Accuracy of Patient-Specific 3D-Printed Drill Guides for Pedicle and Lateral Mass Screw Insertion: An Analysis of 76 Cervical and Thoracic Screw Trajectories

Abstract

Study design: Single-center retrospective case series.

Objective: The purpose of this study was to assess the safety and accuracy of three-dimensional (3D)-printed individualized drill guides for pedicle and lateral mass screw insertion in the cervical and upper-thoracic region, by comparing the preoperative 3D surgical plan with the postoperative results.

Summary of background data: Posterior spinal fusion surgery can provide rigid intervertebral fixation but screw misplacement involves a high risk of neurovascular injury. However, modern spine surgeons now have tools such as virtual surgical planning and 3D-printed drill guides to facilitate spinal screw insertion.

Methods: A total of 15 patients who underwent posterior spinal fusion surgery involving patient-specific 3D-printed drill guides were included in this study. After segmentation of bone and screws, the postoperative models were superimposed onto the preoperative surgical plan. The accuracy of the realized screw trajectories was quantified by measuring the entry point and angular deviation.

Results: The 3D deviation analysis showed that the entry point and angular deviation over all 76 screw trajectories were 1.40 ± 0.81 mm and 6.70 ± 3.77°, respectively. Angular deviation was significantly higher in the sagittal plane than in the axial plane (P = 0.02). All screw positions were classified as "safe" (100%), showing no neurovascular injury, facet joint violation, or violation of the pedicle wall.

Conclusions: 3D virtual planning and 3D-printed patient-specific drill guides appear to be safe and accurate for pedicle and lateral mass screw insertion in the cervical and upper-thoracic spine. The quantitative 3D deviation analyses confirmed that screw positions were accurate with respect to the 3D-surgical plan.Level of Evidence: 4.

Figure 1

Example of a lateral mass (A) and pedicle (B) drill guide, with reinforcing cross connections, laminar hooks, and metallic inlays.

Figure 2

3D deviation analysis method. The (A) preoperative plan and the (B) postoperative result are (C) fused, level by level, using registration algorithms. (D) The screw shanks are manually separated and an analytical cylinder is auto-fitted. (E) A deviation analysis is performed by measuring the 3D angle, the 2D sagittal (yellow) and axial (red) angles, between corresponding plan and result. The entry point deviation is measured in millimeters, here displayed in purple and pointed out by a black arrow.

Figure 3

The use of a custom-made drill guide for immature C3 vertebrae, showing (A) the design, featuring a centrally located torus indicated by a black arrow, (B) 3D-print, (C) intraoperative positioning, and (D) postoperative image.

Figure 4

Where no photographs are available, the situation is illustrated using images of a similar case outside this series. (A) Positioning the C1 lateral mass guide, (B) sliding the sleeve underneath the arch, (C) intraoperative view, (D) the tip of the sleeve positioned between the arch and nerve root. The C2 nerve roots are indicated by white arrows.