[Design and experimental study of individual drill templates for atlantoaxial pedicle screw fixation].
OBJECTIVE
To explore and evaluate the accuracy and feasibility of individual rapid prototype (RP) drill templates for atlantoaxial pedicle screw implantation.


METHODS
Volumetric CT scanning was performed in 8 adult cadaveric atlas and axis to collect Dicom format datas. Then three-dimensional (3D) images of atlas and axis were reconstructed and the parameters of pedicles of 3D model were measured by using software Mimics 10.01. The 3D model was saved by STL format in Mimics. The scattered point cloud data of 3D model were processed and the 3D coordinate system was located in software Imageware 12.1. The curves and surfaces of 3D model were processed in software Geomagic Studio 10. The optimal trajectory of pedicle screw was designed and a template was constructed which accorded with the anatomical morphology of posterior arch of atlas and lamina of axis by using software Pro/Engineer 4.0. The optimal trajectory of pedicle screw and the template were integrated into a drill template finally. The drill template and physical models of atlas and axis were manufactured by RP (3D print technology). The accuracy of pilot holes of drill templates was assessed by visually inspecting and CT scanning.


RESULTS
The individual drill template was used conveniently and each template could closely fit the anatomical morphology of posterior arch of atlas and lamina of axis. Template loosening and shifting were not found in the process of screw implantation. Thirty-two pedicle screws were inserted. Imaging and visual inspection revealed that the majority of trajectories did not penetrate the pedicle cortex, only 1 cortical penetration was judged as noncritical and did not injury the adjacent spinal cord, nerve roots, and vertebral arteries. The accuracy of atlas pedicle screw was grade 0 in 15 screws and grade I in 1 screw, and the accuracy of axis pedicle screw was grade 0 in 16 screws.


CONCLUSIONS
The potential of individual drill templates to aid implantation of atlantoaxial pedicle screw is promising because of its high accuracy.
Department of Orthopedics, First Affiliated Hospital, Chongqing Medical University, Chongqing 400016, PR China.
Wei
W
Qin
Zhengxue
Z
Quan
Yang
Y
Liu
Yunsheng
Y
Ou
D000328:Adult; D001863:Bone Screws; D001270:Cervical Atlas / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D021621:Imaging, Three-Dimensional; D016268:Internal Fixators; D025321:Surgery, Computer-Assisted / Q000295:instrumentation / Q000379:methods*; D014057:Tomography, X-Ray Computed