Lumbar Disc Herniation – High-Yield Review

Introduction

Lumbar disc herniation is one of the most common causes of:

• Low back pain
• Radiculopathy
• Sciatica

Most herniations occur in the lower lumbar spine and may compress adjacent nerve roots, leading to neurological symptoms.

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Basic Anatomy

Components of the Spine

The spine consists of:

• Vertebrae
• Intervertebral discs
• Spinal canal
• Neural elements

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Neural Anatomy

Spinal Cord

The spinal cord typically ends at:

• T12–L1 level

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Conus Medullaris

The terminal portion of the spinal cord is called the:

• Conus medullaris

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Cauda Equina

Below the conus lies the:

• Cauda equina

which consists of lumbar and sacral nerve roots.

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Lumbar Spine Overview

The lumbar spine contains:

• Five vertebrae: L1–L5

Inferiorly, the lumbar spine articulates with:

• Sacrum

The lumbosacral junction is:

• L5–S1

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Structure of the Intervertebral Disc

The disc has two major components.

1. Nucleus Pulposus

Characteristics:

• Soft
• Gelatinous
• Shock-absorbing center

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2. Annulus Fibrosus

Characteristics:

• Tough fibrous outer ring
• Contains the nucleus pulposus
• Provides structural stability

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Common Levels of Herniation

The most commonly affected levels are:

1. L5–S1
2. L4–L5

These segments experience the greatest mechanical stress.

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Nerve Root Involvement

Important Rule

• Posterolateral herniation affects the traversing nerve root
• Foraminal herniation affects the exiting nerve root

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Common Patterns

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Types of Disc Herniation

1. Disc Bulge / Protrusion

Characteristics:

• Mild herniation
• Annulus remains intact

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2. Disc Extrusion

Characteristics:

• Annulus disrupted
• Disc material extends outward

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3. Disc Sequestration

Characteristics:

• Free disc fragment
• No continuity with parent disc
• May undergo spontaneous resorption

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Locations of Disc Herniation

Posterolateral Herniation

Most Common Type

Characteristics:

• Compresses a single nerve root
• Produces classic radiculopathy

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Foraminal Herniation

Less Common

Occurs in approximately 8–10% of cases.

Characteristics:

• Compresses exiting nerve root
• Often causes severe radicular pain

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Central Disc Herniation

Rare but Dangerous

Can compress multiple nerve roots within the cauda equina.

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Clinical Features

May cause:

• Severe low back pain
• Bilateral lower limb symptoms
• Bladder dysfunction
• Bowel dysfunction

Central herniation is a neurological emergency.

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Cauda Equina Syndrome

Clinical Importance

Cauda equina syndrome is a surgical emergency.

Early recognition is critical because delayed treatment may result in permanent neurological deficit.

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Clinical Features

Typical symptoms include:

• Bladder dysfunction
• Bowel dysfunction
• Saddle anesthesia
• Bilateral lower limb weakness
• Bilateral sensory loss

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Examination

Important components include:

• Perianal sensation
• Digital rectal examination
• Anal sphincter tone

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Investigation

Requires:

• Emergency MRI

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Treatment

Management includes:

• Emergency decompression surgery

Timing of surgery strongly influences neurological recovery.

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Discogenic Back Pain (Internal Disc Disruption)

Pathophysiology

Occurs due to:

• Annular tear
• Early disc degeneration

without major nerve root compression.

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Clinical Features

Typical findings include:

• Pain worsened by sitting
• Pain worsened by flexion
• Limited forward bending
• Relief with extension

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Important Difference

Discogenic pain usually does not produce:

• Radiculopathy
• Neurological deficit

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Clinical Correlation and MRI

Important Principle

MRI findings must always be correlated with:

• Clinical symptoms
• Physical examination

Imaging abnormalities alone should not determine treatment.

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Natural History

Important observations include:

• Many lumbar disc herniations improve spontaneously
• Large extruded discs may resorb over time
• Not all herniations require surgery

Conservative treatment is successful in most patients.

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Red Flags in Lumbar Disc Disease

Important warning signs include:

• Cauda equina syndrome
• Progressive neurological deficit
• Severe motor weakness
• Bladder or bowel dysfunction

These findings require urgent evaluation.

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Key Clinical Pearls

• Most lumbar disc herniations occur at L4–L5 and L5–S1.
• Posterolateral herniation is the most common pattern.
• Foraminal herniation affects the exiting nerve root.
• Central herniation may cause cauda equina syndrome.
• Discogenic pain differs from radiculopathy.
• MRI abnormalities must always correlate clinically.
• Many disc herniations improve without surgery.
• Early diagnosis of cauda equina syndrome is critical.