Which muscle originates from the anterior inferior iliac spine?

• A. Psoas major
• B. Gluteus maximus
• C. Rectus Femoris
• D. Vastus lateralis

Answer: (C)

The AIIS marks the origin of the straight head of the rectus femoris, a muscle of the quadriceps group. Rectus femoris is unique among the quadriceps in starting from the pelvis and crossing two joints, with its straight head attaching directly to the anterior inferior iliac spine and a second, reflected head arising from the ilium just above the acetabulum. This placement lets the muscle contribute to hip flexion (due to crossing the hip joint) and knee extension (due to crossing the knee joint). Other muscles listed originate from different pelvic or femoral sites: psoas major from the lumbar spine, gluteus maximus from the posterior ilium and sacrum, and vastus lateralis from the femur, not the AIIS.