| Degenerative lumbar disease is a common cause of low back pain. Patients, whohaving received ineffective conservative treatment, often require surgery for furthertreatment. The Spinal fusion surgery using screw-rod fixation system is the goldstandard of surgical treatment for lumbar degenerative disease. The internal fixationsystem can ensure the fusion between the vertebras, and the stability of the bridgesegment. However, spinal fusion surgery has been found could cause abnormalpressure in adjacent segments. In the adjacent segments of spinal surgery, the highstiffness of pedicle screw-rod system, possibly played a role in accelerating theprocess of degeneration. Therefore，non-fusion technologies have been proposed, andthe most representative internal fixation device is Dynesys. It replaces the titanium rodof crew-rod fixation system，which connecting ipsilateral pedicle screws，by a spacerand a rope. If its advanced design idea could bring a satisfactory effect in practicalapplication, curative effect; and if its preliminary application in foreign countries couldbe replicated in China, Is under extensive research.Objective:1.Build lumbar spine (L2-L5) finite element model, and verify itseffectiveness;2.Build Dynesys system and traditional screw-rod system implantinglumbar spine finite element model;3. Comparison among3models: apply the sametorques (flexion, extension, lateral bending, axial rotation) to the three kinds of models,calculate by the finite element analysis software, and compare intervertebral stress andROM of the3model (the standard model of lumbar spine, rigid fixation model,Dynesys dynamic fixation models) at the implanted level (L3-L4) and the cranialadjacent level (L2-L3);4.Comparison among different methods: preliminary comparethe results of present study，previous retrospective studies of our department and theresults in vitro studies.Methods:1. Build and validate L2-L5lumbar spine finite element model:choosing lumbar spine CT date of healthy male patients, using Mimics software tosegment tomographic images extracting bone and intervertebral disc, build a three-dimensional geometric model. Using HyperMesh mesh software to do thepre-process, such as meshing3D model, giving the material properties. Calculating byAbaqus software. Verifying the validity of the finite element model through the patternof disk annulus stress distribution,"compression force-displacement" curve.2. Buildand finite element analysis the models of Dynesys system and nails-rod system fixinglumbar: building the internal fixation models by Pro/Engineer software. Simulatingsurgical implanting the two kinds of internal fixation system models at L3-L4bymimics software. Comparing a geometrically simplified monosegmental dyamicfixation device and a rigid fixator for their effcts on intersegmental rotation, intradiscalpressure, facet joint forces.Results:1.We built L2-L5finite element model including vertebras, intervertebraldiscs, ligaments, and we also verified its effectiveness.2. We built Dynesys system andscrew-rod system fixing lumbar finite element models.3. Comparing with thestandard model of lumbar spine, in Dynesys dynamic fixation models，the range ofmotion of the implanted level was reduced by67%，the range of motion of the cranialadjacent level increased by11%；in rigid fixation model，the range of motion of theimplanted level was reduced by81.6%，the range of motion of the cranial adjacentlevel increased by21.3%. Dynamic neutralization system unloaded most of the stress,and caused a litter effect at the cranial adjacent level comparing with the standardmodel of lumbar spine. The effect on discs and facet joints stress causing by Dynesyssystem is between fixed and non-fixed by screw-rod fixation system.4. Thepreliminary results of Dynesys for the range of motion at the implanted level and thecranial adjacent level are similar to the published results of our department and theresults of others in vitro Experiment.Conclusion:1. Based on Quantitative Computed Tomography, we built a standardfinite element model of the lumbar spine that had passed the Validation.2. The Dynesyssystem can provide stability for implanted segment. Comparing with screw-rod system,Dynesys cause a litter effect on the range of motion, discs and facet joints stress at theimplanted level and cranial adjacent level. |
PDF Full Text Request