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  • Epidemiology
    • 95% involve L4/5 or L5/S1 levels
      • L5/S1 most common level
    • peak incidence is 4th and 5th decades
    • only ~5% become symptomatic
    • 3:1 male:female ratio
  • Pathoanatomy
    • recurrent torsional strain leads to tears of outer annulus   which leads to herniation of nucleus pulposis
  • Prognosis
    • 90% of patients will have improvement of symptoms within 3 months with nonoperative care.
    • size of herniation decreases over time (reabsorbed) 
      • sequestered disc herniations show the greatest degree of spontaneous reabsorption
      • macrophage phagocytosis is mechanism of reabsorption
  • Complete intervertebral disc anatomy and biomechanics
  • Disc composition
    • annulus fibrosis
      • composed of type I collagenwater, and proteoglycans  
      • characterized by extensibility and tensile strength
        • high collagen / low proteoglycan ratio (low % dry weight of proteoglycans) 
    • nucleus pulposus
      • composed of type II collagenwater, and proteoglycans
      • characterized by compressibility
        • low collagen / high proteoglycan ratio (high % dry weight of proteoglycans) 
          • proteoglycans interact with water and resist compression
        •  a hydrated gel due to high polysacharide content and high water content (88%)
  • Nerve root anatomy
    • key difference between cervical and lumbar spine is 
      • pedicle/nerve root mismatch
        • cervical spine C6 nerve root travels under C5 pedicle (mismatch)
        • lumbar spine L5 nerve root travels under L5 pedicle (match)
        • extra C8 nerve root (no C8 pedicle) allows transition
      • horizontal (cervical) vs. vertical (lumbar) anatomy of nerve root
        • because of vertical anatomy of lumbar nerve root a paracentral and foraminal disc will affect different nerve roots
        • because of horizontal anatomy of cervical nerve root a central and foraminal disc will affect the same nerve root
  • Location Classification
    • central prolapse
      • often associated with back pain only
      • may present with cauda equina syndrome which is a surgical emergency
    • posterolateral (paracentral)  
      • most common (90-95%)
      • PLL is weakest here
      • affects the traversing/descending/lower nerve root    
        • at L4/5 affects L5 nerve root
    • foraminal (far lateral, extraforaminal)   post
      • less common (5-10%)
      • affects exiting/upper nerve root    
        • at L4/5 affects L4 nerve root
    • axillary
      • can affect both exiting and descending nerve roots
  • Anatomic classification
    • protrusion
      • eccentric bulging with an intact annulus
    • extrusion
      • disc material herniates through annulus but remains continuous with disc space
    • sequestered fragment (free)
      • disc material herniates through annulus and is no longer continuous with disc space
  • Symptoms 
    • can present with symptoms of
      • axial back pain (low back pain)
        • this may be discogenic or mechanical in nature
      • radicular pain (buttock and leg pain)
        • often worse with sitting, improves with standing
        • symptoms worsened by coughing, valsalva, sneezing
      • cauda equina syndrome (present in 1-10%)
        • bilateral leg pain
        • LE weakness
        • saddle anesthesia
        • bowel/bladder symptoms
  • Physical exam  
    • see lower extremity neuro exam
    • motor exam
      • ankle dorsiflexion (L4 or L5)
        • test by having patient walk on heels
      • EHL weakness (L5) 
        • manual testing
      • hip abduction weakness (L5)
        • have patient lie on side on exam table and abduct leg against resistance
      • ankle plantar flexion (S1)
        • have patient do 10 single leg toes stands
    • provocative tests
      • straight leg raise
        • a tension sign for L5 and S1 nerve root
        • technique
          • can be done sitting or supine
          • reproduces pain and paresthesia in leg at 30-70 degrees hip flexion
        • sensitivity/specificity
          • most important and predictive physical finding for identifying who is a good candidate for surgery
      • contralateral SLR
        • crossed straight leg raise is less sensitive but more specific
      • Lesegue sign
        • SLR aggravated by forced ankle dorsiflexion
      • Bowstring sign
        • SLR aggravated by compression on popliteal fossa
      • Kernig test
        • pain reproduced with neck flexion, hip flexion, and leg extension
      • Naffziger test
        • pain reproduced by coughing, which is instigated by lying patient supine and applying pressure on the neck veins
      • Milgram test
        • pain reproduced with straight leg elevation for 30 seconds in the supine position
    • gait analysis
      • Trendelenburg gait
        • due to gluteus medius weakness which is innervated by L5
  • Radiographs
    • may show
      • loss of lordosis (spasm)
      • loss of disc height
      • lumbar spondylosis (degenerative changes)
  • MRI without gadolinium
    • modality of choice for diagnosis of lumbar and cervical disc herniations
      • highly sensitive and specific
      • helpful for preoperative planning
      • useful to differentiate from synovial facet cysts
    • however high rate of abnormal findings on MRI in normal people
    • indications for obtaining an MRI
      • pain lasting > one month and not responding to nonoperative management or
      • red flags are present
        • infection (IV drug user, h/o of fever and chills)
        • tumor (h/o or cancer)
        • trauma (h/o car accident or fall)
        • cauda equina syndrome (bowel/bladder changes)
  • MRI with gadolinium
    • useful for revision surgery
    • allows to distinguish between post-surgical fibrosus (enhances with gadolinium) vs. recurrent herniated disc (does not enhance with gadolinium)
  • Nonoperative
    • rest and physical therapy, and antiinflammatory medications  
      • indications
        • first line of treatment for most patients with disc herniation
          • 90% improve without surgery
      • technique
        • bedrest followed by progressive activity as tolerated
        • medications
          • NSAIDS
          • muscle relaxants (more effective than placebo but have side effects)
          • oral steroid taper
        • physical therapy
          • extension exercises extremely beneficial
          • traction
          • chiropractic manipulation
    • selective nerve root corticosteroid injections 
      • indications
        • second line of treatment if therapy and medications fail
      • technique
        • epidural
        • selective nerve block
      • outcomes
        • leads to long lasting improvement in ~ 50% (compared to ~90% with surgery)
        • results best in patients with extruded discs as opposed to contained discs
  • Operative
    • laminotomy and discectomy (microdiscectomy) post 
      • indications   
        • persistent disabling pain lasting more than 6 weeks that have failed nonoperative options (and epidural injections) 
        • progressive and significant weakness
        • cauda equina syndrome
      • technique
        • can be done with small incision or through "tube" access
      • rehabilitation
        • patients may return to medium to high-intensity activity at 4 to 6 weeks 
      • outcomes
        • outcomes with surgery compared to nonoperative
          • improvement in pain and function greater with surgery  
        • positive predictors for good outcome with surgery
          • leg pain is chief complaint 
          • positive straight leg raise
          • weakness that correlates with nerve root impingement seen on MRI
          • married status
        • negative predictors for good outcome with surgery
          • worker's compensation  
            • WC patients have less relief from symptoms and less improvement in quality of life with surgical treatment
    • far lateral microdiskectomy post
      • indications
        • for far-lateral disc herniations
      • technique
        • utilizes a paraspinal approach of Wiltse 
Complications of Surgery
  • Dural tear (1%)
    • if have tear at time of surgery then perform water-tight repair
  • Recurrent HNP
    • can treat nonoperatively initially
    • outcomes for revision discectomy have been shown to be as good as for primary discectomy
  • Discitis (1%)
  • Vascular catastrophe
    • caused by breaking through anterior annulus and injuring vena cava/aorta

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