Department of Chemical and Materials Engineering, University of Auckland, Level 8, Room 1.810, 20 Symonds Street, Auckland 1010, New Zealand.
Eur Spine J. 2010 Sep;19(9):1468-78. doi: 10.1007/s00586-010-1383-0. Epub 2010 May 1.
The role of torsion in the mechanical derangement of intervertebral discs remains largely undefined. The current study sought to investigate if torsion, when applied in combination with flexion, affects the internal failure mechanics of the disc wall when exposed to high nuclear pressure. Thirty ovine lumbar motion segments were each positioned in 2 degrees axial rotation plus 7 degrees flexion. Whilst maintained in this posture, the nucleus of each segment was gradually injected with a viscous radio-opaque gel, via an injection screw placed longitudinally within the inferior vertebra, until failure occurred. Segments were then inspected using micro-CT and optical microscopy in tandem. Five motion segments failed to pressurize correctly. Of the remaining 25 successfully tested motion segments, 17 suffered vertebral endplate rupture and 8 suffered disc failure. Disc failure occurred in mature motion segments significantly more often than immature segments. The most common mode of disc failure was a central posterior radial tear involving a systematic annulus-endplate-annulus failure pattern. The endplate portion of these radial tears often propagated contralateral to the direction of applied axial rotation, and, at the lateral margin, only those fibres inclined in the direction of the applied torque were affected. Apart from the 2 degrees of applied axial rotation, the methods employed in this study replicated those used in a previously published study. Consequently, the different outcome obtained in this study can be directly attributed to the applied axial rotation. These inter-study differences show that when combined with flexion, torsion markedly reduces the nuclear pressure required to form clinically relevant radial tears that involve cartilaginous endplate failure. Conversely, torsion appears to increase the disc wall's resistance to radial tears that do not involve cartilaginous endplate failure, effectively halving the disc wall's overall risk of rupture.
扭转在椎间盘力学紊乱中的作用仍未得到充分定义。本研究旨在探讨在高核压力下，扭转与屈曲结合应用时是否会影响椎间盘壁的内部失效力学。将 30 个绵羊腰椎运动节段分别置于 2 度轴向旋转加 7 度屈曲的位置。在保持该姿势的同时，通过放置在下方椎体纵轴上的注射螺钉，逐渐向每个节段的核内注入粘性放射状不透射线凝胶，直到发生故障。然后使用 micro-CT 和光学显微镜同时对节段进行检查。有 5 个运动节段未能正确加压。在其余 25 个成功测试的运动节段中，17 个发生了椎体终板破裂，8 个发生了椎间盘失效。成熟运动节段发生椎间盘失效的频率明显高于不成熟节段。椎间盘失效最常见的模式是涉及系统性环板-终板-环板失效模式的中央后向放射状撕裂。这些放射状撕裂的终板部分通常沿施加的轴向旋转的相反方向传播，并且在外侧边缘，只有那些倾向于施加扭矩方向的纤维受到影响。除了施加的 2 度轴向旋转外，本研究中采用的方法与之前发表的研究中采用的方法相同。因此，本研究中获得的不同结果可以直接归因于施加的轴向旋转。这些研究之间的差异表明，扭转与屈曲结合使用时，会显著降低形成涉及软骨终板失效的临床相关放射状撕裂所需的核压力。相反，扭转似乎增加了椎间盘壁对不涉及软骨终板失效的放射状撕裂的抵抗力，有效地将椎间盘壁的整体破裂风险降低了一半。
