Piriformis (muscle and syndrome)

The piriformis muscle is flat, pyramid-shaped, and oblique (slanted). This muscle originates to the anterior of the S2-S4 vertebrae, the sacrotuberous ligament, and the upper margin of the greater sciatic foramen. This muscle passes through the greater sciatic notch and inserts on the superior surface of the greater trochanter(bony bump) of the femur(large bone in the upper leg). With the hip extended, the piriformis muscle is the primary external rotator; however, with the hip flexed, the piriformis muscle itself becomes a hip abductor (Muscle which when activated, normally moves an extremity or limb away from the body). Piriformis syndrome is pain in the hip, buttocks, or thigh. It is caused by pressure on the piriformis muscle in the hip. The pain is a deep ache and gets worse with exercise or sitting for long periods. In 10% of the population the sciatic nerve passes through the piriformis instead of under it as normal. Conditions which cause the muscle to become short and contracted increase the nerve compression. Not all cases are due to the nerve passing through the muscle.