| Objective: Pedicle screws, as an milestone in the spine surgery history,has been widely used in the spine surgery, such as trauma, tumor, deformityand degenerative diseases. With stripping the paraspinal musclesexcessively, the traditional open insertion of pedicle screws causedextensive blood loss, muscle denervation, muscle atrophy andpost-operative muscle pain. Therefore, the minimally invasive surgery forpedicle screws insertion has been used by more and more scholars. For theanatomic variations of the pedicle, classic Magerl projection method andAP/lateral position projection method can not completely meet the highaccuracy requirements of the percutaneous pedicle screws placement. Forthis reason, many navigation and robot assisted technology had beenapplied in the spine surgery, which has greatly improved the accuracy of thepercutaneous pedicle screws placement. At present, however, all navigationand robot assisted technology used in percutaneous pedicle screwsimplantation base on the images of “C†or “O†arm. The quality of “C†or“O†arm images is not high in thoracic, obesity patients and patients withsevere osteoporosis, which influente the navigation accuracy forpercutaneous pedicle screws implantion. Navigation technology based onCT images has been absent currently.As a navigation system based on CT images, computer-assistednavigation thermoplastic elastomer film localization system which wasfirstly recommended to apply in orthopedics by our hospital, has performedsuperiority in percutaneous fixation of sacroiliac joint dislocation andnondisplaced anterior/posterior column fracture of acetabular. According tothe problems with the current technology of percutaneous pedicle screws implantation and the knowledge of computer-assisted navigationthermoplastic elastomer film localization system, we apply the technologyto percutaneously insert Kirschner wire in pedicle and evaluate itsfeasibility and accuracy.Methods: With the computer-assisted navigation thermoplastic elastomerfilm localization system, we inserted Kirschner wire(2.5mm) in bilateralpedicle of T12and L2of each specimen. Each specimen was inserted fourKirschner wires(total24). Put the specimen by prone position on the bottomof the positioning system. Took the thermoplastic elastomer film into a watertank with the temperature at62℃. Covered the specimens’ back by thethermoplastic elastomer film after it was soften, with the surface sticking fullyas far as possible. Fixed the thermoplastic elastomer film on the bottom. Asthe temperature dropped, the thermoplastic elastomer film became hardgradually. Put the thermoplastic elastomer film, specimen and the bottom onthe CT examination table. Select any plane with the same direction of the CTscan by the3D laser tracking device, and marked three points(not in the sameline) with lead particulate to determine benchmark planar. The benchmarkplanar must be in the cope of CT scans. The image data of thin layer CT scansaround with L1was transmitted to the treatment planning system. By thissystem, determined the benchmark planar which was marked by three leadparticulate, and confirmed the origin of the space coordinates in thebenchmark planar, named (0,0,0) point. Reconstruction the planes parallellingto the end plate of T12with1mm thick by the treatment planning system.And then selected the layer which the inner diameter of pedicle was widest. Inthis layer, we can select optimum needle passage which meet thethermoplastic elastomer film at a point at back, marked as A. Drew thevertical line of the optimum needle passage on the plane which the innerdiameter of pedicle was widest, and lengthen its two sides to cross with thethermoplastic elastomer film at two sides of the specimens, marked as B andC. Determined the space coordinates of A, B and C by referring to the originpoint, and input them into3D laser tracking device, which would automatically position the points of A, B and C in the thermoplastic elastomerfilm. Marked A, B and C points with marker pens, and determined the entrypoint and needle passage by the3D gunsight, then drilled the Kirschner wireinto the bone by electric drills. Finish the Kirschner wires insertion of L2inthe same method. Observed the Kirschner wires’ position by thin layer CTscans around with L1after inserting them, and obtained the actual needlepassage coordinates by using the treatment planning system.Recorded the planned and actual entry/out points coordinates of theKirschner wires, and calculated the space distances between the planned andactual points using coordinates figure, then did statistics analysis. Measuredthe the deviation angle between the actual and planned needle passage on theaxial plane, and pedicle violations were noted with respect to the degree anddirection of the screw misplacement, recorded number of facet jointsviolations, and recorded the preoperative preparation time of the thermoplasticelastomer film system.Results: In this experiment, we inserted24Kirschner wires into6specimen. Compared with theory D-value (0mm), the D-value betweenplanned and actual entry/out point coordinate of needle passage (d1) had nostatistical difference(P <0.05). The median and interquartile range of distancebetween the planned and actual entry point coordinate of needle passage are3.04mm,1.69mm respectively. The distance between the planned and actualout point of needle passage (d2) is3.45±1.21mm. The deviation angle betweenthe actual and planed needle passage on the axial plane of vertebral was2.98°±1.62°. The ratio of the actual needle passage which deviated toward themedial or lateral side of the planed ones was17:7. The number of pedicleviolations was3, of which2Kirschner wires’ misplacement degree variedwithin2mm, one Kirschner wire cut through the lateral cortex of pediclecompletely. The preoperative preparation time of the thermoplastic elastomerfilm system was20min-45min, average28min, of which the time to pave thethermoplastic elastomer film was4min-6min, average5min, the plan time ofideal needle passage was15min-40min, average20min, only2needle passage were planed more than30min at the begininng of the experiment, theothers were all finished within30min.Conclusion: The computer-assisted navigation thermoplastic elastomerfilm localization system provide accurate spatial orientation and stable pathnavigation for percutaneous pedicle screws insertion. This technology cansignificantly decrease the fluoroscopic time, and has excellent security andefficiency. As a new location method for minimally invasive pedicle screwsimplantion, there are bright prospect to apply this technique. However, it isessential to develop special navigation system workstation to improve workefficiency, and combine with the mechanical arm or robot technology toimprove the efficiency, accuracy and stability of pedicle screw placement. |
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