|Origin||Superior two thirds of iliac fossa
Inner lip of the iliac crest
Lateral aspect of the sacrum
|Insertion||Lesser trochanter of femur|
|Action||Flexion of the hip joint|
|Nerve||Femoral nerve (L2-L4)|
Deep circumflex iliac artery
Location & Overview
The iliacus muscle is somewhat fan shaped and connects the hip to the femur. It is one of the muscles of the iliopsoas muscle group. The other two iliopsoas muscles are the psoas major and psoas minor. ‘Iliopsoas’ is an abbreviation of the term ‘iliopsoas musculotendinous unit’ which is also sometimes shortened to ‘IPMU’. Bundles of the iliacus muscle’s fibers merge with the psoas major as they approach the femur to form a common tendon which inserts onto the lesser trochanter. Both the iliacus and the psoas major also pass under the inguinal ligament. The psoas minor does not pass under the inguinal ligament because it is connecting onto the hip rather than the femur  .
Origin & Insertion
The iliacus originates at the superior two-thirds of the iliac fossa. The superior portion of this origin also connects onto the inner lip of the iliac crest. The origin point also spans onto the lateral aspect of the sacrum. The iliacus muscle then works its way downward in an inferior direction (along with the psoas major) passing deep to the inguinal ligament. Bundles of iliacus muscle’s fibers then merge with fibers of the psoas major muscle as they approach their insertion point and attach onto the lesser trochanter of the femur  .
The main and primary action of the iliacus muscle is to cause flexion of the hip joint. This hip flexion can occur by lifting the leg upwards, or if both legs are in a fixed position, then the hips can hinge instead bringing the torso forward towards the legs. The iliacus works alongside its iliopsoas muscle group partner the psoas major when performing hip flexion    .
The iliacus muscle is innervated by the femoral nerve (L2-L4) .
The arteries which supply blood to the iliacus muscle are the iliolumbar artery, deep circumflex iliac artery, obturator artery, and femoral artery.
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|↑2, ↑6||Lifshitz L, Bar Sela S, Gal N, Martin R, Fleitman Klar M. Iliopsoas the Hidden Muscle: Anatomy, Diagnosis, and Treatment. Curr Sports Med Rep. 2020 Jun;19(6):235-243. doi: 10.1249/JSR.0000000000000723. PMID: 32516195.|
|↑4||Siccardi MA, Tariq MA, Valle C. Anatomy, Bony Pelvis and Lower Limb, Psoas Major. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK535418/|
|↑7, ↑9, ↑10||Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincot Williams & Wilkins; 2017.|
|↑8||Anderson CN. Iliopsoas: Pathology, Diagnosis, and Treatment. Clin Sports Med. 2016 Jul;35(3):419-433. doi: 10.1016/j.csm.2016.02.009. Epub 2016 Mar 28. PMID: 27343394.|