Feasibility and Safety of 2 C1 Pedicle Screw Trajectories

STUDY DESIGN: Retrospective morphometric CT analysis. OBJECTIVES: To characterize C1 pedicle/lateral mass morphometry in an adult Indian cohort and compare the feasibility/safety of straight (S) versus medially angulated (M) C1 pedicle screw trajectories. SUMMARY OF BACKGROUND DATA: C1 pedicle fixation can provide robust biomechanical stability; however, careful assessment of patient anatomy is needed to avoid neurovascular injury. METHODS: Cervical CT angiograms from 100 adults (50 male, 50 female; 200 pedicles; 2011-2022) were reconstructed for multiplanar/3D measurements. Twenty-three parameters were recorded, including pedicle height, axial path length, corridor width, clearances to vertebral artery foramen (VAF) and internal carotid artery (ICA), angular freedom from VAF/ICA, and anterior arch exit zones. Paired t tests compared S versus M; sex-stratified analyses used α=0.05. RESULTS: Mean pedicle height was 3.4±0.6 mm; 44.5% of pedicles were ≥3.5 mm, and 77.0% ≥3.0 mm. ICA location: Zone 3 (77.0%), Zone 2 (22.0%), Zone 1 (1.0%). Compared with S, M showed a wider corridor (8.3 vs. 6.6 mm), greater VAF clearance (4.1 vs. 3.3 mm) and ICA clearance (9.9 vs. 5.8 mm), and larger angular freedom from VAF (24.5 vs. 12.1 degrees) and ICA (20.3 vs. 5.2 degrees); axial path length was similar (25.4 vs. 24.9 mm). Exit zones differed: S exited Zone 2 in 100%, whereas M exited predominantly Zone 1 (96%). All paired comparisons P value <0.01. Males had larger atlas dimensions and safety corridors than females ( P <0.01). CONCLUSIONS: Most C1 pedicles in this cohort could not reliably accommodate a 3.5-mm screw. Medially angulated trajectories created wider corridors and improved vascular clearance while maintaining length, suggesting a safer option when anatomy permits. Preoperative CT and adjunctive techniques remain critical in narrow pedicles.