Stefanakis Manos, Luo Jin, Pollintine Phillip, Dolan Patricia, Adams Michael A
*School of Science and Engineering, University of Nicosia, Cyprus †University of Roehampton, London, United Kingdom; and ‡Centre for Comparative and Clinical Anatomy, University of Bristol, Bristol, United Kingdom.
Spine (Phila Pa 1976). 2014 Aug 1;39(17):1365-72. doi: 10.1097/BRS.0000000000000389.
Mechanical study on cadaver motion segments.
To determine whether high gradients of compressive stress within the intervertebral disc are associated with progressive disc degeneration.
Mechanical loading can initiate disc degeneration but may be unimportant in disease progression, because degenerative changes cause the disc to be increasingly "stress-shielded" by the neural arch. However, the most typical feature of advanced disc degeneration (delamination and collapse of the annulus) may not depend on absolute values of compressive stress but on gradients of compressive stress that act to shear annulus lamellae.
A total of 191 motion segments (T7-T8 to L5-S1) were dissected from 42 cadavers aged 19 to 92 years. Each was subjected to approximately 1 kN compression, while intradiscal stresses were measured by pulling a pressure transducer along the disc's midsagittal diameter. "Stress gradients" in the annulus were quantified as the average rate of increase in compressive stress (MPa/mm) between the nucleus and the region of maximum stress in the anterior or posterior annulus. Measurements were repeated before and after creep loading and in simulated flexed and erect postures. Disc degeneration was assessed macroscopically on a scale of 1 to 4.
As grade of disc degeneration increased from 2 to 4, nucleus pressure decreased by an average 68%, and maximum compressive stress in the annulus decreased by 48% to 64%, depending on location and posture. In contrast, stress gradients in the annulus increased by an average 75% in the anterior annulus (in flexed posture) and by 108% in the posterior annulus (in erect posture). Spearman rank correlation showed that these increases were statistically significant.
Despite stress-shielding by the neural arch, gradients of compressive stress increase with increasing grade of disc degeneration. Stress gradients act to shear adjacent lamellae and can explain progressive annulus delamination and collapse.
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对尸体运动节段进行力学研究。
确定椎间盘内高梯度压应力是否与椎间盘进行性退变相关。
机械负荷可引发椎间盘退变，但在疾病进展过程中可能并不重要，因为退变改变会使椎间盘越来越多地被神经弓“应力屏蔽”。然而，晚期椎间盘退变的最典型特征（纤维环分层和塌陷）可能并不取决于压应力的绝对值，而是取决于作用于剪切纤维环薄片的压应力梯度。
从42具年龄在19至92岁的尸体上解剖出191个运动节段（T7 - T8至L5 - S1）。每个运动节段承受约1 kN的压缩力，同时通过沿着椎间盘矢状径拉动压力传感器来测量椎间盘内应力。纤维环中的“应力梯度”被量化为髓核与前或后纤维环最大应力区域之间压应力（MPa/mm）的平均增加率。在蠕变加载前后以及模拟屈曲和直立姿势下重复测量。通过宏观评估将椎间盘退变分为1至4级。
随着椎间盘退变等级从2级增加到4级，髓核压力平均降低68%，纤维环中的最大压应力根据位置和姿势降低48%至64%。相比之下，前纤维环（屈曲姿势）的应力梯度平均增加75%，后纤维环（直立姿势）的应力梯度平均增加108%。Spearman等级相关性显示这些增加具有统计学意义。
尽管存在神经弓的应力屏蔽，但压应力梯度随着椎间盘退变等级的增加而增加。应力梯度作用于剪切相邻薄片，可解释纤维环的进行性分层和塌陷。
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