| Objective:To determine the three-dimensional stability of atlantoaxial joint(AAJ) with anterior approach screw fixation through C2 vertebral body to C1 lateral mass(ASM) for AAJ instability or dislocation, by the experimental method and the finite element analysis (FEA).To provide the biomechanical basis for the reconstruction of AAJ.And whether to solve the replacement of the experiemental method by using FEA.Method:1. 25 human moist cadaveric specimens(C0-C3) were randomly divided into 5 groups.The three-dimensional range of motion (TDRM) C1 relative to C2 was measured under five different conditions,the intact state of occipitoatlantoaxial complex group (group IOC), typeâ…¡odontoid fracture group (group TOF), posterior C1-C2 transarticular screw fixation group (group PTS), group ASM, AMS and Gallie technique group (group ASMG). The obtained data were statistically analysed. 2.To gain the data by CT scanning occipitocervical specimen(C0-C3), and they were imputed the Mimics 10.0 software to extract the bone and ligament of C0-C3, and modified the model.Then it were imported the FEA software Patran2005 by the OUT format to product tetrahedron mesh, and derived by the OUT format. The material parameters were distributed to the model in the Mimics software. So the three-dimensional finite element model(TDFEM) was completed.3. The TDFEM of IOC, TOF, PTS, ASM and ASMG ,in corresponding with Experimental groups, were established by Patran2005. The C3's bottom of the models were restrainted by defining six-freedom degree for zero.Then they were mobiled in flexion/ extension,left/right lateral bending, left/right axial rotation by loading 1.5Nm at C0, analysed between the displacement of AAJ and the stress of various sections of the atlantoaxial vertebra by Patran2005.Result:1.There was generally significant difference between group IOC and other groups,and between group TOF and group PTS, ASM and ASMG by statistical analysis (p<0.001).Group ASMG, ASM and PTS significantly decreased range of motion in all directions.There was generally significant difference between group ASMG and group ASM and PTS in flexion and extension and lateral bendings by statistical analysis (p<0.05). It was significant difference between group ASMG and group ASM and PTS in flexion and extension and lateral bendings by statistical analysis (p<0.05),and no difference in axial rotation by statistical analysis (p>0.05).2.The establishment of the atlantoaxial vertebra TDFEM included Cortical bone,Cancellous bone and ligament. The model highly simulate cervical vertebra structure and the material property, which structure was integrated.The spatial structure surveyed high accuracy, and the unit divided fine. The node and element number of the IOC TDFEM respectively was 9178 and 40356. Results indicated that the facet of atlantoaxial lateral joints and the front part of C2 body were the stress concentration regions and also high bone mineral density regions.3.It is quite similarity for the result of between the experiment and FEA. ASMG ,PTS and ASM can obviously reduce the three-dimensional range of motion C1 relative to C2.Conclusion:1.ASM can provide the satisfied stability.It provides the equivalent effect to Margerl.It is a reliable surgery choice for the treatment of instability or dislocation of AAJ.2. In vivo biomechanics studies show that ASMG has unique feature in the reconstruction of the atlantoaxial stability,especially in controlling the unstability of flexion, extension and lateral bendings.3.Combining usage of Mimics and MCS.Patran2005,the constructing TDFEM has the advantages of the intact structure and precise element which can simulate the further biomechanical research of AAJ.So it may replace the experimental method. |
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