Iliacus muscle

The iliacus is a flat, fan-shaped muscle that fills the iliac fossa on the inner surface of the hip bone. It joins with the psoas major to form the iliopsoas, the main flexor of the hip joint.

Origin

The muscle fibres arise from an extensive anterior-to-posterior region, beginning at the upper two-thirds of the iliac fossa and the inner lip of the iliac crest, and extending posteriorly to the anterior aspect of the lateral ala of the sacrum, the sacroiliac joint, and its supporting ligaments, including the anterior sacroiliac and iliolumbar ligaments.

Course and Relations

The iliacus muscle fibres bundle together with those of the psoas major. Together they pass underneath the inguinal ligament as iliopsoas and in front of the hip joint before inserting onto the femur.

Both iliacus and psoas major are covered by the iliac fascia, and form part of the floor of the femoral triangle in the upper anterior thigh.

Insertion

Lesser trochanter of the femur via the common iliopsoas tendon (shared with the psoas major). Some of them being prolonged on to the body of the femur for about 2.5 cm. below and in front of the lesser trochanter.

Blood supply

Iliolumbar artery (from internal iliac) and medial circumflex femoral artery (from deep femoral artery).

Actions

• Flexes the thigh at the hip joint.

• Stabilizes the hip joint during standing.

• It helps lift the thigh or bend the trunk forward (as in walking, running, or climbing stairs)

Clinical correlate

• Infection (from spine or abdomen) can track into the upper thigh along the iliacus fascia, creating an iliopsoas abscess.