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Background  To improve the strength of posterior spine fixation in patients with osteoporosis, some scholars have proposed a method of simultaneously inserting traditional pedicle screws and cortical bone trajectory screws into the pedicle. However, due to the difficulty of the operation and few clinical applications, the safety and accuracy of this method are still unclear. The purpose of this study was to investigate the safety and accuracy of double-trajectory lumbar screw placement guided by surgical guide templates.    Methods  Six wet lumbar specimens were selected for computed tomography (CT) scanning, a three-dimensional (3D) model of the lumbar spine was established using computer software, and surgical guide templates for double-trajectory [traditional pedicle trajectory (TPT) and cortical bone trajectory (CBT)] lumbar screw placement at various segments of the lumbar spine were designed and printed using a 3D printer. Screw placement was guided only by the surgical guide template, with no fluoroscopy. Postoperative CT examination was performed to determine whether the screw penetrated the screw path and the location and depth of penetration of the cortex. The preoperative and postoperative sagittal and axial angles of CBT screws or TPT screws were also measured and compared.    Results  Four screws were placed in each vertebral body of six lumbar specimens for a total of 120 screws. Screw grades: 99 screws as grade 0, 15 as grade 1, six as grade 2, and zero as grade 3. Thus, grade 0 accounted for 82.5% of the screws. No significant differences in the preoperative and postoperative angles of the screws were found ( P  > 0.05).    Conclusions  3D-printed surgical guide templates for double-trajectory screw placement can reduce the difficulty of surgery and the use of intraoperative fluoroscopy. Using such templates is a safe, feasible, and accurate screw placement method.

Double-trajectory lumbar screw placement guided by a set of 3D-printed surgical guide templates: a cadaver study