SPONDYLOLISTHESIS
Classification | Grading | Fusion Decisions
WILTSE CLASSIFICATION
Critical Must-Knows
- Isthmic = pars defect, young, L5-S1
- Degenerative = facet arthropathy, older, L4-L5
- Meyerding grades I-V based on slip percentage
- High-grade (greater than 50%) usually needs reduction consideration
- Fusion indicated for symptomatic with instability or progression
Examiner's Pearls
- "Scotty dog sign on oblique X-ray = pars defect
- "Degenerative rarely exceeds Grade II
- "L5 radiculopathy common in isthmic L5-S1
- "Slip angle more important than grade for high-grade
Clinical Imaging
Imaging Gallery
Critical Exam Concepts
Wiltse Classification
Know the types. Dysplastic (I), Isthmic (II - most common), Degenerative (III), Traumatic (IV), Pathologic (V).
Meyerding Grades
Based on slip percentage. Grade I (less than 25%), II (25-50%), III (50-75%), IV (75-100%), V (spondyloptosis, greater than 100%).
High-Grade Management
Greater 50% controversial. Consider reduction to improve sagittal balance. Risk of L5 root stretch. In-situ fusion vs reduction.
Surgical Approach
Isthmic: often ALIF or circumferential. Degenerative: TLIF or posterolateral. Match technique to pathology.
Isthmic vs Degenerative Comparison
| Feature | Isthmic (Type II) | Degenerative (Type III) |
|---|---|---|
| Age | Young (teens to 30s) | Older (greater 50) |
| Level | L5-S1 (90%) | L4-L5 (most common) |
| Pars | Defect (lysis) | Intact |
| Mechanism | Pars fracture | Facet arthropathy |
| Max slip | Can progress to high-grade | Rarely exceeds Grade II |
DITPPWiltse Classification
Memory Hook:DITPP: the ways vertebrae slip!
25-50-75-100Meyerding Grading
Memory Hook:Divide the vertebra into quarters to grade the slip!
PAINSSurgical Indications
Memory Hook:When listhesis causes PAINS, consider surgery!
Overview and Epidemiology
Two Common Types
Isthmic and degenerative are most common. Isthmic = young, pars defect, L5-S1. Degenerative = older, intact pars, L4-L5. Know the differences for exams!
Isthmic Risk Factors
- Extension sports (gymnastics, cricket fast bowling)
- Adolescent growth spurt
- Genetic predisposition
- Male more than female
- Repetitive hyperextension
Degenerative Risk Factors
- Age greater than 50
- Female more than male (3:1)
- Facet orientation (sagittal)
- Disc degeneration
- Hormonal factors (postmenopausal)
Pathophysiology and Mechanisms
Pars Defect (Spondylolysis)
Location: Isthmus between superior and inferior articular processes.
Scotty dog sign: On oblique X-ray, pars defect appears as "collar" on the Scotty dog (neck = pars).
Mechanism: Fatigue fracture from repetitive hyperextension and rotation.
Bilateral defects: Allow vertebra to slip forward (listhesis).
Unilateral pars defect = spondylolysis without listhesis.
Scotty Dog Sign
On oblique lumbar X-ray: The Scotty dog represents the posterior elements. Eye = pedicle, nose = transverse process, ear = superior facet, front leg = inferior facet, neck = pars. A "collar" on the neck = pars defect.
Classification Systems
Wiltse-Newman Classification
| Type | Name | Mechanism | Level |
|---|---|---|---|
| I | Dysplastic | Congenital facet abnormality | L5-S1 |
| II | Isthmic | Pars defect (lytic, elongated, acute) | L5-S1 |
| III | Degenerative | Facet arthropathy, intact pars | L4-L5 |
| IV | Traumatic | Acute fracture other than pars | Any |
| V | Pathologic | Tumor, infection, bone disease | Any |
Type II subtypes: IIa (lytic/fatigue fracture), IIb (elongated intact pars), IIc (acute pars fracture).
Clinical Assessment
History
- Back pain: Worse with extension
- Leg pain: Radicular pattern
- Claudication: If associated stenosis
- Activity: Sports history (isthmic)
- Age of onset: Young = isthmic, old = degenerative
Examination
- Posture: May see hyperlordosis or flexed stance
- Step-off: Palpable in high-grade
- Hamstrings: Tight (especially high-grade)
- Gait: Waddling if severe (pelvic waddle gait)
- Neuro: L5 and S1 root testing
Root Involvement by Level
| Level | Exiting Root | Traversing Root | Clinical |
|---|---|---|---|
| L4-L5 | L4 | L5 | L5 radiculopathy common (degenerative) |
| L5-S1 | L5 | S1 | L5 radiculopathy (foraminal narrowing in isthmic) |
High-Grade Signs
High-grade spondylolisthesis findings: Palpable step-off, flattened buttocks (vertical sacrum), tight hamstrings, waddling gait, trunk shortened. May have severe sagittal imbalance.
Investigations
Plain Radiographs
Views:
- AP, lateral (standing preferred)
- Oblique (Scotty dog for pars)
- Flexion-extension (dynamic instability)
Assess:
- Meyerding grade (lateral view)
- Slip angle
- Pars defect (oblique)
- Dynamic motion
Standing laterals better demonstrate true slip.
Slip Angle
Slip angle (angle between L5 and S1) is more important than grade for high-grade slips. High slip angle indicates worse sagittal imbalance and higher risk of progression.
Management Algorithm
Non-Operative Management
Acute pars stress reaction (young athlete):
- Bracing (Boston overlap brace) 6-12 weeks
- Activity modification
- Physical therapy (flexion-based, core)
- May heal if caught early (bone scan or MRI edema positive)
Chronic/established:
- PT, core strengthening
- Activity modification
- Weight management
- Monitor for progression
Many patients with low-grade slips remain asymptomatic.
Pars Repair Option
Direct pars repair (Buck fusion, Scott wiring, pedicle screw-hook construct) is an option in young patients with single-level isthmic spondylolysis, no significant disc degeneration, and no or minimal slip. Preserves motion.
Surgical Technique
Posterolateral Fusion with Instrumentation
Indications: Most low-grade listhesis.
Technique:
- Prone positioning
- Midline approach, exposure of transverse processes
- Pedicle screw placement
- Decompression if needed (laminectomy, foraminotomy)
- Decortication and bone grafting to transverse processes
Key point: Adequate decompression of affected roots while achieving solid fusion.
L5 Root in High-Grade Reduction
L5 nerve root at significant risk with reduction of high-grade slips. The root is draped over the sacral dome and tethered. Aggressive reduction can stretch and injure it. Consider partial reduction and neuromonitoring.
Complications
| Complication | Notes | Prevention/Management |
|---|---|---|
| Pseudarthrosis | 5-15% depending on technique | Adequate graft, rigid fixation, smoking cessation |
| L5 root injury (high-grade) | With reduction | Partial reduction, neuromonitoring |
| Adjacent segment disease | Long-term | Consider minimizing fusion length |
| Progression (non-op) | Especially in young | Monitor, early fusion if progressing |
| Dural tear | 5-10% | Careful technique, primary repair |
Fusion Rate Factors
Fusion rates affected by: Number of levels, smoking, biology, technique, bone graft quality. Interbody fusion has higher rates than posterolateral alone.
Postoperative Care
Spondylolisthesis Fusion Recovery
Pain control. DVT prophylaxis. Early mobilization. Brace if used. Neurological checks (especially after high-grade reduction).
Activity restrictions (no BLT: bending, lifting, twisting). Wound care. Gradual walking increase. Brace compliance if prescribed.
Radiographs to assess. Begin PT for core strengthening. Gradual activity increase. Wean brace.
Fusion consolidation. Return to activities. Final radiographs for fusion assessment. CT if fusion in doubt.
Fusion Assessment
Solid fusion signs: No motion on flexion-extension, bridging bone, no lucencies around hardware. CT scan gold standard for fusion assessment.
Outcomes and Prognosis
Prognostic Factors
Better outcomes:
- Low-grade slip
- Predominant leg pain
- Good bone quality
- Non-smoker
- Single level
Worse outcomes:
- High-grade slip
- Predominant back pain
- Osteoporosis
- Smoker
- Multi-level disease
Evidence Base and Key Studies
SPORT Trial - Spondylolisthesis
- Surgery superior for degenerative listhesis with stenosis
- Decompression + fusion better than conservative
- High crossover rate
- As-treated analysis strongly favored surgery
Fusion with vs without Instrumentation
- Instrumentation improves fusion rates
- Similar clinical outcomes if fused
- Pedicle screws standard of care
- May allow earlier mobilization
High-Grade Reduction
- Partial reduction often sufficient
- Full reduction increases neurological risk
- Sagittal balance improvement important
- No RCTs comparing approaches
Interbody vs Posterolateral Fusion
- Interbody has higher fusion rates
- Similar clinical outcomes in some studies
- Better disc height restoration with interbody
- Higher complication rate with interbody
Pars Repair in Athletes
- High success in selected patients
- Preserves motion
- Patient selection critical
- Best for single-level, no disc disease
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Young Athlete with Back Pain
"A 17-year-old fast bowler presents with back pain worse with extension and bowling. X-rays show bilateral pars defects at L5 with Grade I spondylolisthesis. How do you manage?"
Scenario 2: Degenerative Spondylolisthesis with Stenosis
"A 68-year-old woman has failed conservative treatment for neurogenic claudication. MRI shows L4-L5 stenosis and Grade I degenerative spondylolisthesis with 4mm dynamic instability. What is your surgical plan?"
Scenario 3: High-Grade Spondylolisthesis
"A 15-year-old girl presents with worsening back pain and hamstring tightness. X-rays show L5-S1 isthmic spondylolisthesis Grade III (55% slip) with high slip angle. What are the management considerations?"
MCQ Practice Points
Wiltse Classification Question
Q: What is the most common type of spondylolisthesis? A: Type II (Isthmic) - pars defect from fatigue fracture. Most common level is L5-S1.
Level Difference Question
Q: What is the most common level for degenerative spondylolisthesis? A: L4-L5. Degenerative rarely exceeds Grade II. Isthmic is most common at L5-S1.
Meyerding Question
Q: What defines high-grade spondylolisthesis? A: Grade III or higher (greater than 50% slip). Grade III = 50-75%, Grade IV = 75-100%, Grade V = spondyloptosis.
Scotty Dog Question
Q: What does the collar on the Scotty dog sign represent? A: Pars interarticularis defect (spondylolysis). Seen on oblique lumbar X-ray.
High-Grade Risk Question
Q: What nerve root is most at risk during reduction of high-grade L5-S1 spondylolisthesis? A: L5 nerve root. Draped over sacral dome and tethered; stretched with reduction.
Australian Context
Australian Practice
- Common in young athletes (cricket, gymnastics)
- SPORT trial influences practice
- Both TLIF and ALIF commonly used
- Growing use of navigation
- Emphasis on sagittal balance
Orthopaedic Relevance
- Common viva topic
- Know Wiltse and Meyerding
- Isthmic vs degenerative differences
- Surgical indications and approach selection
- High-grade management principles
Orthopaedic Exam Focus
Know the classifications (Wiltse, Meyerding), differences between isthmic and degenerative, surgical indications (PAINS), and high-grade reduction controversy.
SPONDYLOLISTHESIS
High-Yield Exam Summary
Wiltse Classification (DITPP)
- •I Dysplastic: congenital facet
- •II Isthmic: pars defect (most common)
- •III Degenerative: facet arthropathy
- •IV Traumatic: acute fracture
- •V Pathologic: tumor/infection
Meyerding Grades
- •I: 0-25% (low-grade)
- •II: 25-50% (low-grade)
- •III: 50-75% (high-grade)
- •IV: 75-100% (high-grade)
- •V: greater 100% (spondyloptosis)
Isthmic vs Degenerative
- •Isthmic: young, L5-S1, pars defect
- •Degenerative: old, L4-L5, intact pars
- •Degenerative rarely exceeds Grade II
- •Isthmic can progress to high-grade
Surgical Indications (PAINS)
- •Progressive slip
- •Associated neurological deficit
- •Intractable pain (failed conservative)
- •Nerve compression
- •Sagittal imbalance
High-Grade Considerations
- •In-situ vs reduction controversy
- •L5 root at risk with reduction
- •Slip angle more important than grade
- •Often needs circumferential fusion
Key Imaging Signs
- •Scotty dog collar = pars defect
- •Standing laterals best for grading
- •Flexion-extension for instability
- •MRI for neural compression assessment