What is the mechanism of spinal cord injury from cervical spinal stenosis?

Mechanism of Spinal Cord Injury from Cervical Spinal Stenosis

The primary mechanism of spinal cord injury in cervical spinal stenosis involves compression of the spinal cord between hypertrophic spondylotic disc-osteophyte complexes anteriorly and buckled ligamentum flavum posteriorly, particularly during hyperextension movements. 1

Pathophysiological Mechanisms

Anatomical Factors

• Canal Diameter Classification:

  • Absolute stenosis: canal diameter ≤10 mm
  • Relative stenosis: canal diameter <13 mm but >10 mm 1, 2
  • Torg-Pavlov ratio ≤0.8 indicates presence of stenosis 1

• Compression Elements:

  • Anterior: Disc-osteophyte complexes, osteophytic bars
  • Posterior: Hypertrophied ligamentum flavum, facet joints
  • Dynamic narrowing during neck movements, particularly hyperextension 1, 3

Injury Cascade

1. Initial Mechanical Compression:

   • Even minor trauma or hyperextension in a stenotic canal can cause significant cord compression 3, 2
   • In patients with pre-existing stenosis, minimal trauma can lead to significant increase in spinal cord compression 3

2. Secondary Injury Mechanisms:

   • Ischemic insult to the cord due to vascular compromise 1
   • Inflammatory response and edema formation
   • Hematomyelic cavity formation within central gray matter 1

3. Systemic Effects:

   • Cervical injuries can produce respiratory failure
   • Loss of cardiovascular sympathetic innervation leading to hypotension
   • Secondary immunodeficiency ("immune paralysis") due to loss of sympathetic innervation to lymphatic organs 1

Clinical Presentation

Central Cord Syndrome

• Most common presentation in older adults with cervical stenosis
• Characterized by:
  • Disproportionately greater motor impairment in upper than lower extremities
  • Bladder dysfunction (typically urinary retention)
  • Varying degrees of sensory loss below the injury level 1
• Often occurs in older individuals after falls or low-energy trauma 1, 3

Risk Factors

• Age >40 years (especially in Asian populations) 2
• Pre-existing cervical spinal canal stenosis
• Degenerative changes including OPLL (ossification of posterior longitudinal ligament) 2

Diagnostic Considerations

Imaging Assessment

• MRI: Gold standard for assessing soft tissue and neural element damage 4

  • Can detect T2 signal hyperintensity indicating edema, inflammation, or neurodegeneration 1
  • Best for visualizing cord compression by disc herniation, bone fragments, and hematomas 1

• CT: Superior for identifying bony stenosis and fractures

  • Sensitivity of 94-100% for bony abnormalities 4
  • Less sensitive for soft tissue injuries 1

Prognostic Indicators

• Residual spinal canal diameter strongly correlates with neurologic outcome:
  • Patients with canal diameter <10 mm have significantly higher risk of neurologic deterioration after minor trauma (88% vs 21% in those with canal ≥10 mm) 2
  • Surgical outcomes are also poorer in patients with absolute stenosis (<10 mm) 2

Clinical Implications

Vulnerability to Minor Trauma

• Even indirect minor trauma to the neck can cause irreversible changes in the spinal cord when marked stenosis is present 2
• Falls in elderly and sports-related injuries in younger patients are common mechanisms 5, 6

Treatment Considerations

• Early surgical decompression (<24 hours) results in superior neurological recovery 1
• Surgical intervention is recommended for patients with severe symptoms and evidence of cord effacement 4
• Laminectomy with fusion is preferred over laminectomy alone to prevent late deformity 4

Pitfalls and Caveats

• Spinal cord injury is generally associated with major trauma and may be overlooked in patients with minor trauma 3
• Symptoms can be diverse and variable, making diagnosis challenging 3
• Physical neurological examination, particularly testing peripheral reflexes, is crucial for rapid diagnosis 3
• Cervical spine CT should be assessed not only for acute traumatic injury but also for possible stenosis of the cervical spinal canal 3

In patients with coexisting cervical and lumbar stenosis, cervical decompression should be prioritized in cases of absolute stenosis to prevent further cord damage, while relative stenosis with predominant radiculopathy may warrant lumbar intervention first 7.