What is the pathophysiology and management of closed burst lumbar fractures?

Pathophysiology and Management of Closed Burst Lumbar Fractures

Burst fractures of the lumbar spine are characterized by axial compression of the vertebral body without concomitant shear, rotation, or translational injury, resulting in fragmentation of the vertebral body and potential compromise of the spinal canal. 1

Pathophysiology

Mechanism of Injury

• Burst fractures occur primarily due to high-energy axial compressive loads, typically from:
  • Falls from height
  • Motor vehicle accidents
  • Severe trauma with vertical loading

Anatomical Characteristics

• Vertebral body fragmentation with centrifugal displacement of fragments
• Potential retropulsion of posterior vertebral body fragments into the spinal canal
• Possible compromise of the spinal canal ranging from 20-90% 2
• May involve failure of the posterior elements in more severe cases

Classification

According to the AO Spine classification system, burst fractures are categorized as Type A3 injuries:

• Type A: Compression injuries
  • A3: Burst fractures with fragmentation of the vertebral body 1
• More severe injuries may progress to:
  • Type B: Distraction/tension band injuries (involving posterior ligamentous complex)
  • Type C: Translation injuries (complete disruption of all elements)

Neurological Impact

• Neurological status is classified from N0 (intact) to N4 (complete spinal cord injury) 1
• Interestingly, the degree of canal compromise does not necessarily correlate with neurological deficit severity 3
• L5 burst fractures specifically tend to cause minimal neurological deficits due to the wider spinal canal at this level 3

Diagnostic Approach

Imaging

• Initial Assessment:
  • Plain radiographs: Evaluate alignment, vertebral height loss, and interpedicular widening
  • CT scan (preferred): Characterize vertebral body fragmentation, canal compromise, and posterior element involvement 1
  • MRI: Essential for evaluating posterior ligamentous complex integrity and soft tissue injuries
    • May modify classification and treatment decisions in up to 31% of cases 1

Clinical Evaluation

• Neurological assessment using the AO Spine neurological modifier system:
  • N0: Intact neurological state
  • N1: Transient neurological symptoms
  • N2: Radiculopathy
  • N3: Incomplete spinal cord or cauda equina injury
  • N4: Complete spinal cord injury 1

Management

Initial Stabilization

• Immediate spinal immobilization for suspected spinal injuries
• Adequate pain control and hemodynamic monitoring
• Maintenance of blood pressure to optimize spinal cord perfusion 1

Non-Operative Management

• Indicated for:

  • Neurologically intact patients (N0)
  • Stable burst fractures
  • Minimal canal compromise
  • Minimal kyphosis
  • No posterior ligamentous complex injury 4, 1

• Treatment Options:

  • External bracing or no bracing are equally effective (Grade B recommendation) 4
  • When bracing is chosen, a thoracolumbosacral orthosis for approximately 3 months 3
  • Early mobilization (within 10-14 days) 3

Surgical Management

• Indicated for:

  • Neurological deficit (N1-N4)
  • Significant canal compromise
  • Significant kyphosis (>30°)
  • Posterior ligamentous complex injury
  • Type B and C injuries 1

• Surgical Approaches:

  • Posterior segmental instrumentation and fixation (PSIF)
  • PSIF with decompression (preferred for neurological deficits)
  • Combined anterior and posterior approaches for severe cases 2, 5
  • Short-segment fixation (one level above and below the fracture) is often sufficient 5

Treatment Algorithm Based on AO Spine Severity Score

• Score ≤3: Initial conservative treatment
• Score 4-5: Consider both surgical and non-surgical treatment
• Score ≥6: Preference for initial surgical treatment 1

Outcomes and Prognosis

• Neurological Recovery:

  • 79% of surgically treated patients show neurological improvement 2
  • Isolated partial nerve-root deficits typically resolve regardless of treatment method 6
  • Complete nerve-root paralysis may benefit from anterior decompression 6

• Radiographic Outcomes:

  • Surgical treatment provides better anatomical restoration
  • Non-operative treatment may result in some residual deformity, but this doesn't necessarily correlate with clinical outcomes 6

• Functional Outcomes:

  • Most patients experience occasional back pain regardless of treatment method
  • Long-term functional outcomes are similar between operative and non-operative groups for stable fractures 6

Special Considerations

• L5 Burst Fractures:

  • Rare but typically stable injuries with minimal neurological deficits
  • Conservative management is often effective 3
  • No significant loss of lordosis or progressive collapse typically occurs 3

• Contiguous Burst Fractures:

  • Extremely rare but require individualized surgical approaches based on fracture pattern and neurological status 7

• Complications:

  • Highest complication rates (33.3%) occur in patients with pre-operative neurological deficits managed non-operatively 2
  • Instrumentation failure is rare with appropriate surgical technique 5

The management decision should be based on fracture stability, neurological status, and degree of deformity, with the primary goal of preserving neurological function and preventing progressive deformity.