Feasibility of C2 Pedicle Screw Fixation with the "in-out-in" Technique for Patients with Basilar Invagination

Panjie Xu; Junyu Lin; Hang Xiao; Jianying Zheng; Wei Ji

doi:10.1097/BRS.0000000000004757

Feasibility of C2 Pedicle Screw Fixation with the "in-out-in" Technique for Patients with Basilar Invagination

Spine (Phila Pa 1976). 2023 Jun 20. doi: 10.1097/BRS.0000000000004757. Online ahead of print.

Authors

Panjie Xu¹, Junyu Lin^{1

2}, Hang Xiao¹, Jianying Zheng¹, Wei Ji¹

Affiliations

¹ Division of Spine Surgery, Department of Orthopedics, Nanfang Hospital, Southern Medical University, Guangzhou, China.
² Department of Orthopaedics and Traumatology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, China.

PMID: 37339267
DOI: 10.1097/BRS.0000000000004757

Abstract

Study design: Retrospective study.

Objective: To evaluate the feasibility of C2 pedicle screw (C2PS) fixation with the "in-out-in" technique in patients with basilar invagination (BI).

Summary of background data: The "in-out-in" technique is a fixation technique in which the screw enters the vertebrae through the parapedicle. The technique has been used in upper cervical spine fixation. However, anatomic parameters associated with the application of this technique in patients with BI are unclear.

Methods: We measured the C2 pedicle width (PW), the distance between vertebral artery (VA) and the transverse foramen (VATF), the safe zone and the limit zone. The lateral safe zone is the distance from the medial/lateral cortex of the C2 pedicle to the VA (LPVA/MPVA), and the medial safe zone is the distance from the medial/lateral cortex of the C2 pedicle to the dura (MPD/LPD). The lateral limit zone is the sum of LPVA/MPVA and VATF (LPTF/MPTF), and the medial limit zone is the distance from the medial/lateral cortex of the C2 pedicle to the spinal cord (MPSC/LPSC). PW, LPVA, MPVA and VATF were measured on the reconstructed CT angiography. PW, MPD, LPD, MPSC and LPSC were measured on MRI. We define a width greater than 4 mm as safe for screw. The t-test was used to compare the parameters between male and female, left and right sides in all patients, and PW in CTA and MRI data in the same patient. For intrarater reliabilities, interclass correlation coefficients were calculated.

Results: A total of 154 patients (49 CTA, 143 MRI) were included. The average PW, LPVA, MPVA, LPTF, MPTF, MPD, LPD, MPSC and LPSC were 5.30 mm, 1.28 mm, 6.60 mm, 2.45 mm, 8.94 mm, 2.09 mm, 7.07 mm, 5.51 mm and 10.48 mm, respectively. Furthermore, in patients with PW ˂4 mm, 53.6% of MPVA, 86.2% of LPTF, and all limit zones were larger than 4 mm.

Conclusions: In patients with basilar invagination, there is sufficient space medially and laterally to the C2 pedicle for partial screw encroachment to achieve "in-out-in" fixation, even if the pedicle is small.

Level of evidence: 4.