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Psoas Minor Muscle Anatomy

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Origin
  • Vertebral bodies of T12-L1 vertebrae and adjacent intervertebral disc
Insertion
  • Iliopectineal eminence and pectineal line of the pubis (pecten pubis)
Action
  • Very weak flexion of the trunk
Innervation
  • Anterior rami of lumbar nerves (L1-L2)
Blood Supply
  • Lumbar arteries
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Location & Overview

The psoas minor is a flat, relatively thin muscle located in the lumbar region of the back and extending to the pubic region. It is able to provide very weak flexion of the trunk, specifically in the lumbar region. It is superficial to the psoas major muscle and the iliacus muscle (meaning it is more anterior than both of these muscles and closer to the skin’s surface). The psoas minor and major muscles are sometimes referred to collectively as the ‘psoas muscle’.[1,2] The psoas minor muscle is bilaterally absent (missing from both sides) in about 40% of the population. It can also be missing unilaterally (from just one side).[3]

The name of the psoas minor muscle is believed to originate from the Ancient Greek word ‘ψόᾱ’, which translates to ‘muscles of the loins’ in English.

psoas minor muscle
Here we can see the psoas minor muscle by itself.
psoas minor from a slightly lateral view
Here we can see the psoas minor from a more lateral view.
psoas minor highlighted in red among the other muscles
Here we can see the psoas minor highlighted in red among the other muscles of the pelvic and abdominal region. The psoas minor is a deep muscle, therefore superficial muscles such as the abdominal muscles have been removed from the image to reveal the psoas minor. The muscle located right behind the psoas minor is the psoas major.
iliopsoas muscle
Here we can see the psoas minor, psoas major, and iliacus muscles. The psoas major and iliacus are collectively known as the iliopsoas muscle. You can also see the inguinal ligament and how the psoas major and iliacus pass behind it through the gap between the inguinal ligament and the pelvis.

Origin & Insertion

The psoas minor muscle originates from the last thoracic and first lumbar vertebrae (T12-L1). It also originates from the adjacent intervertebral disc (that is, it connects to the disc between T12-L1). The psoas minor then continues in an inferior direction toward the pelvis and inserts on the iliopectineal eminence and pectineal line of the pubis (also known as the pecten pubis) via a long tendon.[3,1,2] Guerra et al. determined that the tendon comprised 57% of the total length of the muscle.[4]

origin of the psoas minor
Pictured here, we can see the origin of the psoas minor highlighted in red. The origin is on the vertebral bodies of the T12-L1 vertebrae and the adjacent intervertebral disc between them.
insertion of the psoas minor
Pictured here, we can see the insertion of the psoas minor highlighted in blue. This is located on the iliopectineal eminence (lateral portion of the marked area) and pectineal line (medial portion of the marked area).

Action & Function

The psoas minor provides very weak assistance during flexion of the trunk. The absence of the psoas minor in some individuals does not seem to result in reduced functionality, suggesting it is a relatively unimportant muscle, especially when compared to its psoas major counterpart.[1,3,2]

Image of a person demonstrating the movement of trunk flexion.
This image shows an example of trunk flexion, which involves bending the torso forward. The opposite of trunk flexion is trunk extension. The psoas minor can weakly assist with flexion of the trunk, specifically in the lumbar region.

Innervation

The psoas minor is innervated by branches from the anterior rami of the upper lumbar nerves, most commonly described as L1, with L2 also listed in some sources. These nerve roots form part of the lumbar plexus, a nerve network that lies within or close to the psoas major muscle. This is relevant because the psoas minor lies directly on the anterior surface of the psoas major.[5,6]

Blood Supply

Blood is supplied to the psoas minor mainly by the lumbar arteries. There may also be minor contributions from the arterial network that supplies the adjacent psoas major, which receives branches from the lumbar, iliolumbar, obturator, external iliac, and femoral arteries.[5]

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] Protas M, Voin V, Wang JM, Iwanaga J, Loukas M, Tubbs RS. A Rare Case of Double-Headed Psoas Minor Muscle with Review of its Known Variants. Cureus. 2017;9(6):e1312. Published 2017 Jun 5. doi:10.7759/cureus.1312
  3. [3] Dragieva P, Zaharieva M, Kozhuharov Y, Markov K, Stoyanov GS. Psoas Minor Muscle: A Cadaveric Morphometric Study. Cureus. 2018;10(4):e2447. Published 2018 Apr 8. doi:10.7759/cureus.2447
  4. [4] Anatomical study of the psoas minor muscle in human fetuses (article in Spanish-English) Guerra DR, Reis FP, Bastos AdA, et al. http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-95022012000100024&lng=en&nrm=iso&tlng=en Int J Morphol. 2012;30:136–139.
  5. [5] Standring S, editor. Gray’s anatomy: the anatomical basis of clinical practice. 42nd ed. Amsterdam: Elsevier; 2021.
  6. [6] Dalley AF II, Agur AMR. Moore’s Clinically Oriented Anatomy. 9th ed. Philadelphia: Wolters Kluwer; 2023.

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