Analysis Of The Relativity Of The Material Attribute, Modality Attribute, Configuration Attribute Of Lumber Based On The 3D Modality Data Of MDCT And The Fracture Risk Using The Finite Element Method

Currently, the development of finite element analysis (FEA) has entered into the era in which the objective of study is shifting from physiological status to pathological status. At the beginning of pathological era of FEA, with the scarcity of the source of pathologic data, there are three major limitations in FEA study:analysis of one segment instead of the whole lumbar spine, analysis of only one case instead of the population with the same disease, analysis of pseudo-pathological status by simply assign abnormal material properties into an entirely morphologically normal lumbar spine.To overcome the limitations of the pathological era of FEA listed above, our study introduced a new method of study object selection, which included the whole lumbar spine instead of one segment; include multiple cases instead of solely one case, included typical pathologic cases instead of pseudo-pathological cases with normal morphology. The FEA study based on the genuine pathologic lumbar spine will reveal the actual stress distribution of pathologic status which is far more close to the reality. The pathological FEA study would provide us with a better understanding of pathologic status of spinal disease and corresp-onding biomechanical remote cause and subsequent prognosis.Materials and methods:(1) Case selection:The inclusion criterion of case selection is essential for the typical characteristics of morphological properties of the lumbar spine and subsequent accurate analysis of FEA study. During the past three years (from Jan.2008 to Dec.2010) 9670 lumbar CT examinations were taken and recorded in the PACS(picture archiving and communication system) and EMR (Electronic Medical Record) system in our hospital. The inclusion criteria for screening are fragile fractures (fractures happen from falling down at standing height) for senile fracture group, and young control group and senile non-fracture control group. The exclusion criteria are violent lumbar fractures (1301 cases), bone metabolism related diseases (such as hyperparathyroidism, nephritic bone disease, and so on), metastatic malignant tumors, primary spine tumors, hepatic cirrhosis, typeâ… diabetes, typeâ…¡diabetes. With the inclusion and exclusion criteria,751 cases were enrolled in our study for the first step of screening for fracture-related indices with significant statistical correlation. The screening and selection of the typical cases of lumbar spine was based on the three-dimensional lumber morphological data evaluated through the technique of MPR (multi-planer reconstruction), MIP (maximum intensity projection), and VR (volume rendering). There were 20 variants for each vertebra. The overall morphological variants of the whole lumbar spine were 104. The morphological variants of senile fracture group, senile non-fracture group and young control group were obtained and screened for fragile fracture related indices through logistic regression analysis.(2) The raw DICOM data of the lumbar spine underwent the processing of tissue mark, three dimensional cutting, three dimensional home-position, multi-planer reconstruction with the software of SYNGO on the Workstation of SIEMENS. After the DICOM data transmission from SYNGO to MIMICS, the models of lumbar spine were set up. The FEA analyses were carried out by the software of ABAQUS with the assignment of material properties for both vertebrae and intervertebral discs.(3) The FEA analysis of lumbar spine of different groups:The typical cases of each group were selected according to the median value of the correlated indices. To observe the effect of changes of material properties of the lumbar disc (disc degeneration) and the effect of changes of morphological properties (disc space narrowing) on the biomechanics of the lumbar spine in different groups of degeneration, four typical cases of models were established as wj, wj-f, zj, and dhy, respectively.(4) The FEA analysis of the correlation between the fracture risk and the degeneration of lumbar disc in senile females:The typical cases of each group were selected according to the median value of the correlated indices. To observe the effect of degree of intervertebral disc degeneration on the changes of biomechanics of lumbar spine, five typical cases of models were established as wj, wj-f, dhy, nfx, and ylq, respectively. The objective of this study was to observe the degree of disc space narrowing on the biomechanical changes of the lumbar spine without the interference of other factors. Therefore, the monofactorial analysis was guaranteed by the case selection with the same CT value, assignment of the same elastic modulus for the degenerated disc, with the sole variant of intervertebral disc height. Moreover, we should observe whether there was the cascade effect of higher fracture risk correlated with the fractures already existed on the vertebra T12.ResultsThe evaluation of the disc space shows that the risk of vertebral fracture increased with the severity of disc space narrowing. Based on the odds ratio (OR) for grade 0 disc space, the changes of OR value of grade 1 disc space and grade 3 disc space for L1 to L5 are listed below:from 1.18 to 39.11 in L1, from 1.56 to 12.8 in L2, from 2.67 to 9.9 in L3, from 1.94 to 12.68 in L4, from 1.39 to 7.95 in L5, respectively. The disc space of L1-2 showed the most evident negative correlation with vertebral fracture risk. In comparison with the cases of disc distance of posterior height (DPH) greater than 0.48cm in L1-2 disc, the cases of DPH less than 0.32cm in L1-2 disc showed an increase of 18.54 times of vertebral fracture risk.In the FEA study of different age groups, the stress distribution status of vertebral bodies, intervertebral discs and endplates were observed under different loading condition of neutral standing, flexion and extension. The FEA results of vertebral body, intervertebral disc and endplate showed that not only the degenerative changes of material property of the intervertebral disc had an effect on the stress distribution of the lumbar spine; morphological changes of vertebral body and intervertebral disc also played an important role in the stress distribution in lumbar spine between different age groups.In the FEA study of correlation between lumbar disc degeneration and vertebral fracture risk in senile groups, the stress distribution status of vertebral bodies, intervertebral discs and endplates were observed under different loading condition of neutral standing, flexion and extension. The FEA results showed that the more disc space height reduction, the more stress concentration. The cascade fracture risk increases in case of an existed vertebral fracture.Conclusions:Disc space narrowing showed an obvious positive correlation with vertebral fracture risk. Based on FEA biomechanical analysis, we present a further new point of view that not only the material properties, but also the morphological properties of both intervertebral discs and vertebrae, and even the macromorphology of the whole lumbar spine will play an important role in the biomechanical stress distribution of lumbar spine. We presented an until-now unrecognized new view on the interactive relations between pathological stress distribution and pathological structure and morphology. That is to say, pathological structure and morphology generates the pathological stress distribution, and the pathological stress distribution triggers further morphological and structural degeneration. The interactive relation of the spine (spine-vertebra-disc-vertebra-spine) increases the risk of osteoporotic vertebral fractures.The innovation points of our study:(1) The innovation of objective selection in FEA study:We carried out FEA study on the genuine pathologic cases to reveal the actual stress distribution of pathologic status which is far more close to the reality. Currently, the development of finite element analysis (FEA) has entered into the era in which the objective of study is shifting from physiological status to pathological status. At the beginning of pathological era of FEA, with the scarcity of the source of pathologic data, there are three major limitations in FEA study:analysis of one segment instead of the whole lumbar spine, analysis of only one case instead of the population with the same disease, analysis of pseudo-pathological status by simply assign abnormal material properties into an entirely morphologically normal lumbar spine. To overcome the limitations of the pathological era of FEA listed above, our study introduced a new method of study object selection, which included the whole lumbar spine instead of one segment; include multiple cases instead of solely one case, included typical pathologic cases instead of pseudo-pathological cases with normal morphology. The FEA study based on the genuine pathologic lumbar spine will reveal the actual stress distribution of pathologic status which is far more close to the reality. The pathological FEA study would provide us with a better understanding of pathologic stress distribution of lumbar spine and corresponding effect of pathologic stress distribution on the further degeneration of intervertebral discs and vertebrae. The innovation of objective selection in our FEA study enrolled the whole pathologic lumbar spine as objectives, which fulfill the genuine pathologic FEA study.(2) The innovation of scientific selection of typical cases:The typical case selection was based on the screening of 10 categories of 104 morphological indices, which could reflect the overall morphological properties of the lumbar spine. Fragile fracture related indices were determined through logistic regression analysis. The selections of typical cases in each group were determined according to the median value of the correlated indices. The scientific selection of typical cases was fulfilled through screening in a large sample with statistical analysis. The cases with indices at median values provided us with typical morphological and material properties, which could reflect typical biomechanical changes in FEA study. The screening and statistical analysis in case selection guaranteed us with a scientific, reliable and feasible source of data for FEA analysis. The typical biomechanical changes of typical cases would provide us with a better understanding of typical pathological stress distribution characteristics and the corresponding causes, development, and prognosis of the lumbar diseases.(3) The innovation of FEA model construction (automatic, standardized, and accurate construction of FEA model):Currently, as the most widely-used software in FEA model construction, MIMICS is limited in the functions of three- dimensional processing, which hindered the speed and accuracy of FEA model construction. Therefore, the feasibility of multi-segment analysis and large sample analysis is restricted. The model construction on the software of MIMICS is conducted manually. The margin between bone and soft tissue is discerned and cut manually slice by slice, which is not only time-consuming but also not accurate in tissue margin determination. The subjective error in margin determination will lead to loss of important data of image. The modern CT data are consisted of hundreds of slices, which made the work of model construction tedious with low accuracy. We innovatively introduced the method of three-dimensional image processing procedure on SYNGO 3D software of SIEMENS workstation before DICOM data transmission to the MIMICS. The raw DICOM data of the lumbar spine underwent the processing of automatic tissue mark, three dimensional cutting, three dimensional home-position, multi-planer reconstruction with the software of SYNGO on SIEMENS workstation. After the successful DICOM data transmission from SYNGO to MIMICS, the models of lumbar spine were set up. The technique of high-resolution automatic tissue mark and three dimensional cutting greatly improved the efficiency and accuracy of model construction in the FEA study. The time of model construction was ten times less than before. The automatic, standardized, and accurate construction of FEA model made it feasible for the multi-segment analysis and large sample analysis of lumbar spine.(4) The innovation of the results of FEA analysis:Based on FEA biomechanical analysis, we present a further new point of view that not only the material properties, but also the morphological properties of both intervertebral discs and vertebrae, and even the macromorphology of the whole lumbar spine will play an important role in the biomechanical stress distribution of lumbar spine. We present an until-now unrecognized new view on the interactive relations between pathological stress distribution and pathological structure and morphology. That is to say, pathological structure and morphology generates the pathological stress distribution, and the pathological stress distribution triggers further morphological and structural degeneration. The interactive relation of the spine (spine-vertebra-disc-vertebra-spine) increases the risk of osteoporotic vertebral fractures.The points of innovations listed above have not been reported up to date in the published literature both domestic and abroad.