Lumbar disc herniation and radiculopathy

01OverviewDefinition, clinical context and the essential points that orientate the chapter.

Intervertebral discs consist of a hydrated nucleus pulposus contained by annulus fibrosus and endplates. Ageing, loading and genetic susceptibility promote dehydration and annular fissuring. A focal protrusion or extrusion can narrow the lateral recess or foramen and irritate a lumbar root through mechanical deformation and inflammation. Radiculopathy means objective or clinical root dysfunction; radicular pain may occur without measurable weakness, and axial low-back pain alone is not synonymous with a compressed root.

Root localisation combines pain, paraesthesia, motor testing and reflexes rather than trusting one feature. L4 dysfunction may cause anterior thigh or medial leg symptoms, weak knee extension and a reduced patellar reflex. L5 often causes dorsum-of-foot pain, weakness of great-toe extension, ankle dorsiflexion or hip abduction, with no consistently useful deep-tendon reflex. S1 tends toward posterior calf or lateral-foot symptoms, weak plantar flexion and a reduced ankle reflex. Overlap is common, pain inhibition can mimic weakness and diabetes or peripheral entrapment can blur the pattern.

Disc level and root are not interchangeable. In the lumbar canal, a posterolateral disc usually compresses the traversing root: L4–5 therefore commonly affects L5. A foraminal or extraforaminal L4–5 disc lies beside the exiting L4 root. This distinction prevents wrong-level reasoning and explains why a report describing a disc at one vertebral level must be correlated with the neurological pattern and side.

Most uncomplicated episodes improve without surgery, and extruded disc material may regress. Initial care therefore emphasises understandable prognosis, activity rather than bed rest and exercise matched to ability. Escalation is driven by emergency sphincter or saddle symptoms, progressive deficit, persistent disabling leg-dominant symptoms and concordant imaging—not by disc size in isolation. NICE NG59 covers people aged 16 and over with low-back pain and sciatica, but does not replace an emergency cauda equina pathway or a specialist operation-specific guideline.

Key points

Lumbar radiculopathy is nerve-root dysfunction: leg pain usually follows a dermatomal tendency and may be accompanied by root-specific sensory loss, weakness or depressed reflexes; common MRI abnormalities are not automatically causal.
A posterolateral L4–5 disc usually affects the traversing L5 root, while L5–S1 commonly affects S1; far-lateral or foraminal discs more often affect the exiting root.
New bladder, bowel or sexual disturbance, or new perineal numbness, with severe radiating low-back pain triggers immediate referral for cauda equina assessment under NICE NG127—do not wait for every classic feature.
Do not routinely image uncomplicated low-back pain or sciatica in non-specialist care; specialist imaging is appropriate only when its result is likely to change management.
Begin with explanation, encouragement to remain active and tailored exercise. NICE advises against gabapentinoids, other antiepileptics, oral corticosteroids and benzodiazepines for sciatica and against opioids for chronic sciatica.
Consider decompression only when non-surgical treatment has not improved pain or function and radiological findings are consistent with the sciatic symptoms; imaging alone is not an operative indication.

02AetiologyUnderlying causes, associations and risk factors, with why each one matters.

Degenerative annular failure

Disc dehydration and annular fissuring permit focal protrusion or extrusion, commonly posterolaterally where a traversing root can be affected.

Foraminal or far-lateral herniation

A more lateral fragment compromises the exiting root and can create a pattern different from the common lateral-recess lesion.

Non-disc compression

Facet or ligament hypertrophy, synovial cyst, tumour, infection and haemorrhage can mimic a disc-related root syndrome.

03PathophysiologyThe causal sequence from the underlying abnormality to symptoms and harm.

1
Mechanical deformation
Contact and pressure impair root conduction and perfusion, particularly within a constrained lateral recess or foramen.
2
Chemical radiculitis
Inflammatory mediators from disc material help explain severe radicular pain even when gross compression appears modest.
3
Cauda equina compromise
A large central lesion can affect multiple lumbosacral roots controlling lower limbs, perineal sensation and pelvic-organ function.

04Clinical features and red flagsSymptoms, examination findings, patterns of presentation and time-critical warnings.

L4 radiculopathy

Pain or altered sensation may involve the anterior thigh and medial shin. Test knee extension and the patellar reflex, recognising overlap with L3 and femoral neuropathy.

L5 radiculopathy

Symptoms commonly reach the lateral leg or dorsum of the foot. Test great-toe extension, ankle dorsiflexion, hip abduction and heel walking; distinguish common fibular neuropathy by distribution and inversion/hip-abduction findings.

S1 radiculopathy

Posterior calf or lateral-foot symptoms, weak plantar flexion, difficulty toe walking and a reduced ankle jerk suggest S1, but Achilles disease and length-dependent neuropathy can confound testing.

Cauda equina syndromeRed flag

Ask explicitly about urinary sensation, initiation and retention, continence, bowel control, sexual function and altered saddle sensation. New dysfunction with severe radiating low-back pain requires immediate pathway referral even without bilateral sciatica.

Progressive focal deficitRed flag

Repeat power testing when pain is controlled and compare sides. A new or worsening objective motor deficit changes urgency and should be discussed promptly with spinal services.

Non-radicular mimics

Hip disease, sacroiliac pain, vascular claudication, meralgia paraesthetica, fibular neuropathy, polyneuropathy and serious visceral disease can all produce leg symptoms. Re-examine when the story and root pattern disagree.

Red flags requiring action

New urinary retention, impaired urinary sensation, overflow incontinence, faecal incontinence, loss of sexual function or new saddle/perineal numbness with radiating low-back pain requires immediate cauda equina assessment.
Rapidly progressive or severe motor deficit, especially bilateral weakness, foot drop or loss of walking ability, requires urgent spinal review rather than routine conservative follow-up.
Fever, immunosuppression, injecting-drug use, recent bacteraemia or spinal procedure raises spinal infection; constant night pain, weight loss or cancer history raises malignant compression.
Significant trauma, osteoporosis or long-term glucocorticoids raises fracture; a pulsatile abdominal mass, collapse or vascular risk can indicate a non-spinal emergency.
Painful weakness with upper-motor-neuron signs, a sensory level or arm involvement is not explained by a single lumbar root and should prompt reconsideration of cord or brain disease.
A painless progressive deficit, systemic neuropathy pattern or symptoms not following a root distribution should not be forced into a disc diagnosis merely because MRI shows degeneration.

05InvestigationsWhat to request, why it matters and how to interpret it.

Investigation order

Read from the initial assessment onwards. Tests may run in parallel in urgent care; first-line, preferred, confirmatory, definitive and gold-standard labels appear only when the chapter explicitly states them.

01
Focused neurological and sacral examinationFirst step
Why
Localise the root, quantify weakness and identify cauda equina or cord features.
Interpretation and limitations
Record myotomal power, dermatomal sensation, knee and ankle reflexes, gait and relevant sacral findings. A normal single bedside sign does not override new bladder, bowel, sexual or saddle symptoms.
02
Bladder scan after voiding when cauda equina is suspected
Why
Identify clinically significant retention and support immediate bladder care while urgent assessment proceeds.
Interpretation and limitations
A raised residual strengthens concern, but a low residual does not exclude incomplete cauda equina syndrome and must not delay referral or MRI.
03
Lumbar MRI
Why
Demonstrate disc, root and cauda equina anatomy when emergency assessment is required or when specialist results will change management.
Interpretation and limitations
Match level, side and compressed traversing or exiting root to the clinical syndrome. Degenerative bulges are frequent incidental findings; discordance demands diagnostic review.
04
CT or CT myelography
Why
Provide bony or canal detail when MRI is unavailable or contraindicated under specialist direction.
Interpretation and limitations
CT is less informative for many soft-tissue and neural questions; myelography is invasive and is not routine first-line testing for uncomplicated sciatica.
05
Electrodiagnostic testing
Why
Clarify chronic root dysfunction or distinguish radiculopathy from peripheral neuropathy when clinical and imaging findings remain discordant.
Interpretation and limitations
Denervation supports axonal root injury but may be absent early; a normal study does not exclude painful radiculopathy and it does not replace emergency imaging.
06
Targeted laboratory tests
Why
Investigate infection, inflammation, malignancy or metabolic neuropathy only when history and examination raise those alternatives.
Interpretation and limitations
FBC, inflammatory markers, cultures or metabolic tests answer a differential question; they are not routine confirmatory tests for mechanical disc herniation.

06Differential diagnosisRealistic alternatives and the features that help distinguish them.

Hip pathology

Groin-dominant pain, reduced hip rotation and mechanical hip provocation suggest a joint source rather than isolated lumbar-root disease.

Peripheral nerve lesion

Fibular neuropathy can cause foot drop; preserved inversion and absent hip-abduction weakness help separate it from L5 root disease.

Vascular disease

Exertional calf pain linked to metabolic demand, vascular risk and abnormal pulses differs from posture-dependent neural symptoms.

Spinal infection or malignancy

Systemic features, immune risk, cancer history or non-mechanical night pain demand targeted urgent investigation for a destructive spinal process.

07ManagementImmediate care, first-line treatment, alternatives and escalation.

01Persistent sciatica pathwayConcordant lumbar disc radiculopathyFirst stepLeg-dominant radicular pain or deficit persists without cauda equina or another emergency.

1Explain the likely course, support normal activity and work where possible, and offer a tailored exercise-based programme with review of function and neurological change.
2If pain or function remains substantially impaired, arrange specialist assessment; obtain imaging only when the result is likely to change management, and require clinical–radiological concordance.
3For acute severe sciatica, consider an epidural injection of local anaesthetic and steroid through an appropriately skilled service after risk discussion; this is not routine treatment for every disc.
4Consider spinal decompression when non-surgical treatment has not improved pain or function and the radiology is consistent with the sciatic symptoms; discuss natural history, likely leg-pain benefit and operative risks.
5Reassess diagnosis if pain remains axial, widespread or discordant, and continue rehabilitation whether surgery is chosen or not.

02Emergency pathwayPossible cauda equina compressionNew bladder, bowel, sexual or saddle dysfunction accompanies severe radiating low-back pain.

1Refer immediately under the local suspected cauda equina pathway and obtain urgent specialist MRI; document timing but do not wait for outpatient investigations.
2Support ABC, analgesia and bladder care, perform serial lower-limb and sacral assessment, and involve the spinal surgical team promptly if compression is demonstrated.
3DefinitiveAfter definitive treatment or exclusion, provide a named plan for residual bladder, bowel, sexual, motor and pain review.

03Diagnostic reconsideration pathwayDiscordant persistent leg symptomsSymptoms persist but the examination and lumbar imaging do not identify the same root and side.

1Re-examine the lumbar roots, hips, peripheral nerves and vascular system and revisit serious systemic alternatives from the history.
2Use targeted electrodiagnostic, vascular, hip or laboratory investigation only when it answers the revised differential question.
3Avoid disc-directed injection or surgery until a credible symptomatic target is established, and agree functional management meanwhile.

Key medicines and prescribing safety2 treatments · regimens, roles and cautions

May provide limited short-term symptom relief while activity and rehabilitation continue.

Oral NSAID

If selected for an adult, use the lowest effective dose for the shortest possible period according to the chosen product and individual risk.

For sciatica, NICE highlights limited evidence of benefit and risk of harm. Consider gastrointestinal, renal, hepatic and cardio-renal toxicity, age, pregnancy and interacting medicines; use gastroprotection and monitoring when indicated.

NICE found no overall evidence of benefit and evidence of harm for these drug classes in sciatica.

Gabapentinoids, other antiepileptics, oral corticosteroids and benzodiazepines

Do not initiate for sciatica as routine treatment.

If already prescribed, discuss risks and review safe withdrawal rather than stopping dependence-forming medicines abruptly. This recommendation is specific to sciatica and does not erase other licensed indications.

08ComplicationsImportant consequences, why they occur and why they matter clinically.

Persistent motor deficit

Prolonged or severe axonal injury may leave foot drop, calf weakness or altered gait despite pain improvement.

Cauda equina dysfunction

Delayed relief of major central compression risks enduring bladder, bowel, sexual, sensory and lower-limb motor disability.

Chronic pain and deconditioning

Fear, inactivity, sleep disturbance and work loss can maintain disability after the acute inflammatory episode settles.

Treatment harm

NSAID toxicity, medicine dependence, injection complications and operative neural or dural injury require proportionate consent and follow-up.

09Monitoring and follow-upTreatment response, safety checks and longer-term review.

At every review, ask again about bladder, bowel, sexual and saddle symptoms and document any progression of motor deficit.
Track walking, sleep, work and daily function as well as a pain score; improvement in participation often precedes complete pain resolution.
If using an NSAID, review adverse-effect risk, concurrent medicines, renal function and gastroprotection according to the person and product.
After injection or surgery, define who reviews neurological recovery, wound or procedure complications and recurrent symptoms.
Escalate sooner if a previously stable deficit worsens, the pain becomes systemic or non-mechanical, or clinical findings cease to fit the imaged lesion.

10Special situationsVariants, exceptions and circumstances that change the usual approach.

Traversing versus exiting root

A posterolateral L4–5 disc usually affects L5; a far-lateral L4–5 disc more often affects L4. State both disc level and clinical root.

Straight-leg raise

Reproduction of familiar distal radicular pain supports lower-lumbar root irritation; isolated hamstring stretch or back pain is not a positive equivalent.

MRI is a correlation test

A dramatic-looking disc on the wrong side or at the wrong root is not an explanation until the mismatch is resolved.

Pain and deficit differ

Severe pain does not necessarily mean severe axonal loss, while progressive painless weakness can be clinically urgent.

11Common pitfallsFrequent interpretation and management errors.

01
Waiting for painless retention or bilateral sciatica before activating a cauda equina pathway.
02
Ordering routine early MRI and then treating an incidental disc rather than the patient.
03
Calling every leg symptom sciatica without documenting a plausible root pattern and alternatives.
04
Continuing ineffective dependence-forming medicines without review, or stopping them abruptly without withdrawal planning.
05
Offering decompression for axial low-back pain alone under a recommendation intended for concordant sciatica.

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