Iliacus Muscle

Origin

The iliacus muscle originates from the:

- inner lip of iliac crest;

- superior two thirds of the iliac fossa;

- ala of sacrum;

- anterior sacroiliac ligaments.

Insertion

The fibers of the iliacus muscle travel anteroinferiorly and insert onto the tendon of the psoas major, which inserts onto the lesser trochanter of the femur.

Key Features & Anatomical Relations

The iliacus muscle is one of the two muscles that form the iliopsoas muscle, the other being the psoas major muscle. It is a large, broad, convergent type of skeletal muscle. Within the greater pelvis, the fibers of the iliacus muscle converge as they travel anteroinferiorly towards the inguinal ligament. After it passes deep to the lateral one third of the inguinal ligament, the iliacus muscle travels inferiorly within the anterior compartment of thigh towards its insertion site.

The iliacus muscle is located:

- anterior to the capsule of the hip joint and the iliopectineal bursa;

- posterior to the inguinal ligament;

- medial to the ilium and sartorius muscle;

- lateral to the psoas major muscle and the femoral and lateral femoral cutaneous nerves.

Actions & Testing

Overall, the iliopsoas muscle is involved in multiple actions:

- during unilateral contraction, it flexes the thigh at the hip joint;

- during bilateral contraction, it flexes the trunk.

The iliacus muscle cannot be tested in isolation, therefore both muscles of the iliopsoas are tested simultaneously by flexing the thigh at the hip joint against resistance while in the supine position with the knee flexed (Standring, 2016).

List of Clinical Correlates

- Iliopsoas tendinitis

- Thomas test

References

Standring, S. (2016) Gray's Anatomy: The Anatomical Basis of Clinical Practice. Gray's Anatomy Series 41st edn.: Elsevier Limited.