Department of Orthopaedic Surgery, University of California, San Francisco, CA 94143, USA.
J Biomech. 2010 May 7;43(7):1422-5. doi: 10.1016/j.jbiomech.2010.02.004. Epub 2010 Feb 23.
In vitro multi-axial bending testing using pure moment loading conditions has become the standard in evaluating the effects of different types of surgical intervention on spinal kinematics. Simple, cable-driven experimental set-ups have been widely adopted because they require little infrastructure. Traditionally, "fixed ring" cable-driven experimental designs have been used; however, there have been concerns with the validity of this set-up in applying pure moment loading. This study involved directly comparing the loading state induced by a traditional "fixed ring" apparatus versus a novel "sliding ring" approach. Flexion-extension bending was performed on an artificial spine model and a single cadaveric test specimen, and the applied loading conditions to the specimen were measured with an in-line multiaxial load cell. The results showed that the fixed ring system applies flexion-extension moments that are 50-60% less than the intended values. This design also imposes non-trivial anterior-posterior shear forces, and non-uniform loading conditions were induced along the length of the specimen. The results of this study indicate that fixed ring systems have the potential to deviate from a pure moment loading state and that our novel sliding ring modification corrects this error in the original test design. This suggests that the proposed sliding ring design should be used for future in vitro spine biomechanics studies involving a cable-driven pure moment apparatus.
体外多轴弯曲测试采用纯力矩加载条件已成为评估不同类型手术干预对脊柱运动学影响的标准方法。简单的缆索驱动实验装置已被广泛采用，因为它们所需的基础设施很少。传统上，采用了“固定环”缆索驱动设计；然而，人们一直担心这种设置在施加纯力矩时的有效性。本研究涉及直接比较传统“固定环”装置与新型“滑动环”方法引起的加载状态。在人工脊柱模型和单个尸体标本上进行屈伸弯曲测试，并使用在线多轴力传感器测量施加在标本上的加载条件。结果表明，固定环系统施加的屈伸力矩比预期值低 50-60%。这种设计还会产生相当大的前-后剪切力，并且在标本的长度上会产生不均匀的加载条件。本研究的结果表明，固定环系统有可能偏离纯力矩加载状态，而我们的新型滑动环修改纠正了原始测试设计中的这个错误。这表明，在涉及缆索驱动纯力矩装置的未来体外脊柱生物力学研究中，应采用所提出的滑动环设计。
