Canadian Memorial Chiropractic College, Toronto, Ontario, Canada.
J Biomech. 2012 Feb 2;45(3):484-90. doi: 10.1016/j.jbiomech.2011.11.051. Epub 2011 Dec 21.
Despite the findings that peak anterior shear load is highly correlated with low-back pain reporting, very little research has been conducted to determine how vertebral shear injury potential is influenced. The current study quantified the combined effects of vertebral joint compression and flexion/extension postural deviation from neutral on ultimate shear failure. Ninety-six porcine cervical specimens (48C3-C4, 48C5-C6) were tested. Each specimen was randomly assigned to one of twelve combinations of compressive force (15%, 30%, 45%, or 60% of predicted compressive failure force) and flexion/extension postural deviation (extended, neutral, or flexed). Vertebral joint shear failure was induced by applying posterior shear displacement of the caudal vertebra at a constant rate of 0.15 mm/s. Throughout shear failure tests, vertebral joint kinematics were measured using an optoelectronic camera and a series of infrared light emitting diodes while shear force was measured from load cells rigidly interfaced in series with linear actuators that applied the shear displacement. Measurements of shear stiffness, ultimate force, displacement, and energy stored were made from the force-displacement data. Compressive force and postural deviation demonstrated main effects without a statistically significant interaction for any of the measurements. Shear failure force increased by 11.1% for each 15% increment in compressive force (p<0.05). Postural deviation from neutral impacted ultimate shear failure force by a 12.8% increase with extension (p<0.05) and a 13.2% decrease with flexion (p<0.05). Displacement at ultimate failure was not significantly altered by either compressive force or postural deviation. These results demonstrate that shear failure force may be governed by changes in facet articulation, either by postural deviation or by reducing vertebral joint height through compression that alter the moment arm length between the center of facet contact pressure and the pars interarticularis location. However, objective evidence of this alteration currently does not exist. Both compression and flexion/extension postural deviation should be equally considered while assessing shear injury potential.
尽管已经发现峰值前向剪切载荷与腰痛报告高度相关，但很少有研究确定椎体剪切损伤潜力是如何受到影响的。本研究定量分析了椎体关节压缩和屈伸姿势偏离中立位对最终剪切失效的综合影响。九十六个猪颈椎标本（48C3-C4、48C5-C6）进行了测试。每个标本都随机分配到十二种压缩力（预测压缩失效力的 15%、30%、45%或 60%）和屈伸姿势偏离中立位（伸展、中立或弯曲）的组合之一。通过以 0.15mm/s 的恒定速率施加尾椎的后向剪切位移来诱导椎体关节剪切失效。在整个剪切失效测试过程中，使用光电摄像机和一系列红外发光二极管测量椎体关节运动学，同时通过与线性致动器刚性接口的负载细胞测量剪切力，线性致动器施加剪切位移。从力-位移数据中测量剪切刚度、最终力、位移和存储能量。压缩力和姿势偏差对任何测量都没有表现出统计学上显著的相互作用的主要影响。压缩力每增加 15%，剪切失效力就会增加 11.1%（p<0.05）。与中立位相比，姿势偏离会使最终剪切失效力增加 12.8%（p<0.05），而弯曲会使最终剪切失效力减少 13.2%（p<0.05）。压缩力或姿势偏差都不会显著改变最终失效时的位移。这些结果表明，剪切失效力可能受关节突关节变化的影响，这种变化可以通过姿势偏差或通过压缩减小椎体关节高度来改变关节突关节接触压力中心和关节突间部位置之间的力臂长度来实现。然而，目前还没有这种变化的客观证据。在评估剪切损伤潜力时，应同时考虑压缩力和屈伸姿势偏差。
