Research Institute MOVE, VU University Amsterdam, Van der Boechorststraat 9, NL-1081 BT Amsterdam, The Netherlands.
J Biomech. 2012 Jun 26;45(10):1753-8. doi: 10.1016/j.jbiomech.2012.05.009. Epub 2012 May 28.
Experimental modal analysis is a non-destructive measurement technique, which applies low forces and small deformations to assess the integrity of a structure. It is therefore a promising method to study the mechanical properties of the spine in vivo. Previously, modal parameters successfully revealed artificially induced spinal injuries. The question remains however, whether experimental modal analysis can be applied successfully in human spinal segments with mechanical changes due to physiological processes. Since quasi-static mechanical testing is considered the "gold standard" for assessing intervertebral stiffness, the purpose of our study was to examine if the mechanical properties derived from vibration testing and quasi-static testing correlate. Six cadaver human spines (L1-L5) were loaded quasi-statically in bending and torsion, while an optical system measured the angular rotations of the individual motion segments. Subsequently, the polysegmental spines were divided into L2-L3 and L4-L5 segments and a shaker was used to vibrate the upper vertebra, while its response was obtained from accelerometers in anteroposterior and mediolateral directions. From the resulting frequency response function the eigenfrequencies (ratio between stiffness and mass) and vibration modes (pattern of motion) were determined. The vibration results showed clear eigenfrequencies for flexion-extension (mean 121.83Hz, SD 40.05Hz), lateroflexion (mean 132.17, SD 34.80Hz) and axial rotation (mean 236.17Hz, SD 81.45Hz). Furthermore, the correlation between static and dynamic tests was significant (r=0.73, p=0.01). In conclusion, the findings from this study show that experimental modal analysis is a valid method to assess the mechanical properties of human lumbar motion segments.
实验模态分析是一种无损测量技术，它应用低力和小变形来评估结构的完整性。因此，它是研究脊柱在体内力学性能的一种很有前途的方法。以前，模态参数成功地揭示了人为诱导的脊柱损伤。然而，问题仍然是，实验模态分析是否可以成功地应用于由于生理过程而导致机械变化的人体脊柱节段。由于准静态机械测试被认为是评估椎间刚度的“金标准”，因此本研究的目的是检验振动测试和准静态测试得出的力学特性是否相关。六个尸体人类脊柱（L1-L5）在弯曲和扭转中进行准静态加载，同时光学系统测量各个运动节段的角旋转。随后，将多节段脊柱分为 L2-L3 和 L4-L5 节段，并使用振动器振动上一个椎体，同时从前后和侧向方向的加速度计获取其响应。从得到的频率响应函数中确定固有频率（刚度与质量之比）和振动模式（运动模式）。振动结果显示出明显的屈伸（平均 121.83Hz，SD 40.05Hz）、侧屈（平均 132.17，SD 34.80Hz）和轴向旋转（平均 236.17Hz，SD 81.45Hz）固有频率。此外，静态和动态测试之间的相关性具有统计学意义（r=0.73，p=0.01）。总之，本研究的结果表明，实验模态分析是评估人类腰椎运动节段力学性能的有效方法。
