Acaroglu E R, Iatridis J C, Setton L A, Foster R J, Mow V C, Weidenbaum M
Department of Orthopaedics and Traumatology, Hacetepe University, Ankara, Turkey.
Spine (Phila Pa 1976). 1995 Dec 15;20(24):2690-701. doi: 10.1097/00007632-199512150-00010.
Samples of human lumbar (L3-L4) anulus fibrosus from four different anatomic sites (anterior outer, posterolateral inner), ranging from normal to severely degenerate, were studied in uniaxial tension and measured for water content.
To evaluate the effects of aging and degeneration on the tensile properties and hydration of the anulus fibrosus in a site-specific manner. The relationship between hydration and parameters of the tensile behavior were investigated.
Degeneration and aging have been shown to be related to dramatic changes in the composition and structure of the anulus fibrosus. The associated changes in the tensile, compressive, and shear properties of the anulus fibrosus have not been documented. Numerical studies using finite element models have attempted to simulate the degenerative process by incorporating estimated mechanical properties meant to represent the degenerate anulus fibrosus. Their results present findings that suggest that altered material properties of the anulus fibrosus affect the mechanics of the entire intervertebral disc.
Samples of human lumbar anulus fibrosus were classified by grade of degeneration based on a morphologic grading scheme. Multiple layer anulus specimens from four sites in the disc were tested in uniaxial tension under quasistatic conditions in a physiologic saline bath. The tensile modules, Poisson's ratio, failure stress and strain, the strain energy density to failure, and the corresponding hydration were determined for each sample.
The Poisson's ratio, failure stress, and strain energy density of the anulus fibrosus were found to be affected significantly by degeneration, with some evidence of a sensitivity of the tensile modulus to grade of degeneration. All material properties were found to exhibit a significant and greater dependence on site within the disc than on degenerative grade. Weak correlations between aging and the Poisson's ratio and strain energy density were observed. Water content of anulus fibrosus tissue was not affected by degeneration or aging, although correlations with tensile properties were observed.
The dramatic changes in morphology, composition, and structure that occur in anulus fibrosus with aging and degeneration are accompanied by specific variations in the tensile properties, which were generally small in magnitude. Position of the anulus fibrosus within the intervertebral disc, particularly in the radial direction, appeared to be the most important variable affecting anulus fibrosus tensile properties. This dependence on position did not change with either aging or degeneration. Results from the present study may be useful in future finite element models to assess how altered material properties of the anulus fibrosus during degeneration and aging may affect the mechanics of the entire intervertebral disc.
对来自四个不同解剖部位（前外侧、后内侧）、从正常到严重退变的人腰椎（L3 - L4）纤维环样本进行单轴拉伸研究，并测量其含水量。
以部位特异性方式评估衰老和退变对纤维环拉伸性能及水合作用的影响。研究水合作用与拉伸行为参数之间的关系。
已表明退变和衰老与纤维环的组成和结构的显著变化有关。纤维环拉伸、压缩和剪切性能的相关变化尚未见文献报道。使用有限元模型的数值研究试图通过纳入估计的力学性能来模拟退变过程，这些力学性能旨在代表退变的纤维环。其结果表明纤维环材料性能的改变会影响整个椎间盘的力学性能。
根据形态学分级方案，将人腰椎纤维环样本按退变等级分类。在生理盐浴中准静态条件下，对椎间盘四个部位的多层纤维环标本进行单轴拉伸测试。测定每个样本的拉伸模量、泊松比、破坏应力和应变、破坏时的应变能密度以及相应的水合作用。
发现纤维环的泊松比、破坏应力和应变能密度受退变显著影响，有证据表明拉伸模量对退变等级敏感。所有材料性能对椎间盘内部位的依赖性显著且大于对退变等级的依赖性。观察到衰老与泊松比和应变能密度之间存在弱相关性。纤维环组织的含水量不受退变或衰老影响，尽管观察到其与拉伸性能相关。
随着衰老和退变，纤维环在形态、组成和结构上的显著变化伴随着拉伸性能的特定变化，这些变化幅度通常较小。纤维环在椎间盘中的位置，特别是在径向方向上，似乎是影响纤维环拉伸性能的最重要变量。这种对位置的依赖性不会随衰老或退变而改变。本研究结果可能对未来有限元模型评估退变和衰老过程中纤维环材料性能改变如何影响整个椎间盘的力学性能有用。
