====== C2 pedicle screw placement ======

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see also [[C1 pedicle screw placement]].

[[Cervical pedicle screw placement]].

Check CT scan or MRI to rule-out aberrant location of [[vertebral artery]] or unusual location of [[foramen transversarium]] before placing [[C2 pedicle screw]]s. Some find [[intraoperative image guidance
]] systems to be helpful.

{{::c2_pedicle_screw_placement.png?700|}}

===== Technique =====

1. ENTRY palpate the medial and superior aspect of the pars with a Penfield 4 dissector.
Enter at the estimated center of the surface projection of the C2 pars at the midpoint medio-laterally in the supero-medial quadrant of the surface of the C2 isthmus

2. TRAJ 20–30° medially (through the central axis of the C2 pedicle), 25° superiorly (on lateral
fluoroscopy, place the screw parallel to the pars). To assist with trajectory, expose the proximal upper and medial border of the C2 pars interarticularis, and use a Penfield 4 to palpate during drilling 

3. drill a shallow entry point, then drill with drill-stop set at 12 mm, monitoring progress at inter- vals under fluoro and palpating with probe, and if no breakout, then complete drilling by gradu- ally increasing drilling depth by 2 mm increments either up to 15-20 mm to stay in the pedicles, or up to ≈ 30 mm depth to perform osteosynthesis for a hangman’s fracture.  If withdrawal of the drill is followed by brisk bleeding, the screw should be inserted immediately to stop the bleeding. This bleeding may be from the vertebral artery; however, it is usually due to injury to the venous plexuses, and will not have any ill e   ects. In such cases it is best to not place the con- tralateral screw and to obtain an angiogram very soon post-op

4. SCREWS 3.5 mm dia. Screw length is not critical except when attempting to bridge a fracture gap (osteosynthesis) e.g. with a hangman’s fracture in which case screws of 20–30 mm length are placed to avoid penetrating anterior C2 cortex (lag screws are used for this, or the proximal bone can be overdrilled); for most purposes screw lengths of 15–20 mm length are used. Shorter screws (15-16 mm length) can still grip the pedicle with lower risk of injury.