Spondylolisthesis (Adult)

1. Clinical Overview

Summary

Spondylolisthesis is the anterior (forward) displacement of one vertebral body relative to the adjacent caudal vertebra, resulting from various aetiologies affecting spinal stability. The term derives from the Greek "spondylos" (vertebra) and "olisthesis" (to slip). In adults, this condition represents a spectrum of pathologies unified by vertebral translation but distinguished by fundamentally different underlying mechanisms. [1,2]

The two predominant types in adults are:

• Isthmic (Type II): Defect or elongation of the pars interarticularis (spondylolysis), typically originating in adolescence/young adulthood from repetitive stress, becoming symptomatic in adult life.
• Degenerative (Type III): Age-related facet joint arthropathy and ligamentous degeneration, typically affecting patients > 50 years, most commonly at L4/L5.

Most commonly affected levels:

• Isthmic: L5/S1 (85-95% of cases)
• Degenerative: L4/L5 (70-80% of cases), followed by L5/S1

Clinical presentation varies from asymptomatic incidental findings to disabling mechanical back pain, radiculopathy, neurogenic claudication, or rarely cauda equina syndrome. The Meyerding classification grades severity based on percentage of vertebral body translation (Grades I-V). The Wiltse classification categorizes by aetiology (Types I-VI). [3,4]

Management is predominantly conservative for low-grade stable slips (physiotherapy, activity modification, analgesia). Surgical intervention (decompression with or without fusion) is reserved for high-grade slips, progressive neurological deficit, spinal instability, or failure of > 6 months conservative therapy. Modern fusion techniques include posterolateral fusion, posterior lumbar interbody fusion (PLIF), transforaminal lumbar interbody fusion (TLIF), and anterior lumbar interbody fusion (ALIF). [5,6]

Clinical Pearls

"Pars Defect = Isthmic Type": Bilateral pars interarticularis defects (spondylolysis) allow anterior vertebral translation. Common in athletes with repetitive lumbar hyperextension (gymnasts, fast bowlers, divers, weightlifters). Stress fracture typically occurs in adolescence but may remain asymptomatic until adulthood.

"L5/S1 Isthmic, L4/L5 Degenerative": Isthmic spondylolisthesis predominantly affects L5/S1 (lumbosacral junction experiences greatest shear forces). Degenerative type most common at L4/L5 (mobile segment with sagittal-oriented facets predisposing to anterior translation).

"Step-Off Sign": Palpable gap or prominence between spinous processes on clinical examination, pathognomonic of higher-grade slips (Meyerding III-V). May be accompanied by visible lumbar lordosis increase.

"Scotty Dog Sign": Classic radiographic finding on 45° oblique lumbar X-ray. Normal vertebra resembles a Scotty dog; pars defect appears as a "collar" or "broken neck" on the dog. Gold standard for identifying spondylolysis.

"Intact Pars in Degenerative Type": Unlike isthmic spondylolisthesis, degenerative type has intact pars interarticularis. Slip occurs due to facet joint incompetence, not bone defect. Typically self-limiting (rarely >Grade II) as intact posterior elements prevent further displacement.

"Hamstring Tightness in High-Grade Slips": Compensatory mechanism for lumbosacral kyphosis and anterior pelvic tilt. Results in characteristic crouched, flexed-knee gait. Common in pediatric/adolescent high-grade slips but may persist into adulthood.

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2. Epidemiology

Demographics

At-Risk Populations

Natural History

Isthmic Type:

• Pars defect (spondylolysis) typically develops age 5-7 during ambulation/increased activity
• 75-80% remain asymptomatic throughout life
• If progression to listhesis occurs, typically by late adolescence/early 20s
• Slip progression rare after skeletal maturity (less than 5% adults progress)
• High-risk period: adolescent growth spurt (may progress 10-20% during growth)

Degenerative Type:

• Self-limiting slip (rarely exceeds Grade II/50%) due to intact posterior elements
• Progression rate: 3-8% over 5 years in established listhesis
• Associated spinal stenosis in 60-80% of symptomatic cases
• Natural history generally stable in adulthood [10]

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3. Classification

Wiltse Classification (Aetiological)

Proposed by Wiltse et al. (1976), remains the gold standard classification system. [11]

Meyerding Grading (Severity of Slip)

Quantifies percentage of vertebral body translation on lateral radiograph. [12]

Measurement Technique:

1. Lateral lumbar radiograph in standing position
2. Divide superior endplate of caudal vertebra into 4 equal segments
3. Measure anterior displacement of posterior-inferior corner of cranial vertebra
4. Grade I = slip confined to first quarter; Grade II = second quarter; etc.

Slip Angle (Taillard Angle)

Slip angle = Angle between superior endplate of S1 and inferior endplate of L5

• Normal: less than 10°
• Increased angle (> 45°) indicates greater instability and higher risk of progression
• Important prognostic indicator in high-grade slips [13]

Spinal-Pelvic Parameters (Sagittal Balance)

Critical for surgical planning in high-grade slips:

High pelvic incidence (> 60°) is associated with increased risk of isthmic spondylolisthesis and slip progression. [14]

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4. Anatomy and Pathophysiology

Functional Anatomy

Pars Interarticularis:

• Narrow isthmus of bone between superior and inferior articular processes
• Anatomical "stress riser" – weakest point of neural arch
• Withstands significant shear and tensile forces during spinal extension/rotation
• Vascular watershed area → poor healing capacity
• Bilateral pars defects eliminate posterior column integrity → allows anterior translation

Three-Column Spine Concept (Denis):

• Anterior column: Anterior longitudinal ligament, anterior 2/3 vertebral body/disc
• Middle column: Posterior 1/3 vertebral body/disc, posterior longitudinal ligament
• Posterior column: Pedicles, facets, lamina, spinous process, interspinous/supraspinous ligaments
• Spondylolisthesis disrupts posterior column integrity (pars defect in isthmic; facet incompetence in degenerative)

Lumbar Biomechanics:

• L5/S1 experiences greatest shear forces due to lumbosacral angle (shear force = body weight × sin[sacral slope])
• Normal pars withstands 1000-2000N; failure occurs at ~700N in repetitive loading
• L4/L5 most mobile lumbar segment → prone to degenerative facet changes

Pathophysiology: Isthmic Spondylolisthesis (Type II)

Stage 1: Pars Stress Reaction (Spondylolysis Development)

1. Repetitive Microtrauma: Lumbar hyperextension (gymnastics, fast bowling, diving) → repetitive pars loading
2. Stress Response: Bone microfractures exceed repair capacity
3. Stress Fracture: Unilateral or bilateral pars fracture (spondylolysis)
4. Non-Union: Pars has poor vascularity (watershed zone) → fibrocartilaginous non-union common
5. Pars Elongation: Repeated fracture-healing cycles → pars elongation (Type IIb)

Stage 2: Listhesis Development

1. Bilateral Pars Defects: Loss of posterior column integrity
2. Shear Forces: Body weight + sacral slope angle → anterior shear force on L5
3. Anterior Translation: L5 slides anteriorly on S1
4. Disc Degeneration: Altered biomechanics → L5/S1 disc degeneration
5. Hamstring Contracture: Compensatory pelvic retroversion → functional hamstring shortening

Stage 3: Neural Compression

1. Foraminal Stenosis: Anterior vertebral slip → posterior-superior migration of superior facet → foraminal narrowing → L5 nerve root compression
2. Central Stenosis: High-grade slips → buckling of ligamentum flavum and disc bulge → central canal compromise
3. Fibrocartilaginous Mass: Pars defect filled with fibrocartilage ("Gill's lesion") → mass effect on traversing S1 nerve root [15]

Pathophysiology: Degenerative Spondylolisthesis (Type III)

Stage 1: Facet Joint Degeneration

1. Disc Degeneration: Age-related disc desiccation → loss of disc height → altered facet loading
2. Facet Arthropathy: Abnormal loading → facet cartilage degeneration → osteophyte formation
3. Joint Remodeling: Facet joint orientation changes (sagittal → more coronal orientation)
4. Joint Incompetence: Advanced arthropathy → loss of facet joint restraint to anterior translation

Stage 2: Ligamentous Degeneration

1. Ligamentum Flavum Laxity: Age-related elastin degradation → ligamentous hypertrophy and laxity
2. Capsular Incompetence: Facet capsule stretching → reduced resistance to shear
3. Posterior Longitudinal Ligament Laxity: Disc degeneration → PLL redundancy

Stage 3: Segmental Instability and Listhesis

1. Anterior Translation: Facet incompetence + ligamentous laxity → anterior slip (self-limiting to Grade II due to intact pars)
2. Dynamic Instability: Flexion-extension radiographs may show > 3mm translation or > 10° rotation
3. Spinal Stenosis: Slip + facet hypertrophy + ligamentum flavum hypertrophy + disc bulge → "triple compression" (central, lateral recess, foraminal stenosis)
4. Neurogenic Claudication: Positional stenosis → ischemia of cauda equina/nerve roots → claudication symptoms [16]

Molecular Mechanisms

Genetic Susceptibility:

• COL1A1 polymorphisms: Altered type I collagen → reduced bone quality
• VDR gene variants: Vitamin D receptor polymorphisms → bone mineralization defects
• MMP (matrix metalloproteinase) upregulation: Accelerated disc/ligament degeneration
• Familial clustering supports genetic component (25-30% have affected first-degree relative) [17]

Inflammatory Cascade:

• IL-1β, TNF-α, IL-6 upregulation in degenerate facet joints and discs
• Prostaglandin E2 production → sensitization of nociceptors
• Nerve growth factor (NGF) expression in degenerate discs → neoinnervation → discogenic pain

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5. Clinical Presentation

Symptoms

Red Flags (Cauda Equina Syndrome)

Rare (less than 1% of spondylolisthesis) but catastrophic complication requiring emergency surgery:

Action: Emergency MRI within 24 hours; urgent surgical decompression within 48 hours for optimal neurological recovery. [18]

Examination Findings

Inspection:

• Increased Lumbar Lordosis: Compensatory hyperlordosis above listhesis level
• Palpable Step-Off: Gap or prominence between L5 and S1 spinous processes (high-grade slips, especially in thin patients)
• Visible/Palpable Transverse Abdominal Crease: High-grade slips with shortened trunk height
• Waddling Gait: Flexed hips and knees, wide-based stance (high-grade slips)

Palpation:

• Midline tenderness over affected level
• Paraspinal muscle spasm
• Step-off between spinous processes (Grade III+)

Range of Motion:

• Extension: Painful/limited (reproduces symptoms in isthmic type)
• Flexion: May relieve pain in degenerative type with stenosis
• Hamstring Tightness: Positive straight leg raise (SLR) due to hamstring contracture (NOT nerve root tension); typically bilateral, painless limitation at 30-50°

Neurological Examination:

Special Tests:

• Stork Test (One-Leg Hyperextension Test): Stand on one leg (ipsilateral to pain) and hyperextend lumbar spine. Positive if reproduces back/leg pain. Sensitivity ~50%, specificity ~70% for spondylolysis. [8]
• Flexion-Extension Relief: Pain relief with forward flexion suggests stenosis (degenerative type); pain with extension suggests pars pathology (isthmic type).

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6. Investigations

Imaging Modalities

X-Ray Signs

Meyerding Measurement Technique

1. Obtain standing lateral lumbar radiograph (functional position)
2. Identify posterior-inferior corner of superior vertebral body
3. Divide superior endplate of inferior vertebra into four equal quadrants
4. Measure anterior displacement:
   • Grade I: Posterior-inferior corner in first quadrant (0-25%)
   • Grade II: Second quadrant (26-50%)
   • Grade III: Third quadrant (51-75%)
   • Grade IV: Fourth quadrant (76-100%)
   • Grade V: Complete displacement beyond fourth quadrant (> 100% = spondyloptosis)

Additional Measurements

Slip Percentage (Taillard Method):

• Slip percentage = (a/b) × 100%
• a = horizontal distance from posterior edge of S1 to posterior edge of L5
• b = anteroposterior diameter of S1
• More precise than Meyerding grading

Boxall Slip Angle:

• Angle between inferior endplate of L5 and superior endplate of S1
• Normal: less than 10°

• 45°: High risk of progression

• 55°: Severe deformity, often requires reduction [13]

Disc Angle:

• Angle between L5 and S1 endplates
• Indicates lumbosacral kyphosis in high-grade slips

Laboratory Investigations

Generally not required unless suspecting alternative diagnosis:

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7. Differential Diagnosis

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8. Management

Management Algorithm

ADULT SPONDYLOLISTHESIS DIAGNOSED
(Imaging confirms vertebral slip)
            ↓
ASSESS RED FLAGS
- Cauda equina syndrome?
- Progressive neurological deficit?
- High-grade unstable slip?
            ↓
┌───────────┴────────────┐
RED FLAGS PRESENT        RED FLAGS ABSENT
         ↓                        ↓
  URGENT MRI          CLASSIFY TYPE AND GRADE
  Neurosurgical       - Wiltse classification (I-VI)
  referral less than 48hrs     - Meyerding grade (I-V)
  Urgent surgery      - Assess stability (flexion-extension X-rays)
                      - Neurological status
                               ↓
                   GRADE I-II, STABLE, MINIMAL SYMPTOMS
                               ↓
                   CONSERVATIVE MANAGEMENT (6 months)
                   - Physiotherapy (core stability)
                   - NSAIDs/analgesia
                   - Activity modification
                   - Patient education
                               ↓
                   Reassess at 6-12 weeks
                               ↓
                   ┌─────────┴──────────┐
              IMPROVED            NO IMPROVEMENT
                   ↓                     ↓
           Continue therapy    ADVANCED IMAGING (MRI)
           Monitor             Assess:
           annually            - Neural compression?
                              - Spinal stenosis?
                              - Dynamic instability?
                                       ↓
                              SURGICAL INDICATIONS?
                              - Persistent pain > 6mo
                              - Neurological deficit
                              - Stenosis with claudication
                              - Grade III+ slip
                              - Progressive slip
                                       ↓
                                   YES → SURGERY
                                   (Decompression ± Fusion)
                                       ↓
                              SURGICAL PLANNING
                              - Posterolateral fusion vs
                              - Interbody fusion (PLIF/TLIF/ALIF)
                              - Reduction vs in situ fusion
                              - Instrumentation strategy

Conservative Management (First-Line)

Successful in 80-85% of Grade I-II stable spondylolisthesis with appropriate patient selection. [5]

Monitoring During Conservative Management:

• Clinical review: 6-12 weeks
• Repeat X-rays (standing lateral): 6-12 months (assess progression)
• Indications for earlier review: New/progressive neurology, increasing pain, red flags

Surgical Management

Indications:

Surgical Options:

1. Decompression Alone (Laminectomy)

Indication: Degenerative spondylolisthesis with stenosis, stable slip (Grade I), no significant back pain component
Procedure: Bilateral laminectomy, medial facetectomy (less than 50% facet resection), foraminotomy
Evidence: Controversial. SPORT trial showed fusion superior to decompression alone for long-term outcomes. [21]
Risk: Iatrogenic instability (15-30%) → may require subsequent fusion

2. Posterolateral Fusion (PLF)

Technique:

• Midline exposure, subperiosteal dissection to transverse processes
• Decortication of facets, transverse processes, lamina
• Autograft (iliac crest) or allograft bone placement
• ± Pedicle screw instrumentation (increases fusion rate from 65-85% to 90-95%) [6]

Indications: Isthmic spondylolisthesis, low-grade degenerative with axial pain predominance
Advantages: Familiar technique, preserves disc height
Disadvantages: No direct neural decompression, donor site morbidity (autograft), lower fusion rate without instrumentation

3. Posterior Lumbar Interbody Fusion (PLIF)

Technique:

• Bilateral laminectomy and facetectomy
• Discectomy via posterior approach
• Bilateral interbody cages (PEEK/titanium) with bone graft
• Posterior pedicle screw fixation

Indications: Degenerative spondylolisthesis with stenosis, Grade I-II listhesis, discogenic pain component
Advantages: Direct neural decompression, disc height restoration, anterior column support (360° fusion), high fusion rate (> 95%)
Disadvantages: Dural tear risk (10-15%), nerve root retraction injury, technically demanding [22]

4. Transforaminal Lumbar Interbody Fusion (TLIF)

Technique:

• Unilateral laminectomy and facetectomy (working side)
• Discectomy via transforaminal approach
• Single large interbody cage (oblique placement)
• Bilateral pedicle screw fixation

Indications: Degenerative spondylolisthesis with stenosis, Grade I-II isthmic listhesis, unilateral radiculopathy
Advantages: Unilateral approach (less dural retraction), lower dural tear rate (5-8%), adequate decompression, excellent fusion rate (> 95%)
Disadvantages: Limited access to contralateral side, incomplete disc removal [23]
Most popular technique for degenerative spondylolisthesis in current practice

5. Anterior Lumbar Interbody Fusion (ALIF)

Technique:

• Anterior retroperitoneal approach (vascular mobilization)
• Anterior longitudinal ligament release
• Complete discectomy
• Large interbody cage (or two cages)
• ± Posterior instrumentation (360° fusion)

Indications: High-grade isthmic spondylolisthesis requiring reduction, L5/S1 level (easier access), failed prior posterior fusion
Advantages: Excellent disc access, large graft area, lordosis restoration, avoids posterior scar tissue (revision surgery)
Disadvantages: Vascular injury risk (0.5-5%), retrograde ejaculation (males, 1-5%), sympathetic plexus injury, visceral injury [24]
Often combined with posterior instrumentation for high-grade slips

6. Minimally Invasive Techniques (MIS-TLIF)

Technique: Tubular retractor system, unilateral facetectomy, single cage, percutaneous pedicle screws
Advantages: Reduced blood loss, shorter hospital stay, less muscle dissection
Disadvantages: Learning curve, limited visualization, contraindicated in high-grade slips
Evidence: Similar fusion rates and clinical outcomes to open TLIF; reduced short-term pain [25]

7. Pars Repair (Buck's Technique)

Indication: Young patients (less than 30 years) with spondylolysis (pars defect) WITHOUT significant slip (less than 5mm), failed conservative management
Technique: Pars defect freshening, screw fixation across defect (Buck's screws, pedicle screw-hook construct, or cable fixation)
Advantages: Motion preservation (no fusion), faster recovery
Disadvantages: High non-union rate (20-30%), limited indications, not suitable if established listhesis or disc degeneration present
Evidence: Level III-IV; limited long-term data; rarely performed in modern practice [26]

Surgical Decision-Making: Decompression vs Fusion

Evidence: Landmark Spine Patient Outcomes Research Trial (SPORT) demonstrated fusion superior to decompression alone for degenerative spondylolisthesis at 4-year follow-up (ODI, SF-36 scores). [21]

High-Grade Slip Management (Grade III-V)

Controversial Area: Reduction vs In Situ Fusion

In Situ Fusion (Most Common):

• Fusion without reduction of slip
• Lower neurological complication risk
• Technically easier
• Risk: Residual deformity, sagittal imbalance

Reduction and Fusion:

• Partial or complete reduction of slip
• Restores sagittal alignment and disc height
• Risk: L5 nerve root stretch injury (10-30% transient, 2-5% permanent) [27]
• Indications: Young patients, severe deformity, sagittal imbalance

Fibular Allograft Dowel Technique: Anterior column support in spondyloptosis (Grade V)

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9. Complications

Non-Operative Complications

Surgical Complications

Intraoperative Complications

Early Post-Operative Complications (0-6 weeks)

Late Complications (> 6 weeks)

Complications Specific to High-Grade Slip Reduction

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10. Prognosis and Outcomes

Natural History

Surgical Outcomes

Success Rates (defined as significant improvement in pain/function scores):

Outcome Measures:

• Oswestry Disability Index (ODI): Typically improves 20-30 points post-operatively
• Visual Analogue Scale (VAS) for pain: Leg pain improves more than back pain
• SF-36: Significant improvement in physical function domains

Predictors of Poor Outcome:

• Smoking (doubles pseudarthrosis risk)
• Workers' compensation/litigation involvement
• Pre-operative opioid use
• Depression/psychological comorbidity
• Multilevel fusion
• Revision surgery
• Age > 70 years (higher complication rate, though good pain relief possible) [28]

Long-Term Outcomes

• Adjacent Segment Disease: 15-30% at 10 years; 10-15% require revision surgery
• Sagittal Balance: Critical for outcome; PI-LL mismatch > 10° associated with worse outcomes
• Patient Satisfaction: 70-85% satisfied at 5 years; satisfaction declines over time (ASD, recurrent pain)

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11. Prevention

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12. Evidence and Guidelines

Key Guidelines

Landmark Studies

1. Meyerding (1932): Original description of grading system for spondylolisthesis severity (Grades I-V). [12]

2. Wiltse et al. (1976): Comprehensive aetiological classification system (Types I-VI) – remains gold standard. [11]

3. Herkowitz & Kurz (1991): Prospective RCT comparing decompression alone vs decompression + fusion for degenerative spondylolisthesis. Fusion group superior outcomes (96% good/excellent vs 44%). Established fusion as standard for degenerative type. [31]

4. SPORT Trial (Weinstein et al., 2007-2009): Multicenter RCT comparing operative vs non-operative management for degenerative spondylolisthesis. Significant superiority of surgery at 2-4 years (intention-to-treat analysis weakened by crossover; as-treated analysis strong). [21]

5. Ghogawala et al. (2016): RCT comparing decompression alone vs decompression + fusion for lumbar stenosis with Grade I spondylolisthesis. Fusion group superior physical health scores at 2-4 years. [32]

Evidence Summary

Conservative vs Surgical Management:

• Level I evidence: Fusion superior to decompression alone for degenerative spondylolisthesis with stenosis
• Level II evidence: Conservative management effective for low-grade stable slips (80-85% success)
• Level III evidence: Surgery indicated for high-grade slips, neurological deficit, or conservative failure > 6 months

Fusion Techniques:

• Level I evidence: Instrumented fusion superior to non-instrumented (higher fusion rate)
• Level II evidence: Interbody fusion (PLIF/TLIF/ALIF) higher fusion rate than posterolateral fusion
• Level II evidence: TLIF vs PLIF – similar outcomes, TLIF lower dural tear rate
• Level III evidence: MIS-TLIF vs open TLIF – similar long-term outcomes, MIS reduced short-term pain

Reduction vs In Situ Fusion:

• Level III evidence: In situ fusion safer (lower neurological complication rate); reduction improves alignment but higher L5 nerve injury risk; no consensus on optimal approach for high-grade slips

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13. Patient and Layperson Explanation

What is Spondylolisthesis?

Spondylolisthesis means one of the bones in your spine (vertebra) has slipped forward over the bone below it. Think of your spine as a stack of building blocks – if one block slides forward, it can pinch nerves and cause pain. This most often happens in the lower back (lumbar spine).

Why Does It Happen?

There are two main types:

1. Isthmic (Stress-Related):

   • Common in younger people and athletes (gymnasts, cricketers, divers)
   • Repetitive bending backwards causes a stress fracture in part of the vertebra (called the "pars")
   • Over time, the fracture allows the bone to slip forward

2. Degenerative (Wear-and-Tear):

   • Common in older adults (over 50 years), especially women
   • The joints and ligaments in your spine wear out with age
   • This allows the vertebra to slip forward gradually

What Are the Symptoms?

• Lower back pain – usually worse with standing, walking, or bending backwards
• Leg pain or numbness – if nerves are pinched (travels down buttock, thigh, calf, or foot)
• Heavy/tired legs when walking – relieved by sitting down or bending forward (called "neurogenic claudication")
• Tight hamstrings – in some cases, especially younger people with severe slips

Warning Signs (Seek immediate medical help):

• Loss of bladder or bowel control
• Numbness around buttocks/groin
• Weakness in both legs
• These may indicate serious nerve compression requiring emergency treatment

How Is It Diagnosed?

• X-rays: Show the slipped bone and measure how far it has slipped
• MRI scan: If you have leg pain/numbness, shows whether nerves are being pinched
• CT scan: Sometimes used to see bone detail

How Is It Treated?

Most people do NOT need surgery. Treatment depends on severity:

Non-Surgical Treatment (First-Line):

• Physiotherapy: Strengthening your core muscles (abdomen and back) stabilizes your spine – most important treatment
• Pain relief: Paracetamol, anti-inflammatory tablets (ibuprofen), stronger painkillers if needed
• Activity modification: Avoid activities that make pain worse (heavy lifting, excessive bending); stay active with gentle exercise (walking, swimming)
• Injections: Steroid injections around pinched nerves for temporary relief (if physiotherapy alone insufficient)

Success rate: 80-85% of people improve with non-surgical treatment over 3-6 months.

Surgical Treatment: Surgery considered if:

• Pain/disability continues after 6 months of physiotherapy
• Severe nerve compression causing leg weakness/numbness
• Severe slip (> 50%)
• Bladder/bowel problems (emergency)

Types of Surgery:

• Decompression: Removing bone/tissue pressing on nerves
• Spinal fusion: Joining the slipped bone to the bone below with screws and bone graft, preventing further slippage and stabilizing the spine
• Success rate: 80-90% improvement in pain and function

Will It Get Worse?

• Adults: Most slips are stable and do NOT get worse over time. Once you've stopped growing (after adolescence), progression is rare.
• Adolescents: Slips can progress during growth spurts, so monitoring with X-rays is important.
• Regular follow-up with your doctor ensures early detection if progression occurs.

Can I Still Be Active?

Yes! The goal is to keep you active and mobile.

• Avoid: High-impact sports, heavy lifting, repetitive bending backwards (if these worsen pain)
• Recommended: Swimming, cycling, walking, yoga (modified), Pilates – activities that strengthen your core without excessive spine stress
• Most people return to normal daily activities after treatment

What If I Ignore It?

• Mild slips often remain stable and may not worsen
• However, untreated severe nerve compression can lead to permanent nerve damage (weakness, numbness)
• If you have warning signs (bladder/bowel problems, severe leg weakness), seek immediate medical attention

Key Takeaway

Spondylolisthesis is a manageable condition. Most people improve with physiotherapy and lifestyle modifications without needing surgery. Even if surgery is needed, outcomes are generally very good. Staying active, maintaining a healthy weight, and strengthening your core muscles are the best ways to manage this condition long-term.

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14. Examination Focus

Common FRCS(Tr&Orth) / Neurosurgery Viva Questions

Question 1: Classification and Pathoanatomy

Examiner: "Classify spondylolisthesis for me."

Model Answer: "I use the Wiltse classification, which categorizes by aetiology into six types:

• Type I: Dysplastic (Congenital) – Abnormal L5-S1 facets from birth; highest risk of severe slip/spondyloptosis
• Type II: Isthmic – Pars interarticularis lesion; subtype IIa is fatigue fracture (most common), IIb is elongated pars, IIc is acute traumatic fracture
• Type III: Degenerative – Facet joint arthropathy with intact pars; self-limiting to Grade II; common L4/L5 in older females
• Type IV: Traumatic – Acute fracture of posterior elements excluding pars
• Type V: Pathological – Bone destruction from tumour, infection, metabolic disease
• Type VI: Iatrogenic – Post-surgical destabilization

For grading severity, I use the Meyerding classification (Grades I-V based on percentage slip: I=0-25%, II=25-50%, III=50-75%, IV=75-100%, V=> 100% or spondyloptosis).

Additional assessment includes slip angle (Boxall angle – angle between L5 and S1 endplates; > 45° indicates instability) and sagittal balance parameters (pelvic incidence, pelvic tilt, sacral slope)."

Question 2: Scotty Dog Sign

Examiner: "What is the Scotty Dog sign and what does it represent?"

Model Answer: "The Scotty Dog sign is seen on 45° oblique lumbar radiographs. A normal vertebra in oblique view resembles a Scotty dog profile, where:

• The transverse process is the nose
• The pedicle is the eye
• The superior articular process is the ear
• The inferior articular process is the front leg
• The pars interarticularis is the neck

A pars defect (spondylolysis) appears as a lucent line through the neck, described as a 'collar' or 'broken neck' on the Scotty dog. This indicates isthmic spondylolisthesis (Type II) pathology. It's the classic sign for diagnosing pars interarticularis fractures."

Question 3: Isthmic vs Degenerative

Examiner: "How do you differentiate isthmic from degenerative spondylolisthesis clinically and radiologically?"

Model Answer:

Clinically:

• Isthmic: Younger patients (adolescent/young adult onset), athletic history (gymnastics, fast bowling), may have hamstring tightness
• Degenerative: Older patients (> 50 years), female predominance (4-6:1), neurogenic claudication common

Radiologically:

• Isthmic:

  • Pars defect visible on oblique X-ray (Scotty dog collar sign) or CT
  • Predominantly L5/S1 level
  • Can be high-grade (III-V)
  • Disc space often preserved initially

• Degenerative:

  • Intact pars (no collar sign)
  • Predominantly L4/L5 level
  • Self-limiting to Grade I-II (maximum 50%)
  • Facet joint arthropathy, osteophytes, disc degeneration visible
  • Associated spinal stenosis common (60-80%)

On CT, degenerative type shows facet hypertrophy, sclerosis, and joint space narrowing with intact pars. Isthmic type shows clear pars defect with or without fibrous tissue filling."

Question 4: Surgical Management

Examiner: "A 62-year-old woman with Grade I L4/L5 degenerative spondylolisthesis has failed 6 months of physiotherapy. MRI shows central stenosis. What are your surgical options and how do you decide?"

Model Answer: "The key decision is decompression alone versus decompression plus fusion.

Assessment:

• Instability: Flexion-extension X-rays (> 3mm translation or > 10° rotation = unstable)
• Pain pattern: Predominantly leg pain (stenosis) vs significant back pain (mechanical instability)
• Slip grade: Grade I
• General health: Age 62, likely medically fit

Options:

1. Decompression alone (laminectomy ± foraminotomy):

   • Indication: Stable slip, leg pain predominant, minimal back pain
   • Advantage: Smaller operation, faster recovery
   • Disadvantage: 15-30% risk iatrogenic instability requiring subsequent fusion
   • Evidence: SPORT trial showed fusion superior at 4 years

2. Decompression + fusion (TLIF preferred):

   • Indication: Any instability, significant back pain component, patient medically fit
   • Advantage: Addresses stenosis AND instability; superior long-term outcomes
   • Disadvantage: Longer operation, higher complication rate, adjacent segment disease risk
   • Technique: TLIF (unilateral approach, single cage, bilateral pedicle screws) – current gold standard

My recommendation: Given failed conservative management, Grade I with stenosis, and age 62, I would recommend decompression + fusion (TLIF) based on Level I evidence from SPORT and Ghogawala trials showing superiority over decompression alone.

Consent: Discuss risks (infection 2-5%, dural tear 5-8%, nerve injury 2-5%, non-union 5-10%, adjacent segment disease 15-30% at 10 years)."

Question 5: High-Grade Slip Management

Examiner: "An 18-year-old gymnast has Grade IV L5/S1 isthmic spondylolisthesis. Discuss your management."

Model Answer: "This is a high-grade isthmic spondylolisthesis in a young patient – challenging surgical problem.

Assessment:

• Neurology: Detailed motor/sensory/reflex examination; check for cauda equina symptoms
• Imaging: Standing lateral X-ray (Meyerding grade, slip angle), MRI (neural compression, disc degeneration), assess sagittal balance (pelvic incidence, pelvic tilt, sacral slope)
• Functional impact: Pain severity, activity limitation

Surgical Planning (assuming significant symptoms/functional impairment):

The key decision is reduction vs in situ fusion:

In Situ Fusion (preferred by many):

• Fusion without reducing slip
• Advantages: Lower L5 nerve root injury risk, technically simpler
• Disadvantages: Residual deformity, potential sagittal imbalance
• Technique: ALIF (anterior approach, large cage, good lordosis restoration) + posterior instrumentation (360° fusion)

Reduction + Fusion (selected cases):

• Partial reduction to improve alignment
• Advantages: Improved cosmesis, better sagittal balance
• Disadvantages: 10-30% L5 nerve root injury risk (stretch injury → foot drop)
• Technique: Posterior reduction with instrumentation ± ALIF; intraoperative neuromonitoring essential

My approach: Given young age (18 years), I would discuss both options. If sagittal balance acceptable, I'd favor in situ ALIF + posterior fusion (lower neurological risk). If significant deformity/imbalance, consider careful reduction with neuromonitoring, accepting higher nerve injury risk.

Consent: Emphasize L5 nerve injury risk (foot drop), non-union (5-10%), infection, adjacent segment disease, need for prolonged rehabilitation."

Clinical Case Scenario (Short Case)

Examiner Instruction: "Examine this patient's lumbar spine and present your findings."

Expected Findings (Grade III spondylolisthesis):

• Inspection: Increased lumbar lordosis, palpable step-off at L5/S1, waddling gait
• Palpation: Midline tenderness, step-off between L5 and S1 spinous processes
• Movement: Limited/painful extension, hamstring tightness (bilateral SLR limited to 40°)
• Neurology: L5 radiculopathy (weak ankle dorsiflexion, EHL weakness, reduced sensation first web space)

Presentation: "This patient has clinical signs consistent with high-grade spondylolisthesis, likely L5/S1, with L5 radiculopathy. I would confirm with standing lateral lumbar X-ray and MRI for surgical planning."

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