Study design: Analysis using three-dimensional simulation software for spinal screw placement and computed tomographic scan images.
Purpose: To assess the feasibility of achieving multiple (three or four) screw fixation points in C2 vertebra by using a combination of pedicle and laminar screws.
Overview of literature: Secure C2 fixation using multiple screws is required or beneficial in some unique cases. However, to the best of our knowledge, there have been no reports analyzing the feasibility of multiple screw fixation in C2.
Methods: We used 1.0-mm interval computed tomographic scan images of 100 patients (50 men and 50 women) and screw trajectory simulation software. The diameter of all screws was set at 3.5 mm, considering its common usage in real surgery. The anatomical feasibility of placing both pedicle and laminar screws on the same side was evaluated. For all feasible sides, the three-dimensional distance between the screw entry points was measured.
Results: In 85% of cases, both pedicle and laminar screws could be placed on both sides, allowing for the insertion of 4 screws. In 11% of cases, 2 screws could be placed on one side, while only 1 screw was feasible on the other side, resulting in the placement of 3 screws. In all 181 sides where both types of screws could be inserted, the distance between their entry points exceeded 16.1 mm, which was sufficient to prevent the collision between the screw heads.
Conclusions: C2 vertebra can accommodate three (11%) or four (85%) screws in 96% of cases.
Keywords: C2; Laminar screw; Multiple screw fixation; Pedicle screw.