Burst Fractures

Where this sits. The burst fracture is the middle-column injury within thoracolumbar fractures, and it is most often confused with the flexion-distraction Chance fracture, where the posterior column fails in tension rather than the middle column in compression, and where the abdominal viscera must be cleared. The two things that decide management here are the posterior ligamentous complex and the neurology, which is why spinal cord injury and cauda equina syndrome carry the deficit side of the decision. The osteoporotic vertebral fracture that mimics a burst on a plain film is managed entirely differently, on vertebroplasty and kyphoplasty.

The definition. A burst fracture is a vertebral body fracture involving both the anterior and the posterior cortex, with retropulsion of bone into the spinal canal: failure of the anterior and middle columns together. A compression fracture involves the anterior column only, wedging the body while the posterior wall stays intact. Middle column involvement is the distinction that matters, because it indicates higher instability and different treatment considerations.

Mechanism. Axial loading, the commonest mechanisms being falls from height and motor-vehicle accidents with a vertical load. Energy is transmitted through the disc into the vertebral body, which explodes outward - hence "burst" - and the posterior wall fragment retropulses into the canal.

Who and where. The fracture peaks at the thoracolumbar junction (T12-L2), and L1 is the commonest level. The distribution is bimodal: young patients with high-energy trauma, with a male predominance in that group, and elderly patients with osteoporotic fractures.

The differential. What else produces a fractured or abnormal thoracolumbar vertebra:

The three columns. Denis divides the vertebra into three columns, and a burst fracture is defined by which of them fail. The middle column is the one that makes the diagnosis.

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The thoracolumbar junction. T12-L2 is the transition zone where load transfers from the rigid thoracic spine to the mobile lumbar spine. Stress concentrates there, and L1 bears a significant axial load.

Stability. A burst is by definition a middle column failure, but the posterior column may be untouched, and it is the PLC that decides stability rather than the appearance of the canal. An intact PLC makes this a stable burst, which can often be braced; a disrupted PLC makes it an unstable burst, which needs surgery.

Four systems are in play and they answer different questions. McCormack's load-sharing score asks whether the anterior column can still take load, Denis describes the fracture pattern, TLICS decides whether to operate, and AO Spine supplies the morphological label.

Load-Sharing ClassificationDenis Burst SubtypesTLICS for BurstAO Classification

McCormack Load-Sharing Classification (LSC)

The score predicts failure of posterior-only fixation by grading what is left of the anterior column's load-bearing capacity. Three parameters each score 1 to 3, so the total runs from 3 to 9.

Comminution

1 Point

Little (less than 30%)

2 Points

Moderate (30-60%)

3 Points

Severe (more than 60%)

Fragment apposition

1 Point

Good (minimal displacement)

2 Points

Partial (fragments still touch)

3 Points

None (gross displacement)

Kyphosis correction needed

1 Point

Little (less than 3 degrees)

2 Points

Moderate (4-9 degrees)

3 Points

Severe (more than 9 degrees)

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)

Reading the score. A total of 3-6 means posterior-only fixation is acceptable. 7-9 carries a high risk of posterior-only failure, and the anterior column needs support.

The 7-Point Rule

LSC 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.

Mnemonic

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

Hook:CAK: Count the Comminution, Apposition, and Kyphosis - 7+ needs anterior column support!

Denis Classification of Burst Fractures

The subtypes turn on which endplate fails, and on whether rotation or lateral compression is added to the axial load.

Type A - both endplates

Pattern

2-fragment; 25% of burst fractures

Mechanism and features

Axial compression

Type B - superior endplate only

Pattern

2-fragment; most common, 70%

Mechanism and features

Flexion plus axial load; the classic pattern

Type C - inferior endplate only

Pattern

2-fragment; rare, 5%

Mechanism and features

Extension

Type D - burst-rotation

Pattern

3-fragment, more laterally comminuted

Mechanism and features

Rotation plus axial load; higher instability

Type E - lateral burst

Pattern

Unilateral body comminution

Mechanism and features

Lateral compression; associated with scoliotic deformity

Type	Pattern	Mechanism and features
Type A - both endplates	2-fragment; 25% of burst fractures	Axial compression
Type B - superior endplate only	2-fragment; most common, 70%	Flexion plus axial load; the classic pattern
Type C - inferior endplate only	2-fragment; rare, 5%	Extension
Type D - burst-rotation	3-fragment, more laterally comminuted	Rotation plus axial load; higher instability
Type E - lateral burst	Unilateral body comminution	Lateral compression; associated with scoliotic deformity

Why Type B predominates. The classic injury is a fall from height in which the patient lands on the feet or buttocks, so the spine is loaded in flexion and the superior endplate is the one that gives.

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TLICS Applied to Burst Fractures

Scoring a burst. Morphology scores 2 by definition. The PLC scores 0 if intact, 2 if indeterminate and 3 if injured, and neurology scores 0-3 as in any other thoracolumbar injury.

The thresholds. A total of 3 or less is non-operative, 4 is surgeon's discretion, and 5 or more is operative. A burst with an intact PLC and normal neurology therefore scores 2 and is braced; add either a PLC injury or a deficit and the total reaches the operative range.

Burst, PLC intact, intact

Morphology

2

PLC

0

Neuro

0

Total

2

Treatment

Brace

Burst, PLC disrupted, intact

Morphology

2

PLC

3

Neuro

0

Total

5

Treatment

Surgery

Burst, PLC intact, incomplete

Morphology

2

PLC

0

Neuro

3

Total

5

Treatment

Surgery

Burst, PLC disrupted, incomplete

Morphology

2

PLC

3

Neuro

3

Total

8

Treatment

Urgent surgery

Scenario	Morphology	PLC	Neuro	Total	Treatment
Burst, PLC intact, intact	2	0	0	2	Brace
Burst, PLC disrupted, intact	2	3	0	5	Surgery
Burst, PLC intact, incomplete	2	0	3	5	Surgery
Burst, PLC disrupted, incomplete	2	3	3	8	Urgent surgery

AO Spine Classification for Burst

A3 and A4. Bursts are type A injuries. A3 is an incomplete burst involving one endplate, subdivided into A3.1 superior, A3.2 inferior and A3.3 lateral. A4 is a complete burst involving both endplates, the most severe type A injury, with complete loss of anterior column integrity.

Modifiers. Add a B modifier if there is a posterior tension band injury and an N modifier for neurological status. AO provides the detailed morphological description, which makes it the better language for documentation, while TLICS is more practical for the immediate treatment decision.

History. Take the mechanism in detail - the height of the fall, the type of collision - because it is an axial loading mechanism that suggests a burst. Then ask about weakness, numbness and bladder function.

Examination. What to look for, and what to record:

• Inspection: bruising, kyphotic deformity
• Palpation: step-off, interspinous gap, tenderness
• Neurological: a complete lower limb examination
• Log-roll: examine the entire spine

Associated injuries. A burst from a fall from height keeps company with calcaneal fractures, and with femoral and pelvic injuries; high-energy mechanisms bring abdominal visceral injury. Another spinal level is injured in 10-15%, non-contiguous with the first.

Two studies decide the treatment. CT defines the fracture and MRI defines the ligaments, and the decision needs both: CT supplies the load-sharing score, MRI supplies the PLC component of TLICS.

What to measure on the CT. Four numbers come off the scan and feed the decision:

• Canal compromise percentage: (1 - fractured canal/normal canal) x 100
• Vertebral body comminution: percentage of the body involved
• Fragment apposition: contact between fragments
• Kyphosis: local or regional sagittal angle

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What to read on the MRI. STIR sequences show ligament injury directly, and the same study shows any compression of the cord or cauda equina. The structures that carry the PLC verdict, and what injury looks like in each:

Two decisions, two tools. TLICS decides whether to operate; McCormack's load-sharing score decides what to build.

What goes wrong. Ignoring the load-sharing score is a common cause of failure, and the rest is bone quality, fusion biology and the specific risks of the anterior approach.

Without surgery. Outcomes for the stable burst are good. Some kyphosis progression is accepted, and most patients return to normal function.

After surgery. Fusion rates are high with adequate fixation, and constructs matched to the load-sharing score fail less often. Neurological recovery depends on the initial injury, and a cauda equina injury carries a better prognosis than a cord injury.

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).
• Rates of neurological deficit vary enormously with WHO IS COUNTED, and the two figures on this page are not in conflict once that is stated. Across unselected burst fractures a deficit is present in roughly 15-25%. By contrast, in a tertiary referral series of 105 thoracolumbar/lumbar bursts only 18% were neurologically INTACT - 82% had a deficit and 26 had complete paraplegia - because severe injuries are what get referred (Mohanty et al, J Orthop Surg (Hong Kong) 2008, DOI). In that series mean canal compromise was 50% in those with a deficit versus 36% in those intact, and the correlation held at T11/T12 (p=0.007) but not at L1 (p=0.42). Quote the population before quoting the percentage.
• 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).