The psoas major is the largest muscle in cross section at
the lower levels of the lumbar spine.
5 It has fibrous at-
tachments to the anterior aspect of all lumbar transverse
processes and to the anteromedial aspect of all the lumbar
discs and adjoining bodies with the exception of the L5/
S1 disc.
6 For their relative positions on the spine, the at-
tachments on the transverse processes are named the pos-
terior attachments and those on the disc and bodies are
called the anterior attachments. These attachments con-
stitute the individual fascicles. The fascicles of the psoas
major are approximately similar in length throughout the
lumbar spine and have a unipennate fiber orientation.
Muscle fiber length within the anterior fascicles ranges
from 3 to 8 cm and 3 to 5 cm in the posterior fascicles.
7
The fascicles are oriented inferolaterally and come to-
gether as a common tendon which descends over the pel-
vic brim and shares a common insertion with the iliacus
muscle on the lesser trochanter of the femur.