Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom.
Department of Bioengineering, Imperial College London, London SW7 2AZ, United Kingdom.
Spine J. 2019 Dec;19(12):2013-2024. doi: 10.1016/j.spinee.2019.07.012. Epub 2019 Jul 18.
The use of finite element (FE) methods to study the biomechanics of the intervertebral disc (IVD) has increased over recent decades due to their ability to quantify internal stresses and strains throughout the tissue. Their accuracy is dependent upon realistic, strain-rate dependent material properties, which are challenging to acquire.
The aim of this study was to use the inverse FE technique to characterize the material properties of human lumbar IVDs across strain rates.
A human cadaveric experimental study coupled with an inverse finite element study.
To predict the structural response of the IVD accurately, the material response of the constituent structures was required. Therefore, compressive experiments were conducted on 16 lumbar IVDs (39±19 years) to obtain the structural response. An FE model of each of these experiments was developed and then run through an inverse FE algorithm to obtain subject-specific constituent material properties, such that the structural response was accurate.
Experimentally, a log-linear relationship between IVD stiffness and strain rate was observed. The material properties obtained through the subject-specific inverse FE optimization of the annulus fibrosus (AF) fiber and AF fiber ground matrix allowed a good match between the experimental and FE response. This resulted in a Young modulus of AF fibers (-MPa) to strain rate (ε˙, /s) relationship of YMAF=31.5ln(ε˙)+435.5, and the C parameter of the Neo-Hookean material model of the AF ground matrix was found to be strain-rate independent with an average value of 0.68 MPa.
These material properties can be used to improve the accuracy, and therefore predictive ability of FE models of the spine that are used in a wide range of research areas and clinical applications.
Finite element models can be used for many applications including investigating low back pain, spinal deformities, injury biomechanics, implant design, design of protective systems, and degenerative disc disease. The accurate material properties obtained in this study will improve the predictive ability, and therefore clinical significance of these models.
近几十年来，由于有限元（FE）方法能够量化整个组织内部的应力和应变，因此越来越多地用于研究椎间盘（IVD）的生物力学。它们的准确性取决于真实的、应变率相关的材料特性，而这些特性很难获得。
本研究旨在使用逆有限元技术来描述跨应变率的人类腰椎 IVD 的材料特性。
一项人体尸体实验研究与逆有限元研究相结合。
为了准确预测 IVD 的结构响应，需要对组成结构的材料响应进行预测。因此，对 16 个腰椎 IVD（39±19 岁）进行了压缩实验，以获得结构响应。对每个实验的 FE 模型进行了开发，然后通过逆 FE 算法运行，以获得特定于个体的组成材料特性，从而使结构响应准确。
实验观察到 IVD 刚度与应变率之间呈对数线性关系。通过对纤维环（AF）纤维和 AF 纤维基质的特定于个体的逆 FE 优化获得的材料特性，可以很好地匹配实验和 FE 响应。这导致 AF 纤维的杨氏模量（MPa）与应变率（ε˙，s）的关系为 YMAF=31.5ln(ε˙)+435.5，并且发现 AF 基质的 Neo-Hookean 材料模型的 C 参数与应变率无关，平均值为 0.68 MPa。
这些材料特性可用于提高在广泛的研究领域和临床应用中用于脊柱的 FE 模型的准确性，从而提高其预测能力。
有限元模型可用于多种应用，包括研究腰痛、脊柱畸形、损伤生物力学、植入物设计、保护系统设计和退行性椎间盘疾病。本研究中获得的准确材料特性将提高这些模型的预测能力和临床意义。
