【作者】 关海山；

【导师】 杨惠林；

【作者基本信息】 苏州大学 ， 骨外科学， 2007， 博士

【摘要】 椎体成形术(Vertebroplasty)和椎体后凸成形术(Kyphoplasty)治疗骨质疏松性椎体压缩骨折(osteoporotic vertebral compression fractures,OVCFs)所致的顽固性腰背痛,可以起到缓解疼痛、稳定伤椎、改善患者活动状况的目的。Kyphoplasty弥补了Vertebroplasty不能恢复椎体高度、纠正后凸畸形的缺陷,并且骨水泥渗漏率较低。Kyphoplasty和Vertebroplasty自应用临床以来取得了初步的令人鼓舞的临床效果,但是术后邻近椎体发生骨折时有报道,越来越引起临床医生的重视。Kyphoplasty和Vertebroplasty术后邻近椎体再骨折究竟是骨质疏松症的自然发生过程,或是手术干预、椎体强化的结果,或是二者兼而有之,临床和生物力学研究都仍未达成共识。第一部分胸腰椎节段有限元模型屈伸过程中肌肉力的模拟目的研究胸腰椎节段(T12-L1-L2)屈伸过程中竖脊肌力、椎间盘压力和椎体表面von Mises应力的变化。方法建立T12-L1-L2节段三维有限元模型,并采用离体生物力学实验资料来验证模型有效性。以Follower load代替节段间局部肌肉力的作用。分别在T12-L1-L2节段屈曲-10°、-5°、0°、5°、10°、15°、20°时,模拟上身重力(260N)、竖脊肌力以及Follower load(0、100、200N)作用,观察竖脊肌力、椎间盘压力和椎体表面von Mises应力的变化。结果随着T12-L1-L2节段屈曲角度增大,竖脊肌力、椎间盘压力以及椎体表面von Mises应力也随之逐渐增大。T12-L1-L2节段屈曲-10°、0°以及20°时,竖脊肌力分别需要0N、150N和410N才能维持平衡。Follower load可以减小竖脊肌力,并使椎间盘压力增高,但是对椎体表面von Mises应力影响不明显。如果忽略所有肌肉力作用,模型在纯弯矩作用下屈伸相同的角度,椎间盘压力和椎体表面von Mises应力将相应发生明显变化,较有肌肉力作用时明显降低。结论脊柱生物力学研究中不能忽视脊柱周围肌肉力的作用,胸腰椎屈曲角度和肌肉力影响椎间盘压力和椎体表面von Mises应力。如果忽略所有肌肉力的作用,椎间盘压力、椎体表面von Mises应力将会发生明显改变。Follower load代替节段间局部肌肉力作用,可以获得理想的椎间盘压力,使模拟脊柱真实载荷状况具有了可行性。第二部分骨质疏松椎体骨水泥强化之生物力学评估目的研究胸腰椎节段(T12-L1-L2)不同程度骨质疏松椎体预防性骨水泥强化对治疗椎体、邻近椎体以及椎间盘的生物力学影响。方法通过调整椎体松质骨、皮质骨的弹性模量建立不同程度骨质疏松的胸腰椎节段(T12-L1-L2)三维有限元模型,并模拟L1椎体经1.0GPa和3.0GPa两种弹性模量的骨水泥强化过程。观察在上身重力(260N)、竖脊肌力和Follower load(200N)作用下,轻度疏松、重度疏松模型L1椎体骨水泥强化前后治疗椎体、邻近椎体最大von Mises应力、椎间盘压力变化。结果骨质疏松使L1椎体的压缩刚度下降,经骨水泥强化以后椎体刚度和强度增加。骨质疏松对椎间盘压力、椎体最大von Mises应力影响较大。与正常骨质比较,轻度疏松模型的椎间盘压力增高22.6%,椎体皮质骨最大von Mises应力增高50.2%,重度疏松模型的椎间盘压力增高36.2%,椎体皮质骨最大von Mises应力增高77.7%。骨水泥强化以及骨水泥弹性模量差异对椎间盘压力、椎体最大von Mises应力影响较小。骨水泥强化使椎间盘压力增高2.2%-3.1%,邻近椎体皮质骨最大von Mises应力减小2.6%-4.6%,治疗椎体皮质骨最大von Mises应力增高4.6%-5.7%。结论骨质疏松影响胸腰椎节段的生物力学性质,使松质骨应力水平降低,弹性模量较高的椎体皮质骨承担较大的应力。椎间盘压力与骨质疏松程度、椎体皮质骨、松质骨应力分布有关。骨质疏松的胸腰椎节段经骨水泥强化以后,虽然治疗椎体的刚度、强度增加,承担了较大的应力,但是骨水泥以及骨水泥弹性模量差异对邻近节段椎体、椎间盘的应力水平以及应力分布影响十分有限。第三部分椎体成形术和椎体后凸成形术对邻近椎体、椎间盘的生物力学影响目的研究胸腰椎节段(T12-L1-L2)在L1椎体楔形骨折前、椎体成形术(Vertebroplasty)和后凸成形术(Kyphoplasty)后维持直立位所需要竖脊肌力,以及骨折椎体经骨水泥强化治疗以后椎间盘压力、邻近椎体终板最大von Mises应力变化。方法建立胸腰椎节段(T12-L1-L2)重度骨质疏松三维有限元模型,并模拟L1椎体楔形压缩骨折、Vertebroplasty和Kyphoplasty。在Vertebroplasty和Kyphoplasty模型中,L1椎体作为治疗椎体,其前缘高度分别较正常椎体降低35%和10%。研究在上身重力(260N)、竖脊肌力和Follower load(200N)作用下,T12-L1-L2节段L1椎体骨折前和Vertebroplasty、Kyphoplasty治疗后维持直立位所需的竖脊肌力,以及骨折椎体骨水泥强化以后椎间盘压力、邻近椎体终板最大von Mises应力变化。结果L1椎体楔形压缩骨折使上身重心位置前移,重力弯矩增大,因此需要竖脊肌力增大以恢复躯体平衡。如果上身重心位置没有代偿后移,与骨折前比较,Vertebroplasty和Kyphoplasty的竖脊肌力分别增高183%、56%;此时Vertebroplasty的椎间盘压力和终板最大von Mises应力增高60%,Kyphoplasty的椎间盘压力和终板最大von Mises应力分别增高22%、21%。如果上身重心位置代偿后移,竖脊肌力将会下降,椎间盘压力与终板最大von Mises应力相应降低。与骨折前比较,Vertebroplasty的椎间盘压力增高27%、终板最大von Mises应力增高39%,Kyphoplasty的椎间盘压力增高6.5%、终板最大von Mises应力增高10.1%。骨水泥强化对椎间盘压力、终板最大von Mises应力的影响很小,尚不及重心位置代偿以后脊柱额外载荷造成的的影响。结论椎体压缩骨折使重心位置向前转移,需要竖脊肌力增大以维持平衡,造成脊柱负载增加,因此,椎间盘压力和终板应力增高。椎体内注入骨水泥对邻近椎体终板应力、椎间盘压力影响较小。即使重力的位置发生代偿,由于脊柱负载增加,楔形骨折对椎间压力、终板应力的影响也远远高于骨水泥强化所造成的影响。Kyphoplasty恢复了椎体高度、纠正了后凸畸形,使重力弯矩、竖脊肌力减小,原本增高的椎间压力、终板应力降低。更多还原

【Abstract】 Chapter 1. Investigation of Muscle Forces for Flexion and Extension by Using a Finite Element Model of the Thoracolumbar SpineStudy Design. The muscle forces, intradiscal pressure, and von Mises stresses in the cortical bone were calculated using a finite element model of the thoracolumbar spine. Objectives. To investigate the trunk muscle forces during flexion and extension in the thoracolumbar spine and to determine their influence on intradiscal pressure and stresses in the cortical bone.Summary of Background Data. The spine is primarily stabilized by muscle forces. However, little is known about the influence of trunk muscle forces on the deformation of, and stresses in, the spine. In most studies, muscle forces are neglected.Methods. A three-dimensional finite element model of the ligamentous thoracolumbar spine was created. It was validated by use of experimental data from in vitro measurements on cadaver specimens. Good agreement between analytical and experimental results proved achievable. The model was loaded with the upper body weight (260N), a compressive follower load (0N, 100N, and 200N, respectively) to account for the local muscle forces, and a force in the m. erector spinae. The force in the m. erector spinae, intradiscal pressure, and stresses in the cortical bone were estimated during extension and flexion in the thoracolumbar spine.Results. The force in the m. erector spinae increased with the flexion angle. The estimated forces in the erector spinae were 0N for 10°extension, 150N for standing, and 410N for 20°flexion in the thoracolumbar spine. Intradiscal pressure and von Mises stresse in the cortical bone increased with the flexion angle, but were slightly influenced by extension. The force in the m. erector spinae was decreased, and intradiscal pressure was increased with increasing the follower load. Intradiscal pressure and stresses in the cortical bone will be changed considerably when the muscle forces were neglected and only a pure moment was applied.Conclusions. This study confirms that the muscle forces should not be neglected for biomechanical studies at the spine. The muscle forces have a strong influence on intradiscal pressure and stresses in the cortical bone during extension and flexion in the thoracolumbar spine. Applying a follower load instead of a great number of small forces simulating the local muscles makes realistic loading in vitro studies feasible.Chapter 2. Biomechanical determination of bone cement augmentation of osteoporotic vertebral body in the thoracolumbar spine Study Design. The effect of prophylactic bone cement augmentation on osteoporotic thoracolumbar spinal units was determined using finite element models.Objectives. To estimate the stress levels in the bone of treated and adjacent vertebral bodies following prophylactic bone cement augmentation.Summary of Background Data. Osteoporosis is the most frequent skeletal disease of the elderly, leading to weakness of the bony structures. Cement injection into vertebral bodies has been used to treat osteoporotic compression fractures of the spine. The clinical results are encouraging. However, it remains unclear whether adjacent vertebral body fractures are related to the natural progression of osteoporosis or if adjacent fractures are a consequence of bone cement augmentation. Experimental biomechanical studies showed significant increase in stiffness and strength of treated bodies.Methods. In finite element models of the ligamentous thoracolumbar spine different levels of bone tissue loss (moderate osteoporosis and severe osteoporosis) were simulated by changing the elastic modulus of the cortical and trabecular bone. The elastic modulus of bone cement inserted in the L1 vertebral body was varied between 1.0GPa and 3.0GPa. In order to simulate‘standing’, the models were loaded with the upper body weight (260N), a follower load (200N), and a case-dependent force in the m. erector spinae. The intradiscal pressure and stresses in the cortical and trabecular bone were investigated during standing. Results. L1 vertebral body compressive stiffness decreased when moderate osteoporosis and severe osteoporosis were simulated. The intradiscal pressure and von Mises stresses in the cortical and trabecular bone depended strongly on the grade of osteoporosis in the vertebral body. Intradiscal pressure increased by 22.6% for moderate osteoporosis, and by 36.2% for severe osteoporosis compared intact model. Maximum von Mises stress in the cortical bone increased by 50.2% for moderate osteoporosis, and by 77.7% for severe osteoporosis compared intact model. The effects of bone cement augmentation and elastic modulus of bone cement on intradiscal pressure and stresses in the adjacent cortical and trabecular bone were smaller. For the treated vertebral body stresses in the cortical and trabecular bone were increased.Conclusions. Osteoporosis may lead to decreased compressive stiffness and reduced spinal stability. The grade of osteoporosis has stronger effects on the biomechanical behavior of thoracolumbar spine. The effects of bone cement augmentation are much smaller.Chapter 3. Biomechanical Effects of Vertebroplasty and Kyphoplasty on Adjacent Vertebral Body and Intervertebral Disc Study Design. The effects of vertebroplasty and kyphoplasty on the adjacent vertebral body and intervertebral disc were investigated using finite element models of the thoracolumbar spine.Objectives. To estimate the force in the m. erector spinae, intradiscal pressure, and von Mises stresses in the endplates during standing for a severe osteoporotic thoracolumbar spine, as well as after vertebroplasty and kyphoplasty treatment.Summary of Background Data. Vertebroplasty and kyphoplasty are frequently used for internal stabilization of a fractured vertebral body. Fractures in the adjacent vertebral body after vertebroplasty or kyphoplasty do occur occasionally. A wedge-shaped compression fracture shifts the centre of gravity of the upper body anteriorly and generally. However, it is unclear how a wedge-shaped compression fracture of a vertebral body increases muscle forces and intradiscal pressure.Methods. A wedge-shaped L1 vertebral body was simulated in finite element models of the severe osteoporotic thoracolumbar spine. For the vertebroplasty and kyphoplasty model an anterior height reduction of 35% and 10%, respectively, related to the severe osteoporotic model were assumed. In order to simulate‘standing’, the models were loaded with the upper body weight (260N), a follower load (200N), and a case-dependent force in the m. erector spinae. The force in the m. erector spinae, intradiscal pressure, and von Mises stresses in the endplates were investigated during standing.Results. A wedge-shaped vertebral body shifted the centre of gravity of the upper body anteriorly. This increased the flexion bending moment and thus the force in the m. erector spinae necessary for balancing the spine. Without compensation of upper body shift, the force in the m. erector spine increased by 183% for vertebroplasty and by only 56% for kyphoplasty compared to the severe osteoporotic spine. Intradiscal pressure increased by 60% and 22% for vertebroplasty and kyphoplasty, respectively. Maximum von Mises stress in the endplates increased by 60% and 21% for vertebroplasty and kyphoplasty, respectively. In contrast, with shift compensation of the upper body, the increase in the muscle forces was much lower, increase in intradiscal pressure was only 27% and 6.5%, and increase in maximum von Mises stress in the endplates was only 39% and 10.1% for for vertebroplasty and kyphoplasty, respectively. Bone cement augmentation had a much smaller effect on intradiscal pressure and maximum von Mises stress in the endplates. Moreover the effect of upper body shift after a wedge-shaped vertebral body fracture on spinal load was more pronounced than that of stiffness due to cement infiltration.Conclusions. The advantages of kyphoplasty found in this study will be apparent only if nearly full fracture reduction is achieved. Our results do not suggest that the adjacent vertebral body fractures after vertebroplasty or kyphoplasty are caused by the higher stiffness of the treated vertebral body but by the anterior shift of the upper body.更多还原