A Correlation Study Between Intervertebral Disc Degeneration And Vertebral Fracture Cascade

Part ?A Finite Element Analysis of Adjoining Vertebrae Biomechanical Changes Following Intervertebral Disc DegenerationObjective: To create a finite element model of a human lumbar segment and analyze the effects of the different stages of intervertebral disc degeneration on the stress distribution in the adjacent vertebrae.Methods: We obtained the normal lumbar segment geometry from a healthy 24-male volunteer based on a high resolution computer tomography(CT)scan with a slice thickness of 0.699 mm.All computer tomography scan images were first put out in dicom format and then put into three-dimensional reconstruction software mimics-17.The bone structure of L2-4 lumbar segment was reconstructed in mimics-17 based on the CT scan images.The 3D model was then input into forward engineering software 3-matic 9 for surface smoothing and intervertebral disc building.The endplates,nucleus and annulus constituting discs were built based on the anatomical structure from human intervertebral disc.All parts of L2-4 3D model were then put into Abaqus CAE for material properties assignation,parts assembling and step,interaction and boundary condition managing.The finite element would be computed after meshing.In addition to the healthy disc,three different simplified grades of disc degeneration(mild,moderate and severe)were created.We modeled these degenerated discs by decreasing nucleus size and disc height,accompanied by nucleus hardening modeled by increasing Young's modulus.We modeled the mild disc degeneration by increasing nucleus Young's modulus,the moderate degeneration by decreasing nucleus size and increasing Young's modulus,the severe degeneration by decreasing nucleus size and disc height accompanying with Young's modulus increase.A compressive load of 500 N was put on the upper surface of L2 for modelling the lumbar loading on standing.The stress distribution in the adjacent vertebrae was analyzed during different stages of intervertebral disc degeneration.Results: The validation of material model of L2-4 was performed for compression.The distribution of compressive stress in L3-4 intervertebral disc for health disc was 0.1-0.2MPa,and for severe degeneration disc was 0.06-0.09 MPa,which demonstrated high bio-fidelity in disc pressure on human standing posture.A healthy intervertebral disc distributes spinal loads evenly on adjacent vertebrae and the maximum stress on the posterior and anterior part in the down surface of L3 was 1.0 MPa and 0.8 MPa respectively.The maximum stress distribution in the anterior part of L3 gradually narrowed in consisting with the grade of disc degeneration.In severe disc degeneration,the maximum stress distribution in the posterior part of L3 enlarged accompanying with the maximum stress distribution in the anterior part narrowed.More compressive load was observed transferring from the anterior part to the posterior part in the sagittal stress nephogram.Conclusion: This finite element model was validated for analyzing the stress distribution changes on adjacent vertebrae affected by disc degeneration.Disc degeneration transfers compressive load bearing from the anterior vertebral body to the posterior in upright postures.Part ? An Experimental Study of Vertebral Trabecular Structure Changes Following Intervertebral Disc DegenerationObjective: To analyze the regional changes of vertebral trabecular structure following disc degeneration loaded rat tail vertebrae.Methods: Thirty Sprague-Dawley rats were randomly assigned into five groups of equal size.Group 1 served as an assessment of disc degeneration induced by needle puncture.A18-gauge needle was inserted in the coronal plane at the level of the annulus fibrosus of Co8-10 and Co9-10,Co7-8 and Co10-11 as the control level.Group 2 served as the sham group for trabecular structure analysis.Group 3,rats were bent between the eighth and tenth coccygeal vertebrae.Two wires were fixed at a 40° angle on the concave side of the bending tail.Groups 4,rats were bent with a compression load of 4.5 N.Group 5,rats were bent with a compressive load of 4.5 N following disc degeneration induced by needle puncture.Magnetic resonance imaging,histological examination and gene expression analysis were performed on discs in group 1 at day 7 after the needle puncture.The ninth coccygeal vertebrae of rats assigned to Groups 2-5 were scanned by Micro-Computed Tomography after 14 days.The differences in trabecular bone structure between Group 2-5 were assessed by bone volume fraction(BV/TV),trabecular number(Tb.N),trabecular thickness(Tb.Th)and trabecular separation(Tb.Sp).Results: Magnetic resonance imaging,histological and gene expression results showed significant degenerative changes in needle-punctured discs compared with adjacent control discs(P<0.05).The group 5 showed significant increases in BV/TV,Tb.N and Tb.Th and a decrease in Tb.Sp compared with the group 2-4(P<0.05).Vertebral trabecular structure in the concave region improved significantly whereas the convex region was of significant lower trabecular bone quality with disc degeneration.The difference of trabecular bone quality between the convex and concave region increased significantly following loading and disc degeneration.The difference of trabecular bone quality in the convex and concave region between group 2 and group3 was not significant(P>0.05).Conclusion: This model is useful to assess the relationship between disc degeneration and trabecular bone structure changes under loading conditions.Disc degeneration promotes vertebral trabecular structure regional inhomogeneity.The convex region of the vertebrae has the lower trabecular bone quality than the concave region.Part ? Age-Related Sagittal Structure Changes on Human Lumbar Intervertebral Disc and Vertebral bodyObjective: To observe the age-related sagittal structure changes on lumbar discs and vertebrae,analyze the relationship of structure changes between discs and vertebrae and compare the difference between men and women.Methods: A total of 17098 people with lumbar magnetic resonance images were collected by PACUS medical software from January 2010 to December 2015 in our hospital outpatient.Lumbar MRI images with disc degeneration of grade ?or ? were included in the study according to Pfirmann disc degeneration classification.MRI images with disc herniation or vertebral fracture or spinal deformity or tumor were excluded from the study.Ten people were included in each age from 20-64 both in men and women.All lumbar MRI images were put out in Dicom format and then put into Mimics 17 software for sagittal structure measurement.The anterior,middle and posterior disc and vertebral height and disc space angle,lumbar lordosis angle,the global lumbosacral angle and funnel angle were measured.The differences of structure changes in every five years and differences between men and women were compared.The relationship of structure changes between discs and vertebrae were analyzed.Results: Lumbar disc middle height increased by aging.The differences of disc middle height changes from L1-L5 between men and women were not significant(P>0.05),whereas L5-S1 disc middle height increased much in men more than in women(P<0.001).The vertebral middle height of L1,L2 and L5 decreased significantly by aging in men than in women(P<0.05),where the differences of L3 and L4 were not significant(P=0.54 and 0.12 respectively).Linear relationships were found between disc and vertebral structure changes both in men and women(RR=-0.74 and-0.65 respectively).Disc space angle,lumbar lordosis angle,the global lumbosacral angle and funnel angle increased by aging but the differences between men and women were not significant(P>0.05).Conclusion: Sagittal structures of lumbar spine changed by aging.Linear relationships were found between disc middle height increase and vertebral middle height decrease.Part ? A Clinic Analysis of Vertebral Fracture CascadeObjective: To observe the clinical characteristics of vertebral fracture cascade,analyze the relationship between the baseline fractures and the subsequent fractures and compare the distribution of subsequent fracture following vertebral augmentation or conservative treatment.Methods: 1363 patients admitted in our hospital with vertebral fracture were retrospectively analyzed from July 2012 to August 2016.There were a total of 190 patients with vertebral fracture cascade,160 cases of female and 30 cases of male.The minimum and maximum age was 54 and 95 respectively with average age 73.9±9.4.The location and sequence of all baseline and subsequent vertebral fractures were record.According to different treatment on baseline vertebral fracture,the patients were divided into vertebral augmentation group and conservative treatment group.The relationship between the baseline and subsequent fractures were analyzed and the different distributions of subsequent fracture following vertebral augmentation and conservative treatment were compared.Results: There were 293 baseline vertebral fractures and 275 subsequent fractures,which mainly located in thoracolumbar spine T11-L2 with incidence of 63% and 57% respectively.The fracture incidence on T12/L1 was 60% of all thoracolumbar spine T11-L2 fractures.The closer distance to baseline fracture,the subsequent fracture incidence was higher.For people with zero,one,two,three,four and five vertebrae distance,the incidence of subsequent vertebral fracture was 36%,26%,15%,11% and 4% respectively.A linear relationship was found between the subsequent fracture and the baseline fracture.The correlation coefficient was 0.90 with 95% confidence interval(0.72,0.97).Seventy-five patients were included in vertebral augmentation group with 110 baseline vertebra fractures and 89 subsequent fractures.And 115 patients were included in conservative treatment group with 183 baseline vertebral fractures and 160 subsequent fractures.The differences of age,baseline fracture and subsequent fracture distributions between vertebral augmentation group and conservative treatment group were not significant(P>0.05).According to the direction of fracture development,the cascade fractures were divided into up,down,both ends and central direction.The incidences were 39.8%,39.2%,8.4% and 12.6% respectively.Conclusion: A linear relationship was found between the subsequent fracture and the baseline fracture.The closer distance to baseline fracture,the subsequent fracture incidence was higher.The main direction of cascade fracture was up or down spiral development.The incidence of both ends and central spiral development was low.Vertebral fracture cascade may be a nature result of spine degeneration and vertebral augmentation didn't increase the risk of subsequent vertebral fracture.