Disc Prolapse & Radiculopathy

Prolapsed intervertebral disc (PIVD/PLID) is among the commonest causes of low back pain with radiating leg symptoms and a perennial NEET PG favourite. These notes cover lumbar and cervical disc disease, the dermatomal/myotomal maps, the named provocative tests, MRI imaging, and the conservative-to-surgical management ladder.

Definition & basic anatomy

The intervertebral disc has two parts: a peripheral annulus fibrosus (concentric collagen lamellae) and a central gelatinous nucleus pulposus (notochord remnant, high proteoglycan/water content). Disc prolapse = displacement of nucleus pulposus material beyond the normal confines of the annulus, usually posterolaterally (the posterior longitudinal ligament is strong centrally but thin laterally, and the annulus is thinnest posterolaterally).

High-yield: The disc herniates posterolaterally because the posterior longitudinal ligament reinforces the midline. This causes compression of the traversing (descending) nerve root, not the exiting root.

Classification of disc herniation (morphological)

Type	Description	Key point
Bulge	Symmetrical extension of disc beyond margins (>50% circumference)	Often physiological/degenerative, not a true herniation
Protrusion	Focal herniation; base wider than the dome	Annulus intact
Extrusion	Herniated material with neck narrower than the dome ("toothpaste")	Through annular tear
Sequestration	Free fragment, no continuity with parent disc	Migrates; may resolve spontaneously

High-yield: Sequestrated discs have the highest spontaneous resorption rate (macrophage-mediated, vascular exposure of nucleus), whereas a contained protrusion resorbs least.

Which root is hit? The "traversing vs exiting" rule

This is the single most tested concept. In a posterolateral (paracentral) herniation, the disc compresses the nerve root that is about to exit one level below (the traversing root).

Rule: A paracentral disc at level X compresses the lower-numbered… no — the root of the level below (e.g., L4–L5 disc → L5 root; L5–S1 disc → S1 root).

A far-lateral (foraminal/extraforaminal) herniation compresses the exiting root of that same level (e.g., far-lateral L4–L5 disc → L4 root).

Flow for localisation: Identify pain dermatome → map to a single root → decide paracentral (traversing root) vs foraminal (exiting root) → confirm level on MRI.

High-yield: The commonest lumbar levels are L4–L5 (most common overall) and L5–S1, together accounting for ~90–95% of lumbar PIVD. Hence L5 and S1 radiculopathy dominate exam questions.

Lumbar radiculopathy — dermatome & myotome map

Root	Disc (paracentral)	Pain/sensory	Motor weakness	Reflex lost
L4	L3–L4	Anterior thigh → medial leg	Quadriceps, tibialis anterior (dorsiflexion/inversion)	Knee jerk ↓
L5	L4–L5	Lateral leg → dorsum of foot, great toe	EHL (great-toe extension), foot drop, gluteus medius	None reliably (no major reflex) — Trendelenburg may be +ve
S1	L5–S1	Posterior leg → lateral foot, little toe, sole	Plantar flexion (gastrocnemius), eversion	Ankle jerk ↓

High-yield: Pure weakness of great-toe extension (EHL) points to L5. A lost ankle jerk with calf weakness points to S1. A lost knee jerk with quadriceps weakness points to L4.

Mnemonic for reflexes — "S1, S2 buckle my shoe (ankle); L3, L4 kick the door (knee)."

Provocative / nerve-tension tests (lumbar)

• Straight Leg Raise (SLR / Lasègue test): With patient supine, the examiner lifts the straight leg. Positive when radicular pain radiates below the knee between 30°–70° of elevation (tension on L5/S1 roots, i.e., sciatic nerve). Pain only in the back or only beyond 70° is not specific.
• Bragard's test: After SLR reaches the painful point, lower the leg slightly (relieving pain) then dorsiflex the foot — reproduction of radicular pain = positive (confirms neural tension).
• Lasègue is sensitive; the crossed (well-leg) SLR is specific.
• Crossed SLR (Fajersztajn): Raising the asymptomatic leg reproduces pain in the symptomatic leg — highly specific for a large central/axillary disc herniation.
• Femoral nerve stretch test (reverse Lasègue): Prone, knee flexed/hip extended → anterior thigh pain = upper lumbar (L2–L4) root involvement.

High-yield: SLR is sensitive but not specific; crossed SLR is specific but not sensitive. Positive SLR between 30–70° is the classic value.

Cervical disc prolapse & radiculopathy

Commonest levels: C6–C7 (→ C7 root, most common) and C5–C6 (→ C6 root). Same paracentral logic: in the cervical spine the root exits above the corresponding pedicle, so a C5–C6 disc compresses the C6 root (the exiting root, because cervical roots exit above their numbered vertebra).

Root	Disc	Sensory	Motor	Reflex
C5	C4–C5	Lateral arm	Deltoid, biceps	Biceps
C6	C5–C6	Lateral forearm, thumb + index	Biceps, wrist extensors	Biceps/brachioradialis
C7	C6–C7	Middle finger	Triceps, wrist flexors, finger extensors	Triceps
C8	C7–T1	Little + ring finger	Hand intrinsics (grip)	None

• Spurling's test: Extension + lateral flexion of the neck towards the affected side, with axial compression → reproduces radicular arm pain. Specific for cervical radiculopathy.
• Shoulder abduction (relief) sign: Placing the hand on the head relieves pain (decompresses the root).
• Lhermitte's sign: Electric shock down the spine on neck flexion → suggests cord/myelopathy or posterior column irritation.

High-yield: Spurling's test = cervical radiculopathy. Lhermitte's = think cervical myelopathy/cord (also MS, B12 deficiency).

Myelopathy vs radiculopathy (frequently differentiated)

Feature	Radiculopathy	Myelopathy
Lesion	Nerve root (LMN)	Spinal cord (UMN below level)
Pain	Dermatomal arm/leg pain prominent	Often painless; gait/hand clumsiness
Tone/reflexes	↓ (hypotonia, hyporeflexia)	↑ (spasticity, hyperreflexia, clonus)
Special signs	Spurling +ve	Hoffmann's, Babinski, inverted radial reflex, gait ataxia, bowel/bladder
Hands	Sensory in dermatome	Myelopathy hand — loss of dexterity, finger escape sign
Management	Mostly conservative	Early surgical decompression (progressive)

High-yield: Positive Hoffmann's sign and Babinski with hyperreflexia in the arms = cervical myelopathy → MRI and surgical referral, because myelopathy is progressive and an indication for decompression.

Pathophysiology

Disc degeneration begins with loss of proteoglycan and water in the nucleus (decreasing from ~90% to ~70% with age) → reduced disc height, annular fissuring, and mechanical incompetence. Radicular pain is dual: (1) mechanical compression of the root, and (2) chemical/inflammatory radiculitis — exposed nucleus pulposus releases phospholipase A2, TNF-α, IL-1, nitric oxide, sensitising the dorsal root ganglion. This explains why pain can be severe even with modest compression and why anti-inflammatory therapy helps.

Clinical features

• Low back pain preceding or accompanying dermatomal leg pain (sciatica) worsened by sitting, coughing, sneezing, straining (Valsalva — Naffziger / Dejerine triad).
• Pain typically eased by lying down, worse on forward flexion.
• Paraesthesia, numbness, dermatomal weakness, depressed reflexes.
• Antalgic gait, lumbar list (sciatic scoliosis), paraspinal spasm.

Cauda equina syndrome (CES) — surgical emergency. Caused by a large central disc herniation compressing multiple sacral roots. Look for: saddle anaesthesia, urinary retention with overflow incontinence, faecal incontinence, bilateral sciatica, reduced anal tone, sexual dysfunction. Urgent MRI and decompression within 24–48 h.

Red flags (TUNA FISH)

Trauma, Unexplained weight loss, Neurological deficit, Age >50 / <20, Fever, IV drug use, Steroid use, History of cancer. Red flags mandate imaging rather than a trial of conservative care.

Diagnosis & investigation of choice

• MRI is the investigation/imaging of choice (gold standard) — best soft-tissue and neural detail, shows disc morphology, root compression, and excludes tumour/infection. No radiation.
• CT myelography — when MRI is contraindicated (pacemaker, claustrophobia) or for bony detail.
• Plain X-ray — limited; shows disc-space narrowing, alignment, excludes spondylolisthesis/instability (flexion-extension views).
• Nerve conduction studies / EMG — when level is unclear or to differentiate from peripheral neuropathy/plexopathy.

High-yield: MRI is highly sensitive but findings must correlate clinically — ~20–30% of asymptomatic adults have disc bulges/protrusions on MRI. Treat the patient, not the scan.

Management

The cornerstone is that most lumbar disc prolapses resolve with conservative care within 6–12 weeks (natural history is favourable; sequestrated fragments resorb).

Conservative ladder:

1. Short relative rest (≤2 days) then early mobilisation — prolonged bed rest is harmful.
2. NSAIDs (drug of choice for pain), paracetamol; short course of muscle relaxants.
3. Neuropathic agents — gabapentin/pregabalin, amitriptyline for radicular pain.
4. Physiotherapy — core strengthening, McKenzie extension exercises, posture.
5. Epidural / transforaminal steroid injection — for persistent radicular pain not settling.

Surgical indications (don't memorise the disc, memorise the deficit):

• Cauda equina syndrome — emergency.
• Progressive or severe motor deficit (e.g., foot drop).
• Failure of conservative treatment ≥6 weeks with disabling radiculopathy.
• Recurrent disabling episodes.

Procedure of choice: Microdiscectomy / open discectomy for the herniated fragment. Laminectomy for central stenosis/CES. Fusion only if instability/spondylolisthesis. Cervical: Anterior Cervical Discectomy and Fusion (ACDF) is the standard; laminoplasty/laminectomy for multilevel myelopathy.

High-yield: Surgery gives faster relief of leg pain than conservative care but outcomes converge at ~1–2 years (SPORT trial). The clearest hard indications remain CES and progressive motor loss.

Decision flow: Sciatica + MRI-confirmed disc → no red flags/CES → conservative 6 weeks → improving? continue : → persistent/severe → epidural steroid → still failing or progressive deficit/CES → discectomy.

Complications

• Of disease: chronic radicular pain, persistent neurological deficit/foot drop, CES, recurrent prolapse.
• Of surgery: recurrent disc herniation (most common, ~5–15%), dural tear/CSF leak, nerve-root injury, epidural haematoma, infection/discitis, and failed back surgery syndrome (epidural fibrosis, arachnoiditis).

Key differentials of sciatica/back-leg pain

Condition	Distinguishing feature
Lumbar canal stenosis	Older patient; neurogenic claudication relieved by flexion (sitting/leaning on trolley — "shopping-cart sign"); pseudo-claudication
Vascular (intermittent) claudication	Relieved by standing still, absent pulses, no postural relief
Piriformis syndrome	Buttock pain, pain on FAIR position, normal MRI disc
Sacroiliitis / facet arthropathy	Localised, no dermatomal deficit
Spinal tumour / metastasis	Night pain, weight loss, red flags, MRI mass
Spinal TB (Pott's)	Constitutional symptoms, gibbus, contiguous vertebral + disc destruction with paraspinal abscess
Peripheral neuropathy	Glove-stocking, non-dermatomal, normal SLR

High-yield: Neurogenic claudication (disc/stenosis) is relieved by flexion/sitting, whereas vascular claudication is relieved by rest/standing — a classic two-liner MCQ.

Recently asked / exam angle

• "L4–L5 disc compresses which root?" → L5 (traversing root in paracentral herniation). Reverse trap: far-lateral L4–L5 hits L4.
• EHL weakness / great-toe extensor weakness → L5 radiculopathy.
• Lost ankle jerk + calf weakness → S1; lost knee jerk + quadriceps weakness → L4.
• SLR positive angle → 30–70°; crossed SLR = specific for large herniation.
• Spurling's test → cervical radiculopathy; Lhermitte's / Hoffmann's → cervical myelopathy.
• Investigation of choice → MRI.
• Most common level: lumbar L4–L5; cervical C6–C7.
• Cauda equina → saddle anaesthesia + retention → emergency decompression.
• Highest spontaneous resorption → sequestrated disc.
• Most common complication after discectomy → recurrent herniation.

Rapid revision

1. Disc herniates posterolaterally; PLL protects the midline.
2. Paracentral disc → traversing root (L4–L5 → L5; L5–S1 → S1).
3. Far-lateral/foraminal disc → exiting root (L4–L5 → L4).
4. L5 = great-toe extensor (EHL) weakness, foot drop; no reliable reflex loss.
5. S1 = ankle-jerk loss + plantar-flexion weakness; L4 = knee-jerk loss + quadriceps.
6. SLR positive 30–70°; crossed SLR is specific; Bragard adds dorsiflexion.
7. Spurling's = cervical radiculopathy; C6–C7 disc → C7 root (most common cervical).
8. Hoffmann's + Babinski + hyperreflexia = cervical myelopathy → decompress.
9. MRI is the investigation of choice; correlate clinically (asymptomatic discs are common).
10. Conservative care for 6 weeks; NSAIDs are first-line; epidural steroid for refractory radiculopathy.
11. Surgical indications: CES, progressive motor deficit, refractory pain → microdiscectomy (cervical → ACDF).
12. Cauda equina = emergency; recurrent herniation is the commonest post-discectomy complication.