Abstract
In this paper, the displacement and the strain behaviors under a forward bending moment at a spine model that consists of four vertebras and three intervertebral discs were investigated. The spine model used for the measurement test is calf's lumbar vertebra. Intervertebral discs that compose a spine are main elements that enable free movement of a human body, and they also play roles of a buffer corresponding to the load applied to the spine. In consideration of such a fact, we tried to measure an overall deformation behavior of the spine and a detailed strain distribution of an intervertebral disc simultaneously, and the relation of the bending deformation of the spine and the strain behavior of the intervertebral disc was examined. The spine is considered as if a structure consists of solid vertebras linked by flexible intervertebral discs, the bending angle at the intervertebral disc was obtained from the overall deformation of a test spine that has been measured with laser displacement sensor at typical points. On the other hand, detailed displacements distribution on a surface of the intervertebral disc was measured by Electronic Speckle Pattern Interferometry (ESPI) method, and strain distribution were calculated based on the displacements distribution. The results showed that although changes of the strain in the vertebral body area were little, the strain concentration at the intervertebral disc became larger according to an increase of forward bending moment. Moreover, compressive strain on the side of the belly of the intervertebral disc was measured, and tensile strain on the backed side was observed. In addition, the relation between the bending angle at the intervertebral disc that dominated overall deformation of a spine and maximum strain value obtained at the surface of the intervertebral disc was shown.
