Management of Lumbar Spine Subluxation with Flexion and Extension
For lumbar subluxation demonstrating instability on flexion-extension radiographs, surgical fusion is indicated when accompanied by deformity or radiographic instability, while isolated subluxation without these features should be managed with decompression alone if symptomatic.
Diagnostic Assessment
The critical first step is determining whether true instability exists. Flexion-extension radiography showing lack of motion between segments is highly suggestive of solid fusion or stability, while excessive motion indicates instability 1. However, pain can significantly limit flexion during conventional radiography, potentially underestimating the degree of instability 2. Consider using hands-on-knees positioning during flexion radiography to achieve deeper flexion and more accurate assessment of segmental motion 2.
Key Radiographic Criteria:
- Flexion of ≥20 degrees or lateral bend of ≥10 degrees without vertebral fracture indicates complete posterior ligament disruption and partial annular disruption 3
- Modern CT with fine-cut axial and multiplanar reconstruction is the most effective noninvasive method for assessing spinal stability 1
- Multiple imaging modalities should be used when evaluating suspected instability, as no single radiographic technique perfectly correlates with surgical exploration 1
Treatment Algorithm
For Subluxation WITH Deformity or Instability:
Surgical fusion is recommended 4. The presence of radiographic instability on flexion-extension views or associated deformity fundamentally changes the treatment paradigm from decompression alone to fusion.
For Subluxation WITHOUT Deformity or Instability:
Decompression alone is recommended (Grade B) 4. In the absence of deformity or instability, lumbar fusion has not been shown to improve outcomes and therefore is not recommended 4.
Important Clinical Considerations
Pattern Recognition:
Different subluxation patterns produce different stenosis patterns 5:
- Open subluxations (toward convex apex, typically L3-4): Produce contralateral lateral recess and foraminal stenosis (71% of cases)
- Closed subluxations (on concavity, typically L1-2): Produce ipsilateral stenosis (82% of cases)
Surgical Technique Selection:
If fusion is indicated based on instability:
- Compression instrumentation for most flexion-distraction injuries 6
- Distraction instrumentation when associated with burst fractures 6
- External fixation (body cast) should supplement internal fixation to prevent flexion and rotation, as internal fixation alone can fail 3
Critical Pitfalls to Avoid
Do not rely on static plain radiography alone - it is accurate in only approximately two-thirds of patients and is not recommended as a stand-alone modality 1
Metallic instrumentation interferes with radiographic fusion assessment - CT imaging is superior in the presence of spinal hardware 1
Pain limits flexion during conventional radiography - this may cause you to underestimate instability; use hands-on-knees positioning for more reproducible results 2
Do not perform fusion for isolated stenosis without instability - this is a Grade B recommendation against fusion in this scenario 4
Wire loops through spinous processes can fail with extreme flexion - if using internal fixation, always supplement with external immobilization 3