The positioning of the lumbar plexus within the psoas muscle is somewhat
controversial. Winnie, for example, described the plexus as lying between the psoas and
quadratus lumborum muscles. From this description, “psoas compartment block” was
termed for the lumbar plexus block. Other names for the same thing are “lumbar plexus
block”, “lumbar paravertebral block”, “quadratus lumborum block” and “fascia iliaca
block” to name a few. Most authors described the plexus and its nerve branches within
the psoas muscle between its anterior and posterior masses. The ventral rami of the first
three and the major part of the fourth lumbar spinal roots (L2, L3, and L4) form the
lumbar plexus. A contribution from the 1st lumbar nerve (L1) is common. As soon as
the ventral rami of these spinal nerve roots exit the intervertebral foramina, they become
embedded in the psoas muscle, anterior to the transverse processes. At the L4 to L5
level, however, the lumbar plexus branches are still medial and close to the transverse
processes. The distance of the lumbar plexus to the skin varies with body habitus and
gender. Capdevila and his colleagues described the distances as varying from 57 to 93
mm in women and from 61 to 101 mm in men.
The macro-, microanatomy, and sonoanatomy (static) of the lumbar plexus, its nerve
roots, and relationships to other structures are discussed in this chapter.
Keywords: Acute pain medicine, Fascia iliaca, Femoral nerve, Genitofemoral
nerve, Iliohypogastirc nerve, Ilioinguinal nerve, Intervertebral foramina, Lumbar
paravertebral block, Lumbar plexus, Lumbar plexus block, Lumbosacral trunk,
Macroanatomy, Microanatomy, Obturator nerve, Psoas compartment block, Psoas
muscle, Quadratus lumborum block, Quadratus lumborum muscle, Regional
anesthesia, Sciatic nerve, Sonoanatomy, Spinal nerve roots, Transverse processes,
Ventral rami.
