Iliacus and Psoas Major Muscles

Iliacus and Psoas Major Muscles are one of the posterior abdominal wall in addition to Quadratus lumborum muscle. The iliacus and psoas major merge inferiorly; collectively form iliopsoas muscle.
Psoas is a Greek word meaning “muscle of the loin.” (Butchers refer to the psoas of animals as the tenderloin.)
Quadratus Lumborum, Iliacus and Psoas Major Muscles Anatomy
Iliacus Muscle
The iliacus is a large triangular muscle that lies along the lateral side of the inferior part of the psoas major. Most of its fibers join the tendon of the psoas major. Together, the psoas and iliacus form the iliopsoas, the chief flexor of the thigh. It is also a stabilizer of the hip joint and helps maintain the erect posture at this joint. The iliacus and psoas major share in hip flexion; however, only the psoas can produce movement (flexion or lateral bending) of the lumbar vertebral column.
See Also: External Oblique Muscle
Origin | Superior two thirds of iliac fossa, Ala of sacrum Anterior sacroiliac ligament |
Insertion | Lesser trochanter of femur |
Innervation | Femoral nerve (L2-L4) |
Blood Supply | Iliolumbar, deep circumflex iliac, obturator, and femoral artery |
Action | Flexes thigh and stabilizes hip joint, acts with psoas major muscle. |

Psoas Major Muscle
Psoas Major Muscle is a long, thick, fusiform muscle that lies lateral to the lumbar vertebrae. Psoas is a Greek word meaning “muscle of the loin.” The psoas major passes inferolaterally, deep to the inguinal ligament to reach the lesser trochanter of the femur. The lumbar plexus of nerves is embedded in the posterior part of the psoas major, anterior to the lumbar transverse processes.
The psoas major is also a postural muscle that helps control the deviation of the trunk and is active during standing.
The posterior surfaces of the kidney are related to the psoas major muscles medially, This close relationship of the kidneys to the psoas major muscles explains why extension of the hip joints may increase pain resulting from inflammation in the pararenal areas. These muscles flex the thighs at the hip joints.
See Also: Hip Muscles Anatomy
Origin | Anterior surfaces and lower borders of transverse processes of L1 – L5 bodies and discs of T12 – L5 |
Insertion | Lesser trochanter of femur |
Innervation | Direct fibers of L1 – L3 of lumbar plexus (L1, L2, L3) |
Blood Supply | Lumbar branch of iliopsoas branch of internal iliac artery |
Action | Flex the torso and thigh with respect to each other |

Quadratus Lumborum Muscle
The quadrilateral quadratus lumborum forms a thick muscular sheet in the posterior abdominal wall. It lies adjacent to the lumbar transverse processes and is broader inferiorly. Close to the 12th rib, the lateral arcuate ligament crosses the quadratus lumborum. The subcostal nerve passes posterior to this ligament and runs inferolaterally on the quadratus lumborum. Branches of the lumbar plexus run inferiorly on the anterior surface of this muscle.
See Also: Hip Pain Causes See Also: Thomas Test Interpretation for Hip Flexibility
Origin | Iliac crest, iliolumbar ligament |
Insertion | Transverse processes of L1 – L4 and the inferior border of the 12th rib. |
Innervation | Anterior rami of T12 – L4 nerves. |
Blood Supply | Lumbar, median sacral, iliolumbar and subcostal arteries. |
Action | Extension and lateral flexion of the vertebral column. It also fixes the 12th rib during inspiration, so that the contraction of diaphragm is more efficient. |
See Also: Quadratus Lumborum Muscle

References & More
- Clinically Oriented Anatomy – 8th Edition
- Siccardi MA, Tariq MA, Valle C. Anatomy, Bony Pelvis and Lower Limb: Psoas Major. [Updated 2023 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK535418/
- Bordoni B, Varacallo M. Anatomy, Abdomen and Pelvis, Quadratus Lumborum. [Updated 2023 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK535407/
- Bordoni B, Varacallo M. Anatomy, Bony Pelvis and Lower Limb, Iliopsoas Muscle. [Updated 2023 Apr 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK531508/
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