Colorado State University, Ft. Collins, CO, USA.
Acta Biomater. 2011 Feb;7(2):700-9. doi: 10.1016/j.actbio.2010.09.003. Epub 2010 Sep 8.
Spinal ligaments provide stability and contribute to spinal motion patterns. These hydrated tissues exhibit time-dependent behavior during both static and dynamic loading regimes. Therefore, accurate viscoelastic characterization of these ligaments is requisite for development of computational analogues that model and predict time-dependent spine behavior. The development of accurate viscoelastic models must be preceded by rigorous, empirical evidence of linear viscoelastic, quasi-linear viscoelastic (QLV) or fully nonlinear viscoelastic behavior. This study utilized multiple physiological loading rates (frequencies) and strain amplitudes via cyclic loading and stress relaxation experiments in order to determine the viscoelastic behavior of the human lower cervical spine anterior longitudinal ligament, the posterior longitudinal ligament and the ligamentum flavum. The results indicated that the cyclic material properties of these ligaments were dependent on both strain amplitude and frequency. This strain amplitude-dependent behavior cannot be described using a linear viscoelastic formulation. Stress relaxation experiments at multiple strain magnitudes indicated that the shape of the relaxation curve was strongly dependent on strain magnitude, suggesting that a QLV formulation cannot adequately describe the comprehensive viscoelastic response of these ligaments. Therefore, a fully nonlinear viscoelastic formulation is requisite to model these lower cervical spine ligaments during activities of daily living.
脊柱韧带提供稳定性，并有助于脊柱运动模式。这些水合组织在静态和动态加载状态下均表现出时变行为。因此，为了开发模拟和预测时变脊柱行为的计算模型，对这些韧带进行准确的粘弹性表征是必要的。准确的粘弹性模型的开发必须以前瞻性的、经验性的线性粘弹性、准线性粘弹性（QLV）或完全非线性粘弹性行为为基础。本研究通过循环加载和应力松弛实验，利用多个生理加载速率（频率）和应变幅度，以确定人下颈椎前纵韧带、后纵韧带和黄韧带的粘弹性行为。结果表明，这些韧带的循环材料性能取决于应变幅度和频率。这种依赖于应变幅度的行为不能用线性粘弹性公式来描述。在多个应变幅度下进行的应力松弛实验表明，松弛曲线的形状强烈依赖于应变幅度，这表明 QLV 公式不能充分描述这些韧带的综合粘弹性响应。因此，在日常生活活动中模拟这些下颈椎韧带需要使用完全非线性粘弹性模型。
