Finite Element Analysis Of Percutaneous Cement Discplasty Combined With Percutaneous Vertebroplasty

Background:Low back pain and mobility disorders caused by intervertebral disc degeneration in elderly patients are common clinical diseases in orthopedics.The intervertebral discs continue to degenerate with age,the nucleus pulposus degenerates and disappears(Vacuum Phenomenon),the intervertebral height decreases,the intervertebral foramen narrows and mechanical compression of the nerve roots occurs,which causes symptoms such as local pain and radiating pain in the lower limbs.The common surgical treatment method for this disease is spinal canal decompression combined with interbody fixation and fusion.However,for most elderly patients often complicated with cardiopulmonary diseases,diabetes and osteoporosis and other basic medical diseases,some patients cannot tolerate conventional surgical treatment and can only choose conservative treatment.But drugs and physical therapy have little effect because they cannot fundamentally solve the disease.The introduction of percutaneous cemented discoplasty(PCD)has attracted the attention of spine surgeons.Theoretically,the restoration of intervertebral height after PCD can relieve the compression of the foramicular root to achieve pain relief;However,some complications may occur,such as the fracture of the adjacent endplate and the spinal stenosis and nerve root compression caused by the insertion of the cement mass into the spinal canal have attracted people’s attention.The reason may be the insufficient vertebral strength of the adjacent vertebrae and the instability of the lumbar spine,so it is very important to enhance the strength of the adjacent vertebrae and improve the stability of the lumbar spine.Based on these reasons,three modified techniques were designed to strengthen the vertebral and anchor the cement mass,which maybe reduce the risk of vertebral fracture and bone cement prolapse.Objective:1.To develop a finite element model that can be used to study the mechanics of the lumbar spine.2.To design PCD and three modified surgical models(L4 vertebra,L5 vertebra percutaneous vertebroplasty combined with PCD,L4 and L5 double vertebra PVP combined with PCD),and to analyze the mechanical properties of the lumbar spine after PCD and the three modified surgical models by finite element analysis.3.Four treatment modalities,L4/5PCD,L4PVP combined with L4/5PCD,L5PVP combined with L4/5PCD,and L4 and L5 vertebral PVP combined with L4/5PCD,will be compared with finite element analysis in order to find the optimal mechanical performance solution.Materials and Methods:1.Modelling:A finite element model of the(L1-L5)whole lumbar spine was developed using multiple software based on CT data of the lumbar spine.Validation:The motion of the lumbar spine in 6 directions was simulated in the FEA software and the results were compared with in vitro experimental data reported in previous literature to verify the validity of the model.2.Different cement blocks(L4/5PCD,L4PVP+L4/5PCD,L4/5PCD+L5PVP,L4PVP+L4/5PCD+L5PVP)were designed and assembled into a validated finite element model of the lumbar spine for finite element analysis.3.Comparative analyses of lumbar mobility,stresses in the upper and lower endplates of adjacent vertebrae,stresses on the fibrous annulus and displacement of bone cement were performed under loads of 400 N concentrated force vertically downwards and 10 N·m torque for four different models in six active directions.Results:1.A finite element model of the lumbar spine was successfully established,and the results of the finite element analysis of the model were compared with the results of in vitro experiments reported in the previous papers,and the finite element model was within the range of validity,which can be used for the next step of the study.2.Four different experimental models(L4/5PCD,L4PVP+L4/5PCD,L4/5PCD+L5PVP,L4PVP+L4/5PCD+L5PVP)were designed and analyzed,and the mobility of the 4-5 segments of the lumbar spine in all four groups of models was substantially decreased compared to the normal lumbar spine,with L4PVP+L4/5PCD+L5PVP of the experimental group was the lowest mobility among the four groups of experimental models.3.In the six activity directions,the maximum stress values of the upper and lower endplates of the intervertebral space bone cement in all four groups were higher than those in the control model,but the maximum stress values of the endplates after PVP vertebral enhancement were reduced.The maximum stress value of the both of upper and lower endplates of the experimental group L4PVP+L4/5PCD+L5PVP were reduced.4.In the four experimental models,the maximum displacement of the cement and the maximum stress on the annulus of the L4PVP+L4/5PCD+L5PVP was minimized.For combining with single PVP,both models had less stress on the annulus than L4/5PCD,while the cement in L4PVP+L4/5PCDwas slightly more displaced than L4/5PCD.Conclusions:1.The established lumbar spine finite element model data was compared with previous in vitro experimental data and successfully passed validation,which can be.applied to lumbar spine mechanical testing and surgical simulation experiments.2.The modified procedure provides better lumbar stability compared to L4/5PCD,with the L4PVP+L4 5PCD+L5PVP group providing the best stability.3.The risk of endplate fracture increased after cement implantaton,,but the risk of endplate fracture is reduced after PVP vertebral augmentation,of which the risk of endplate fracture is lowest with double vertebral augmentation.4.The cement was anchored after modified surgery.The risk of cement dislodgement decreasing for the modified procedure,being lowest for L4PVP+L4/5PCD+L5PVP and then following L4/5PCD+L5PVP.5.L4PVP+L4/5PCD+L5PVP has the best mechanical environment which can not only reduce the risk of adjacent vertebral fragility fracture,but also reduce the risk of vertebral space cement prolapse.It may be a minimally invasive procedure for treatment with vacuum sign for symptomatic lumbar instabilty.