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
Clinical 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 has a high failure rate if LSC 7 or more (36% broken screws in original McCormack series)
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
| C | Comminution Little=1, Moderate=2, Severe=3 |
| A | Apposition of fragments Good=1, Partial=2, None=3 |
| K | Kyphosis correction required Little (less than 3deg)=1, Moderate (4-9deg)=2, Severe (more than 9deg)=3 |
| C | Comminution Little=1, Moderate=2, Severe=3 |
| A | Apposition of fragments Good=1, Partial=2, None=3 |
| K | Kyphosis correction required Little (less than 3deg)=1, Moderate (4-9deg)=2, Severe (more than 9deg)=3 |
Hook:CAK: Count the Comminution, Apposition, and Kyphosis - 7+ needs anterior column support!
BURSTBurst Definition
| B | Both cortices fractured Anterior AND posterior body wall |
| U | Usually axial load Classic mechanism |
| R | Retropulsion into canal The key feature |
| S | Second column (middle) Denis middle column involved |
| T | Two columns injured Anterior + middle columns |
| B | Both cortices fractured Anterior AND posterior body wall | S | Second column (middle) Denis middle column involved |
| U | Usually axial load Classic mechanism | T | Two columns injured Anterior + middle columns |
| R | Retropulsion into canal The key feature |
Hook:BURST = Both walls fractured with Retropulsion - defines middle column involvement!
ABUSEDenis Burst Subtypes
| A | Type A - Both endplates Superior and inferior involvement |
| B | Type B - Superior only Most common (70%) |
| U | Unique pattern Type C - Inferior only |
| S | Shear component Type D - Burst-rotation |
| E | Eccentric (lateral) Type E - Lateral burst |
| A | Type A - Both endplates Superior and inferior involvement | S | Shear component Type D - Burst-rotation |
| B | Type B - Superior only Most common (70%) | E | Eccentric (lateral) Type E - Lateral burst |
| U | Unique pattern Type C - Inferior only |
Hook:ABUSE: Type A-Both, B-Upper, Type C-Lower, D-Shear, E-Eccentric lateral!
7UPWhen to Add Anterior
| 7 | LSC score 7 or more High anterior column load |
| U | Unstable anterior column Cannot support load |
| P | Posterior-only will fail High hardware failure rate |
| 7 | LSC score 7 or more High anterior column load |
| U | Unstable anterior column Cannot support load |
| P | Posterior-only will fail High hardware failure rate |
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
Differential diagnosis (what else produces a fractured/abnormal thoracolumbar vertebra):
Differential Diagnosis of a Thoracolumbar Burst Fracture
| Diagnosis | Distinguishing feature | Key discriminator |
|---|---|---|
| Compression (wedge) fracture | Anterior column only; posterior body wall intact, no retropulsion | Intact posterior vertebral wall on CT (AO type A1/A2) |
| Chance / flexion-distraction injury | Tension-band failure through bone and/or PLC; seat-belt mechanism | Posterior element distraction, interspinous widening (AO type B) |
| Fracture-dislocation | Translation/rotation, three-column failure, usually a neurological deficit | Vertebral translation/facet dislocation (AO type C) |
| Osteoporotic fragility fracture | Low energy, elderly; may still burst with canal compromise | DEXA, low-energy mechanism, marrow oedema pattern on MRI |
| Pathological fracture (metastasis/myeloma) | Atypical level, pedicle/posterior-element destruction, soft-tissue mass | Lytic lesion, pedicle erosion, abnormal marrow signal on MRI |
Do not miss the mimic
Before calling a vertebral fracture a "burst", confirm a traumatic mechanism proportionate to the injury. A low-energy or atypical fracture demands MRI to exclude a pathological cause - posterior-element/pedicle destruction or a soft-tissue mass points to metastasis or myeloma, which changes the entire pathway (staging, biopsy, oncological MDT).
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 a high failure rate with short-segment posterior-only fixation. In McCormack's original series, 10 of 28 (36%) short-segment constructs developed broken screws, clustered in the most comminuted bodies. These patients need anterior column reconstruction (corpectomy + cage) OR a longer posterior construct OR a 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 has a high broken-screw/failure rate when LSC is 7 or more (36% in the original McCormack series). 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
McCormack Load-Sharing Classification (landmark)
- Consecutive series of 28 three-column fractures fixed with short-segment Steffee screws and plates; 10 of 28 (36%) developed broken screws
- 9-point scale grading damaged vertebral body, fragment spread, and corrected traumatic kyphosis (each 1-3)
- Screw breakage clustered in patients with the greatest vertebral body comminution
- Tool to predict posterior short-segment failure and select fractures for anterior strut reconstruction
Canal Compromise vs Neurological Deficit
- 105 thoracolumbar/lumbar burst fractures; 18% were neurologically intact despite a burst
- Mean canal compromise 50% in patients with a deficit vs 36% in those intact
- Type of Denis burst did not correlate with severity of deficit (p=0.835)
- No significant overall relationship between canal compromise and deficit at L1 (p=0.42)
TLICS - Thoracolumbar Injury Classification and Severity Score (landmark)
- Consensus system scoring three characteristics: injury morphology, integrity of the posterior ligamentous complex, and neurological status
- Burst morphology scores 2; PLC scores 0 (intact), 2 (indeterminate) or 3 (injured); neurology 0-3
- A composite score stratifies to non-operative (3 or less), surgeon discretion (4), or operative (5 or more)
- Also guides the optimum operative approach for surgical patterns
AO Spine Thoracolumbar Injury Classification (landmark)
- International consensus morphological system: type A (compression), type B (tension-band disruption), type C (translation/displacement)
- Burst fractures are type A3 (incomplete, single endplate) and A4 (complete, both endplates)
- Substantial reliability for identifying the main injury type (kappa = 0.72)
- Adds neurological grade (N) and patient-specific modifiers (e.g. M1 indeterminate PLC)
Exam Viva Scenarios
Use these scenarios to practise clinical reasoning and management decisions
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 - short segment posterior-only constructs have a high failure rate at this threshold (36% broken screws in McCormack's original series).
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.
Guidelines, Registries & Global Practice
Global epidemiology
- Burst fractures cluster at the thoracolumbar junction (T11-L2), which acts as the transition from the rigid kyphotic thoracic spine to the mobile lordotic lumbar spine; in cohorts of conservatively treated thoracolumbar fractures the junction is the commonest site and an independent risk factor for late kyphotic collapse (Guzey et al, Turk Neurosurg 2018, DOI).
- A large burst-fracture series found roughly 18% of patients were neurologically intact despite the burst, with mean canal compromise of 50% in those with a deficit versus 36% in those intact (Mohanty et al, J Orthop Surg (Hong Kong) 2008, DOI).
- Bimodal distribution: high-energy injuries (falls from height, motor-vehicle collisions) in younger men, and low-energy osteoporotic/fragility bursts in older patients - the latter behaving more like an AO type A injury at higher risk of progressive collapse.
Classification systems are the global common language - the AO Spine thoracolumbar system (type A3 incomplete / A4 complete burst) reached substantial reliability (kappa 0.72) in an international consensus study (Vaccaro et al, Spine 2013, DOI) and TLICS provides the cross-board decision threshold (operative at a score of 5 or more; Vaccaro et al, Spine 2005, DOI).
Guidance Across Boards & Societies
| Body / framework | Stance on the neurologically intact burst | Evidence level |
|---|---|---|
| AO Spine TL algorithm | Type A3/A4 with intact PLC and no deficit: non-operative is acceptable; operative if tension-band (B) or translation (C) component | Consensus + cohort |
| TLICS (international, ABOS/FRCS use) | Score 3 or less non-operative, 4 surgeon discretion, 5 or more operative; burst alone scores 2 | Consensus (Level 5) |
| Level 1 RCT evidence (Wood) | No benefit of surgery for the stable, neurologically intact burst; fewer complications without surgery | Level 1 |
| AO / McCormack construct planning | If operating, LSC 7 or more favours anterior column support or a longer/index-screw construct | Level 4 |
Where practice genuinely differs
The big international controversy is the neurologically intact burst with an indeterminate PLC. Reliance on MRI for the PLC, the weight given to canal compromise, and the threshold for early posterior-only stabilisation vary between units and resource settings. High-resource centres increasingly favour MRI-guided non-operative care (supported by the Wood RCT); limited-resource settings may stabilise earlier to allow upright mobilisation and reduce nursing burden. There is no implant registry for spinal trauma comparable to the arthroplasty joint registries (NJR, AOANJRR, AJRR), so trauma evidence rests on RCTs and cohorts rather than registry survival data.
Documentation & Medicolegal
Document for every burst fracture:
- Complete neurological examination (and a digital rectal/perianal exam where cauda equina is possible)
- TLICS and AO Spine type with rationale
- LSC assessment when operating
- MRI for PLC integrity (especially the indeterminate PLC)
- Informed consent covering hardware failure and the option of non-operative care
Common pitfalls: failing to calculate LSC (hardware failure), inadequate consent on failure rates, not documenting PLC assessment, and missing non-contiguous fractures (10-15% of cases).
BURST FRACTURES
Clinical 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% (much higher if LSC 7+ posterior-only; 36% in McCormack series)
- •Non-union: 5-10%
- •Adjacent segment disease: up to 30%
- •Risk factors: diabetes, smoking, osteoporosis