MSK ILS 9: Gross Anatomy of Lumbar & Sacral Plexuses

lumbar plexus formed by

anterior rami of spinal nerves L1 to L3 & part of L4

lumbosacral trunk formed by

• rest of anterior ramus of L4 & anterior ramus of L5 [& sometimes S1]

• enters pelvic cavity

sacral plexus

joins with anterior rami of S1 to S3 & part of S4

Lumbar Plexus nerves

• Ilio-hypogastric L1 [sometimes T2]

• Ilioinguinal L1

• Genitofemoral L1-L2

• Lateral femoral cutaneous [nerve of thigh] L2-L3 [posterior division]

• Obturator L2-L4 [anterior division]

• Femoral L2-L4 [posterior division]

ilioinguinal & iliohypogastric

L1

• muscular innervation [inferior portions]

  • transversus abdominus

  • internal oblique

• cutaneous innervation

  • inguinal & pubic regions

Genitofemoral

L1, L2

• muscular innervation

  • cremaster muscle

• cutaneous innervation

  • genital

    • scrotum

    • mons pubis & labia majora

• femoral

  • anterior medial thigh [femoral triangle]

Lateral femoral cutaneous nerve of thigh

L2, L3

• muscular innervation

  • NONE

• cutaneous innervation

  • anterolateral skin of thigh

    • meralgia paresthestica

      • “gunslinger neuralgia”

obturator

L2, L3, L4

• muscular innervation

  • medial compartment [adduction]

    • Direct branch

      • obturator externus

        • lateral rotation

    • Anterior branch [adduction & flexion of hip]

      • adductor longus

      • adductor brevis

      • gracilis [flex knee]

      • pectineus

        • slight flexion in 20% of pple

    • Posterior branch

      • adductor magnus [adductor part only]

        • adduction, extension

        • ischiocondylar [hamstring] part supplied by tibial division of sciatic nerve

• cutaneous innervation

  • small patch on medial thigh

Femoral

L2, L3, L4

• muscular innervation

  • anterior compartment [flex hip, extends knee]

  • Iliacus

    • flex hip

    • psoas major supplied directly by anterior rami L1-L3

  • sartorius

    • flex hip & knee

  • pectineus

    • flex hip

    • 20% obturator

  • quadriceps femoris [knee extension]

    • rectus femoris [flex hip, extends knee]

    • vastus medialis

    • vastus lateralis

    • vastus intermedius

• cutaneous innervation

  • anterior cutaneous branches [anteromedial skin of thigh]

  • saphenous nerve [medial skin of leg]

sacral plexus

• superior gluteal [L4, L5, S1]

• inferior gluteal [L5, S1, S2]

• posterior femoral cutaneous [S1, S3, S4]

• Pudendal [S2, S3, S4]

• Sciatic [L4-S3] mixed

  • Common fibular [L4-S2]

    • posterior division

  • Tibial [L4-S3]

    • anterior division

superior clunial & middle clunial

superior clunial [L1, L2, L3]

middle clunial [S1, S2, S3]

• from posterior rami

• innervate superior & medial portions of buttock

lateral thigh rotators

• nerve to piriformis [S1, S2]

• nerve to obturator internus [L5, S1, S2]

• nerve to quadratus femoris [L4, L5, S1]

nerve to obturator internus

innervates obturator internus & superior gemellus

nerve to quadratus femoris

innervates quadratus femoris & inferior gemellus

superior gluteal nerve

[L4, L5, S1]

• muscular innervation

  • gluteus medius

    • abducts hip

    • helps flex, extend, & medially rotate

  • gluteus minimus

    • abducts hip

    • medial rotation

  • tensor fascia latae [TFL]

    • abducts hip

    • tenses fascia latae

• trendenlenburg test

  • drop of contralateral hip

inferior gluteal nerve

[L5, S1, S2]

• muscular innervation

  • gluteus maximus

    • hip extensor & externally rotates

    • upper fibers: aid in abduction

    • lower fibers: aid in adduction

      • together, help raise from seated position

posterior femoral cutaneous nerve [of thigh]

[S1, S2, S3]

cutaneous innervation of inferior buttock [inferior clunial nerve], thigh, variable portions of scrotum or labium majus [perineal branches]

pudendal nerve

[S2, S3, S4]

• muscular innervation

  • external anal sphincter

  • external urethral sphincter

  • muscles of pelvic floor

• cutaneous innervation

  • perineum

  • anus

sciatic nerve

[L4, L5, S1, S2, S3]

• divides at popliteal fossa into tibial nerve & common fibular

• muscular innervation of “hamstring” [direct branches from sciatic]

  • common fibular

    • biceps femoris [short head]

  • tibial

    • semitendinosus

    • semimembranosus

    • biceps femoris [long head]

    • adductor magnus

Sciatic - Common Fibular - Superficial fibular

• lateral compartment of leg

  • fibularis longus

  • fibularis brevis

• cutaneous innervation of lateral leg [lateral sural cutaneous nerve] & dorsum of foot

Sciatic - Common Fibular - Deep fibular

• anterior compartment of leg

  • tibialis anterior

  • extensor digitorum longus

  • extensor hallucis longus

  • fibularis tertius

  • dorsum of foot

  • extensor digitorum brevis

  • extensor hallucis brevis

• cutaneous innervation of skin btwn 1st & 2nd toes [1st webspace]

common fibular injury

• occurs at neck of fibula

• affects anterior & lateral compartment of legs

• no dorsiflexion = foot drop

sciatic - tibial - plantar nerves

• posterior compartment of leg

• superficial [plantarflexion]

  • gastrocnemius

  • soleus

  • plantaris

• deep [invert foot, flex toes]

  • popliteus

  • tibialis posterior

  • flexor digitorum longus

  • flexor hallucis longus

• plantar nerves [medial & lateral nerves]

  • all plantar muscles [flex, adduct, & abduct toes]

• cutaneous innervation

  • sural nerve

    • posterior leg, lateral ankle, & foot [pinky toe]

      • dual formation: medial sural cutaneous nerve [from tibial] unites w/ sural communicating branch [from common fibular]

  • calcaneal branches

    • skin of heel

  • proper plantar branches

    • skin of sole of foot

sciatic nerve injury: piriformis syndrome

• compression of sciatic nerve due to compression of piriformis

• damage to medial aspect of buttock puts sciatic, inferior gluteal, & posterior cutaneous nerve of thigh at risk

  • stab wound/intragluteal injections

• damage to sciatic → paralysis of hamstrings

  • impaired thigh extension & knee flexion