Institute for Orthopaedic Research and Biomechanics, Ulm University, Helmholtzstraße 14, D - 89081 Ulm, Germany.
J Biomech. 2011 Apr 7;44(6):1164-9. doi: 10.1016/j.jbiomech.2011.01.018. Epub 2011 Feb 4.
Osteoporotic vertebral fractures constitute a major clinical problem in ageing societies. A third of all vertebral fractures is caused by falls, 15% by lifting heavy loads or traffic accidents and over 50% are not relatable to a traumatic event. In the latter case vertebrae show sinter processes which indicate the accumulation of damage and permanent deformation. Accumulated damage may not be visible on radiographs but increases the risk of fracture and could lead to vertebral collapse. Clear understanding of the accumulation of damage and residual strains and their dependence on loading mode and direction is important for understanding vertebral fractures. Altogether, 251 cylindrical samples (8×18-25mm) were obtained from 50 male and 54 female fresh frozen human vertebrae (T1-L3) of 65 (21-94) years. Vertebrae were randomly assigned to three groups cranial-caudal, anterior-posterior and latero-lateral. Specimens were mechanically loaded in compression, tension or torsion in five load steps at a strain rate of 0.2%/s. Three conditioning cycles were driven per load step. Stress-strain curves were reconstructed from the force-displacement or from the moment-twist angle curves. Damage accumulated from 0 to 86% in compression, from 0 to 76% in tension and from 0 to 86% in torsion through the five load steps. Residual strains accumulated from 0 to -0.008mm/mm in compression, 0 to 0.006mm/mm in tension and 0 to 0.026rad/rad in torsion. Significantly less damage (p<0.05) but not residual strains accumulated in transverse directions. This study provides detailed experimental insights into the damage behaviour of vertebral trabecular bone under various loads occurring in vivo. Damage but not residual strain evolution seems to be anisotropic. Both seem to evolve differently under different loading modes. The results could be of importance in understanding vertebral fractures.
骨质疏松性椎体骨折是老龄化社会中的一个主要临床问题。三分之一的椎体骨折是由跌倒引起的，15%是由提重物或交通事故引起的，超过 50%的骨折与创伤事件无关。在后一种情况下，椎体显示出烧结过程，表明损伤和永久变形的积累。在射线照相中可能看不到累积的损伤，但会增加骨折的风险，并可能导致椎体塌陷。清楚地了解损伤和残余应变的积累及其对加载模式和方向的依赖性对于理解椎体骨折很重要。总共从 50 名男性和 54 名女性新鲜冷冻人椎体（T1-L3）中获得了 65（21-94）岁的 251 个圆柱形样本（8×18-25mm）。椎体随机分配到三个组：颅尾、前后和侧侧。标本以 0.2%/s 的应变速率在压缩、拉伸或扭转中进行五次加载步的机械加载。每个加载步驱动三个调节循环。从力-位移或从力矩-扭角曲线重建应力-应变曲线。在五个加载步中，压缩中从 0 到 86%、拉伸中从 0 到 76%、扭转中从 0 到 86%，损伤逐渐积累。在压缩中从 0 到-0.008mm/mm、拉伸中从 0 到 0.006mm/mm、扭转中从 0 到 0.026rad/rad，残余应变逐渐积累。横向方向的损伤积累（p<0.05）但残余应变较小。本研究提供了详细的实验见解，了解体内发生的各种载荷下椎体松质骨的损伤行为。损伤但不是残余应变似乎是各向异性的。在不同的加载模式下，它们的演变似乎也不同。这些结果对于理解椎体骨折可能很重要。
