Finite Element Analysis:Distribution And Dose Of Bone Cement On Recurrent Fracture Of Lower Lumbar Spine After PKP

Objective:Osteoporotic vertebral compression fracture(OVCF)is a common cause of pain and even disability in the elderly,and the incidence increases steadily with the increase of aging.Percutaneous kyphoplasty(PKP)is a common operation for clinical treatment of OVCFs.Some studies suggest that the poor distribution or dose of bone cement during PKP may increase the strength of the vertebral body and lead to local stress concentration,and even accelerate the degeneration of the adjacent vertebral body,resulting in the occurrence of adjacent vertebral body fracture(AVF).At present,there is no consensus on the distribution and dose of the best bone cement during PKP,and the relationship between the distribution and dose of bone cement and postoperative AVF is still controversial.In recent years,it has been found that there is a gradual increase in the number of patients with lumbar OVCFs.Compared with the thoracic vertebrae,the lumbar vertebrae are more active and the load of the supported spine is greater.Studies have shown that compression fractures in the lumbar region are more traumatic than those in the thoracic region.However,the previous biomechanical studies of OVCFs are mostly focused on the thoracolumbar vertebrae,while the biomechanical studies of the lower lumbar vertebrae are relatively few.Therefore,the lower lumbar segment of L3-S5 was selected as the research object to explore the biomechanical relationship between the distribution and dose of bone cement and lower lumbar spine,so as to provide a theoretical basis for clinical treatment of OVCFs and prevention of AVF.Methods:Using the method of finite element analysis,a three-dimensional finite element model(FEM)of normal human body L3-S5 was established,and the spinal state of patients with moderate osteoporosis was simulated by giving the corresponding material parameters to the model.A certain load was applied to the model to simulate the movement state of sudden fall of human body,and the data of vertical displacement,Von Mises stress and Von Mises strain of L3,L4 and L5 vertebrae were collected.Based on the above model,the PKP operation was simulated on the L4 vertebra of the model,and the three-dimensional finite element model of L3-S5 after PKP was established.According to the different distribution and dose of bone cement on L4 vertebral body,the reference volume index,distribution index and diffusion index simulated unilateral and bilateral pedicle approach at the same time,and the model was divided into 8groups.Under the same conditions,8 groups of models were loaded with the same load as before operation,and the biomechanical data were collected.Finally,the biomechanical data of each group before and after PKP were analyzed to study the effect of the distribution and dose of bone cement on the biomechanics of each vertebral body.Results:1.This study successfully established a three-dimensional finite element model of lumbosacral segment(L3-S5)of human osteoporotic spine.2.Compared with the data before PKP,the fracture volume of L4 vertebrae in each group after PKP decreased,and the maximum Von Mises strain and stress of L4 vertebrae changed greatly.3.Compared with the data before PKP,the fracture volume of L3 and L5 vertebrae increased after PKP,but the maximum Von Mises strain and stress of L3 and L5 vertebrae did not change significantly.4.There were differences in the volume ratio of L4 vertebral fracture,the maximum Von Mises stress and strain of cortical bone and cancellous bone between the 8 groups after PKP.The volume ratio of L3 and L5 vertebral fracture,the maximum Von Mises stress of cortical bone and cancellous bone are slightly different,and the maximum Von Mises strain is slightly different.Conclusion:1.PKP may have a certain effect on recurrent fractures of the operative vertebrae and adjacent vertebrae,and the effect on the operative vertebrae is to some extent related to the distribution and dose of bone cement.2.Under the action of instantaneous stress,PKP has less effect on adjacent vertebral re-fracture but greater influence on operative vertebral re-fracture,so the effect of long-term stress accumulation on AVF should be considered.3.At the same dose of bone cement,the symmetrical distribution of bone cement along the midline formed by bilateral pedicle approach was better than that of unilateral approach in the protection of operative vertebrae and adjacent vertebrae.4.Under different doses of bone cement,with the increase of the relative volume of bone cement,the protection of the operative vertebrae is strengthened,which has little effect on the adjacent vertebrae in a certain range,and the excess may increase the possibility of AVF.