10.1 Background

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  Disk disease is often described as a result of two pathologies:

  
  
  
  
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    Disk herniation characterized by herniated nucleus pulposus (HNP).

    
    
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    Degenerative disk disease (DDD).

  
  
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  These conditions are common and commonly asymptomatic:

  
  
  
  
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    10% of asymptomatic individuals younger than 40 years have HNP on magnetic resonance imaging (MRI).

    
    
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    25% of asymptomatic individuals younger than 40 years have DDD on MRI.

  
  
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  The progression of a pathologic intervertebral disk may result in compression of adjacent neural structures including the spinal cord and neural roots.

10.2 Etiology and Pathophysiology

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  HNP:

  
  
  
  
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    Secondary to stress on annulus of disk:

    
    
    
    
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      Most often posterolateral as the supportive posterior longitudinal ligament (PLL) is weakest here.

    
    
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    Increased risk for herniation from aging and disk degeneration:

    
    
    
    
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      Decreased water content and proteoglycan content of nucleus pulposus.

    
    
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    Characteristics of herniation:

    
    
    
    
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      Protrusion:

      
      
      
      
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        Base (neck) wider than head of herniation.

        
        
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        Herniation of nuclear pulposus penetrates through annular fibers but remains within the annular margin.

      
      
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      Extrusion:

      
      
      
      
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        Base narrower than head of herniation.

        
        
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        Herniation tears through annular margin.

        
        
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        Can displace (migrate) cranially or caudally.

      
      
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      Sequestration:

      
      
      
      
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        Free disk fragment separated from original herniation.

  
  
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  DDD (spondylosis):

  
  
  
  
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    Aging of disk results in biochemical component changes ( Fig. 10.1 ):

    
    
    
    
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      Decreased cross-linking of collagen, decreased water content.

      
      
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      Decreased blood supply to outer annulus:

      
      
      
      
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        Lactate increases with resultant acidic changes, further degenerating disk.

    
    
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    Decreased strength from degenerative changes leads to chronic tears throughout annulus.

    
    
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    Degenerative cycle includes the following:

    
    
    
    
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      Disk degeneration (disk bulging, decreased disk space).

      
      
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      Joint degeneration (facet arthrosis and uncinate spurring).

      
      
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      Ligamentous alterations (ligamentum flavum thickening due to loss of disk height).

      
      
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      Spinal deformity (kyphosis, following the loss of disk height and transfer of load to the uncovertebral and facet joints).

10.3 Symptoms and Clinical findings

(Table 10.1)

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  Both DDD and HNP result in tearing of disks with eventual impingement of nearby neural elements including spinal cord.

  
  
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  Axial neck pain:

  
  
  
  
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    Unclear etiology.

    
    
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    Peripheral disk contains nociceptors and PLL:

    
    
    
    
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      Annular tears and herniation potentially activates these receptors.

  
  
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  Radiculopathy:

  
  
  
  
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    Radiating pain in a pattern consistent with the nerve root involved:

    
    
    
    
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      With or without neurologic symptoms (lower motor neuron symptoms).

    
    
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    Occurs from direct impingement of nerve roots exiting the spinal cord and vertebral column ( Fig. 10.2 ):

    
    
    
    
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      Lateral HNP or osteophytes can compress exiting nerve root near neural foramen:

      
      
      
      
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        Known as neuroforaminal stenosis.

      
      
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      Cervical nerve root travels above the similar-named pedicle (i.e., the C5 nerve root travels above the C5 pedicle).

      
      
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      DDD osteophytes or narrowing of neural foramen, compressing nerve root.

    
    
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    Inflammation from tears results in chemical radiculitis, furthering radicular symptoms.

  
  
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  Myelopathy:

  
  
  
  
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    Upper motor neuron symptoms:

    
    
    
    
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      Patients may present with classic findings:

      
      
      
      
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        Gait instability.

        
        
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        Weakness and clumsiness in manual dexterity.

        
        
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        Axial neck pain and stiffness.

        
        
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        Diffuse numbness/tingling not isolated to single dermatome.

    
    
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    Occurs from central compression of spinal cord:

    
    
    
    
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      Herniation or osteophytic spurs causing narrowing of cervical spinal cord canal ( Fig. 10.2 ):

      
      
      
      
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        Known as central stenosis.

        
        
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        Torg–Pavlov ratio: ratio of width of cervical canal to cervical body diameter:

        
        
        
        
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          <0.8 = central stenosis.

          
          
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          Normal is 1.0.

    
    
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    Microtrauma from neck flexion/extension along with vascular injury furthers injury to spinal cord.