Courtesy: Medical Lectures Made Easy

Introduction

The lumbar plexus is a complex network of nerves formed by the ventral rami of spinal nerves L1 to L4, with occasional contribution from T12.

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Location

The plexus is located within the psoas major muscle, situated along the posterior abdominal wall.

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Functions

The lumbar plexus provides motor and sensory innervation to:

• Lower abdominal wall

• Anterior thigh

• Medial thigh

• Genital region (cutaneous supply)

• Portions of the lower limb

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Branches of the Lumbar Plexus

The major branches include:

1. Ilioinguinal nerve

2. Genitofemoral nerve

3. Lateral femoral cutaneous nerve

4. Femoral nerve

5. Obturator nerve

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1. Ilioinguinal Nerve

Root

• L1

Course

• Travels through the inguinal canal

Function

Provides sensory innervation to:

• Scrotum (male)

• Labia majora (female)

• Upper medial thigh

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2. Genitofemoral Nerve

Roots

• L1–L2

Divisions

The nerve divides into:

• Genital branch

• Femoral branch

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Genital Branch

Course

• Passes through the inguinal canal

Function

• Sensory supply to scrotum or labia majora

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Femoral Branch

Course

• Travels beneath the inguinal ligament

Function

• Supplies skin over the proximal anterior thigh

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3. Lateral Femoral Cutaneous Nerve

Roots

• L2–L3

Course

• Passes beneath the inguinal ligament

Function

• Provides sensory innervation to the anterolateral thigh

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Clinical Correlation: Meralgia Paresthetica

Cause

• Compression of the lateral femoral cutaneous nerve

Symptoms

• Burning pain

• Tingling sensation

• Numbness over the anterolateral thigh

Common Risk Factors

• Tight clothing

• Obesity

• Pregnancy

• Pelvic compression

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4. Femoral Nerve

Roots

• L2–L4

Course

• Emerges from the lateral border of psoas major

• Passes beneath the inguinal ligament

• Enters the femoral triangle

Distribution

• Supplies muscles of the anterior thigh

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Muscles Supplied by the Femoral Nerve

Hip Flexors

• Pectineus

• Sartorius

• Iliopsoas

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Iliopsoas Muscle

Function

• Primary hip flexor

• Assists in lateral rotation

Insertion

• Lesser trochanter of femur

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Knee Extensors (Quadriceps Femoris)

Muscles include:

1. Rectus femoris

2. Vastus medialis

3. Vastus lateralis

4. Vastus intermedius

Function

• Extension of the knee

Insertion

• Patella – Patellar tendon andTibial tuberosity

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Saphenous Nerve

Key Features

• Terminal branch of femoral nerve

• Longest sensory nerve in the body

• Passes through the adductor canal

Sensory Supply

• Medial leg

• Medial aspect of foot

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Adductor Canal

Contents

• Femoral artery

• Femoral vein

• Saphenous nerve

• Nerve to vastus medialis

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Clinical Correlation: Femoral Neck Fracture

Presentation

• Shortened limb

• External rotation

Mechanism

The iliopsoas muscle pulls the limb into:

• Flexion

• External rotation

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Additional Muscles

Sartorius

• Functions: Hip flexion, abduction, lateral rotation

• Innervation: Femoral nerve

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Pectineus

• Functions: Hip flexion and adduction

• Innervation:

  • Primarily femoral nerve

  • Occasionally obturator nerve

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5. Obturator Nerve

Roots

• L2–L4

Course

• Passes through the obturator canal

Distribution

• Supplies the medial compartment of the thigh

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Muscles Supplied

• Adductor longus

• Adductor brevis

• Adductor magnus (partial)

• Gracilis

• Obturator externus

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Function

• Primary action: Adduction of the thigh

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Gracilis Muscle

Features

• Long, slender muscle

• Commonly used in graft procedures

Clinical Note

• Functionally expendable

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Pes Anserinus

Components

Insertion of three muscles:

1. Sartorius

2. Gracilis

3. Semitendinosus

Location

• Medial surface of the proximal tibia

Meaning

• Latin for “Goose Foot”

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Adductor Hiatus

Description

An opening in the adductor magnus muscle

Structures Passing Through

• Femoral artery

• Femoral vein

Continuation

These vessels become:

• Popliteal artery

• Popliteal vein

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Connection to Sacral Plexus

Lumbosacral Trunk

• Formed by: L4 and L5 nerve roots

• Connects lumbar plexus to sacral plexus

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Summary Table

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Key Clinical Conditions

• Meralgia paresthetica ? Compression of lateral femoral cutaneous nerve

• Femoral neck fracture ? Shortened, externally rotated limb

• Adductor muscle injuries ? May involve obturator nerve