Department of Mechanical Engineering, University of Bath, Bath, United Kingdom.
Spine (Phila Pa 1976). 2010 Feb 15;35(4):386-94. doi: 10.1097/BRS.0b013e3181b0ef26.
Mechanical testing of cadaveric spines.
To test the hypothesis that, in the ageing spine, vertebrae deform more than discs, and contribute to time-dependent creep.
Intervertebral discs and vertebrae deform under load, narrowing the intervertebral foramen and increasing the risk of nerve root entrapment. Little is known about compressive deformations when elderly spines are subjected to sustained physiologic loading.
A total of 117 thoracolumbar motion segments, aged 19 to 96 yrs (mean, 69), were subjected to 1kN compressive loading for 0.5, 1, or 2 hours. Deformations during the first 7 seconds were designated "elastic" and subsequent deformations as "creep". A 3-parameter model was fitted to experimental data in order to characterize their viscous modulus E1, elastic modulus E2 (initial stiffness), and viscosity eta (resistance to fluid flow). Intradiscal pressure (IDP) was measured using a miniature needle-mounted transducer. In 17 specimens loaded for 0.5 hours, an optical MacReflex system measured compressive deformations separately in the disc and each vertebral body.
On average, the disc contributed 28% of the spine's elastic deformation, 51% of the creep deformation, and 38% of total deformation. Elastic, creep, and total deformations of 84 motion segments in 2-hour tests averaged 0.87, 1.37, and 2.24 mm respectively. Measured deformations were predicted accurately by the model (average r2 = 0.97), but E1, E2, and eta depended on the duration of loading. E1 and eta decreased with advancing age and disc degeneration, in proportion to falling IDP (P < 0.001). Total compressive deformation increased with age, but rarely exceeded 3 mm.
When the ageing spine is compressed, vertebral bodies show greater elastic deformations than intervertebral discs, and creep by a similar amount. Responses to axial compression depend largely on IDP, but deformations appear to be limited by impaction of adjacent neural arches. Total compressive deformations are sufficient to cause foraminal stenosis in some individuals.
尸体脊柱的力学测试。
验证假设，即在老年脊柱中，椎体比椎间盘更容易变形，并导致与时间相关的蠕变。
椎间盘和椎体在负荷下变形，使椎间孔变窄，增加神经根受压的风险。对于老年人的脊柱在持续生理负荷下的压缩变形知之甚少。
共对 117 个胸腰椎运动节段（年龄 19-96 岁，平均 69 岁）进行 1kN 的压缩加载 0.5、1 或 2 小时。前 7 秒的变形指定为“弹性”，随后的变形为“蠕变”。采用三参数模型对实验数据进行拟合，以描述其粘性模量 E1、弹性模量 E2（初始刚度）和粘度 η（抵抗流体流动的能力）。使用微型针式安装换能器测量椎间盘内压（IDP）。在 17 个加载 0.5 小时的标本中，光学 MacReflex 系统分别测量椎间盘和每个椎体的压缩变形。
平均而言，椎间盘贡献了脊柱弹性变形的 28%，蠕变变形的 51%和总变形的 38%。2 小时测试中 84 个运动节段的弹性、蠕变和总变形平均分别为 0.87、1.37 和 2.24mm。模型准确地预测了测量的变形（平均 r2=0.97），但 E1、E2 和 η 取决于加载的持续时间。E1 和 η 随年龄和椎间盘退变而降低，与下降的 IDP 成比例（P<0.001）。总压缩变形随年龄增长而增加，但很少超过 3mm。
当老年脊柱受压时，椎体的弹性变形比椎间盘大，蠕变也相似。对轴向压缩的反应在很大程度上取决于 IDP，但变形似乎受到相邻神经弓撞击的限制。总压缩变形足以导致一些个体椎间孔狭窄。
