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.