C1-2 Fusion

Operation: C1-2 dorsal internal fixation and fusion- Harms-Goel Technique

  • Introduction- C1 lateral mass screws and C2 pedicle screws is a technique originally described by Goel (1994) and later popularized by Harms and Melcher (2001).
  • Positioning
    • Mayfield pins- you want the pins below the equator and anteriorly placed so that the patient is (a) resting in pins and (b) you have room to attach the Mayfield to the bed
  • Prep and Landmarks
    • Identify: The inion and C2
    • Shave and prep to just above the inion
  • Incision and approach
    • Incision: The incision is placed in the midline from just below the inion to the top of C3 spinous process. You do not want to extend dissection to where you can see the skull base but you want to have enough room to dissect out C1, 2, and the top of 3
  • Operative details
    • Take great care to stay in the MIDLINE. Use the very tip of the bovie to meticulously follow your way down the dorsal raphe until you dissect out the very large, bifid C2 spinous process.
    • Use cerebellar (Anderson) retractors and when able use miskimons insert these with the handle facing superiorly so that it is out of your way
    • Bleeding- Bleeding is a major issue in this operation as the epidural venous plexus between in C1 and 2 can be quite robust.
      • The use of gelfoam and alternating between sides can assist in making the dissection as painless as possible
    • C1 dissection- The dissection of C1 can be carried out with a bovie and a penfield 1. The posterior ring of 1 needs to be identified completely and this dissection needs to extend laterally enough to identify the lateral mass. The lateral mass of one is located inferior and anterior to the posterior ring (ie you can’t see it once the entire dorsal part of C1 exposed because it is underneath the visible part of 1 and is hidden by the C2 nerve root).
      • Division of the C2 nerve root is describe in the literature but is rarely needed as you can retract the nerve inferiorly to located the lateral mass of C1
    • C2 dissection- The entire spinous process, lamina, pars, and pedicle of C2 needs to be exposed. The dissection does not need to destabilize the C2-3 facet complex.
      • The C2 pars/pedicle is a nice landmark that is easily identified on the superior surface of C2 and delineates the dura and spinal cord medially and helps you find the lateral mass of C1 (which will be superiolateral)
    • C3 dissection- often times the superior part of C3 lamina and spinous process needs to be identified to aid in placement of the C2 pedicle screws.
    • C1 lateral mass screws
      • Use the drill with guide set to 14mm to make the pilot holes in the lateral mass
      • Use an appropriate length screw to traverse the lateral mass and provide enough length to attach to the C2 screws with a rod below
      • This means that if you need a have measure the lateral mass to be 20mm you will need a 20mm threaded portion on a 30mm screw. This extra 10mm UNTHREAEDED portion will allow the head of the screw to protrude from the under surface of the C1 ring without irritating the C2 nerve root.
    • C2 pedicle screws- they actually traverse the pedicle into the vertebral body of C2
      • The screw is centered in the middle of the C2 isthmus and the angle of the screw is directed in a 20 degree convergent, superior direction to the appropriate depth as judged by preoperative imaging.
      • Average C2 pedicle screw- 3.5 or 4.0 x 20mm screw
    • C2- pars screws- The pars screws has a more inferior starting point and is angled superiorly up toward and into the pars. These screws are typically shorter (16mm) and have less purchase than a C2 pedicle screw
    • Link the C1-2 screws with Rods on both sides.
    • Iliac crest- the posterior iliac crest is dissected with great care taking to avoid the cluneal nerves which are located more anterior-lateral.
      • A wedge of bone is harvest with an osteotome
    • Wiring and fusion
      • The wiring of the allograft iliac crest requires some artistry in that you need to shape the graft to fit over the spinous process of C2 and you also need to carve troughs in the lateral aspect of the graft to accommodate the wires.
      • Wiring- Take an O-Vicryl and with the dull end of the needle pass it under the arch of C1. Remove the needle and tie the vicryl to the middle of the wire. Pull the half way point of the wire under the ring of C1 in the superior direction. This loop will hook over the inferior part of the C2 spinous process. The free ends will attach underneath the C2 spinous process as well.
      • Assure that you have decorticated C1-2 and that your graft fits before securing the graft with wires.
  • Postop Orders
    • Davol drains to full compression
    • Lortab
    • Morphine/Dilaudid PCA
    • Robaxin
    • Foley and drains out in the AM

 

 

Joseph MillerC1-2 Fusion

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