Axial back pain extremely common:

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  Most common cause is muscle strain, followed by degenerative disease of spine.

Natural aging and genetic predisposition lead to lumbar disk degeneration:

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  Decreased water content and blood supply to annulus of disk:

  
  
  
  
  • 
    

    Results in acidic changes and degeneration of intervertebral disk.

    
    
  • 
    

    After birth, the nucleus pulposus decreases in size and cellularity in proportion to the intervertebral disk.

Lumbar disk degeneration can result in a mixture of pathologies:

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  Disk herniation characterized by herniated nucleus pulposus (HNP).

  
  
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  Spondylosis characterized by degeneration of intervertebral disk and osteophyte formation.

  
  
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  Spondylolisthesis characterized by slippage of vertebral body.

Mean age of onset is 35 years:

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  Over 50% of individuals over 60 years of age exhibit degenerative changes on imaging.

Background and etiology

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  90% of herniated disks occur at L4/L5:

  
  
  
  
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    Increased risk for herniation from aging and disk degeneration.

  
  
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  Chronic or significant acute stress on annulus of intervertebral disk:

  
  
  
  
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    Leads to annular tears and HNP.

    
    
  • 
    

    Results in direct compression of neural elements.

Characteristics of herniation (see Chapter 11: Cervical Disk Disease).

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  Protrusion:

  
  
  
  
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    Herniation remains within annular margin.

  
  
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  Extrusion:

  
  
  
  
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    Herniation tears through annular margin but contained by posterior longitudinal ligament:

    
    
    
    
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      Extends into spinal canal.

      
      
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      Can displace cranially or caudally.

  
  
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  Sequestration:

  
  
  
  
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    Separation of herniated disk fragment from intervertebral disk.

Symptoms and clinical findings:

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  Axial back pain:

  
  
  
  
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    Controversial etiology.

    
    
  • 
    

    Nociceptors along annulus and posterior longitudinal ligament thought to contribute to axial pain with annular tears.

    
    
  • 
    

    Recurrent torsional strain may also lead to outer annulus tears.

    
    
  • 
    

    Worse pain with lumbar flexion in the absence of lumbar spinal stenosis.

  
  
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  Radiculopathy:

  
  
  
  
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    Radiating pain in distribution of affected nerve root dermatome:

    
    
    
    
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      Can be associated with sensory or motor deficits of compressed nerve root.

      
      
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      Decreased reflexes of involved nerve root.

    
    
  • 
    

    Herniation impinging of exiting nerve roots:

    
    
    
    
    • 
      

      In neuroforamen (neuroforaminal stenosis):

      
      
      
      
      • 
        

        Far-lateral herniation.

        
        
      • 
        

        Affects exiting nerve root.

        
        
      • 
        

        Nerve roots exit below pedicle (L4 exits at L4–L5 disk).

    
    
  • 
    

    Herniation of traversing nerve roots ( Fig 11.1 ):

    
    
    
    
    • 
      

      In spinal canal (spinal stenosis):

      
      
    • 
      

      Paracentral/posterolateral herniation.

      
      
    • 
      

      Affects nerve root traversing to exit at next disk level (L4–L5 paracentral herniation affects L5):

      
      
      
      
      • 
        

        Improvement of leg pain with bending forward due to increased space within spinal canal:

        
        
        
        
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          Known as neurogenic claudication due to the intermittent symptomology.

          
          
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          Distinguish from vascular claudication: pain is not relieved by standing still.

  
  
• 
  

  Cauda equina and conus syndromes ( Table 11.1 ):

  
  
  
  
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    Orthopaedic emergencies.

    
    
  • 
    

    Herniation compressing multiple lumbar and sacral nerve roots within the thecal sac or the conus medullaris (T12–L1):

    
    
    
    
    • 
      

      Large central herniation.

Imaging:

• 
  

  X-ray:

  
  
  
  
  • 
    

    Initial evaluation for bony deformities.

    
    
  • 
    

    Often first line for evaluating general degenerative lumbar pathology:

    
    
    
    
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      Assess for disk space narrowing.

      
      
    • 
      

      Unable to determine disk pathology from plain radiographs.

    
    
  • 
    

    AP and lateral for examining alignment.

    
    
  • 
    

    Flexion/extension for examining instability.

  
  
• 
  

  MRI:

  
  
  
  
  • 
    

    Modality of choice for assessing nerve root or spinal cord compression along with disk and ligamentous pathology:

    
    
    
    
    • 
      

      Loss of T2 signal within disk nucleus ( Fig. 11.2 ).

    
    
  • 
    

    Modic’s changes:

    
    
    
    
    • 
      

      Describes vertebral degeneration seen on MRI:

      
      
      
      
      • 
        

        Associated changes on T1- and T2-weighted MRIs with progressive degeneration ( Table 11.2 ).

  
  
• 
  

  Computed tomography (CT) scan:

  
  
  
  
  • 
    

    Limited use:

    
    
    
    
    • 
      

      If MRI contraindicated.

Treatment:

• 
  

  Conservative therapy:

  
  
  
  
  • 
    

    Majority of patients will improve with nonoperative management.

    
    
  • 
    

    Decreasing mechanical stress, maintaining ideal body weight, and smoking cessation all associated with improved outcomes.

    
    
  • 
    

    Nonoperative treatment includes rest, physical therapy (PT), anti-inflammatory medication (NSAIDs), muscle relaxants, and oral steroids. 90% of patients improve nonoperatively:

    
    
    
    
    • 
      

      Corticosteroid injections are a second line therapy.

  
  
• 
  

  Operative management:

  
  
  
  
  • 
    

    Indications:

    
    
    
    
    • 
      

      Failure of conservative therapy for at least 12 weeks.

      
      
    • 
      

      Worsening or new onset of neurological deficits.

      
      
    • 
      

      Removal of herniation (microdiskectomy), disk replacement (arthroplasty), or lumbar fusion.