The iliacus muscle is one of the muscles of the posterior abdominal wall and contributes to the iliopsoas muscle and tendon.

Summary

• origin: superior 2/3s of the iliac fossa, anterior sacroiliac ligaments and anterior sacral ala

• insertion: into the psoas major tendon to form iliopsoas tendon which inserts on the lesser trochanter of the femur

• blood supply: iliolumbar artery, branches of femoral, obturator and deep circumflex iliac arteries

• innervation: femoral nerve

• action: stabilizer and flexor of the hip

Gross anatomy

The iliacus is a large muscle that fans out over the iliac fossa and converges inferiorly to form a tendon which merges with that of the psoas major muscle, forming the iliopsoas muscle. The tendon descends, passing deep to the lateral aspect of the inguinal ligament, to insert on the lesser trochanter of the femur.

Relations

The muscle lies in the concavity of the iliac fossa, lateral to the psoas major muscle. There are several nerves of the lumbar plexus that pass over the anterior surface of the muscle, including (from lateral to medial):

• lateral femoral cutaneous nerve

• femoral nerve

• genitofemoral nerve

• obturator nerve

• lumbosacral trunk

Deep to the muscle in the inferior 1/3 of the iliac fossa where there is no muscular attachment lies the iliac bursa which may or may not communicate with the hip joint.

Origin

The iliacus muscle originates from the iliac fossa (upper two-thirds), internal lip of the iliac crest, lateral aspect of the sacrum, anterior sacroiliac and iliolumbar ligaments.

Insertion

The iliacus merges with the psoas major muscle and form a common tendon that inserts on the lesser trochanter of the femur.

Arterial supply

The iliacus muscle is mainly supplied by the iliolumbar artery - a branch of the internal iliac artery. Besides that, it also receives arterial blood supply from the branches of the femoral, obturator and deep circumflex iliac arteries.

Innervation

The iliacus is innervated by the femoral nerve (L2, L3) that arises from the lumbar plexus.

Action

The iliacus muscle provides flexion of the thigh and trunk in addition to assisting in the external rotation of the thigh.

See also

• psoas major