Psoas Minor, Iliacus and Quadratus Lumborum

Psoas Minor

The Psoas Minor muscle is present in the bodies of only 50% of the people. If present, it runs in the downward direction, in front of the psoas major. Resembling the plantaris muscle of the leg in create and shape, it is only restricted to the abdomen.

Origin

• Its origin is from the side of the intervertebral disc between T12 and L1 vertebrae and adjoining parts of their bodies.

Insertion

• From the site of origin, the muscle runs in front of the psoas major and finishes in a long flat tendon that is added into the iliopubic eminence.

Nerve Supply

• It’s supplied by a branch of L1 spinal nerve.

Actions

• It’s a feeble flexor of the trunk.

Iliacus

• It’s a fan-shaped muscle and creates the lateral component of the iliopsoas muscle.

Origin

• It originates from the upper two-thirds of the floor of iliac fossa, inner lip of iliac crest and upper surface of the lateral part of the sacrum.

Insertion

• The fibres converge on and fuse with the lower part of the psoas major laterally and fit with it on the anterior surface of lesser trochanter and an area (2.5 cm long) below it.

Nerve Supply

• It’s supplied by the femoral nerve.

Actions

• Together with the psoas major, it causes flexion of the thigh and the lumbar part of the vertebral column.

Quadratus Lumborum

It’s a quadrilateral muscle which fills the medial half of the gap between the 12th rib, the iliac crest, and the tips of transverse processes of lumbar vertebrae. The quadratus lumborum muscle is enclosed between the anterior and middle layers of the thoraco-lumbar fascia.

Origin

It originates from:

• Posterior 1-third of the inner lip of the iliac crest and iliolumbar ligament.
• Lower 2 to 4 transverse processes of lumbar vertebrae.

Insertion

• The muscles run upward and medially pass posterior to the lateral arcuate ligament to be added into the medial part of the anterior surface of the 12th rib. It’s also added into the upper lumbar transverse processes, posterior to its slides of origin.

Nerve Supply

• It’s supplied by ventral rami of T12-L3/ L4 lumbar spinal nerves.

Actions

All these are as follows:

• It’s a lateral flexor of the lumbar vertebral column.
• It fixes the 12th rib during inspiration for powerful contraction of the diaphragm.
• Muscles of both sides acting collectively stretch the lumbar vertebral column.