Lumbosacral Plexus
● Plexus: a network of nerves
● Lumbosacral plexus: network of nerves consisting of the anterior (or ventral) rami of nerve
roots L1-L4and L4-S4
○ Remember! When a spinal nerve leaves the intervertebral foramen, it branches into
two divisions:
■ 1. Anterior ramus
■ 2. Posterior ramus
■ Explain picture
● Protected by hip, sacrum, ilioposas muscles
○ Peripheral nerves are mostly protected
○ Exception of sciatic
○ But injuries to nerves like femoral are mostly due to trauma
● In general terms, the lumbosacral plexus supplies:
○ Anterior abdomen
○ External genitals
○ Lower extremity
○ Gluteal region
○ Perineum
Let’s break it down...
Lumbar Region
● Anterior rami of spinal roots L1-L4
● Notice...no roots from L5, L4 is in both lumbar and sacral nerve roots
● Location:
○ Arise from lateral aspects of lumbar vertebrae
○ Extend between the superficial and deep heads of the psoas major
○ Anterior to the quadratus lumborum
○ Medial to the psoas major: genitofemoral and obturator nerves
○ Lateral to psoas major: iliohypogastric, ilioinguinal, lateral cutaneous, and femoral
nerves
● 6 nerve branches: Iliohypogastric, Ilioinguinal, Genitofemoral, Lateral Cutaneous, Femoral
and Obturator
Interesting Individuals Gather Large Furry Objects
I(twice) Get Laid On Fridays
Nerve
Origin
Innervation
Iliohypogastric
L1
Muscles in the anterior abdomen, skin covering
the inferior abdomen and buttock
Ilioinguinal
L1
Muscles of anterior abdomen, skin of
superomedial thigh
Male: penis and scrotum
Female: labia majora and mons pubis
Genitofemoral
L1-L2
Skin over anterior thigh
Male: cremaster and scrotum
Female: labia majora
Lateral Cutaneous nerve
of thigh
L2-L3
Skin over the lateral, medial and posterior thigh
Femoral
L2-L4
Hip flexor muscles, knee extensors, skin over
anteromedial thigh to the medial leg and foot
Obturator
L2-L4
Hip adductor muscles, skin over the medial
thigh
A closer look...
● Femoral nerve
○ Largest nerve of lumbar plexus
○ “L2,3,4 help you kick the door”
○ Extends laterally from psoas major to the inguinal ligament
○ Enters the femoral triangle where it divides into its terminal branches
○ Muscle innervations:
■ Pectineus
■ Sartorius
■ Iliacus
■ Rectus femoris
■ Vastus lateralis, medialis, and intermedius
● Obturator nerve
○ Descends from medial aspect of psoas major
○ Enters the thigh via the obturator foramen
○ Divides into terminal branches at the adductor brevis
○ Anterior branch supplies:
■ Adductor longus
■ Adductor brevis
■ Gracilis
■ Pectineus
○ Posterior branch supplies:
■ Obturator externus
■ Adductor magnus
teachmeanatomy.info
Sacral Region
● Anterior (ventral) rami of spinal nerves L4-S4
● Location:
○ On the posterolateral wall of the lesser pelvis, where it is closely related to the
anterior surface of the piriformis
○ Most of its branches leave the pelvis through the greater sciatic foramen
○ Nerves from the sacral plexus innervate the muscles of the posterior and lateral hip,
posterior thigh, and entire lower leg
Nerve
Origin
Innervation
Sciatic Nerve
L4, L5, S1, S2, S3 Articular branches to hip jt, muscular branches to
hamstrings, all leg and foot muscles
Pudendal Nerve
S2, S3, S4
Structures in perineum, sensory to genitalia,
muscular branch to perineal muscles, sphincter
urethrae, external anal sphincter
Superior Gluteal Nerve
L4, L5, S1
Glut. Medius, glut. minimus, tensor fascia latae
Inferior Gluteal Nerve
L5, S1, S2
Gluteus maximus
Nerve to Piriformis
S1, S2
Piriformis
Nerve to Quadratus
Femoris/Inferior Gemellus
L4, L5, S1
Quadratus femoris and inferior gemellus muscles
Nerve to Obturator
Internus/Superior Gemellus
_______________________
L5, S1, S2
Obturator internus and superior gemellus
muscles
Posterior Femoral
Cutaneous
S2, S3
______________
_______________________________________
Cutaneous branches to buttocks and uppermost
medial and posterior surfaces of the thigh.
Some Particularly Nosey People Need Some Interesting News
**The
nerves formed by the sacral plexus are the sciatic and pudendal nerve.
Sciatic Nerve
two main
● Largest and widest nerve in the body
● Anterior rami converge on the anterior surface of piriformis, passes through greater sciatic
foramen inferior to piriformis to enter gluteal region.
● Consists of two nerves: tibial and common fibular nerve. Both are enveloped in one
connective tissue sheath.
● Tibial portion innervates all biarticular muscles with the hamstring group/the posterior
head of adductor magnus. Common fibular portion innervates short head of biceps femoris.
Pudendal Nerve
● Supplies the skin and muscles of the perineum, terminal parts of the reproductive, urinary,
and digestive tract.
● Accompanies internal pudendal artery. Hooks around the ischial spine and sacrospinous
ligament and enters perineum through the lesser sciatic foramen.
Types of Injuries
Sciatica
o Most common cause for back pain
o Injury to sciatic nerve
o Possible causes to injury
·
Herniated disc
·
Dislocated hip
·
Osteoarthritis of lumbosacral spine
·
Pressure from uterus during pregnancy
·
Inflammation
o Pain could radiate from:
·
Buttocks down posterior and lateral aspect of the leg and lateral aspect of the foot
o Affected Areas
·
Common Fibular portion of the Sciatic Nerve
·
Foot drop
·
Equinovarus
·
Tibial portion
·
Calcaneovagus
·
Loss of sensation of the foot or weakness
o Treatment
·
Common options: rest, pain medications, exercises, ice or heat, and massage
·
Rare cases: Surgery
Lumbar Plexus Injuries
o Injuries to femoral nerve
o Cause: stab or gunshot wounds
§ Inability to extend leg
o Injuries to obturator nerve
o Possible cause: Pressure exerted on the nerve during child birth
§ Paralysis of adductor muscles of the thigh