Study On Viscoelastic Properties Of Lumbar Intervertebral Disc Under Vibration Load

Degenerative disc disease(DDD)is one of the most common diseases which brought a lot of inconvenience to the patient’s life and work.Long-term load is one of the most important reason to DDD,and the incidence of lumbar intervertebral disc in the vibration environment for a long time is higher than ordinary people.The health of the lumbar intervertebral disc directly affects the function of the spine and even the activities of the human body.Therefore,it is necessary to study the mechanical properties of lumbar intervertebral disc under vibration compression condition and provide theoretical basis for the prevention and treatment of lumbar disc disease.In this study,the viscoelastic properties of the lumbar intervertebral disc were studied in two aspects: animal experiments and finite element simulation.Creep and relaxation experiments were carried out by using the complete caprine lumbar intervertebral disc and Care universal fatigue test system,and the viscoelastic properties of the lumbar disc under different static compression and vibration compression conditions were studied.The results show that the creep strain curve and the relaxation stress curve of the lumbar intervertebral disc presents the index under compression strain under the compression conditions.In creep experiments,vibration increases the creep strain of lumbar intervertebral disc,and the strain increases with the rise of frequency and amplitude;In relaxation experiments,the vibration reduces the relaxation stress of the lumbar intervertebral disc,Higher frequency caused smaller relaxation stress.Under the condition of static compressive strain,the relaxation stress and speed of lumbar disc increase with the rise of strain.The relaxation constitutive model based on the three parameter model can predict the relaxation characteristics of lumbar intervertebral disc.According to the CT data,a poroelastic finite element model of the human spine L3-L4 segment was developed by ABAQUS,the mechanical properties of lumbar intervertebral disc under different compression were simulated using pore unit,creep strain,stress relaxation,Mises stress,pore pressure and other mechanical parameters of lumbar intervertebral disc were obtained,The simulation results fitted the experimental results.Under compression,the Mises stress of the annulus fibrosus(AF)are higher than that of the nucleus pulposus and the Mises stress of the posterior AF are greater than those of the anterior AF;the pore pressure of AF is greater than that of the nucleus pulposus,and the velocity of the posterior AF are greater than that of the anterior AF.The Mises stress,pore pressure and velocity of lumbar intervertebral disc got greater under vibration and increase with the rise of frequency and amplitude.The vibration made the fluid loss faster in the lumbar intervertebral disc and aggravated the injury of the lumbar intervertebral disc.