| IntroductionThe lower cervical pedicle screw fixation system now has been one of the most frequently used one in lower cervical spine surgery for it’s excellent biomechanical feature. But the operation is hard and dangerous due to the complicated and vital anatomy structure adjacent to pedicle,malposition of screw evokes the descent of stiffness and even operation failure. It’s the key point to this operation that the path of planting screw must accord with the macroaxis of pedicle as far as possible. Combined with3D reconstruction techniques, we use three-dimensional reconstruction software, the pedicle screw channel visualization. The current difficulties is that different individuals of the lower cervical spine there is a difference, it is difficult to achieve a unified set nails., The rapid development of Rapid prototyping technology in recent years, has opened up a new way for the development of spinal surgery. Basing on the three-dimensional reconstruction techniques, rapid prototyping and reverse engineering principles, we design and product personalized navigation template.Reling on vertebral body three-dimensional model preoperative rebuilting, we can visualize of the pedicle screw channel, to observe the pedicle walls of whether the perforation occurred.Virtual design Kirschner preoperative and postoperative kind Kirschner, After CT scan and three-dimensional reconstruction, we registrated, and calculated the size of the change and spatial displacement of three-dimensional point of view.The study evaluated the accuracy of the navigation template designed and the application of scientific Compared with similar studies, we placed greater emphasis on the biological safety of navigation template, to better provide a scientific basis for clinical application.Navigation template has a high accuracy to meet the clinical application.ObjectiveKirschner wire placement of navigation template assisted method of evaluation of the accuracy and feasibility of the principle of reverse engineering and rapid prototyping technology, and CT with3D reconstruction techniques to create personalized navigation template assisted posterior transpedicle fixation cervical Kirschner wire placement; specimen experiment. Virtual design Kirschner preoperative and postoperative kind Kirschner, registration, and calculated the size of the change and spatial displacement of three-dimensional point of view, in order to evaluate the accuracy of the navigation template.Methods1.1Material Select4fresh cervical (C3-C7) cadaversthe soaked in formalin:two male specimens, two female specimens; All specimens were examined with macroscopic observation and imaging screening to exclude anomalies,tumours and tuberculosis and other diseases.The specimens include cervical (C3-C7) rear side of the soft tissue. 1.2Methods1.21Scanning specimens of the lower cervical spine to obtain CT image dataEight specimens of64-slice spiral CT scan in the preoperative. scan conditions: voltage120kV, current150mA, slice thickness0.5mm, matri×512×512. The CT slice data stored in DICOM format.1.22The lower Cervical CT image data import Mimics10.01softwareThe images were stored in DICOM format, and transferred to a workstation running MIMICS10.01software (Materialise, Belgium) to generate a3D reconstruction model of the desired the lower cervical vertebra. And encode the image data of each vertebral body, stored in STL format to spare.1.23To determine the lower cervical spine pedicle isthmusSingle vertebral data (STL format) imported into Geomagic Studio (Geomagic company, American) in the direction along the pedicle axis, using the’ Create feature’ function to find the most narrow pedicle of, that is, pedicle isthmus. Pedicle isthmus wrp format storage.1.24Design cavity block screw positioning rodUsing’ created the features’ function in Geomagic to find the largest inscribed circle of the pedicle isthmus, the largest inscribed circle, storage IGS format; largest inscribed circle data input to the UG, and along the direction of the pedicle axis designed with a diameter of2mm cavity block Kirschner wire positioning rod.1.25Design the three-dimensional model of the lower cervical spineWith Kirschner virtual channel of the lower cervical vertebrae model inputs to the U.S.3D printer Zcorporation (Z Corp. USA) produced by Spectrum Z510molding machine of the three-dimensional printing method for printing. Vertebral body three-dimensional model of the design, mainly through the following steps personalized prepare three-dimensional device; ready Zprint software build process; removal of parts, initial stereotypes. Obtain vertebral body with a Kirschner wire channel and rapid prototyping model.1.26The production of navigation templates2mm long80mm Kirschner wire placed in diameter by the model group, both sides of the C3-C7, reconcile good denture powder around the two Kirschner accumulation, production module, pull out the denture powder to be fully condensing Klinefelterpin on the module for manual separation.1.30C3-C7sample preparationTake four cervical specimens, and preparation. Excluding the rear of the soft tissue of the lamina exposed lamina; removal of the interspinous ligaments and supraspinous ligament exposed spinous process. Kirschner wire placed along the navigation pilot hole the diameter of the Kirschner wire is2mm. Bilateral simultaneous placement of Kirschner wires, a total of40.1.31The second CT scan of the lower cervical spine specimens with a Kirschner wireKirschner wire placed in another spiral CT scan, at the same conditions. Scanned CT images into three-dimensional reconstruction software Mimics,10.01, select the appropriate bone threshold, extract the image gray level of the lower cervical spine, select the appropriate threshold for the three-dimensional reconstruction (using the same thresholds and reconstruction techniques),1.32The actual Kirschner and virtual Kirschner needle position data extractionKirschner wire, spiral CT scanning was carried out again. Will scan the CT tomographic images into three-dimensional reconstruction software Mimics14.01, on the lower cervical spine reconstruction (using the same threshold and reconstruction techniques), with STL output format. In the Geomagic10.0software, virtual Kirschner wires and actual Kirschner wire for registration. Extraction of virtual Kirschner wires and actual Kirschner nail feeding point of the six DOF data.1.33The actual Kirschner and virtual Kirschner needle position difference extractionIn Geomagic Studio10, the preoperative and postoperative data registration. The long axis of the following cervical Z-axis, about the direction of the X-axis, and previously after the direction of Y axis. Transverse process of the central horizontal plane for the0°plane, the median sagittal plane where the plane is0°datum. In Geomagic Qualify11, while the import of preoperative with virtual Kirschner vertebral and postoperative with real Kirschner wires of the vertebral body, for preoperative design of vertebral our virtual Kirschner with creating a feature function, editing the Kirschner needle axis, in IGS format is kept; the same way, we on postoperative placement Kirschner vertebral utilized to create feature function to find the real Kirschner needle axis, in IGS format to store the backup. In the reverse engineering software NX6.0, input virtual Kirschner wire axis curve and real Kirschner wire axis curve, edit. Using NX6.0analysis function of angle measurement function can be calculated with two straight lines in different planes of space angle change numerical size, similarly using distance measurement function to calculate the minimum distance between two straight lines, at the same time can be obtained in each plane displacement projection distance size.ResultsApplication of rapid prototyping and reverse engineering under the principle of design the cervical personalized navigation templates40,which assist40cervical Kirschner wire placement. Intraoperative navigation templates of each of the lower cervical spine and vertebral lamina are closely integrated, the template has a high matching degree and stability. Displacement value of virtual Kirschner of the X-axis and angle changes in the value of the X-axis is-0.203±0.439°nd Y-axis is0.151±0.494°, and Z axis is0.027±0.127°. Displacement value of Kirschner of the X-axis is159.675±99.162mm, Y-axis is-200.456±6.719mm, Z-axis is-283.472±125.079mm and angle changes in the value of the X-axis is0.277±0.317°and Y-axis is0.262±0.416°, and Z axis0.048±0.23°. By paired-Sample T test, the displacement in the X,Y and Z axis direction, have not significant difference p>0.05; angle in X, Y and Z directions were not statistically different.p>0.05. Compared with actual Kirschner, Virtual Kirschner in the X axis displacement when t=0.392, P=0.707, in the Y axis displacement when t=0.641, P=0.542, in the Z axis displacement than that t=-1.836, P=0.109. Virtual Kirschner and actual Kirschner compared, in the X axis angle that the T=-2,184, P=0.065, Y axis angle that the T=-0.407, P=0.696, Z axis angle compared to that t=-0.178, P=0.863. The actual Kirschner wires and the deviation between the virtual Kirschner, X axis displacement deviation is1.58±0.66mm, Y axis deviation is1.96±0.84mm, Z axis deviation is2.33±1.15mm; X axis deviation is1.43±1.18°, Y axis deviation is2.43±1.67°, Z axis deviation is1.14±0.50°.ConclusionThe research and application of lower cervical spine specimen, simulation of posterior pedicle screw fixation operation by the3D reconstruction technology and registration techniques, has a certain clinical application prospect. However, the research and the application of clinical have bigger difference, this personalized navigation template shape and its precision needs to be further improved. |
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