Experiment Study Of Biomechanics On The Three-Dimension Finite Element Model Of The Degenerative Lumbar Spondylolisthesis

[Objective] To study the stress distribution and changes of the lumbar spondylolisthesis, to investigate the function of lumbar disc and facet joints in resisting lumbar displacement through studying the shear force, which can provide reference for the fellow study and clinical treatment.[Methods] The lumbar spondylolisthesis of a volunteer was obtained. CT sectional images of the L4-L5 spondylolisthesis were obtained by scaning L4-L5 motion segment. After the images operated by the computer, we artificially divided the L4-L5 spondylolisthesis into 662 units (including 1162 nodes) according to the 3D-finite division principle, and used computer software (Super-Sap 93) to create a 3D model. The loading on human's body in normal condition was calculated. When adding the relative loading on the model, the condition of 3 kinds of postures were imitated, such as flexion extension and vertical. The stress state of every segment of the L4-L5 spondylolisthesis was calculated, especially shear stress of lumbar disc and facet joints and Von Mises stress of the pars interarticularis. Discussed the action of every segment maintaining spine stability.[Results] According to the theory of three-column of spine, we studied the compressive stress of L4 and L5 vertebra in vertical condition. The compressive stress distributed in anterior segment of L4 vertebra was level with that in posterior (P>0.05). On the contrary, the compressive stress distributed in anterior segment of L5 vertebra was significantly greater than that in posterior (P<0.01). The shear stress distributed in intervertebral disc was increasing gradually from extension to flexion, but in statistics, the shear stress in extension has no difference with that in the vertical (P>0.05). Theshear stress in intervertebral disc mainly distributed annulus fibrosuses. In vertical and extension conditions, the shear stress distribution in the anterior segment of annulus fibrosuses has no difference by comparison with that in the P<0sterior, (P>0.05), but the shear stress on the anterior segment of annulus fibrosuses was significantly greater than that on the P<0sterior in flexion condution. Shear stress on facet joints was greater than that on intervertebral disc (P<0.05). Shear stress distributed in left facet joint was greater than that in right facet joint, especially in flexion condition (P<0.01). Shear stress on the facet joints in flexion and extension condition was greater than that in vertical condition, specially shear stress on the left facet joint had significant difference between three conditions (P<0.01). In any conditions, Von Mises stress on the pars interarticularis was greater than that on pedicles or lamina. Von Mises stress on the pars interarticularis in flexion or extension increased, and there was the most intensive stress in extension. We compared Von Mises stress on the pars interarticularis in extension with that in flexion or vertical, obtained great difference (P<0.05 or P<0.01).[Conclusion] 1 .After lumbar spine displacing toward anterior, the compressive stress transferred the P<0sterior parts to the anterior parts of the lower vertebral body.2. The shear stress on intervertebral disc increased in flexion, and mainly distributed in annulus fibrosuses. There was the most intensive shear stress on anterior parts of annulus fibrosuses.3. The shear stress on facet joints was significantly greater than that on intervertebral disc in flexion/ extension/vertical condition. The shear stress was different between left and right facet joint, which was relative to facet orientation.4. Von Mises stress on the pars interarticularis was significantly greater than that on pedicles or lamina, and Von Mises stress on the pars interarticularis was the most intensive in extension.