The Clinical And Basic Study Of Accurate Transoral C2 Transpedicular Or Articular Mass Screw Placement

[Backgroud] The surgical treatment of irreducible atlantoaxial dislocation (IAAD) is challenging for neurospinal surgeons. Various procedures and devices have been developed with varying levels of success. Among them, anterior transoral release followed by posterior atlantoaxial screw and plate/rod instrumentation is taken as the benchmark procedure. However, the need to turn the patient over intraoperatively after atlantoaxial release, a prolonged operative time and additional posterior iatrogenic trauma makes it a less favorable and potentially risky procedure.We therefore developed the transoral atlantoaxial reduction plate (TARP) system with which transoral release, reduction, decompression, internal fixation and bone grafting can be achieved in a one-staged operation. During the clinical application, we improved it from TARP-I to TARP-III in which C2 transoral articular mass screw or C2 transoral transpedicular screw (C2TOAMS/C2TOTPS) was adopted. It has solved the problem of C2 screw loosening in TARP-Ⅰ and TARP-Ⅱ procedures and it is rigid enough to counteract the redislocation strength between C1 and C2. However, we found the placement of C2TOAMS/C2TOTPS technically demanding and the misplacement of it might cause either concealed or manifested neurovascular injuries. One patient died of cerebral infarction postoperatively caused by VA compression due to C2 screw misplacement encroaching in the VA groove. Thereafter we made every effort to find a way to improve the accuracy of C2TOAMS/C2TOTPS and reduce the potential neurovascular complications.A variety of methods have been developed for the accurate screw placement in the upper cervical area. Among them, anatomical landmarks and fluoroscopic devices assisted freehand screw placement are already used in daily practice. Other effective methods include navigation, drill guides made of stainless steel, robot assistence and even assistance by microscope. There are mainly two problems impeding the application of navigation in transoral upper cervical procedures:First, the limited operative field and exposed bony surface make registration difficult; second, the upper cervical structures are fairly mobile intraoperatively, thus even when registration can be achieved, the "migration phenomenon" is inevitable. Robot-assisted accurate screw placement in the upper cervical area is still in its infancy, while microscope-assisted accurate screw placement is not widely adopted. The strategy of drill guides made of stainless steel was reported by many authors, but as for transoral upper cervical procedures, the space is very limited to manipulate these devices.We therefore developed the TARP-IV to facilitate the application of digital orthopedic techniques, and subsequently we designed a set of individualized drill templates to enhance the accuracy of C2TOAMS/C2TOTPS placement. The single-template strategy has been previously reported by many authors to assist posterior atlantoaxial screw placement. However, our TARP system serves both as a fixation and a reduction device. The entry points of C2TOAMS/C2TOTPS would be determined at the end of the reduction, thus designing a single lock-and-key template to assist screw placement would be impossible. Therefore we adopted the grouped-template strategy to solve this problem. In this study, the accuracy and screw insertion related complications of clinical placed C1 anterior lateral mass screw (C1ALMS) and C2TOAMS/C2TOTPS were evaluated; the specific parameters of clinically placed C2TOAMS/C2TOTPS were measured and compared with the anatomical parameter we previously measured; a set of individualized drill templates were designed to combine with the TARP-IV to assist C2TOAMS/C2TOTPS placement and evaluated through anatomical study.[Objective]1. To evaluate the accuracy and screw insertion related complications of clinically placed C1ALMS and C2TOAMS/C2TOTPS in TARP-III procedures in order to find the main problems existed;2. To measure the specific parameters of clinically placed C2TOAMS/C2TOTPS in TARP-III procedures and compare them with our previously measured anatomical parameters in order to find the main problems existed;3. To design a set of individualized templates to incorporate with TARP-IV to assist C2TOAMS/C2TOTPS placement;4. To evaluate the screw accuracy and simulation by the template-guided C2TOAMS/C2TOTPS placement in human cadavers with simulated atlantoaxial dislocation.[Method]1. The data collection of postoperative TARP-III patients, the aspects to assess and the standards of assessment:1). The general information and radiographic images of the patients who underwent TARP-Ⅲ procedures from March 2008 to August 2012 were obtained from the department of orthopedics and the department of radiology of Liuhuaqiao hospital with the approval of the institutional review board (IRB). A list of 169 patients was initially obtained. Fifty-three patients were excluded due to lack of postoperative thin-sliced (0.625mm) CT scans. The remaining 106 patients that had sufficient data available were included for assessment.2). The aspects to assess:(1) radiographic and clinical accuracy of C1 anterior lateral mass screw (C1ALMS) and C2 transoral articular mass screw or C2 transoral transpedicular screw (C2TOAMS/C2TOTPS) placement; (2) associated clinical complications; (3) fusion status between C1 and C2.3). The standards of assessment:(1) The radiographic accuracy was assessed using the modified All India Institute of Medical Sciences outcome-based classification and the clinical accuracy was assessed by whether there were documented adverse events; (2) The associated clinical complications were assessed by whether there were documented neurovascular complications; (3) The fusion status between C1 and C2 were assessed by reading the follow-up CT scans more than 1 year postoperatively.2. Measurement of parameters of the clinically placed C2TOAMS/C2TOTPS: Seventy-five adult patients who had undergone the TARP-III procedure in our institution from March,2008 to August,2012 were included and the specific parameters of clinically placed C2TOAMS/C2TOTPS were measured. The intraclass correlation coefficient (ICC) was calculated to access the intra-observer reliability and inter-observer repeatability of the measurements. These clinical parameters were compared with our previous measured anatomical parameters and analyzed between the two sides.3. A set of individualized templates were designed according to the thin-sliced CT scans obtained from 4 human cadavers. The templates contained cubic modules and drill guides to facilitate TARP positioning and anterior C2 screw placement. We carried out 2 stages of cadaveric experiment with 2 cadavers in each. Finally, the guided C2 screw placement was evaluated by the modified All India Institute of Medical Sciences outcome based classification.4. A set of individualized templates were designed according to the thin-sliced CT scans obtained from 6 human cadavers. The templates contained cubic modules and drill guides to facilitate TARP positioning and anterior C2 screw placement. We carried out simulative TARP-IV procedures on these cadavers assisted by the templates we designed. Finally, the guided C2 screw placement was evaluated by reading postoperative CT scans and comparing the inserted with the planned screw trajectories.[Result]1. Two hundred twelve C1ALMS and 207 C2TOAMS/C2TOTPS in 106 patients were assessed. The ideal accurate rates were 92.0%(195) and 53.1%(110) and the acceptable accurate rates were 97.6%(207) and 87.0%(180) respectively. One patient died postoperatively due to C2 screw misplacement. There were no symptoms of neurologic and vertebral artery injuries in the rest of the patients. One hundred and two patients (97.1%) achieved solid fusion between C1 and C2. No instrumentation failure due to delayed union or nonunion was observed.2. The distance between the screw entry point of C2TOAMS/C2TOTPS and the lateral articular surface of C2 is 4.5mm on both sides. The distance between the screw entry point on the right and left side and the mid-sagittal plane is 9.3mm and 7.6mm. The intraosseous length is 17.3mm and 16.3mm. The transverse angle is 15.8° and 16.9° and the declination angle is 0.2° and -1.2° respectively. Reliability test of the CT image measurements:intra-observer (ICC=0.94 and 0.95) and inter-observer correlation coefficient (ICC=0.94).3. The templates designed in stage one were difficult to use, while the templates designed in stage two were easy to use and reliable. There were altogether 8 C2TOAMS/C2TOTPS inserted with 4 in stage one and the other 4 in stage two of the cadaveric experiment. There were 2 screws in stage one ranked type I and another 2 ranked type III, whereas in stage two,3 of the placed C2 screws ranked type I and 1 ranked type II.4. The planned entry points and the transverse angles of anterior C2 screws could be simulated in the 6 human cadavers, whereas the declination angles could not be simulated due to the intraoperative blockage of the drill bit and screw driver by the upper teeth.[Conclusion]1. The C1ALMS placement in TARP-III procedures appears to be safe. The cortical breach rate of C2TOAMS/C2TOTPS is high even though the clinically neurovascular complication rate is similar to that of the posterior atlantoaxial procedures. Therefore endeavors should be made incessantly to improve the accuracy of C2TOAMS/C2TOTPS placement and decrease the potential complications.2. The locations of entry points and angles of the C2TOAMS/C2TOTPS in clinical patients are highly variable due to malformation of C2. The declination angles of C2TOAMS/C2TOTPS are insufficient. Individualized preoperative planning and intraoperative guiding are necessary to enhance the accuracy and safety of transoral C2 screw placement.3. It is feasible to use individualized templates to guide C2TOAMS/C2TOTPS placement. The templates designed in stage two are easy to use and reliable.4. The drill templates combined with TARP-IV may improve the accuracy of transoral C2 screw placement and reduce related neurovascular complications.