The piriformis muscle is a small muscle deep to glute max and lies over top of the sciatic nerve. It originates on the anterior sacrum, and inserts on the greater trochanter of the femur. It’s main action is to laterally rotate the femur. When trigger points developed in this muscle they will refer pain into the sacro-iliac region, across the posterior hip and down the leg. This muscle can also be a cause of sciatic nerve irritation if it gets tight, causing “sciatica” symptoms.