A finite element analysis of three alternatives to C2 pedicle screw in the setting of congenital C2-3 fusion and high-riding vertebral arteries

Objective: To investigate the biomechanical properties of three novel screw techniques for C2-3 fused vertebra with high-riding vertebral arteries (HRVAs). Summary of Background Data: There has not been an investigation into the biomechanical properties of alternatives to C2 pedicle screw in the context of C2-3 fused vertebrae and HRVA. Methods Five models were utilized to assess range of motion (ROM) and peak von Mise stress (PVMS) on the screw-rod construct. These models consisted of the following groups: C2 pedicle screw (2PS), subfacetal body screw (SBS), translaminar screw (TLS), lateral mass screw (LMS), C3 pedicle screw (3PS) fixation in the presence of HRVA and C2-3 fusion. The flexion/extension (FE), lateral bending (LB) and axial rotation (AR) on 3 planes were simulated. Results: Compared to the 2PS, the LMS and SBS exhibit similar ROM in FE and LB (<10%). The SBS reduces ROM in AR by 47.87%, while the LMS increases ROM in AR by 26.85%. Compared to 2PS, the 3PS has similar ROM in FE, LB, and AR; but increases PVMS in FE and AR by 43.62% and 29.27%, respectively, and decreases PVMS in LB by 33.81%. Compared to 2PS, the LMS decreases ROM in FE and LB by 11.93% and 14.45%, respectively; but increases PVMS in LB by 25.38%. Compared to 2PS, the SBS increases PVMS in FE, LB, and AR by 126.96%, 74.87%, and 16.97%, respectively. Although the 3PS, LMS, and SBS increase ROM in FE by 14.11%, 4.81%, and 16.89%, respectively, compared to the TLS, they decrease ROM in LB by 72.88%, 67.98%, and 67.87%, respectively, and in AR by 41.68%, 28.05%, and 70.43%, respectively. Although the 3PS and SBS increase PVMS in FE by 45.08% and 129.26%, respectively, compared to the TLS, they decrease PVMS in LB by 73.84% and 30.88%, respectively, and in AR by 8.00% and 16.75%, respectively. The LMS decreases PVMS compared to the TLS in FE, LB, and AR by 11.04%, 66.18%, and 10.77%, respectively. Conclusion: 3PS, LMS, and SBS are biomechanically feasible, may be reasonable options in the setting of congenital C2-3 fusion and high-riding vertebral arteries.