Navigated percutaneous placement of cervical pedicle screws: An anatomical feasibility study.

Introduction: Percutaneous cervical pedicle screw placement is challenging due to complex anatomy, and requires navigation support. It is unclear how to ensure navigation accuracy in minimally invasive procedures. Research question: How accurate is image-guided percutaneous pedicle screw positioning after referencing with only one clamp for the complete subaxial cervical spine? Materials and methods: In six cadavers, all subaxial cervical pedicles were fitted with screws using a standardized procedure. Briefly, a reference clamp was placed via a small skin incision on spinous process C7. The procedure started from C3 and progressed towards C7, without additional imaging, using one registration for all vertebrae. Screws were placed using a navigated screwdriver. Cone-beam CT was performed at three time-points. Screw position was directly intraoperatively evaluated by the surgeons using a modified classification-from Grade 1 (perfect placement) to Grade 5 (highly inaccurate)-and these data were re-evaluated by two independent radiologists. Results: In six human specimens, 10 guidewires each were placed bilaterally in C3-C7. One screw (1.7%) was intraoperatively classified as Grade 3, but as Grade 4 in the second assessment. All other screws were classified as Grades 1-2 (89.8%) or 3 (8.5%). Screw placement accuracy was not significantly impacted by distance to the clamp or side selection. Discussion: In percutaneously navigated screw placement with intraoperative imaging, safe screw placement was possible with a reference clamp on C7. Clinical application of this technique has been limited to individual cases. We also propose a new classification for improving screw accuracy and clinical consequences.