Surgical Risk in Bicortical C1 Lateral Mass Screw Fixation Without Medial Angulation
Teera Tangviriyapaiboon, MD¹
, Sitthisak Phupungtamakoon, MD¹
, Ekkapot Jitpun, MD¹
, Varisa Wongbhanuwich, MD¹
Affiliation : ¹ Department of Neurosurgery, Neurological Institute of Thailand, Bangkok, Thailand
Abstract
Background: Bicortical C1 fixation is one of the techniques for C1 lateral mass (LM) screw fixation to address instability in the cervical spine. Although it offers greater pull-out force and reduces the risk of screw pull-out, improper placement may inadvertently compromise the retropharyngeal segment of the internal carotid artery (ICA).
Objective: To determine the parameter values for the C1 vertebra LM and the ICA location and assess their potential association with the risk of ICA injury from bicortical C1 LM screw fixation.
Materials and Methods: Patients aged ≥15 years old who had undergone computed tomography angiography of the neck at the Neurological Institute of Thailand between 2016 and 2020. The association with the risk of ICA injury was examined using logistic regression analysis.
Results: Of 256 participants, 205 individuals with completed data were included in the analysis, with a mean of 62.0 years. Several parameters were significantly different between the left and the right sides. Only 13 (6.3%) and 26 (12.7%) participants had ICA located inside the non-angulated screws line on the left or the right side, respectively. Only female was found to be associated with the risk of ICA injury in univariable analysis and remained significant in multivariable analysis (aOR 2.20, 95% CI 1.07 to 4.51 for the left side and aOR 2.21, 95% CI 1.07 to 4.57 for the right side). The angle of the screw trajectory and age were not associated with the ICA injury.
Conclusion: Since the angle of screw trajectory to the ICA was not associated with ICA injury risk, and 6.3% and 12.7% of participants were at risk of ICA injury from non-angulated screw placement on the left and right sides, bicortical C1 LM screw placement without medial angulation seemed safe for screw fixation. However, surgeons should individualize screw length based on patient-specific CTA imaging to minimize the ICA injury risk.
Received 10 February 2026 | Revised 1 March 2026 | Accepted 6 March 2026
J Med Assoc Thai 2026;109(6):525-37
Keywords : Bicortical C1 screw insertion; Lateral mass; Computed tomography angiography; Retropharyngeal internal carotid artery
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