Influence Of The Fifth Lumbar Vertebrae Index Decrease On Interarticularis Stress By Finite Element Analysis

Objective: To establish two adults three-dimensional finite element model of L5, which had not lumbar disease, and to verify effectiveness of these models. To discuss the relation between decrease of L5 vertebral index and isthmus stress.Methods:We collected two adults lumbar CT datas, which had not lumbar disease. These L5 vertebral index were 70 and 90. The lumbar CT datas were used for separating and rebuliding L5 vertebral model by mimics 10.0 software. The rough reconstruction model was made optimized such as smooth and to create a surface model by importing geomagic11.0. It was created into solid model through importing UG software. Subsequently, the solid model was imported into ANSYS finite element software to divide into cortical bone and spongy bone and glue them together. The models were endowed for element type and different material properties. When the models were meshed, all nodes of the lowersurface and inferior articular process of the model were constrained in degree of freedom of all direction. And all nodes of the upper surface and superior articular process of the models were applied load step by step. At last, post-processing function of ANSYS could analyze L5 bilateral isthmus stress and calculate displacement of the model. We used statistical method to analyze stress datas by SPSS19.0 software.Results: 1. The finite-element model of L5 vertebral index 70 had 47147 elements and 71601 nodes. The finite-element model of L5 vertebral index 90 had 37895 elements and 57646 nodes. Through applying load to the model step by step, displacement datas were in the reference range of experimental dates of foreign literatures. 2. When we applied 500 N to the two models, isthmus stress value of matched group was 1.04±0.12 and isthmus stress value of reference group was 2.03±0.10(p<0.05). When we applied 1000 N to these two models, isthmus stress value of matched group was 2.30±0.22 and isthmus stress value of reference group was 3.29±0.34(p<0.05). When we applied 1500 N to these two models, isthmus stress value of matched group was 4.05±0.28 and isthmus stress value of reference group was 4.81±0.55(p<0.05). When we applied 2000 N to the models, isthmus stress value of matched group was 6.85±0.52 and isthmus stress value of reference group was 6.85±0.52(p<0.05). Applied 500 N, 1000 N, 1500 N and 2000 N, the resultsof isthmus stress value of matched group and that of reference group were both different(p<0.05).Conclusion: 1. We successfully established two finite element model of L5 vertebral index, which respectively were 70 and 90, and verified effectiveness of these two models. 2. The stress of L5 isthmus of small vertebral index was larger than that of L5 isthmus of large vertebral index. With load increasing, the stress of bilateral isthmus was increased. If isthmus of small L5 vertebral index was under a state of high load for a long time, L5 isthmus may easliy fracture.