APPLIED RADIOLOGICAL ANATOMY

Detailed explanation-1: -Primary actions of the piriformis are hip external rotation (ER) and abduction; however studies suggest it may also perform hip internal rotation (IR) depending on the amount of hip flexion (HF).

Detailed explanation-2: -The piriformis muscle is part of the lateral rotators of the hip, along with the quadratus femoris, gemellus inferior, gemellus superior, obturator externus, and obturator internus. The piriformis laterally rotates the femur with hip extension and abducts the femur with hip flexion.