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Iliacus And Psoas Major Muscles

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Iliacus and Psoas Major Muscles

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Iliacus and Psoas Major Muscles form the posterior abdominal wall in addition to Quadratus lumborum muscle. The iliacus and psoas major merge inferiorly; collectively form iliopsoas muscle.

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
OriginSuperior two thirds of iliac fossa,
Ala of sacrum
Anterior sacroiliac ligament
InsertionLesser trochanter of femur
InnervationFemoral nerve (L2-L4)
Blood SupplyIliolumbar, deep circumflex iliac, obturator, and femoral artery
ActionFlexes thigh and stabilizes hip joint, acts with psoas major muscle.
Iliacus and Psoas Major Muscles anatomy

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.

See Also: Hip Muscles Anatomy
OriginAnterior surfaces and lower borders of transverse processes of L1 – L5
bodies and discs of T12 – L5
InsertionLesser trochanter of femur
InnervationDirect fibers of L1 – L3 of lumbar plexus (L1, L2, L3)
Blood SupplyLumbar branch of iliopsoas branch of internal iliac artery
ActionFlex the torso and thigh with respect to each other
Iliacus and Psoas Major Muscles

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 
OriginIliac crest, iliolumbar ligament
InsertionTransverse processes of L1 – L4 and the inferior border of the 12th rib.
InnervationAnterior rami of T12 – L4 nerves.
Blood SupplyLumbar, median sacral, iliolumbar and subcostal arteries.
ActionExtension 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
Quadratus Lumborum Muscle

References & More

  1. Clinically Oriented Anatomy – 8th Edition
  2. 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/
  3. 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/
  4. 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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