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Indications
  • Excision of herniated discs
  •  Exploration of nerve roots
  •  Spinal fusion
  •  Removal of tumors
Internervous Plane
  • Between two paraspinal muscles (erector spinae)
    • each innervated by segmental nerves coming from posterior primary rami of lumbar nerves
    • damaging posterior primary rami does not denervate paraspinal muscles due to segmental innervation
Preparation
  • Anesthesia
    • general to protect airway in prone position
  • Position
    • prone
    • lateral flexion position
Approach
  • Incision
    • landmarks
      • can palpate spinous process (midline)
      • highest point on iliac crest marks L4-5 interspace
    • make midline incision
  • Superficial dissection
    • incise fat and lumbodorsal fascia to spinous process
      • preserve interspinous ligament
    • detach paraspinal muscles (erector spinae) subperiostally
    • dissect down spinous process and lamina to facet joint
    • move medial to lateral taking down or sparing the facet capsule
    • continue anterior to transverse process if necessary
  • Deep dissection
    • remove ligamentum flavum by cutting attachment to edge of lamina
      • ligamentum flavum attaches to the lamina halfway up the undersurface
    • idenitfy epidural fat and dura
    • using blunt dissection stay lateral to dura and continue to floor of spinal canal
  • Closure
    • fascia is closed with watertight closure
    • closed wound suction drain placed deep to the lumbodorsal fascia if drain is required
Dangers
  • Segmental vessels
    • between facet and transverse process
    • supply paraspinal muscles
    • vigorously cauterize as they are encountered
  • Nerve roots
    • each nerve root must be identified and protected
  • Venous plexus
    • surrounds nerve roots
    • may bleed during blunt dissection
    • stop with Gelfoam or bipolar cautery
  • Iliac vessels
    • can be damaged during discectomy if you pass instruments too far anterior through the annulus
  • Dura
    • dura exposed after entering ligamentum flavum
    • thin spatula tool can be used to gently retract dura away from area of focus
    • epidural veins may bleed and make visualization difficult so hemostasis is of utmost importance
 

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