Deviation analysis of C1-C2 transarticular screw placement assisted by a novel rapid prototyping drill template: a cadaveric study.

Study Design: Cadaveric study. Objective: The aim of this study was to develop and validate the accuracy of a novel navigational template for C1-C2 transarticular screw (C1C2TAS) placement in cadaveric specimens. Summary of Background Data: Currently, C1C2TASs are primarily positioned using a free-hand technique or under fluoroscopic guidance. Screw placement is challenging owing to the small size of the C2 isthmus, which places technical demands on the surgeon. Screw insertion carries a potential risk of neurovascular injury, magnifying the importance of using a precise technique for screw insertion. Materials and Methods: Computed tomography (CT) scans with 0.625-mm wide cuts were obtained from the 32 cadaveric cervical specimens. The CT data were imported into a computer navigation system. We developed 32 three-dimensional drill templates, which were created by computer modeling using a rapid prototyping technique based on the CT data. We constructed drill templates using a custom trajectory for each level and side based on specimen anatomy. The drill templates were used to guide establishment of a pilot hole for screw placement. The entry point and angular direction of the intended screw positions and inserted screw positions were measured by comparing postoperative and preoperative images after the coordinate axes were synchronized. Results: The average displacement of the entry point of the left and right C1C2TAS in the x-, y-, and z- axis was 0.13 +/- 0.90mm, 0.50 +/- 1.50mm, and -0.22 +/- 0.71mm on the left, and 0.21 +/- 1.03mm, 0.46 +/- 1.55mm, and -0.29 +/- 0.58mm on the right. There was no statistically significant difference in entry point and direction between the intended and actual screw trajectory. Conclusions: The small deviations seen are likely due to human error in the form of small variations in the surgical technique and use of software to design the prototype. This technology improves the safety profile of this fixation technique and should be further studied in clinical applications.