Biomechanical Analysis Of Vertebral Augmentation In The Treatment Of Osteoporotic Vertebral Compression Fractures

With the increase in aging in China,the number of patients with osteoporosis is increasing,and the incidence of vertebral compression fractures is also increasing.Osteoporotic vertebral compression fractures(OVCFs)often result in a kyphotic deformity at the fracture site,which can seriously affect the patient’s quality of life and even lead to death.Vertebroplasty is a minimally invasive procedure that is widely used in the treatment of OVCFs.The procedure involves the injection of a certain volume of bone cement into the fractured vertebral body through the pedicle to achieve augmentation of the vertebral body,which can restore some of the lost height and strength of the vertebral body and significantly reduce the patient’s pain in the short term.However,it has been found that some patients develop other complications after vertebroplasty,such as secondary collapse of the vertebral body and leakage of bone cement,which are likely to be related to their postoperative vertebral body mechanical changes.Therefore,it is important to study the mechanism of vertebroplasty complications from the perspective of biomechanics to optimize the surgical plan and reduce the incidence of postoperative complications.The main contents of this study are divided into four parts as follows.(1)The biomechanical effects of the amount of bone cement injected during vertebroplasty on the vertebral body were investigated.Insufficient amounts of bone cement used in vertebroplasty can lead to insufficient strength recovery and recollapse of the fractured vertebral body,while excessive amounts of bone cement injection can result in cement leakage.There is no consistent conclusion on the amount of bone cement to be used in clinical practice.Therefore,in order to investigate the effect of bone cement injection volume on postoperative vertebral biomechanics,a finite element model of normal thoracolumbar spine,an osteoporotic fracture model and a surgical model containing different bone cement injection volumes(2 ml,4 ml and 6ml)were established and compared in this study.The results showed that both cortical and cancellous bone stresses in the vertebral body decreased with increasing bone cement volume in the same posture,but the trend of stress reduction slowed down with increasing bone cement volume,and the degree of stress reduction in the vertebral body in the 6 ml group model was similar to that in the 4 ml model.Postoperative bone cement stress also decreased with increasing bone cement volume,but intradiscal pressure and disc stress distribution were not influenced by bone cement volume.Conclusion: Enhancement of the vertebral body with 4 ml of bone cement reduces both the vertebral body stress and thus the risk of vertebral body refracture,and effectively reduces the probability of bone cement leakage due to excessive injection volume.(2)The biomechanical effects of different degrees of osteoporosis on the postoperative vertebral body were compared.Numerous studies have shown that secondary fractures occur in some patients after vertebroplasty,which may be related to the amount of bone cement injected.However,bone density is an important measure of vertebral strength and stiffness,and studies have shown that a significant portion of secondary fractures after surgery are also related to the patient’s own degree of osteoporosis.However the biomechanical mechanism is not clear.Therefore,in this section,finite element models of the thoracolumbar spine after vertebroplasty were developed for three different degrees of osteoporosis(mild,moderate,and severe),and the peak cortical bone stress,mean cancellous bone stress,and peak endplate stress were compared for each segment of the three models.The results showed that the risk of vertebral re-fracture after vertebroplasty was closely related to the degree of osteoporosis.As the degree of osteoporosis increased,the peak cortical bone stress and peak end-plate stress increased significantly in each segment of the vertebral body,while the mean cancellous bone stress decreased significantly leading to more severe bone loss,thus increasing the risk of vertebral body refracture.(3)The effects of different internal fixation methods on the postoperative biomechanics of the vertebral body were investigated.In clinical practice,vertebroplasty is prone to the risk of cement loosening and displacement in patients with severe osteoporosis,and the conventional nail bar system leads to reduced range of motion of the operated segment and causes a compensatory increase in adjacent vertebral stresses.Therefore,in this paper,we investigated a new type of cement anchor,which is hollow and has a screw design with lateral holes,which can both increase the binding force of the anchor and effectively prevent However,we do not know the biomechanical response of this anchor combined with cement reinforcement to the vertebral body.Therefore,in this study,we analyzed the biomechanical response of the new anchor on the vertebral body by establishing the vertebroplasty model(VFEM),the model of unilateral anchor combined with cement reinforcement(UA+Cement)and the model of bilateral anchor combined with cement reinforcement(BA+Cement)after osteoporotic vertebral compression fracture,and comparing the magnitude of vertebral stress and cement stress in the three groups of models.The biomechanical effects of the new anchors on the vertebral body were compared.The results showed that the BA+Cement group had the most significant reduction in vertebral stress and the best treatment effect among the three models,while the mean cancellous bone stress and endplate stress in UA+Cement tended to increase in some postures compared to the VFEM group.In the vast majority of postures(except posterior extension posture),the minimum values of cemented stresses were found in the BA+Cement group,while the large values were found in the UA+Cement group.In conclusion,according to our study,the levels of vertebral stress and cement stress were significantly lower in the BA+Cement group than in the other two groups,effectively reducing the risk of postoperative vertebral re-fracture and cement loosening.(4)The biomechanical effects of different anchor materials and different degrees of osteoporosis on the postoperative vertebral body after new anchor strengthening were analyzed.In this study,four groups of models with different materials of anchors performing unilateral and bilateral pedicle strengthening were established to compare the mechanical effects of different materials of anchors on the vertebral body;then three different degrees of osteoporosis,mild,moderate and severe,were designed on the basis of the postoperative model of anchors performing bilateral strengthening to investigate how different degrees of osteoporosis affect the mechanical properties of the vertebral body.The study showed that there was no significant difference in the effect of the two materials on the biomechanics of the vertebral body;in the same material anchor model,bilateral arch strengthening was better than unilateral,which was consistent with the results of the effect of different internal fixation methods on the postoperative biomechanics of the vertebral body in Chapter 5;the effect of different degrees of osteoporosis on the postoperative strengthening of the new anchor was consistent with vertebroplasty,and the postoperative cortical bone endplate stress of the vertebral body all increased with the degree of osteoporosis The postoperative cortical bone endplate stresses increase with the degree of osteoporosis,thereby increasing the risk of vertebral re-fracture.