BURST FRACTURES
Axial Load Injury | Middle Column Involved | Load-Sharing Score
BURST FRACTURE ASSESSMENT
Critical Must-Knows
- Burst = middle column involvement (retropulsed posterior body wall)
- PLC status determines stability more than canal compromise
- Load-sharing classification (LSC) predicts need for anterior column support
- LSC 7 or more = anterior reconstruction needed (high failure rate with posterior alone)
- Neurologically intact with intact PLC can often be managed non-operatively
Examiner's Pearls
- "Burst fractures involve both anterior AND middle columns (posterior vertebral body wall)
- "Canal compromise alone does NOT mandate surgery
- "McCormack LSC: comminution + fragment apposition + kyphosis correction
- "Short segment posterior-only fails in approximately 50% if LSC 7 or more
Clinical Imaging
Imaging Gallery
Critical Burst Fracture Exam Points
What Makes It a Burst?
Posterior vertebral body wall fracture with retropulsion into canal. This is middle column involvement in Denis classification. Differentiates from simple compression fracture.
PLC is Key
Canal compromise doesn't determine stability - PLC does. A 50% canal compromise with intact PLC can be braced. A 20% compromise with disrupted PLC needs surgery.
Load-Sharing Score
McCormack LSC predicts posterior-only failure: Comminution (1-3) + Apposition (1-3) + Kyphosis correction (1-3). Score 7+ = anterior column support needed.
Treatment Decision
TLICS guides surgery decision. LSC guides construct choice. Stable burst (TLICS less than 4): brace. Unstable: surgery. LSC 7+: add anterior column.
Quick Decision Guide
| Scenario | TLICS | LSC | Treatment |
|---|---|---|---|
| Burst, PLC intact, neuro intact | 2 | N/A | TLSO brace 8-12 weeks |
| Burst, PLC disrupted, neuro intact | 5 | Assess | Posterior fixation +/- anterior |
| Burst, minimal comminution, neuro intact | 5+ | 3-5 | Short segment posterior fixation |
| Burst, severe comminution, neuro deficit | 7+ | 7+ | Anterior corpectomy + posterior fixation |
CAKLoad-Sharing Score Components
Memory Hook:CAK: Count the Comminution, Apposition, and Kyphosis - 7+ needs anterior column support!
BURSTBurst Definition
Memory Hook:BURST = Both walls fractured with Retropulsion - defines middle column involvement!
ABUSEDenis Burst Subtypes
Memory Hook:ABUSE: Type A-Both, B-Upper, Type C-Lower, D-Shear, E-Eccentric lateral!
7UPWhen to Add Anterior
Memory Hook:7UP = LSC 7 or more means Unstable anterior, Posterior-only fails - need anterior column support!
Overview and Epidemiology
Burst fractures are vertebral body fractures involving both the anterior and posterior cortices with retropulsion into the spinal canal. They represent failure of both anterior and middle columns.
Epidemiology:
- Peak at thoracolumbar junction (T12-L2), especially L1
- Bimodal: young high-energy trauma, elderly osteoporotic
- MVA and falls from height most common mechanisms
- Male predominance in young age group
Burst vs Compression
Compression fracture: Only anterior column (wedge shape, intact posterior wall). Burst fracture: Anterior AND middle columns (posterior wall fractured, retropulsion).
This distinction is critical because middle column involvement indicates higher instability and different treatment considerations.
Mechanism:
- Axial loading (falls from height, MVA with vertical load)
- Energy transmitted through disc into vertebral body
- Body explodes outward (hence "burst")
- Posterior wall fragment retropulses into canal
Anatomy and Biomechanics
Denis three-column concept (essential for burst understanding):
| Column | Structures | Burst Involvement |
|---|---|---|
| Anterior | Anterior 2/3 vertebral body, disc, ALL | Always involved in burst |
| Middle | Posterior 1/3 body, posterior annulus, PLL | By definition involved (key feature) |
| Posterior | Pedicles, facets, laminae, PLC | May or may not be involved |
The Retropulsed Fragment
The posterior vertebral body fragment (middle column) that retropulses into the canal is the defining feature of a burst fracture. This fragment causes:
- Canal compromise
- Potential neurological injury
- Indication for decompression (if deficit present)
Why L1 is most common:
- Thoracolumbar junction (T12-L2) is the transition zone
- Load transfers from rigid thoracic to mobile lumbar
- Stress concentration at this level
- L1 bears significant axial load
Stability considerations:
- Burst = middle column failure
- May have intact posterior column (PLC)
- PLC status is KEY to stability
- Intact PLC = "stable burst" (can often brace)
- Disrupted PLC = "unstable burst" (surgery)
Classification Systems
McCormack Load-Sharing Classification (LSC)
Purpose: Predicts failure of posterior-only fixation by assessing anterior column load-bearing capacity.
| Parameter | 1 Point | 2 Points | 3 Points |
|---|---|---|---|
| Comminution | Little (less than 30%) | Moderate (30-60%) | Severe (more than 60%) |
| Fragment apposition | Good (minimal displacement) | Partial (fragments still touch) | None (gross displacement) |
| Kyphosis correction needed | Little (less than 3 degrees) | Moderate (4-9 degrees) | Severe (more than 9 degrees) |
Score interpretation:
- 3-6: Posterior-only fixation acceptable
- 7-9: High risk of posterior-only failure → need anterior column support
The 7-Point Rule
LSC score of 7 or more predicts approximately 50% failure rate with short segment posterior-only fixation. These patients need anterior column reconstruction (corpectomy + cage) OR longer posterior constructs OR combined approach.
Clinical Assessment
History:
- Mechanism (fall height, MVA type)
- Axial loading mechanism suggests burst
- Neurological symptoms (weakness, numbness, bladder)
- Other injuries (calcaneus fractures common)
Physical examination:
Spine Examination
- Inspection: Bruising, kyphotic deformity
- Palpation: Step-off, interspinous gap, tenderness
- Neurological: Complete lower extremity exam
- Log-roll: Examine entire spine
Associated Injuries
- Calcaneus: Fall from height mechanism
- Other spine levels: 10-15% non-contiguous
- Abdominal: Visceral injury with high-energy
- Lower extremity: Femur, pelvis
Neurological examination:
Neurological Findings Guide
| Finding | Significance | Level Suggestion |
|---|---|---|
| Intact | Good prognosis, consider non-op if stable | N/A |
| Hip flexor weakness | L1-L2 level | Conus/high cauda |
| Knee extension weakness | L3-L4 level | Cauda equina |
| Ankle dorsiflexion weakness | L4-L5 level | Cauda equina |
| Bladder dysfunction | Sacral involvement | Cauda equina syndrome |
Cauda Equina Syndrome
In burst fractures, neurological deficit is typically cauda equina (LMN) rather than cord (UMN) because most burst fractures occur below the conus (which ends L1-L2). Cauda equina syndrome (bladder/bowel dysfunction) is a surgical emergency.
Investigations
Imaging Algorithm
First-line imaging. Defines fracture morphology, canal compromise, comminution. Essential for LSC scoring. 3D reconstruction helpful.
For PLC assessment. STIR sequences show ligament injury. Also shows cord/cauda compression. Essential for TLICS scoring.
10-15% non-contiguous. CT or MRI of entire spine in high-energy trauma.
CT assessment for burst fractures:
Key measurements:
- Canal compromise percentage: (1 - fractured canal/normal canal) x 100
- Vertebral body comminution: Percentage of body involved
- Fragment apposition: Contact between fragments
- Kyphosis: Local or regional sagittal angle
Canal Compromise Controversy
Canal compromise alone does NOT mandate surgery. A patient with 60% canal compromise but intact PLC and no neurological deficit can often be managed non-operatively. The canal remodels over time with up to 50% spontaneous improvement.
MRI assessment:
MRI Findings to Assess
| Structure | Normal | Abnormal |
|---|---|---|
| Supraspinous ligament | Dark line on T2 | High signal, discontinuity |
| Interspinous ligament | Intermediate signal | High T2 signal, widened |
| Ligamentum flavum | Dark on T2 | Signal change, buckling |
| Facet capsules | Congruent joint | Widened, fluid signal |
Management
Conservative Treatment
Indications:
- TLICS score 2-3 (burst, intact PLC, neurologically intact)
- Kyphosis less than 30 degrees
- No progressive neurological deficit
- Compliant patient
Protocol:
Non-Operative Protocol
Pain management, bed rest as tolerated, log-roll precautions. May begin standing with TLSO if pain controlled.
TLSO brace full-time except when supine. Serial X-rays at 2, 6, 12 weeks. Monitor for kyphosis progression.
Gradual brace weaning. Core strengthening. Return to activity based on symptoms and stability.
Monitoring:
- Serial X-rays to check for kyphosis progression
- Kyphosis increase more than 10-15 degrees = consider surgery
- Neurological deterioration = urgent surgery
Wood et al Evidence
The Wood et al RCT (2003) showed no significant difference in functional outcomes between operative and non-operative treatment for stable burst fractures. This supports conservative management for appropriate patients.
Surgical Technique
Consent Points
- Neurological injury: Less than 1% if no pre-op deficit
- Infection: 1-3%
- Hardware failure: 5-15% (higher if LSC 7+ and posterior-only)
- Need for revision: 5-10%
- Adjacent segment disease: Long-term risk
- Anterior approach: Additional risks (ileus, vascular)
Equipment
- Pedicle screws: Polyaxial, appropriate lengths
- Imaging: Fluoroscopy or navigation
- Reduction tools: Lamina spreader for distraction
- If anterior: Structural cage, anterior plate
- Cell saver: For major reconstructions
Complications
| Complication | Incidence | Prevention/Management |
|---|---|---|
| Hardware failure | 5-15% (higher if LSC 7+ posterior-only) | Respect LSC, add anterior if 7+ |
| Loss of kyphosis correction | 10-20% | Index screws, cement augmentation in osteoporosis |
| Non-union | 5-10% | Bone graft, smoking cessation, stable fixation |
| Adjacent segment disease | Up to 30% long-term | Short segment when appropriate |
| Neurological injury | Less than 1% | Careful technique, avoid over-distraction |
| Ileus (anterior) | 10-20% | Gentle handling, early mobilization |
| Vascular injury (anterior) | 1-2% | Vascular surgery backup, careful dissection |
LSC 7+ Failure
Ignoring the load-sharing score is a common cause of failure. Short segment posterior-only fixation fails in approximately 50% when LSC is 7 or more. Always assess LSC and plan accordingly.
Postoperative Care
Rehabilitation Timeline
DVT prophylaxis, pain management, wound care. Mobilize with physio if stable.
Continue mobilization. TLSO if additional support desired. Wound check. X-ray to confirm position.
Progressive activity. Serial X-rays. Core strengthening program. Wean brace if used.
CT at 6-12 months to confirm fusion. Return to activity based on imaging and symptoms. Long-term surveillance for adjacent disease.
Outcomes and Prognosis
Non-operative outcomes:
- Good for stable bursts (TLICS less than 4)
- Some kyphosis progression acceptable
- Canal remodels spontaneously (up to 50%)
- Most return to normal function
Surgical outcomes:
- High fusion rates with adequate fixation
- LSC-appropriate constructs reduce failure
- Neurological recovery depends on initial injury
- Cauda equina has better prognosis than cord
Evidence Base
Load Sharing Classification
- Developed 9-point scale for burst fractures
- Comminution + apposition + kyphosis correction
- Score 7 or more predicts posterior-only failure (50%)
- Guides need for anterior column support
Canal Remodeling
- Canal compromise remodels spontaneously
- Significant improvement by 12 months
- Occurs even without surgery
- Supports non-op for intact neurology
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Stable Burst Fracture
"A 30-year-old falls from 3 meters and lands on his feet. CT shows an L1 burst fracture with 40% canal compromise. He is neurologically intact. MRI shows intact PLC. How do you manage this?"
Scenario 2: Unstable Burst with High LSC
"A 45-year-old woman falls from a roof and has an L1 burst fracture with severe comminution (more than 60%), poor fragment apposition, and 15 degrees of kyphosis. She has incomplete cauda equina syndrome. What is your surgical plan?"
Scenario 3: Hardware Failure
"A 50-year-old male with diabetes had short segment posterior fixation (T12-L2) for an L1 burst fracture 8 weeks ago. He now presents with increasing back pain and X-rays show screw pullout with kyphosis of 30 degrees. How do you manage this failure?"
MCQ Practice Points
Burst Definition Question
Q: What defines a burst fracture and differentiates it from a compression fracture? A: Involvement of the posterior vertebral body wall (middle column) with retropulsion into the canal. Compression fractures only involve the anterior column.
LSC Scoring Question
Q: What are the three components of the McCormack Load-Sharing Classification? A: Comminution (1-3), fragment Apposition (1-3), and Kyphosis correction needed (1-3). Score 7+ predicts posterior-only failure.
LSC Threshold Question
Q: At what LSC score should anterior column reconstruction be considered? A: LSC 7 or more - approximately 50% of short segment posterior-only constructs fail at this threshold.
Canal Compromise Question
Q: A patient has 50% canal compromise but is neurologically intact with intact PLC. Does this require surgery? A: No - canal compromise alone does not mandate surgery. It remodels spontaneously. TLICS would be 2 (non-operative).
Denis Burst Type Question
Q: What is the most common type of burst fracture in the Denis classification? A: Type B (superior endplate) - accounts for 70% of burst fractures.
Ligamentotaxis Question
Q: When is ligamentotaxis most effective for reducing retropulsed fragments? A: When PLL is intact and surgery is performed within 72 hours. Beyond this, fragments become adherent.
Australian Context and Medicolegal Considerations
Trauma System
- Major trauma centers coordinate spine care
- Early transfer for complex/unstable fractures
- Spinal cord injury units for rehabilitation
- TLICS and LSC widely adopted
Guidelines
- State trauma guidelines incorporate TLICS
- Evidence-based approach to non-operative treatment
- LSC increasingly used for construct planning
- Multidisciplinary spine care
Medicolegal Considerations
Documentation requirements:
- Complete neurological examination
- TLICS score calculation with rationale
- LSC assessment for burst fractures
- MRI for PLC assessment documented
- Informed consent including hardware failure risk
Common issues:
- Failure to calculate LSC leading to hardware failure
- Inadequate consent regarding failure rates
- Not documenting PLC assessment
- Missed non-contiguous fractures
BURST FRACTURES
High-Yield Exam Summary
What Makes It a Burst?
- •Posterior vertebral body wall fractured (middle column)
- •Retropulsion of fragment into canal
- •Anterior AND middle column failure
- •Different from compression (anterior only)
Load-Sharing Classification
- •Comminution: Little=1, Moderate=2, Severe=3
- •Apposition: Good=1, Partial=2, None=3
- •Kyphosis correction: Little=1, Moderate=2, Severe=3
- •Score 7+ = anterior column support needed
Treatment Algorithm
- •TLICS less than 4 + intact PLC: TLSO brace
- •TLICS 5+: Posterior pedicle screw fixation
- •LSC less than 7: Short segment (with index screws)
- •LSC 7+: Anterior corpectomy + posterior
Surgical Pearls
- •Index level screws reduce failure
- •Ligamentotaxis works if PLL intact and less than 72h
- •Canal compromise alone doesn't mandate surgery
- •Cement augmentation in osteoporosis
Complications
- •Hardware failure: 5-15% (50% if LSC 7+ posterior-only)
- •Non-union: 5-10%
- •Adjacent segment disease: up to 30%
- •Risk factors: diabetes, smoking, osteoporosis