Feasibility of Atlas Pedicle Screw Fixation Perpendicular to the Coronal Plane-A 3D Anatomic Analysis

Abstract

Study design: An anatomic analysis.

Objective: To investigate the feasibility of the ideal atlas pedicle screw trajectory perpendicular to the coronal plane via atlas digital 3D reconstruction.

Methods: One hundred adult atlases were evaluated in this study. The projection of the corridor for atlas pedicle screw fixation perpendicular to the coronal plane was quickly obtained using the perspective model of 3D reconstruction, and the area, long axis, short axis and width of the pedicle corridor were measured. The inner trajectory was near the lateral wall of the pedicle, and the center of the corridor was point A. The lateral trajectory was near the lateral wall of the transverse foramen, and the center of the trajectory was point C. The midpoint of A and C was B. The length of the inner, middle and lateral trajectorys were measured. The distances from points A, B and C to the posterior tubercle of the atlas and safety swing angle were measured.

Results: From the dorsal view, the pedicle corridor was fitted into an ellipse with an average long axis of 13.6 mm, an average short axis of 5.2 mm, and an average area of 56.3 mm². From the axial view, the pedicle corridor had an average width of 9.4 mm. The average lengths of the inner trajectory, middle trajectory and lateral trajectory were 31.7 mm, 28.7 mm and 25.1 mm, respectively; The average distances from the posterior tubercle to points A, B and C were 17.1 mm, 20.8 mm and 24.5 mm, respectively. The average swing angles from points A, B and C were 16.1°, 25.5°, and 28.1°, respectively.

Conclusion: Atlas pedicle screw fixation perpendicular to the coronal plane is feasible for almost all the volunteers. Pedicle screws close to the pedicle lateral wall of the atlas posterior arch perpendicular to the coronal plane is an advanced technique that is easy to master.

Keywords: 3D reconstruction; anatomy; atlas; pedicle screws.

Figure 1.

3D reconstruction of the atlas. a–b, The cortical bone and cancellous bone of the atlas were segmented and filled completely. c, 3D reconstruction of the atlas.

Figure 2.

3D anatomical morphology of the atlas; a, Axial view of the atlas. Point F represents the anterior tubercle of C1, and point P represents the posterior tubercle. b, Lateral view of the atlas. c–d, Points F and P overlap in the dorsal view of the atlas. e, The pedicle corridor is delineated from the dorsal view. f, Measurement of the long axis (LL, RL), short axis (LS, RS) and area of the pedicle corridor.

Figure 3.

Axial sketch of the atlas. a, The 3 green lines represent the inner, middle and lateral trajectories, respectively. The short yellow lines form a 2.75-mm-wide corridor to holding screws with a diameter of 3.5 mm and reserve 1 mm for the bone cortex. b, Points A, B and C represent the entry point of the inner, middle and lateral corridors, respectively. LA, LB, and LC represent the distances from points P to points A, B and C, respectively. c, The yellow curves form a 2.75-mm-wide corridor to hold screws with a diameter of 3.5 mm and reserve 1 mm for the bone cortex. α, β, γ represent the safe angles of the inner screw swing, middle screw swing and lateral screw swing, respectively.