| Objective: The possibility of using transarticular screw fixation in atlantoaxial dislocation was studied, and a safe intraoperative reducing device was designed. Background: The atlantoaxial diseases may lead to acute or chronic spinal cord compression. The stabilization must be reconstructed. The operative procedure of transarticular screw fixation was dangerous to some degree; therefore, the widely using of this technique was limited. Since its biomechanical stabilization is superior to any other methods, the further popularization is necessary. In the surgical treatment of the dislocation of the atlantoaxial, the reduction methods of the difficult-reducing dislocation, the intraoperative residual dislocation of the reducible dislocation and the intraoperative re-dislocation of the reducible dislocation were some of the urgent problems. By now, an effective method to reduce the dislocation and to keep on till the completing of the fixation was absent. A significant reduction designation must be safe, effective, and easy to operate. It also could achieve reduction in the operation and not impede the fixation. Methods: The anatomic measurements were done on 20 cadaveric models to get the parameters of the transarticular fixation on Chinese atlantoaxial, including the screw entrance pore, the allowed maximum anterior dislocation and the distance of two lateral entrance pore. Atlantoaxial dislocation models were produced on 6 fresh cadaveric upper cervical spine. The atlantoaxial were fixed with transarticular screw bonding wire or not. The dislocation status and reduction status was compared using biomechanical methods. The C~1 and C12 was injured by horizontal shearing force from anterior to posterior on 6 fresh cadaveric models. The shearing forces were recorded by material testing machine. The pulling force of the screw in occipital bone and the compressing force of the axis were also tested, and the results were compared with the maximum shearing forces of the atlantooccipital and atlantoaxial joint. The results were used for the design of the intraoperative device. An intraoperative reduction device through pulling the occipital was designed and was used on cadavers. Results: The implanting angle of atlantoaxial transarticular screw fixation should have an adjustable range. The optimal inferior angulation of the screw placement relative to horizontal plane was 42.84±2.42 0 The transarticular screw can be placed when the atlantoaxial dislocation in a certain degree. There was no significant difference in threedimensional ROM among the injured status fixed with transarticular screw bonding wire or not and the anterior dislocation status with same fixation. The shearing force of the C~1 and C1~2 was 714.63 ±36.02N and 572.49± 153.79N respectively, and the-5-difference was of no significance. But the correspondent distances resulted from the maximum shearing force was 5.23±0.52mm in C~1,11.58±1.97nini in C12, and the difference was significant. It shows that the reduction of the C1~2 dislocation may be achieved by pulling the occipital bone. The maximum pulling force of the occipital screw was 1202.70 ±288.14N, and the maximum resistance of the axis to the anterior-posterior compressing force was 959.72±128.3 iN . They were both stronger than the maximum shearing force of the atlantooccipital and atlantoaxial joint, and the variance was of satistically significance. The result of analog operation to the cadavers showed that the fixation of the new intraoperative atlantoaxial-reducing device was simple and it did not impact the insertion of the transarticular screw. Conclusions:The implanting angle of atlantoaxial transarticular screw fixation should have an adjustable range. The transarticular screw can be placed when the atlantoaxial dislocation in a certain degree, and the biomechanical stabilization was ideal. At the same time, the dangerous of the operative procedure would be increased and the demand to the technique of the operator would be enhanced. The designed intraoper...
|
PDF Full Text Request