Fig 1.
Schematic diagram of positioning the longitudinal axis of the target pedicle perpendicular to the ground by medially and rostrally or caudally rotating the spine.
Fig 2.
Photographs from a lateral view (A) and from diagonally above (B), the longitudinal axis of the target pedicle perpendicularly positioned to the ground by medially and rostrally rotating the sample by adjusting the two angle vise clamps attached to the bottom of the board on which the cadaver was mounted.
The upper angle vise clamp was fastened by the lower angle vise clamp, and the rotating planes were orthogonal to each other.
Fig 3.
Parasagittal (upper and middle) and arbitrary axial planes (lower) obtained by postoperative computed tomography scans.
The black dotted lines indicate the planned pedicle screw (PS) trajectories. The upper panel shows that the rostrocaudal angle of PS placed freehand caudally deviated relative to the planned angle, whereas the middle panel shows that the rostrocaudal angle of PS placed by perpendicular probing and screwing technique (PPST) was almost parallel to the planned angle. The lower panel shows that the mediolateral angle of the right PS placed by PPST was almost parallel to the planned angle, whereas the mediolateral angle of the left PS placed freehand medially deviated to the planned angle.
Table 1.
Average planned rotational angles of the freehand and PPST groups.
Table 2.
Average differences between the pre- and postoperative distances between EP and TRAP or TTP.
Table 3.
Average diameters of the PS, the narrowest width of the pedicle, and the ratio of the PS size to the narrowest pedicle width.
Fig 4.
(A) Mean offsets between the inserted pedicle screw (PS) and preoperatively planned rostrocaudal rotations in the freehand and perpendicular probing and screwing technique (PPST) groups. (B) Mean offsets between the inserted PS and preoperatively planned mediolateral rotations in the freehand and PPST groups. *p <0.05; ****p <0.0001.
Fig 5.
(A) An enlarged image of the lower panel of Fig 3, demonstrating that the left pedicle screw (PS) placed by perpendicular probing and screwing technique (PPST) is contained in both medial and lateral cortical layers of a pedicle, whereas the right PS placed by freehand breaches medial cortical layer of a pedicle. (B) Mean cortical breach distances in the freehand and PPST groups. ***p <0.001.
Table 4.
Screw positioning and direction of unacceptable wall penetration in the freehand and PPST groups according to the Gertzbein and Robbins classification system.