In 25% of the population the sciatic nerve routes THROUGH the piriformis muscle deep in the posterior hip; in the rest of us, this little 3" muscle can impinge the nerve and cause excruciating pain and/or numbness down the leg on the affected side and into the foot even.

Many if not a majority of people who suffer from sciatica don't have a spinal problem-- correction: most of us do have some mild compression in one or more vertebra of the spine, but this seldom develops into a problem. Most sciatica is caused by neuromuscular trigger points in the piriformis or one of its cousins in the Deep Six lateral rotator group of the hip. Trigger points in the gluteus medius can also contribute. But the piriformis muscle is usually the sole cause.

You may be able to release the trigger points yourself. Lie on the floor on a tennis ball, roll your buttock of the affected leg on it till you find a painful spot (about the size of a quarter or even a dime), then press your weight into the ball; breathe deeply...after 3 or so breaths you should feel a "melting" and a lessening of the pain. Roll around some more, searching for other painful spots. A better, more certain solution, however, will be a session of therapeutic massage with a therapist qualified in neuromuscular therapy (NMT), which concentrates specifically on finding and releasing trigger points.