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Iliacus Muscle Anatomy

Quick Overview View Flashcards
Origin
  • Superior two-thirds of the iliac fossa
  • Inner lip of the iliac crest
  • Lateral aspect of the sacrum
Insertion
  • Lesser trochanter of the femur
Action
  • Flexion of the hip joint
Innervation
  • Femoral nerve (L2-L4)
Blood Supply
  • Iliolumbar artery
  • Deep circumflex iliac artery
  • Obturator artery
  • Femoral artery
Last updated: Estimated Reading Time: 6 min

Location & Overview

The iliacus muscle connects the hip to the femur and has a fan-shaped structure. It is part of the iliopsoas muscle group, which also includes the psoas major and psoas minor muscles. The term iliopsoas is a shortened form of iliopsoas musculotendinous unit and is sometimes abbreviated as IPMU. The iliacus muscle fibers merge with those of the psoas major as they approach the femur, forming a common tendon that inserts onto the lesser trochanter of the femur. Both the iliacus and psoas major muscles pass beneath the inguinal ligament. The psoas minor does not pass under the inguinal ligament because it connects to the hip rather than the femur.[1,2]

The inguinal ligament is a tough, fibrous band of connective tissue that connects the anterior superior iliac spine (ASIS) to the pubic tubercle. The inguinal ligament is located in the lower part of the abdomen, where the pelvis meets the thigh. If you place your hands on your hips, the inguinal ligament is located roughly where your fingers would be if you traced a line from the bony protrusion at the front of your hip down to the front of your thigh. An image of the inguinal ligament can be seen in the images below.[3,1,2]

The iliacus muscle is part of a group of muscles located in the inner hip area. These muscles work together to provide stability and strength to the hip joint, allowing for a range of movements such as walking, running, and jumping. Along with the psoas major, psoas minor, obturator externus, obturator internus, superior gemellus, inferior gemellus, piriformis, and quadratus femoris muscles, the iliacus muscle plays an important role in maintaining proper hip function. The iliacus is the primary hip flexor at the hip joint.[3]

iliacus muscle
Here, we can see the iliacus muscle from an anterior view.
iliacus muscle from a lateral view
Here, we can see the iliacus muscle from a slightly more lateral view, giving a better view of the insertion onto the femur.
Iliacus, inferior view
Here, we can see the iliacus from an inferior view.
iliopsoas muscle group and the inguinal ligament
Here, we can see the iliopsoas muscle group and the inguinal ligament.

Origin & Insertion

The iliacus originates at the superior two-thirds of the iliac fossa. The superior portion of this origin also connects to the inner lip of the iliac crest. The origin also spans onto the lateral aspect of the sacrum. The iliacus muscle then passes downward in an inferior direction with the psoas major, deep to the inguinal ligament. Bundles of the iliacus muscle’s fibers then merge with fibers of the psoas major muscle as they approach their insertion point and attach to the lesser trochanter of the femur.[1,4]

iliacus origin marked in red on superior two thirds of the iliac fossa, inner lip of the iliac crest and lateral aspect of the sacrum
Here, we can see the origin of the iliacus marked in red on the superior two-thirds of the iliac fossa, the inner lip of the iliac crest, and the lateral aspect of the sacrum.
iliacus insertion marked in blue on the lesser trochanter of the femur
Here, we can see the insertion of the iliacus marked in blue on the lesser trochanter of the femur.

Action & Function

The main action of the iliacus muscle is to cause flexion of the hip joint. This action can occur by lifting the leg forward and upward. If both legs are fixed, the iliacus can assist in bringing the torso forward toward the legs (i.e., bending over). The iliacus works alongside the psoas major as part of the iliopsoas muscle group to perform hip flexion.[1,2,3,5]

Image of a person demonstrating the movement of hip flexion.
In this image, you can see an example of hip flexion, which is the action of raising your leg in front of you and bending your hip. If both legs are fixed, the torso will lean forward toward the legs. The opposite movement of hip flexion is hip extension. The primary role of the iliacus muscle is to cause flexion of the hip joint.

Innervation

The iliacus muscle is innervated by the femoral nerve (L2-L4). The femoral nerve is the largest nerve of the lumbar plexus. The lumbar plexus is a network of nerves formed mainly by the anterior rami of the lumbar spinal nerves.[3]

femoral nerve
Pictured here is the femoral nerve highlighted in red. The iliacus is innervated by the femoral nerve, from the spinal roots of L2 to L4.
nerves of the thigh and pelvis region
Pictured here, we can see the nerves of the thigh and pelvis region. The image also shows the lumbar plexus, which the femoral nerve is a part of.

Blood Supply

The arteries that supply blood to the iliacus muscle are the iliolumbar artery, deep circumflex iliac artery, obturator artery, and femoral artery.[3]

Image of the arteries of the lower limb
This image shows the arteries of the lower limb.

References

  1. [1] Bordoni B, Varacallo M. Anatomy, Bony Pelvis and Lower Limb, Iliopsoas Muscle. (Updated 2022 Apr 29). In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK531508/
  2. [2] 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.
  3. [3] Moore KL, Agur AMR, Dalley AF. Clinically Oriented Anatomy. 8th ed. Philadelphia: Lippincott Williams & Wilkins; 2017.
  4. [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/
  5. [5] 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.

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