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