Accuracy of Pedicle Screw Placement at the Cervicothoracic Junction (C7–T2) : A Comparative Study of O-arm Navigation versus C-arm Fluoroscopy

Objective: To compare pedicle screw accuracy at the cervicothoracic junction (CTJ; C7-T2) between O-arm navigation and C-arm fluoroscopy and identify level-specific malposition mechanisms through quantitative trajectory analysis. Methods: We retrospectively reviewed 187 screws in 50 patients (C-arm: 82 screws; O-arm: 105 screws) who underwent CTJ fixation between 2018 and 2024. Accuracy was graded using the modified Gertzbein-Robbins classification. Axial trajectory parameters, including insertion angle (IA) and entry point (EP) deviation, were measured relative to the mid-pedicle reference line. Results: The overall Grade A accuracy did not differ significantly between the C-arm (84.1%) and O-arm (78.1%) groups (p=0.555). While accuracy was comparable at C7 and T1, the Grade A accuracy at T2 was significantly lower in the O-arm group (50.0% vs. 83.3%; p=0.025). The O-arm+T2 combination was associated with a markedly higher malposition risk (OR=7.62; p=0.004). In the C-arm group, failure mechanisms were diverse. Conversely, the predominant failure pattern in the O-arm group at T2 was lateral EP shift combined with insufficient convergence, with sagittal plane mismatch in a subset of cases. Conclusion: O-arm navigation confers no overall accuracy advantage at the CTJ and carries a nearly eightfold malposition risk at T2. Careful preoperative anatomical assessment and intraoperative attention to convergence angle are essential at this level, regardless of the imaging modality used.