Patient- Specific Drill Guide Template for Pedicle Screw Insertion into the Atlantoaxial Cervical Spine Using Stereolithographic Modeling: An In Vitro Study

Study Design: Cadaveric study. Purpose: This study aimed to assess the accuracy and feasibility of cervical pedicle screw (CPS) insertion into the atlantoaxial cervical spine using a patient-specific drill guide template constructed from a stereolithographic model. Overview of Literature: CPS fixation is a widely accepted procedure for posterior cervical fixation because of its biomechanical advantages, particularly in the subaxial cervical region. The extremely narrow corridors of the atlantoaxial spine make CPS insertion more difficult, requiring the development of new tools to ensure accurate placement. Methods: Fifteen atlantoaxial cervical vertebra specimens from 15 cadavers were scanned into thin slices using computed tomography. Images of the cadaver spine were digitally processed and rendered stl files so that they could be printed to scale as three-dimensional (3D) plastic models. Manually molded dental acrylic drill guide templates with pins inserted in the pedicles of the plastic cervical models were placed over the 3D printed models. The drill guide templates were used for precise placement of the drill holes in the pedicles of cadaveric specimens for pedicle screw fixation. The accuracy of screw placement was evaluated by an independent evaluator. Results: A total of 60 pedicles (combined C1 and C2) from 15 cadaveric axial cervical vertebrae were evaluated. The total acceptable accuracy for pedicle screw insertion in the atlantoaxial cervical vertebrae is 95%. An accuracy rate of 100% was achieved for C1 while an acceptable accuracy rate of 90% was achieved for C2. Conclusions: The use of a patient-specific drill guide constructed using stereolithography improved the accuracy of CPS placement in a cadaveric model.