The psoas minor muscle ( or ; from grc, ψόᾱ, psóā, muscles of the loins) is a long, slender
skeletal muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
.
When present, it is located anterior to the
psoas major muscle
The psoas major ( or ; from grc, ψόᾱ, psóā, muscles of the loins) is a long fusiform muscle located in the lateral lumbar region between the vertebral column and the brim of the lesser pelvis. It joins the iliacus muscle to form the il ...
.
[Tank (2005), p 93][Gray (2008), p 1372]
Structure
The psoas minor muscle originates from the vertical
fascicle
Fascicle or ''fasciculus'' may refer to:
Anatomy and histology
* Muscle fascicle, a bundle of skeletal muscle fibers
* Nerve fascicle, a bundle of axons (nerve fibers)
** Superior longitudinal fasciculus
*** Arcuate fasciculus
** Gracile fas ...
s inserted on the last
thoracic
The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...
and first
lumbar vertebra
The lumbar vertebrae are, in human anatomy, the five vertebrae between the rib cage and the pelvis. They are the largest segments of the vertebral column and are characterized by the absence of the foramen transversarium within the transverse p ...
e. From there, it passes down onto the medial border of the psoas major, and is inserted to the
innominate line and the
iliopectineal eminence
Medial to the anterior inferior iliac spine is a broad, shallow groove, over which the iliacus and psoas major muscles pass. This groove is bounded medially by an eminence, the iliopubic eminence (or iliopectineal eminence), which marks the point o ...
. Additionally, it attaches to and stretches the deep surface of the
iliac fascia
The iliac fascia, or Abernethy's fascia, is a fascia in the region of the ilium of the pelvis.
It has the following connections:
* ''laterally'', to the whole length of the inner lip of the iliac crest.
* ''medially'', to the linea terminalis of ...
and occasionally its lowermost fibers reach the
inguinal ligament
The inguinal ligament (), also known as Poupart's ligament or groin ligament, is a band running from the pubic tubercle to the anterior superior iliac spine. It forms the base of the inguinal canal through which an indirect inguinal hernia may dev ...
.
[Bendavid (2001), p 58] It is posteriolateral to the
iliopsoas muscle. Variations occur, however, and the insertion on the iliopubic eminence sometimes radiates into the
iliopectineal arch
The Iliopectineal arch is a thickened band of fused iliac fascia and psoas fascia passing from the posterior aspect of the inguinal ligament anteriorly across the front of the femoral nerve to attach to the iliopubic eminence of the hip bone po ...
.
[Platzer (2004), p 234]
The psoas minor muscle receives oxygenated blood from the four
lumbar arteries
The lumbar arteries are arteries located in the lower back or lumbar region. The lumbar arteries are in parallel with the intercostals.
They are usually four in number on either side, and arise from the back of the aorta, opposite the bodies of ...
(inferior to the subcostal artery) and the lumbar branch of the
iliolumbar artery
The iliolumbar artery is the first branch of the posterior trunk of the internal iliac artery.
Structure
The iliolumbar artery is the first branch of the posterior trunk of the internal iliac artery. It turns upward behind the obturator nerve a ...
.
Innervation
The psoas minor muscle is
innervated
A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system.
A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...
by direct branches of the
lumbar spinal nerves.
Variation
The psoas minor muscle is considered inconstant and is often absent, only being present in about 40% of human specimens studied.
[Mcg Farias (1 Jan. 2012). Morphological and morphometric analysis of Psoas Minor Muscle in cadavers. ResearchGate. Retrieved from https://www.researchgate.net/publication/280236296_Morphological_and_morphometric_analysis_of_Psoas_Minor_Muscle_in_cadavers] It has an average length of about 24 cm, of which about 7.1 cm is muscle tissue and about 17 cm is tendon.
Function
The psoas minor is a weak flexor of the lumbar vertebral column.
Other animals
The psoas minor muscle is present in other
mammals
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
, such as
horses
The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million yea ...
.
In horses, it may be palpated during
rectal exams to check for causes of
back pain
Back pain is pain felt in the back. It may be classified as neck pain (cervical), middle back pain (thoracic), lower back pain (lumbar) or coccydynia (tailbone or sacral pain) based on the segment affected. The lumbar area is the most common area ...
.
Additional images
File:Gray236.png, Right hip bone, internal surface
File:Gray245.png, Right femur, posterior surface
File:Slide4nn.JPG, Psoas minor muscle
File:Slide9pp.JPG, Psoas minor muscle
File:Slide6ppp.JPG, Psoas minor muscle
Notes
References
*
* (ISBN for the Americas 1-58890-159-9.)
*
*
{{Authority control
Hip flexors
Hip muscles
Spine flexors
Muscles of the lower limb