Found covered in a thick fascia in the lower portion of the trunk is the iliacus muscle. This muscle is shaped like a triangle, flat, and an exact fit of the iliac fossa found inside the pelvic bone. Together with the psoas major muscle, it is also called the iliopsoas muscle. A portion of this muscle is attached to the iliac fossa two-thirds from its top. Another portion is attached to the inside portion of the iliac crest, also of the pelvic bone. Other fibers of this muscle are also attached to the iliolumbar and anterior sacroiliac ligaments, the base portion of the sacrum, up to the anterior iliac spines. These muscle fibers then converge to insert on the tendon at the lateral side of the psoas major muscle, extending even to the femur bone. The iliacus muscle is innervated by the branches of the third and second nerves of the lumbar area through the femoral nerve. It is part of the hip rotator muscles, which are responsible for the flexing of the thigh on the pelvis and the forward tilting of the pelvis. It is also responsible for maintaining proper posture.
Written and medically reviewed by the Healthline Editorial Team
In Depth: Iliacus