Digital Analysis Of Normal And Degenerative Cervical Intervertebral Disc

Objective: This study aims to reconstruct three-dimensional finite element numerical model of the normal cervical spine using the data of CT and MRI image data from a healthy adult man by computer technology and analysis the stress distribution of a normal cervical disc under different working conditions,to analysis biomechanical change through change material parameters of degenerative cervical disc. The finite element models of normal and degenerative cervical disc can serve as a research platform for the study of cervical spondylosis especially cervical disc herniation on mechanism, prevention, treatment, prognosis,development and evaluation of the artificial disc.Method: A young healthy male adult were selected as a volunteer for data collection. In the same position, spiral CT scan and MRI scans were performed respectively. The scanning range is set from 2cm above skull base to 2cm below the first thoracic vertebral. The image data of CT and MRI was saved in DICOM format and then was loaded into Mimics15.0(trial version) software. By using differen tools of Mimics15.0 software, we reconstructed three-dimensional models of cervical vertebral(C1-C7) and nucleus pulposus(C1-C7),respectively depending on the CT data and the MRI data.Then these models were imported in reverse engineering software Geomagic12.0,which were used to reconstructed the models of cervical disc, cervical terminalis, ligament and annulus fibrosus, respectively using bridge tool, offset function, offset function, boolean operations. The above models were loaded in Mimics15.0 and combined into a complete three-dimensional model of cervical vertebra,then meshed. Finally, the mesh model was imported in Ansys13.0 software.In Ansys13.0 software, by setting appropriate material properties and boundary conditions, the mesh model formed three-dimensional finite element numerical model of the normal cervical spine. To validate the finite element model,loading conditions were setted at C5-C6 level.To simulate cervical disc herniation, disc degeneration model at the C5-C6 segment was established after altering the material properties. The biomechanics analysis was performed using normal and degeneration model undering five working conditions, including axial compression, forward flexion, backward extension, lateral bending and axial rotation.Result: A accurate three-dimensional finite element numerical model of the normal cervical spine(C1-C7) was constructed, using CT and MRI scan image,by combined utilization of medical image processing software Mimics15.0(trial version), Geomagic Studio 12.0 and Ansys13.0, which contained seven vertebrae files, five disc nucleus pulposus files, ten terminalis files, five annulus fibrosus files, one anterior longitudinal ligament file, one posterior longitudinal ligament file and twelve yellow ligament files. The validated model had higher had high simulation and could be used in the following finite element stress analyses. Disc degeneration model was successfully constructed by altering the material properties. The biomechanics analyses of normal and degenerative model were carried out undering five working conditions,such as axial compression, forward flexion, backward extension, lateral bending and axial rotation. Thus the data of deformation displacement and equivalent stress nephogram about normal and degenerative cervical disc were obtained, The results were as follows :Undering axial force, the stress of normal cervical disc was concentrated on the posterior part, with the max stress in the mid point. After the degeneration of cervical discs, the deformation of the nucleus pulposus and annulus fibrosus decreased and deformation area moved backward, the stress of nucleus pulposus didn’t change significantly, the stress of terminalis increased,but the stress of the annulus fibrosus decreased significantly with the higher stress on the mid point of the posterior part than on the posterior lateral sides.Undering physiological activities such as forward flexion, backward extension, lateral bending and axial rotation, the overall stress distribution trend of degeneration disc was roughly identical to the one of normal disc. The stress of annulus fibrosus in normal disc showed that the stress on the mid point of the posterior part was higher than on the lateral sides. After the degeneration of cervical discs, the stress levels of the annulus fibrosus were higher than those of normal discs.But the stress distribution of annulus fibrosus were different:its stress distribution on the mid point of the posterior part undering backward extension and axial compression both were higher than on the posterior lateral sides, which were just the opposite of those undering forward flexion and lateral bending.Conclusion:1 A accurate three-dimensional finite element numerical model of the normal cervical spine(C1-C7) was developed.The validated model had higher simulation and could be used in the following the biomechanical analyses.2 A finite element model of disc degeneration at the C5-C6 segment was was successfully constructed by altering the material properties. Loads were conventional applied to simulate the displacement and equivalent stress changes of cervical disc undering different working conditions.Furthermore we confirmed that the stress of annulus fibrosus on the posterior lateral sides was significantly higher than on the mid point of the posterior part,undering forward flexion and lateral bending conditions,which showed that the posterior lateral sides of cervical disc were easily injured.