Lee Chu-Hee, Landham Priyan R, Eastell Richard, Adams Michael A, Dolan Patricia, Yang Lang
1 The Mellanby Centre for Bone Research, The University of Sheffield, Sheffield, UK.
2 Centre for Applied Anatomy, University of Bristol, Bristol, UK.
Proc Inst Mech Eng H. 2017 Sep;231(9):821-830. doi: 10.1177/0954411917708806. Epub 2017 May 6.
Finite element models of an isolated vertebral body cannot accurately predict compressive strength of the spinal column because, in life, compressive load is variably distributed across the vertebral body and neural arch. The purpose of this study was to develop and validate a patient-specific finite element model of a functional spinal unit, and then use the model to predict vertebral strength from medical images. A total of 16 cadaveric functional spinal units were scanned and then tested mechanically in bending and compression to generate a vertebral wedge fracture. Before testing, an image processing and finite element analysis framework (SpineVox-Pro), developed previously in MATLAB using ANSYS APDL, was used to generate a subject-specific finite element model with eight-node hexahedral elements. Transversely isotropic linear-elastic material properties were assigned to vertebrae, and simple homogeneous linear-elastic properties were assigned to the intervertebral disc. Forward bending loading conditions were applied to simulate manual handling. Results showed that vertebral strengths measured by experiment were positively correlated with strengths predicted by the functional spinal unit finite element model with von Mises or Drucker-Prager failure criteria ( R = 0.80-0.87), with areal bone mineral density measured by dual-energy X-ray absorptiometry ( R = 0.54) and with volumetric bone mineral density from quantitative computed tomography ( R = 0.79). Large-displacement non-linear analyses on all specimens did not improve predictions. We conclude that subject-specific finite element models of a functional spinal unit have potential to estimate the vertebral strength better than bone mineral density alone.
孤立椎体的有限元模型无法准确预测脊柱的抗压强度，因为在实际生活中，压缩载荷在椎体和神经弓上的分布是变化的。本研究的目的是开发并验证一个功能脊柱单元的患者特异性有限元模型，然后使用该模型从医学图像预测椎体强度。总共对16个尸体功能脊柱单元进行扫描，然后进行弯曲和压缩力学测试以产生椎体楔形骨折。在测试前，使用先前在MATLAB中使用ANSYS APDL开发的图像处理和有限元分析框架（SpineVox-Pro），生成具有八节点六面体单元的个体特异性有限元模型。将横观各向同性线弹性材料属性赋予椎体，将简单的均匀线弹性属性赋予椎间盘。应用前向弯曲加载条件来模拟人工搬运。结果表明，实验测得的椎体强度与采用冯·米塞斯或德鲁克-普拉格失效准则的功能脊柱单元有限元模型预测的强度呈正相关（R = 0.80 - 0.87），与双能X线吸收法测得的面积骨密度（R = 0.54）以及定量计算机断层扫描测得的体积骨密度（R = 0.79）呈正相关。对所有标本进行的大位移非线性分析并未改善预测效果。我们得出结论，功能脊柱单元的个体特异性有限元模型有潜力比单独的骨密度更好地估计椎体强度。
