An Intraoperative Trajectory-Determined Strategy of Patient-Specific Drill Template for C2 Transoral Pedicle Insertion in Incomplete Reduction of Atlantoaxial Dislocation: An In Vitro Study

Abstract

Objectives: This study aims to explore a novel intraoperative trajectory-determined strategy of grouped patient-specific drill templates (PDTs) for transoral C₂ pedicle screw insertion (C₂ TOPI) for atlantoaxial dislocation (AAD) with incomplete reduction and to evaluate its efficiency and accuracy.

Methods: Ten cadaveric C₂ specimens were scanned by computed tomography (CT) and randomly divided into two groups (the PDT and freehand groups). A novel intraoperative trajectory-determined strategy of grouped PDTs was created for AAD with incomplete reduction. C₂ TOPI was performed by use of the PDT technique and the fluoroscopy-guided freehand technique. After surgery, the screw deviations from the centroid of the cross-section at the midpoint of the pedicle and screw position grades were assessed in both groups.

Results: Compared to the freehand group, the PDT group had a significantly shorter surgery time than the freehand group (47.7 vs 61.9 min, P < 0.001). The absolute deviations from the centroids between the preoperative designs and postoperative measurements on the axial plane of the pedicle were 1.19 ± 0.25 mm in the PDT group and 1.82 ± 0.51 mm in the freehand group. On the sagittal plane of the pedicle, the corresponding values were 1.10 ± 0.33 mm in the PDT group and 1.70 ± 0.49 mm in the freehand group. The absolute deviations of the free-hand group on both the axial and sagittal planes were higher than that of the freehand group (P < 0.05 and P < 0.05, respectively). For the grade of screw insertion position, nine (90%) were observed in type I and one (10%) in type II in the PDT group, whereas five (50%) were in type I, three (30%) were in type II, and two (20%) in type III in the freehand group. Statistical differences could not be found between the groups in terms of the screw positions (P > 0.05).

Conclusion: The novel intraoperative trajectory-determined strategy of grouped PDTs can be used as an accurate and feasible method for C₂ TOPI for AAD with incomplete reduction.

Keywords: 3D printing; Atlantoaxial joint; Cadaver; Classification; Pedicle screw.

Fig. 1

Calculation of the centroid of the cross‐section at the midpoint of the pedicle of C₂. (A) The midpoint and corresponding cross‐section of each pedicle were determined. (B) After the contour of the cross section was fitted by a maximum ellipse, the centroid was calculated from the maximum ellipse (reprinted from our previous research with permission from Copyright Clearance Center).

Fig. 2

3D model of the C₂ vertebra. (A) 3D C₂ model in which the surfaces of the upper pedicle and anterior vertebra body were removed. (B) 3D‐printed model.

Fig. 3

Grouped PDTs for C₂TOPI. (A) The design models of PDT C, D, and E. (B) 3D‐printed models of PDT C, D, and E.

Fig. 4

Cadaveric C₂TOPI with the assistance of PDT C, D, and E. (A) PDT C was used to guide the insertions of the TRS and setscrew. (B) A TRS was then screwed in the lower hole, and the upper two holes of the TARP were fixed to C₁ with lateral mass screws. (C) After the TRS was screwed in, C₁ and C₂ were relocated to a proper position with the reduction instrument because it might not obtain the complete reduction (surgical simulation diagrams). (D) The TARP was then temporarily fixed with VBSs. (E) PDT D was used to find the intraoperative position of the TARP according to the positions of the VBSs. The entrance points of C2TOPI were determined. (F) After removing the TRS, PDT E1 was attached to the anterior surface of C₂, and the relative position between PDT D and E1 was agglutinated with a medical glue. (G) PDT D and E1 were transferred to the 3D‐printed C₂ model to determine the drilling direction through visual observation. A K‐wire was inserted into the pedicle through the drilling tube (PDT E2). The position of the K‐wire was adjusted through visual observation to locate it at the central C₂ pedicle. The removable components of PDT E1, E2, and E3 were agglutinated together using the same medical glue to determine the drill direction. (H) Simulation diagrams which showed PDT E1, E2, and E3 were agglutinated to determine the drilling direction. (I) PDT D and E were switched back to the cervical specimen to guide C₂TOPI with the determined entrance point and drilling direction. (J) C₂TOPI was completed after the two 3.5‐mm diameter screws were inserted.