Mechanisms of changes in the human spinal column in response to static and dynamic axial mechanical loading

The purpose of this study was to analyze the characteristics of the reaction of the human spinal column to axial static and dynamic loading. Segments of human column from dorsal vertebra XI to lumber vertebra III were exposed to axial static (20 mm/min) and dynamic (200 and 500 mm/min) loading. The measured variables included the load value, whole segment deformation, deformation of the anterior surfaces of intervertebral disk of Th XI –Th XII and dorsal vertebra XII, and acoustic emission signals (indicator of spongy bone microdestruction). It was found that the rate of increase in body deformation is lower than that in the intervertebral disk deformation and that the central parts of the spinal end plate compress greater than the peripheral parts. This difference was larger during static loading than that during dynamic loading. To produce the same deformation of a spinal segment due to dynamic loading as that due to static one, it is necessary to overcome a stronger resistance of a greater number of trabecular bones than that due to static loading. Therefore, it can be concluded that, first, the value of dynamic loading causing the same segment compression should be higher than the value of static loading, and the main practical significance here is that the dynamic strength of the column is markedly higher than the static one; second, spinal hardness during impact is higher than that under the static condition; and, third, the same degree of deformation should result in a larger volume of microdestructions in the case of dynamic loading than that in the case of static loading, which is evidenced by a significant difference in the number of AE signals accumulated prior to fracture. The number of AE signals is 444.2 ± 308.2 and 85.0 ± 36.6 in the case of dynamic and static loading, respectively ( p < 0.05 according to Student’s t test).