骨质疏松椎体增强后对相邻椎体生物力学影响的有限元研究

Biomechanical effects of osteoporosis vertebral augmentation on the adjacent intervertebral levels using a three-dimensional finite element analysis

目的利用骨质疏松腰椎三维有限元模型,探讨椎体成形术中骨水泥的量、不同分布及骨水泥向椎间隙渗漏等对邻近椎体生物力学的影响。方法选取老年男性正常人体脊柱标本一具,范围为L_(4．5),建立L_(4．5)的三维脊柱功能单位的有限元模型。模拟骨水泥在椎体内的不同分布特点,观察不同压力方向时,相邻椎体终板的应力变化。结果不同骨水泥的量对邻近椎体生物力学的影响不大,但骨水泥分布不均匀和骨水泥在椎间隙的渗漏可导致邻近椎体的终板应力增加。结论椎体成形术后骨水泥分布不均匀和骨水泥渗漏到椎间隙可引起邻近椎体终板应力的集中,这可能是邻近椎体骨折的原因。进行椎体成形手术时建议骨水泥均匀分布,并避免渗漏到椎间隙。

Objective To investigate effects of volume, distribution and leakage of bone cement in vertebroplasty on the adjacent intervertebral bodies using an experimentally calibrated and anatomically accurate finite-element model of elderly L4-L5 vertebral bodies. Methods Computed tomography （CT） scanning was done, at 1 mm intervals, on L4-L5 vertebral bodies of the lumbar spine of an old man cadaver that had no abnormal findings on roentgenograms. The L4-L5 motion segment data were obtained from the CT scans to establish in computer a three-dimensional finite element model of L4-L5 functional spinal unit （FSU） with the software Ansys 7.0. Compressive load after virtual vertebroplasty on the damaged model, unipedicular and bipedicular injections and leakage of cement into the intervertebral space, and the resulting endplate and disc stresses of the adjacent vertebral bodies were analyzed in various spatial distributions of the filling material and different loading conditions. An anatomically accurate finite-element model of elderly L4-L5 vertebral bodies was developed. Results The FSU study suggested that changes in stress and strain at adjacent levels were minimal. Furthermore, endplate and disc stresses of the adjacent vertebral bodies were not influenced by bone cement filling volumes or distributions except under bending, whereas asymmetric distribution and leakage of bone cement to the disk increased the stress of adjacent endplates. Conclusion Since asymmetric distribution and significant leakage of cement into the intervertebral space can increase the stresses of endplates of adjacent vertebral bodies and may lead to a fracture, symmetric placement of cement in operation should be achieved and leakage of cement avoided.