An Experimental Study On Accurate Placement Of Posterior Cervical Pedicle Screws Based On 3D Printing Technology

Objective: To explore a method based on digital design and the 3D printing technology to develop the accuracy of the cervical pedicle screw placement.Methods: Computed tomography(CT) thin layer scans were obtained from 12 adult cadaveric cervical specimens and were reconstructed.(1) Screw channels arrangement:The ideal screw channels were decided by analyzing the cross sections of the reconstructed 3D images.(2) Selection of single and double side navigation module:C1- C7 will be divided into four parts, C1, C2, C3- C6 and C7, and there is choice to select single or double side navigation templates according to the bifurcation of the spinous process.(3) Highly precise image registration: The navigation templates were designed based on the way of the three-dimensional cutting and the study of applied anatomy, the bony surface where the soft tissues can be removed.(4) Pedicle screws placement: The the pedicle screws were placed on the cadaver specimens under the navigation of the templates.(5) 3d registration: Then the cadaver specimens were scanned and reconstructed. The preoperative and postoperative models were compared.(6) Statistical analysis: Data of enter point, exit point of these two models were collected and compared using chi-square test.Results:(1) A total of 158 screws were placed. Five screws breached the pedicle cortex with a distance <2 mm, and the accurate rate achieves 98.1%.(2) There was no significant difference between the preoperative and postoperative entry points with an accuracy degree ?1.7 mm(P >0.05). Also, there was no significant difference between the preoperative and postoperative exit points with an accuracy degree ?2.7 mm(P >0.05).(3) The results of the inclination angles of C3–C7 were 25°- 40°.Conclusion: The posterior cervical pedicle screw placement, based on the 3D printing technology, its accuracy depending on:(1) Highly precise image registration. The key point is designing the navigation templates and placing the pedicle screw according to "the bony surface where the soft tissues can be removed ";(2) The ideal screw channels design. The key point is to desigh the screw channels rapidly by the way of the 3D cutting, taking into account the morphological structure of the cervical vertebrae.