Résumé
Objective The three-dimensional (3D) solid model of medulla oblongata-upper cervical spinal cord based on specimen pathological section data was established, and the stress and strain levels of medulla oblongata-upper cervical spinal cord under dentate process compression were obtained by finite element analysis, so as to provide references for clinical research. Methods Mimics was used to process the slice data, so as to establish the point cloud model. SolidWorks was used to locate, edit and optimize the point cloud model, so as to establish the 3D solid model. HyperMesh was used to establish the finite element model and ANSYS was used for finite element analysis. Results The medulla oblongata-upper cervical spinal cord model with clear boundary between gray matter and white matter and white matter fiber bundle was established. The stress and strain levels and stress-strain curves of white matter and gray matter under different compression degrees were obtained. Conclusions Combined with pathological sections of specimens and reverse engineering, the 3D medulla oblongata-upper cervical spinal cord model with clear morphology and structure of gray/white matter can be established. When the medulla oblongata-upper cervical spinal cord is compressed, the stress level of gray matter is lower than that of white matter, and about 20% of compression is the critical state of white matter. When the disease develops beyond the critical state, the biomechanical properties of white matter may fail, resulting in gray matter damage.
Résumé
<p><b>OBJECTIVE</b>To study the biomechanical change of the craniovertebral junction in conditions of atlas assimilation.</p><p><b>METHODS</b>Mimics software was used to process CT data of the craniovertebral junction in a health adult to obtain the three-dimensional reconstruction and the cloudy points of C1, C2 and part of the occipital bone. Then the cloudy points were imported into the Abaqus 6. 8 software to establish the occipito-atlantoaxial finite element model in normal structure. According to the established model in normal structure, the model in conditions of atlas assimilation was set by changing the model parameters. Both models of normal structure and atlas assimilation were loaded with 1. 5 N . m static moment to simulate four motions of flexion, extension, lateral bending and axial rotation respectively. The movement characteristics,joint stress force and ligament deformation was analyzed.</p><p><b>RESULTS</b>Under 1. 5 N . m moment, in model of atlas assimilation the C1-C2 range of movement decreased from 13. 55° to 11.88° in flexion,increased from 13. 22° to 15. 24° in extension and from 4. 05° to 4. 23° in lateral bending and remained unchanged in axial rotation when compared with the normal model. In flexion movement, the contact force of the atlanto-dental joint increased from 1. 59 MPa to 3. 28 MPa and the deflection of apical ligament, tectorial membrane and alar ligament increased 129. 1%, 157. 6% and 75. 1% respectively when compared with the normal model.</p><p><b>CONCLUSIONS</b>The normal C1-C2 motion mode is destructed in conditions of atlas assimilation, leading to the changes of the range of movement,joint stress force and the ligament deformation at C1 C2 junction. The atlantoaxial instability will likely occur in flexion motion.</p>