Life-size 3D modeling for C1-C2 fixation planning: A preoperative tool for atlantoaxial stabilization techniques.

Introduction: Spine instrumentation can be performed with intraoperative computed tomography (CT) guidance, fluoroscopy guidance, or freehand techniques. Surgical fixation of the atlantoaxial (C1-C2) junction without CT guidance remains technically challenging due to complex anatomy and proximity to critical neurovascular structures. Research question: To evaluate the feasibility of low-cost, patient-specific three-dimensional (3D)-printed anatomical models for preoperative planning of C1-C2 instrumentation. Material and methods: High-resolution CT and CT angiography data from 20 individuals were used to generate patient-specific 3D models of the C1-C2 vertebrae and vertebral arteries using open-source segmentation software (3D Slicer®). Models were produced as life-size replicas, with multiple fixation techniques simulated and screw angulations measured in axial and sagittal planes. Results: Twenty patient-specific C1-C2 anatomical models were successfully produced and instrumented. Screw angulations and lengths across all fixation techniques-including C1 lateral mass, C2 pedicle, pars, translaminar, and transarticular screws-remained within established safe anatomical ranges. Each model required approximately 215 min of active printing time and a total hands-on preparation time of approximately 275-320 min, with an additional 24-h curing period for silicone processing. The material cost per model was approximately USD 0.56 using a desktop fused deposition modeling printer. Discussion and conclusion: Low-cost, patient-specific 3D-printed models provide anatomically consistent, life-size representations of the complex atlantoaxial region. These models may represent a practical adjunct for surgical planning, feasibility assessment, and preoperative rehearsal for various C1-C2 fixation strategies without advanced intraoperative technology. Further studies are needed to evaluate their clinical impact.