Spinal Canal Stenosis & Spondylolisthesis

Two of the commonest degenerative spine problems in the NEET PG syllabus, frequently tested together because they often coexist (degenerative spondylolisthesis is a leading cause of acquired central canal stenosis). Mastery hinges on distinguishing neurogenic claudication from vascular claudication, knowing the Meyerding grade, the isthmic vs degenerative dichotomy, and the indications for decompression versus fusion.

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Part A — Lumbar Spinal Canal Stenosis

Definition & classification

Spinal canal stenosis is narrowing of the spinal canal, lateral recess, or neural foramen leading to compression of the cauda equina or exiting nerve roots. The lumbar spine (esp. L4–L5, then L3–L4) is the commonest site.

By anatomy:

• Central canal stenosis – compresses the thecal sac/cauda equina → bilateral, diffuse symptoms (neurogenic claudication).
• Lateral recess (subarticular) stenosis – compresses the traversing nerve root → radicular pain.
• Foraminal/extraforaminal stenosis – compresses the exiting root.

By etiology:

• Congenital/developmental – short pedicles producing a constitutionally narrow trefoil canal (e.g. achondroplasia, idiopathic). Symptoms appear earlier (3rd–4th decade) because there is little reserve space.
• Acquired (degenerative) – the commonest type, 5th–7th decade.

Feature	Congenital stenosis	Acquired (degenerative) stenosis
Age of onset	Younger (30s–40s)	Older (50s–70s)
Mechanism	Short pedicles, narrow canal	Disc bulge + facet hypertrophy + ligamentum flavum buckling
Levels	Often multiple, diffuse	Segmental (L4–L5 commonest)
Classic example	Achondroplasia	Osteoarthritic spine, degenerative spondylolisthesis
Reserve space	Minimal	Normal until degeneration supervenes

High-yield: Achondroplasia is the classic cause of congenital lumbar canal stenosis — short pedicles, decreasing interpedicular distance caudally (normally it increases L1→L5).

Etiology & pathophysiology

The degenerative cascade narrows the canal from three directions — the "trinity" of degenerative stenosis:

1. Anteriorly – disc bulge/protrusion and osteophytes from the vertebral body margins.
2. Posterolaterally – facet joint osteoarthritis with hypertrophy of the superior articular process (narrows the lateral recess).
3. Posteriorly – hypertrophy and infolding (buckling) of the ligamentum flavum.

These dynamically worsen on extension (canal narrows, ligamentum flavum buckles inward) and improve on flexion (canal opens) — the anatomical basis for the shopping-cart sign and the clinical picture below.

Ischaemia of the cauda equina (venous congestion and arterial compromise during walking, when metabolic demand rises) explains the claudication-type symptom rather than fixed pain.

Clinical features — Neurogenic claudication

The hallmark is neurogenic (pseudo-) claudication: bilateral buttock/thigh/leg pain, heaviness, numbness, or weakness brought on by standing and walking, relieved by sitting or bending forward.

High-yield: Shopping-cart sign / simian (stooped) posture — the patient leans forward over a shopping trolley because spinal flexion opens the canal and relieves symptoms. A walking stick or bicycle (flexed posture) is tolerated far better than upright walking.

Other features:

• Walking downhill worsens symptoms (lumbar extension); walking uphill is better tolerated (flexion).
• Cycling is well tolerated (flexed posture) — distinguishes it from vascular cause.
• Symptoms are positional, not purely distance-based, and relief on stopping is slow (minutes) because the patient must change posture.
• Examination is often normal at rest; reflexes/pulses preserved.

Neurogenic vs vascular claudication — the single most tested table

Feature	Neurogenic claudication	Vascular claudication
Underlying cause	Canal stenosis (cauda equina)	Peripheral arterial disease
Pain onset	Standing and walking	Walking only (exertion)
Relief	Bending forward / sitting (posture)	Standing still (rest alone)
Time to relief	Slow (several minutes)	Fast (1–2 min of rest)
Walking uphill	Better tolerated	Worse
Cycling	Well tolerated	Poorly tolerated (provokes pain)
Peripheral pulses	Normal	Diminished/absent
Skin/trophic changes	Absent	Hair loss, shiny skin, ulcers
Distribution	Diffuse, bilateral, proximal→distal	Calf (most), follows arterial supply
ABI	Normal	Reduced (< 0.9)

High-yield mnemonic: "Bicycle test of van Gelderen" — stenosis patient can pedal a stationary bicycle (flexed) without pain but cannot walk far; a vascular patient gets pain on pedalling because muscle demand rises.

Investigation of choice

MRI of the lumbar spine is the investigation of choice — shows the trefoil canal, ligamentum flavum hypertrophy, disc/facet changes and thecal sac compression without radiation.

• CT myelogram – reserved for patients with contraindication to MRI (pacemaker) or post-instrumentation metal artefact; excellent bony detail.
• Plain radiographs (flexion–extension views) – screen for instability/spondylolisthesis; show degenerative changes and the trefoil canal.
• EMG/NCS – to exclude peripheral neuropathy when the picture is unclear.

Radiological cut-offs (commonly quoted):

• AP diameter of lumbar canal: < 10 mm = absolute stenosis, 10–12 mm = relative stenosis (normal ≈ 15–25 mm).
• Cross-sectional dural sac area < 100 mm² suggests significant stenosis (< 75 mm² severe).

Management

Stepwise approach:

Conservative → Medical/interventional → Surgical

1. First line (most patients): activity modification, NSAIDs/paracetamol, physiotherapy (flexion-based exercises, core strengthening), weight loss.
2. Epidural steroid injection for short-term radicular relief.
3. Surgery when conservative measures fail (≥ 3–6 months), with progressive neurological deficit, or cauda equina syndrome (emergency).

Surgical options:

• Decompressive laminectomy – the gold-standard operation; removes lamina + hypertrophied ligamentum flavum ± medial facetectomy to decompress the central canal and lateral recess.
• Laminotomy / "over-the-top" decompression – tissue-sparing alternatives preserving stability.
• Decompression + instrumented fusion – added when there is associated instability, spondylolisthesis, or when wide decompression destabilises the segment (removal of > 50% of both facets or the pars).

High-yield: Decompression alone for stenosis; add fusion if there is instability or coexisting spondylolisthesis (the SPORT trial showed decompression benefits stenosis; fusion is indicated when slip/instability coexists).

Complications

• Cauda equina syndrome (saddle anaesthesia, retention/overflow incontinence, bilateral sciatica) — surgical emergency.
• Progressive motor weakness/foot drop.
• Post-laminectomy instability, dural tear/CSF leak, recurrent stenosis, epidural fibrosis.

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Part B — Spondylolisthesis

Definition

Spondylolisthesis = forward (anterior) slippage of one vertebra over the one below (most often L5 over S1, then L4 over L5). Spondylolysis = a defect (stress fracture) in the pars interarticularis without slip — the precursor of isthmic spondylolisthesis. Retrolisthesis = posterior slip.

High-yield: "Scottie dog with a collar" on oblique lumbar radiograph = pars defect (spondylolysis); the dog's neck is the pars interarticularis. A complete fracture = "decapitated Scottie dog."

Wiltse–Newman classification (etiological types)

Type	Name	Mechanism	Typical level / patient
I	Dysplastic (congenital)	Congenitally deficient L5–S1 facets/sacral dome	L5–S1; high slip risk
II	Isthmic	Pars interarticularis defect (IIa lytic/fatigue #, IIb elongated, IIc acute #)	L5–S1; young athletes
III	Degenerative	Facet & disc arthritis with intact pars	L4–L5; elderly women
IV	Traumatic	Acute fracture of posterior elements (not pars)	Any
V	Pathological	Bone disease (Paget, tumour, infection, osteogenesis imperfecta)	Any
(VI)	Iatrogenic/post-surgical	After wide laminectomy/facetectomy	Operated level

Isthmic vs Degenerative — high-yield comparison

Feature	Isthmic (Type II)	Degenerative (Type III)
Age	Children/young adults, athletes	> 50 yrs, female predominance
Pars	Defective (lysis)	Intact
Commonest level	L5–S1	L4–L5
Mechanism	Repetitive hyperextension (gymnasts, fast bowlers, weightlifters)	Facet arthritis + disc degeneration + sagittal facets
Slip severity	Can be high-grade	Usually low-grade (< grade II)
Canal stenosis	Less common (canal often widened by the slip)	Common → neurogenic claudication

High-yield: Degenerative spondylolisthesis is 3–6× more common in women, classically L4–L5, with an intact pars, and is a leading cause of acquired lumbar canal stenosis. Hormonal/ligamentous laxity and sagittally oriented facets are contributory.

Meyerding grading (must-know)

Based on the percentage of the superior endplate of the lower vertebra over which the upper vertebra has slipped:

Grade	Slip percentage
I	0–25%
II	25–50%
III	50–75%
IV	75–100%
V	> 100% = spondyloptosis (vertebra falls off the one below)

High-yield: Grade ≥ III (i.e. > 50% slip) is "high-grade" and is generally an indication for surgical stabilisation/fusion. Grade V = spondyloptosis.

Additional radiographic measures:

• Slip angle (lumbosacral kyphosis) – best predictor of progression and instability in high-grade slips.
• Pelvic incidence – high PI is associated with higher-grade slips.

Clinical features

• Often asymptomatic and incidental.
• Low back pain worse on extension/activity; may radiate to buttocks/posterior thigh.
• Hamstring tightness and a characteristic "pelvic waddle" / crouched gait in high-grade slips (children).
• Palpable step-off at the spinous processes.
• Radicular pain (L5 root commonly affected in L5–S1 isthmic slips) or neurogenic claudication (especially degenerative type).
• Phalen–Dickson sign – knees-flexed, hips-flexed crouched gait in severe slips.

Investigation

• Lateral standing radiograph – primary tool; quantifies slip (Meyerding) and slip angle. Flexion–extension lateral views demonstrate dynamic instability (translation > 4 mm or angulation > 10° is significant).
• Oblique radiograph – Scottie-dog sign for pars defect.
• MRI – best for neural compression, disc health, and pre-operative planning (investigation of choice for neurological symptoms).
• SPECT / CT – detect early/active pars stress reaction in young athletes before a frank defect appears (CT best defines the bony pars defect).

Management

Stepwise approach:

Asymptomatic / low-grade → observe + activity modification → physiotherapy (core, hamstring stretch, anti-lordotic bracing) → NSAIDs Symptomatic, failed conservative, or high-grade / progressive → surgery

• Young athlete with acute spondylolysis (pars stress fracture): rest, activity restriction, and anti-lordotic bracing can achieve bony healing; pars repair (direct screw fixation) if non-union and no significant disc degeneration.
• Surgery indicated for: intractable pain failing conservative care, progressive neurological deficit, high-grade slip (grade ≥ III), documented instability, or progression in a skeletally immature patient.
• Operation of choice: decompression + posterolateral/interbody spinal fusion (PLIF/TLIF) with instrumentation; reduction may be attempted in high-grade slips (risk of L5 root injury).

High-yield: Unlike isolated stenosis, spondylolisthesis with instability requires FUSION, not decompression alone — decompressing without fusing an unstable slip worsens it.

Complications

• Progressive slip and segmental instability.
• Radiculopathy / cauda equina syndrome.
• Surgical: L5 nerve root injury during reduction of high-grade slips, pseudarthrosis (non-union), adjacent-segment degeneration, hardware failure.

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Key differentials

• Vascular (intermittent) claudication – PAD; absent pulses, ABI < 0.9 (see table above).
• Lumbar disc herniation – more acute, dermatomal, positive SLR; pain often worse on flexion/sitting (opposite of stenosis).
• Hip osteoarthritis – groin pain, restricted internal rotation, pain on FABER; "hip–spine syndrome" overlap.
• Peripheral neuropathy (diabetic) – stocking distribution, no positional relief.
• Trochanteric bursitis / piriformis syndrome – localised tenderness, no canal narrowing.
• Metastatic disease / infection (TB spine) – night pain, constitutional symptoms; pathological spondylolisthesis (Type V).

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Recently asked / exam angle

• Shopping-cart sign and the neurogenic vs vascular claudication table are perennial favourites — expect a clinical vignette of an elderly patient relieved by leaning on a trolley with normal foot pulses (answer: lumbar canal stenosis, MRI, decompressive laminectomy).
• Scottie dog sign image-based question → pars interarticularis defect / spondylolysis.
• Meyerding grade V = spondyloptosis; "> 100% slip" one-liners.
• Achondroplasia → congenital narrow canal, interpedicular distance decreases caudally.
• Degenerative spondylolisthesis: female, L4–L5, intact pars — a recurring "single-best-answer" cluster.
• Most common level: isthmic = L5–S1; degenerative = L4–L5.
• Indication discrimination: decompression alone vs decompression + fusion (add fusion for instability/slip) — increasingly tested in the management-reasoning style.
• van Gelderen bicycle test and uphill-vs-downhill walking discriminators.

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Rapid revision

1. Lumbar canal stenosis = central/lateral recess/foraminal narrowing; commonest at L4–L5.
2. Three culprits: disc bulge + facet hypertrophy + ligamentum flavum buckling; worse on extension, better on flexion.
3. Neurogenic claudication relieved by bending forward/sitting (shopping-cart sign); pulses normal.
4. Vascular claudication relieved by standing still; pulses absent, ABI < 0.9, cycling provokes pain.
5. Investigation of choice for stenosis = MRI; CT myelogram if MRI contraindicated.
6. Canal AP diameter < 10 mm = absolute stenosis.
7. Treatment: conservative first → decompressive laminectomy; add fusion only for instability/spondylolisthesis.
8. Spondylolysis = pars defect (Scottie-dog collar); spondylolisthesis = vertebral slip.
9. Wiltse: dysplastic, isthmic, degenerative, traumatic, pathological (+ iatrogenic).
10. Isthmic = young athlete, L5–S1, defective pars; Degenerative = elderly woman, L4–L5, intact pars.
11. Meyerding: I ≤25, II 25–50, III 50–75, IV 75–100, V > 100% = spondyloptosis; grade ≥ III = high-grade → surgery.
12. Spondylolisthesis with instability → decompression + fusion; beware L5 root injury during high-grade reduction.