Complete Burst Fracture: Definition and Clinical Characteristics
A complete burst fracture is an unstable compression fracture of the vertebral body characterized by centripetal disruption of both the anterior and middle columns with retropulsion of posterior vertebral body wall fragments into the spinal canal, often accompanied by laminar fractures and increased interpediculate distance. 1, 2
Anatomic and Radiographic Features
Key distinguishing characteristics that define a complete burst fracture include:
- Centripetally oriented disruption of the entire vertebral body with failure of both anterior and posterior walls 2
- Retropulsed bone fragments from the posterior vertebral body wall projecting into the spinal canal, causing variable degrees of canal compromise 1, 2
- Laminar fractures (unilateral or bilateral) that typically abut the spinous process, representing posterior element involvement 1, 2
- Increased interpediculate distance on anteroposterior radiographs, indicating lateral expansion of the vertebral body 2
- Vertically oriented fracture lines emanating from the basivertebral foramen through the vertebral body 2
- Marked anterior wedging with loss of vertebral body height 2
Mechanism and Classification
Burst fractures result from high-energy axial compression forces, typically from falls from height or motor vehicle accidents, causing the vertebral body to fail under compressive load with the nucleus pulposus acting as a hydraulic wedge that drives fragments outward and posteriorly into the canal 3, 1.
Under the AO Spine Thoracolumbar Injury Classification System, complete burst fractures are classified as Type A injuries (compression injuries with anterior element failure), though the presence of posterior element fractures and canal compromise indicates greater severity within this category 4.
Clinical Significance in L4 Fractures
For an acute-on-chronic L4 burst fracture specifically:
- L4 burst fractures are relatively uncommon, as most burst fractures occur at the thoracolumbar junction (T11-L2), with lower lumbar burst fractures representing only 1% of all lumbar spine fractures 5
- The "acute-on-chronic" designation suggests a new traumatic injury superimposed on pre-existing degenerative or old traumatic changes, which significantly complicates stability assessment 4
- Neurological deficits at L4 may manifest as radiculopathy affecting L4-L5 nerve roots or cauda equina symptoms, fundamentally changing management from conservative to surgical 4, 6
Stability Assessment
Complete burst fractures are inherently unstable due to disruption of the two-column concept of spinal stability (anterior and middle columns) 1. Critical factors determining treatment include:
- Neurological status: Any deficit mandates surgical evaluation 6, 7
- TLICS score: Scores ≤3 suggest conservative management; scores ≥5 indicate surgical intervention 6
- Load Sharing Classification: For burst fractures, scores of 7-9 points indicate need for combined anterior-posterior fixation, while scores >6 may be treated with posterior fixation alone 4, 6
- Degree of canal compromise, vertebral collapse, and kyphotic deformity 4, 6
Imaging Requirements
CT imaging is essential to fully characterize complete burst fractures, as plain radiographs frequently miss posterior element fractures and underestimate canal compromise 4, 2. MRI provides additional critical information about posterior ligamentous complex integrity, spinal cord edema, epidural hematoma, and noncontiguous injuries, changing classification and management in 24-40% of cases 4.
Common Pitfalls
- Do not confuse with simple compression fractures: Complete burst fractures involve posterior wall disruption with canal compromise, while compression fractures spare the posterior wall 1, 2
- Do not assume neurological integrity means stability: Neurologically intact burst fractures may still be unstable and require surgical intervention based on morphological criteria 4, 6
- Do not rely on plain films alone: CT is mandatory to assess posterior element fractures and canal compromise 4, 2