Psoas Minor Muscle Anatomy

Overview
Origin Vertebral bodies of T12-L1 vertebrae and adjacent intervertebral disc
Insertion Iliopectineal eminence and pectineal line
Action Very weak flexion of the trunk
Nerve Anterior ramus of first lumbar nerve (L1)
Artery Lumbar arteries

Location & Overview

The psoas minor is flat and relatively thin muscle located in the lumbar region of the back and extending to pubis region. It is superficial to the psoas major muscle and the iliacus muscle (meaning it is more anterior than both of these muscles). 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) for about 40% of the population. It can also be missing unilaterally (from just one side) [3].

psoas minor muscle

Pictured here we can see the psoas minor muscle in isolation.

iliopsoas muscle

Here we can see the psoas minor, psoas major and iliacus muscle (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 and adjacent intervertebral disc (i.e it connects to the disc between T12-L1). The psoas minor then continues in an inferior direction towards the pelvis and inserts on the iliopectineal eminence and pectineal line (aka pectin pubis) via a long tendon [4] [5] [6]. Guerra, et al. determined that the tendon comprised 57% of the total length of the muscle [7].

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 T12-L1 vertebrae and 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 on the iliopectineal eminence (lateral portion of the marked area) and pectineal line (medial portion of the marked area).

Actions

The psoas minor provides very weak assistance during flexion of the trunk. The absence of the psoas minor is 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 [8] [9] [10].

Innervation

The psoas minor is innervated by the anterior ramus of first lumbar nerve (L1) [11].

Blood Supply

Blood is supplied to the psoas minor mainly via the lumbar arteries.

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Psoas Minor Flashcards

References

References
1, 5, 8 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, 6, 10, 11 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, 4, 9 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
7 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.