Introduction: C2 pedicle and pars screws require accurate placement to avoid injury to the nearby neurovascular structures. Freehand, fluoroscopically guided, and CT-based navigation techniques have been described in the literature. The purpose of this study is to compare the safety and accuracy of freehand versus navigated technique for c2 pedicle/pars screw placement.

Methods: Retrospective review of consecutive patients treated with posterior fixation constructs containing C2 pars or pedicle screws placed by spine surgeons from 2010 to 2016 at Barrow Neurological Institute. Basic demographic data, intraoperative and postoperative complications, screw diameter and length, method of screw placement (freehand vs. navigated), and incidence of stroke and all-cause mortality within 30 days of the operation were recorded. Accuracy of screw placement was assessed in those patients with intraoperative/postoperative CT imaging available. Screw accuracy was graded independently by two reviewers according to the following criteria: Grade A (no breach of the cortical surfaces), grade B-E (breach with transverse foramen obstruction of 1-25%, 26-50%, 51-75%, 76-100% respectively), Grade M (medial breach). Screws were then divided into acceptable placement (Grades A,B) and unacceptable placement (Grades C-E, M).

Results: A total of 426 c2 pedicle or pars screws (312 freehand, 114 navigated) were placed in 220 patients. Three vertebral artery injuries (2 freehand, 1 navigated; p=1), 5 deaths (4 freehand, 1 navigated; p=1), and 1 stroke in the navigated group (p=.6) occurred. CT imaging was available for accuracy grading of 182 screws (131 freehand, 51 navigated). No breaches (Grade A) occurred in 86% of the freehand screws and 67% of the navigated screws (p=.023). More screws had acceptable placement in the freehand group (94%) than the navigated group (82%) (p=.023).

Conclusions: Freehand is significantly more accurate than CT- based navigation for c2 pedicle/pars screw placement. There was no difference in complication rate between the two techniques.

Patient Care: Understanding the limitations of CT-based navigation in the cervical spine will lead to more accurate placement of C2 pedicle screws with freehand technique. Although this study did not identify a difference in complication rates between the two techniques, more accurate c2 pedicle screws could lead to fewer vertebral artery injuries on a larger scale.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the technique for freehand and navigated placement of c2 pedicle and pars screws. 2)Understand the limitations of CT-based navigation in the cervical spine 3) Understand the importance of direct visualization of the pedicle during c2 screw placement.

References: 1. Du JY, Aichmair A, Kueper J, Wright T, Lebl DR. Biomechanical analysis of screw constructs for antlantoaxial fixation in cadavers: a systematic review. J Neurosurg Spine 22:151-161, 2015 2. Paramore CG, Dickman CA, Sonntag VK. The anatomical suitability of the C1–2 complex for transarticular screw fixation. J Neurosurg 85: 221–224, 1996 3. Mueller CA, Roesseler L, Podlogar M, Kovacs A, Kristof RA. Accuracy and complications of transpedicular C2 screw placement without the use of spinal navigation. Eur Spine J. 19: 809-814, 2010 4. Ondra SL, Marzouk S, Ganju A, Morrison T, Koski T. Safety and efficacy of C2 pedicle screws placed with anatomic and lateral C-arm guidance. Spine (Phila Pa 1976) 31: E263-267, 2006 5. Mason A, Paulsen R, Babuska JM, Rajpal S, Burneikiene S, Nelson EL, Villavicencio AT. The accuracy of pedicle screw placement using intraoperative image guidance systems. J Neurosurg Spine 20: 196-203, 2014 6. Ishikawa Y, Kanemura T, Yoshida G, Matsumoto A, Ito Z, Tauchi R, et al: Intraoperative, full-rotation, three-dimensional image (O-arm)-based navigation system for cervical pedicle screw insertion. Clinical article, J Neurosurg Spine 15: 472–478, 2011 7. Ebraheim NA, Fow J, Xu R, et al. The location of the pedicle and pars interarticularis in the axis. Spine (Phila Pa 1976) 26: E34–37, 2001 8. Hoh DJ, Maya M, Jung A, et al. Anatomical relationship of the internal carotid artery to C-1: clinical implications for screw fixation of the atlas. J Neurosurg Spine 8: 335–340, 2008