🦴 Sciatica Nerve Root Compression Simulator

Normal Lumbar Nerve Roots & the Sciatic Nerve

Five nerve roots merge painlessly into the body's thickest nerve.

• L4–S3: Roots forming sciatic nerve (five nerve root levels)
• ~2 cm: Sciatic nerve width (thickest nerve in body)
• ~1 m: Nerve length (buttock to foot)
• 100%: Foramen clearance (normal) (no root contact)

Root anatomy

Five lumbosacral roots exit through open neural foramina.

Nerve formation

Roots braid together into one sciatic nerve trunk.

Signal conduction

Healthy myelin carries signals fast and pain-free.

Normal conduction velocity runs about 40–70 meters per second.

Mild Disc Bulge or Bone Spur Contact

A small bulge starts touching the nerve root's edge.

• Disc bulge: Typical cause (or early osteophyte)
• <30%: Foramen narrowing (mild encroachment)
• Often none: Symptom onset (or mild ache)
• High: Reversibility (with conservative care)

Disc degeneration

Annulus fibers weaken and the disc begins to bulge.

Bone spur growth

Facet joints may grow small bony overgrowths.

Early nerve contact

Mild pressure barely alters conduction at this stage.

Most mild bulges never progress to symptomatic sciatica.

Radicular Pain Down the Sciatic Distribution

Rising pressure inflames the root and pain travels downward.

• Buttock→leg: Pain pathway (along nerve distribution)
• 30–55%: Foramen narrowing (moderate encroachment)
• Sitting, bending: Common trigger (raises disc pressure)
• Sharp, burning: Pain character (shooting quality)

Mechanical irritation

Direct pressure deforms and inflames nerve fibers.

Inflammatory chemicals

Disc material releases irritants that sensitize the root.

Referred pain pattern

Pain follows the nerve, not the compression site.

Pain often radiates below the knee, unlike simple back strain.

Sensory Loss and Motor Weakness Emerge

Sustained pressure starts blocking sensory and motor signals.

• 55–80%: Foramen narrowing (marked encroachment)
• Numbness: Sensory change (tingling, pins & needles)
• Foot drop risk: Motor change (weak dorsiflexion)
• Diminished: Reflex effect (ankle or knee jerk)

Sensory fiber block

Large fibers fail first, dulling touch and vibration.

Motor fiber block

Weakness appears in muscles the root supplies.

Duration matters

Longer compression deepens both deficits over weeks.

Deficits present over six weeks warrant prompt evaluation.

Severe Nerve Compromise & Permanent Risk

Near-total compression threatens lasting nerve damage.

• >80%: Foramen narrowing (severe encroachment)
• Emergency: Cauda equina risk (if bladder/bowel affected)
• Discectomy: Surgical consideration (or decompression)
• Permanent deficit: Untreated outcome (possible nerve death)

Ischemic injury

Severe pressure cuts blood flow to the nerve root.

Axonal loss

Prolonged ischemia can kill nerve fibers permanently.

Red flag symptoms

Bladder or bowel changes signal a surgical emergency.

Cauda equina syndrome requires decompression within 24–48 hours.