sends sciatica-like symptoms racing down your large sciatic nerve.