How does the iliolumbar artery travel?

• A. Ascends anterior to the SI joint and posterior to the common iliac vessels
• B. Ascends posterior to the SI joint and anterior to the common iliac vessels
• C. Descends along the psoas major
• D. Circles the iliac crest

Answer: (A)

The iliolumbar artery travels superiorly from its origin on the internal iliac artery, then climbs toward the iliac fossa along the pelvic brim. As it ascends, it moves in front of the sacroiliac joint (anterior to it) and stays behind the common iliac vessels (posterior to them). This route—ascending anterior to the SI joint while remaining posterior to the common iliac vessels—fits its course as a branch that supplies the iliacus and psoas muscles and ascends into the abdominal wall.