Mechanics Behavior Simulation And Creep Experiments Of Lumbar Intervertebral Disc

Lumbar intervertebral Disc has a porous viscoelastic properties,liquid in the nucleus pulposus can flow in or out from the tissue under the load,therefore it has the absorption energy and buffer function.The disc plays an important role in maintaining flexible movement and stability,dispersion and cushioning load.Under the action of external force,if the intervertebral disc annulus ruptures,the tissue of nucleus pulposus will prolapse,which leads to the adjacent spinal nerve root oppression or stimulation and caused lumbocrural pain symptoms.So lumbar disc herniation is a common clinical disease.Disc Herniation has close relationship with its mechanics behaviors,it is necessary to study the mechanical behaviors of interertebral disc under various loads,which will provide a theoretical basis for the prevention and clinical treatment of disc disease.In this paper,mechanical behaviors of the lumbar intervertebral disc were simulated by finite element method,the creep behavior was studied experimentally and the creep constitutive equation was established.In order to consider the effect of fluid-structure coupling in lumbar disc,based on Biot theory,a finite element model of L3/L4 segment of normal human lumbar intervertebral disc was created by ANSYS software.The mechanics responses of intervertebral disc under different loads were analyzed,the distribution and the comparison curves of pressure and stress of the different parts of the intervertebral disc were obtained.The results showed that outer annulus pressure was about 15% that of the inner layer and the outer maximum stress was about 4.3 times that of nucleus pulposus under axial compressed load;pressure increased linearly with the axial load increased at the same rates and stress increased at the different rates;the outer annulus stress increased the most obvious.When axial compressed and torsion loads were combined,the holistic annulus stress level was the largest and easiest to break.The creep behavior of the intervertebral disc under compression stress is studied by using the porous elastic finite element model in ABAQUS software.The displacement vs time curves was exponential,and the strain increases with the increase.Creep experiments with fresh porcine lumbar intervertebral disc were implemented under different compression stress and loading rate by an optimized digital image correlation(DIC)technique.The results show that creep curves of the intervertebral disc showed exponential rule change under the compression stress;creep strain increased with the increase of stress as the same loading rate;the larger the loading rate,the smaller the creep strain under the same stress.The constitutive equation of intervertebral disc established by using three-parameter viscoelastic model had good correlation with the experimental results.It can predict the creep properties of intervertebral disc.The research results provide a theoretical basis for furtherstudy of viscoelastic properties of human intervertebral disc in clinical.