MSK TBL 14: Lumbar & Sacral Plexus Functional Anatomy

lumbar plexus formed by

T12 & L1-L4 spinal nerves

• L1-L3 segments to psoas major

• T12-L4 segments to quadratus lumborum

lumbar plexus

• exit spinal cord via intervertebral foramina

• passes thru psoas major muscle

• frequent anastomosis btwn upper part of plexus occur w/ subcostal nerve & btwn L4 spinal nerve & lumbosacral trunk

blood supply to lumbosacral plexus

• lumbar branch of iliolumbar artery [branch of internal iliac artery]

• multiple small collateral arteries to psoas muscle

iliohypogastric nerve sensory branches

• inferior part of abdomen

• lateral aspect of hip

• suprapubic region

• skin over greater trochanter of femur

• scrotum

• labia majora

ilioinguinal nerve sensory branches

• superomedial aspect of thigh

• around pubic symphysis

• root of penus

• superolateral aspect of scrotum or labia majora

genital branch of genitofemoral nerve

• runs in spermatic cord [males] & inguinal canal [female]

• provide motor input to cremaster muscle

• primary sensory supply to skin in pubic region [scrotum, labia majora]

cremaster muscle

contraction raises scrotum

femoral branch of genitofemoral nerve

sensory supply to skin at superoanterior & medial aspect of thigh

[superolateral part of femoral triangle]

cremasteric reflex

• stroke skin of inner thigh → stim sensory fibers of genitofemoral & ilioinguinal nerves

• → motor fibers of genital branch of genitofemoral nerve activate

• cremaster muscle contracts

• → elevation of ipsilateral testicle toward inguinal canal

• protective reflex for thermoregulation of testicles for spermatogensis

• assessment for testicular torsion [absence of reflex = positive for torsion]

for C-section or children requiring inguinal hernia surgery, nerve blocks given to

iliohypogastric, ilioinguinal, or genitofemoral nerves

nerve to piriformis

S1, S2

nerve to obturator internus [& superior gemellus]

L5, S1

nerve to quadratus femoris [& inferior gemellus]

L5, S1

lateral plantar nerve innervates

• abductor digiti minimi

• flexor digiti minimi brevis

• 3rd & 4th interossei

• 2nd, 3rd, 4th lumbricals

• 1st & 2nd plantar interossei

• adductor hallucis