Determining Lumbar Compression Fracture Stability
Physicians determine lumbar compression fracture stability primarily using CT imaging combined with validated classification systems—specifically the AO Spine Thoracolumbar Injury Classification System or TLICS—which assess fracture morphology, posterior ligamentous complex integrity, and neurological status. 1
Primary Assessment Framework
Imaging Requirements
CT scanning is the essential imaging modality for stability assessment. Plain radiographs alone are inadequate—they have a negative predictive value of only 0.62 for detecting potentially unstable fractures 2. CT provides the anatomic detail necessary to evaluate:
- Middle column involvement (retropulsion into spinal canal)
- Posterior element disruption
- Degree of vertebral body comminution
- Multi-level involvement
MRI should be added when:
- Posterior ligamentous complex injury is suspected
- Neurological deficits are present
- Soft tissue injury assessment is needed 3, 4
Classification Systems for Stability Determination
The AO Spine Thoracolumbar Injury Classification System provides the most reliable framework with excellent inter- and intraobserver reliability 1:
Type A (Compression injuries):
- Anterior element injury only
- Posterior ligamentous complex preserved
- Generally stable
Type B (Distraction injuries):
- B1: Posterior tension band failure through bone
- B2: Posterior tension band failure (bony/ligamentous) with anterior vertebral body fracture
- B3: Hyperextension injuries
- Potentially unstable
Type C (Displacement/dislocation):
- Disruption of all elements with displacement
- Unstable
Critical Radiographic Criteria for Instability
A fracture is potentially unstable when any of the following are present 2, 5:
- Two-column involvement (particularly middle + posterior columns per Denis three-column concept) 1, 6
- Middle column involvement with retropulsion
- >50% loss of anterior vertebral body height
- Multiple-level involvement
- Posterior ligamentous complex disruption on MRI
Neurological Component
The neurological examination is a critical determinant of stability and treatment 1:
- N0 = Neurologically intact
- N1 = Transient symptoms
- N2 = Radiculopathy
- N3 = Incomplete cord or cauda equina injury
- N4 = Complete injury
Any neurological deficit elevates concern for instability and typically mandates surgical consultation.
Clinical Decision Algorithm
- Obtain CT scan of the thoracolumbar spine (plain films insufficient)
- Apply AO Classification to determine injury type (A, B, or C)
- Assess for instability markers:
- Two or more column involvement
50% vertebral height loss
- Posterior element fractures
- Multi-level fractures
- Perform detailed neurological examination
- Add MRI if:
- Type B or C injury suspected
- Any neurological deficit present
- Posterior ligamentous complex integrity uncertain
- Calculate TLICS score if using that system (≥5 points suggests surgical management)
Common Pitfalls
Do not rely on plain radiographs alone—they miss critical middle column and posterior element injuries that determine stability 2. The sensitivity is only 0.83 and specificity 0.80 for detecting unstable fractures.
Beware of osteoporotic fractures in elderly patients—these may appear benign on initial imaging but can progress with ambulation 5. Consider repeat CT after mobilization in patients >65 years with compression fractures managed conservatively.
Do not confuse acute versus chronic fractures on plain films—radiographs have only 0.52 sensitivity for determining acuity 7. Subendplate clefts and subendplate density on radiographs increase likelihood of acute fracture, but MRI remains the gold standard for acuity determination.
Special Considerations
For pathologic fractures (malignancy-related), use the Spinal Instability Neoplastic Score (SINS) 8:
- 0-6 points: Stable
- 7-12 points: Potentially unstable
- 13-18 points: Unstable
This system incorporates location, pain, bone quality, alignment, vertebral body collapse degree, and posterolateral involvement.