C1 Posterior Arch Screw Fixation
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C1 posterior arch screw has several advantages over conventional lateral mass screw. The author places the screw using his own freehand technique without fluoroscopic guidance. The screw entry point is determined by inserting an angled curette under the posterior arch and identifying the lateral wall of the spinal canal. The screw is medially directed between 5° and 15°. The sagittal angle of screw placement is determined using a lateral radiograph. The screw trajectory should aim between the caudal 20 and 40% of the C1 anterior arch to avoid violation of the CO–C1 and C1–C2 facet joints. This is termed “the safe zone of C1.” The screw is placed, while the vertebral artery is retracted cranially, and the C2 nerve root is retracted caudally to prevent injuries to them. Care should be taken to avoid internal carotid artery injuries, CO–C1 facet joint violation, and vertical splitting of the posterior arch during tapping or screw insertion.
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