A Clinical and Kinematical Evaluation of Trajectory Planning Software for Posterior Atlantoaxial Transarticular Screw Fixation Surgery

Atlantoaxial instability is a progressive cervical spine condition that often requires surgical intervention. The posterior C1-2 transarticular fixation has been a great advancement for the management of atlantoaxial instability as it provides improved biomechanical stability. However, the surgical risks of serious neurovascular injury associated with this technique remain an obstacle for its wider adoption. The goal of this study is to evaluate the surgical outcome of C1-2 transarticular screw fixation utilizing a lab-designed trajectory planning software (TPS) system and to investigate the likely kinematical impact of deviated screw trajectory. The TPS system was applied to 19 patients (mean age: 61.1 years, range: 35-71 years; 14 males and 5 females) that underwent C1-2 transarticular fixation at our institution. A total of 32 transarticular screws were inserted. Pre-operative computed tomography images were used to render a three-dimensional bone tissue model as well as the corresponding multi-planar digitally reconstructed radiographs. The pre- and post-operative positions of C1 and C2 were also compared. Overall, only one malpositioned screw was identified and no major complications occurred for any of the patients. A comparison of the planned and actual screw insertion trajectories indicated that the vertical angle was the only parameter to have a statistically significant difference. Moderate negative correlation was found between the vertical entry point and the vertical angle, and moderate positive correlation was found between the horizontal entry point and the horizontal angle. The TPS system is a cost-effective clinical implementation that can potentially reduce the associated complication rates for C1-2 transarticular fixation. The system should be viewed as a useful assistive device as well as a potential training and auditing tool for institutions where more expensive navigational systems are not readily available.