Muscle · Pelvis

Iliacus

Musculus iliacus

A broad, fan-shaped muscle that lines the whole inner bowl of the hip bone and converges on the same tendon as psoas major, the two travelling to the thigh together as the iliopsoas. Unlike psoas it has no attachment to the spine at all, so its job is single: flexing the hip. That difference matters in the clinic. Iliacus can only pull the thigh toward the pelvis or the pelvis toward the thigh, so a tight iliacus tips the pelvis forward without gripping the lumbar spine directly — and because it lies against the bone of the iliac fossa, it is far safer to reach than its partner.