Finite element analysis of normal and compressed fracture models under different bending moments

HUANG Gui-xiong; LUO Shi-xing; JI De-peng

doi:10.3969/j.issn.1009-4237.2018.02.005

Abstract：Objective To establish a normal L1-3model and a L2vertebral compression fracture model,and to observe the differences in the stress's distribution of mechanical facet joints and intervertebral discs at different bending moments of two models by using finite element analysis.Methods The study took a healthy volunteer's lumbar three-dimensional CT scan images data,imported to Mimics 16.0,and established lumber 1 to lumber 3 finite element model,including:intervertebral disc,nucleus pulposus and annulus fiber,and removed the L2vertebra upper part based on the normal model to simulate L 2vertebra compression fracture model(I degree),then imported to Hy-permesh 13.0 for meshing.After that,those models were imported to Abaqus 14.2 to create volume meshing and lig-amentous structures.A 500N vertical force was applied on the L 1upper surface,and then the bending moments of 5Nom,10Nom and 15Nom were applied to simulate different magnitudes of flexion and extension.Finally,and the maximum stress and its distribution on L 1-2disc,L2-3disc,L1to L3facet joints were observed.Results The results showed that the compression fracture model,in all conditions,had higher stress than the normal model,and the maximum flexion stress was higher than extension.On the maximum disc stress distributions,from the first working condition to the seventh working condition,the maximum stress's distribution of L1-2of normal model was turning from at right-front of the disc to the left-rear,and the maximum stress's distribution of L1-2fracture model was from the front-left to right-rear.While the maximum stress's distribution of L2-3disc of the normal model and the vertebral compression fracture model were regularly from the right-rear to left-front,and finally,to the right-rear.Facet joint results showed that,from the first working condition to the seventh condition,all facet joints of two models'maximum stress values were expressed as descending,while then ascending.The facet joint maximum stress distribution was irregular.The majority of stress located in the lower right side of the fac-et.Conclusion Finite element analysis suggests that after lumbar compression fractures,the compressive stress of intervertebral disc and facet joint are higher than those of the normal ones,indicating that vertebral compression fracture may accelerate the spinal degeneration.Comparing with facet joint stress distribution,the disc has more regular one.The facet joint's irregular stress distribution may indicate that accelerated degenera-tion site in the posterior spinal column becomes uncertain after fracture.