Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

The lumbosacral plexus is a network of nerves supplying the:

• Lower limb
• Pelvic region

The lumbar plexus forms the upper part of this system.

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Key Features

• Arises from anterior rami of L1–L4
• May receive contribution from T12
• Part of L4 forms the lumbosacral trunk, connecting to the sacral plexus

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Lumbar Plexus

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Origin

Formed from:

• L1
• L2
• L3
• L4
• ± Contribution from T12

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Branches of the Lumbar Plexus

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Six Main Nerves

1. Iliohypogastric nerve
2. Ilioinguinal nerve
3. Genitofemoral nerve
4. Lateral femoral cutaneous nerve
5. Obturator nerve
6. Femoral nerve

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Memory Aid

“I Twice Got Lunch On Friday”

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Nerve Root Contributions

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From One Root

• Iliohypogastric – L1
• Ilioinguinal – L1

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From Two Roots

• Genitofemoral – L1–L2
• Lateral femoral cutaneous – L2–L3

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From Three Roots

• Obturator – L2–L3–L4
• Femoral – L2–L3–L4

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Relation to Psoas Major Muscle

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Lateral Border (Most Nerves)

• Iliohypogastric
• Ilioinguinal
• Lateral femoral cutaneous
• Femoral

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Anterior Surface

• Genitofemoral nerve

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Medial Border

• Obturator nerve

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Major Lumbar Plexus Nerves

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Femoral Nerve

Roots

• L2–L4

Motor Function

• Innervates quadriceps
• Responsible for knee extension

Sensory Supply

• Anterior thigh
• Medial leg (via saphenous nerve)

Clinical Relevance

• Weak knee extension
• Reduced patellar reflex

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Obturator Nerve

Roots

• L2–L4

Motor Function

• Supplies adductor muscles
• Responsible for hip adduction

Sensory Supply

• Medial thigh

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Lateral Femoral Cutaneous Nerve

Roots

• L2–L3

Type

• Purely sensory

Function

• Sensation over lateral thigh

Clinical Relevance

• Compression – Meralgia paresthetica

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Genitofemoral Nerve

Roots

• L1–L2

Branches

• Genital branch
• Femoral branch

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Functions

• Genital branch:
  • Cremaster muscle
  • Genital skin
• Femoral branch:
  • Upper anterior thigh sensation

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Iliohypogastric Nerve

Root

• L1

Function

• Supplies:
  • Abdominal wall muscles
  • Lower abdomen
  • Upper lateral gluteal region

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Ilioinguinal Nerve

Root

• L1

Function

• Supplies:
  • Abdominal wall
  • Upper medial thigh
  • External genitalia

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Key Summary Points

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Structural Overview

• Lumbar plexus arises from L1–L4 (± T12)
• Forms the upper component of the lumbosacral plexus

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Branch Pattern

• 2 nerves from one root
• 2 nerves from two roots
• 2 nerves from three roots

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Important Clinical Nerves

• Femoral nerve — anterior thigh
• Obturator nerve — medial thigh

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Relation to Psoas Major

• Most nerves emerge laterally
• Exceptions:
  • Genitofemoral — anterior
  • Obturator — medial

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Clinical Insight

Understanding this organized pattern helps in:

• Neurological localization
• Diagnosis of nerve injuries
• Surgical planning