Transforaminal "in-out-in" screw technique for posterior C2 fixation in cases with a narrow C2 pedicle: anatomical considerations, technical notes, and preliminary clinical results.

Numerous techniques for C2 screw fixation have been recently reported. However, concerns remain regarding the risk of spinal cord or vertebral artery injury and inadequate biomechanical stability. To our knowledge, the specific transforaminal "in-out-in" screw fixation technique has not been previously reported. This study aimed to investigate the feasibility and preliminary clinical outcomes of a transforaminal "in-out-in" multi-cortical purchase screw for posterior C2 screw fixation. Between October 2022 and March 2023, 10 patients underwent posterior atlantoaxial internal fixation. All patients had severe hypoplasia of the C2 pedicle on at least one side, precluding the use of standard C2 pedicle screws. A transforaminal "in-out-in" screw was used as an alternative. No spinal cord injury, vascular injury, or other major complications were observed. No implant failure was noted at the final follow-up. In conclusion, the transforaminal "in-out-in" screw may achieve rigid three-column fixation with multiple cortical purchases. It represents a safe and effective alternative for posterior C2 fixation in patients with severely narrow C2 pedicles where traditional pedicle screw placement is not feasible.