Biomechanical Study of 3 Atlantoaxial Proactive Vertebral Artery Injury Prevention Fixation Combinations.

OBJECTIVE: To evaluate the biomechanical stability of 3 atlantoaxial proactive vertebral artery injury prevention fixation combinations. METHODS: We used 6 fresh human cadaveric C0-C4 specimens for the biomechanical test with moment control in 6 loading directions. First, range of motion (ROM) was measured in the intact specimens before they were destabilized; next, ROM of the 4 conditions fixed with 4 different fixation combinations were tested in alternating sequence: bilateral transarticular screw (TAS) and 3 test combinations: C1 laminar hook (C1LH) and C2 intralaminar screw (C2ILS) on 1 side combined with TAS (C1LH-C2ILS/TAS) or C1LH and TAS (C1LH-C2ILS/C1LH-TAS) or C1LH and C2ILS on the other side (C1LH-C2ILS/C1LH-C2ILS). RESULTS: ROM of all 4 instrumented sets significantly decreased compared with intact specimens in all the loading cases (flexion, left and right lateral bending, left and right axial rotation) except extension. Compared with the TAS group, all 3 test groups showed higher stiffness in flexion and equivalent stability in the other 5 directions. Side-by-side comparison among the 3 test fixation techniques showed no significant difference. CONCLUSIONS: The combination of C1LH and C2ILS supplemented with contralateral TAS or C1LH and TAS or C1LH and C2ILS was superior to bilateral TAS fixation with regard to biomechanics and vertebral artery safety.