Which muscle functions as an external rotator of the hip?

• A. Gluteus medius
• B. Piriformis
• C. Pectineus
• D. Tensor fasciae latae

Answer: (B)

Rotating the thigh outward at the hip is external rotation. Among these muscles, the piriformis is a classic deep external rotator of the hip, pulling the femur laterally to rotate the leg outward, especially when the hip is in a more extended position. When the hip is flexed, piriformis shifts toward abduction, but its primary external-rotation action in this context is the best match. The gluteus medius is mainly an abductor (with some fibers aiding external rotation), the pectineus acts as a hip flexor/adductor with limited external rotation, and the tensor fasciae latae flexes and abducts (and can medially rotate when flexed). So piriformis best fits the role of an external rotator.