Piriformis origin is on which anatomical surface?

• A. Anterior surface of sacrum
• B. Posterior surface of sacrum
• C. Anterior surface of ilium
• D. Ischial tuberosity

Answer: (A)

The muscle in question starts from the anterior (pelvic-facing) surface of the sacrum. From that ventral sacral origin, its fibers run laterally through the greater sciatic foramen to insert on the upper border of the greater trochanter. This placement lets it help with external rotation of the thigh when the hip is extended and with abduction when the thigh is flexed, while also stabilizing the hip joint. The posterior surface of the sacrum, the ilium, or the ischial tuberosity are not where this muscle originates, so they don’t describe the piriformis origin.