MATERIAL and METHODS: DICOM format data from 60 cases with C1?C2 instability were obtained after computed tomography (CT) was performed. A total of 32 cases underwent surgery via the free-hand technique, whereas 28 cases underwent surgery via a 3D-printed ?pointing-drilling? guide template. The ideal trajectory of the C1 and C2 pedicle screws was designed using a baseplate as a separate complementary template for the corresponding posterior C1?C2 anatomical surface, after which the ?pointingdrilling? guide template was materialized using a 3D printing machine. The 3D-printed ?pointing-drilling? guide template, which was sterilized with low-temperature plasma, was used to locate the starting point and determine the drill trajectory during surgery. The positions of the screws in the axial and sagittal planes of the CT scan were observed and categorized into four grades, after which the operative time, fluoroscopy time, and intraoperative bleeding in the two groups were compared.

RESULTS: No significant difference (p>0.05) in each screw classification grade was observed between the free-hand and ?pointingdrilling? template groups; however, a significant difference was observed (p=0.048) between these two groups. A significant difference (p<0.05) in fluoroscopy times was observed between the free-hand and ?pointing-drilling? template groups. Conversely, no significant differences were observed in bleeding (p=0.491) and operative time (p=0.309) between the free-hand and ?pointingdrilling? template groups.

CONCLUSION: The 3D-printed ?pointing-drilling? guide template technique promoted more secure C1 and C2 pedicle screw placement compared with the free-hand technique in clinics. Keywords : 3D printing, Pedicle screws, Atlanto-axial, Personalized, Template