Effect Of Different Complex Static Compression Loads On The Intervertebral Disc: An In Vivo Bent Rat Tail Model

Objective:This study evaluated how well different magnitudes of compression-induced degenerative changes using a simple bent rat tail model simulated human lumbar lordosis.Methods:25 three-months-old clean level male SD rats,randomly divided into 5 groups in digital table method: control,sham and 3 experimental groups(1,2,3)with 5 rats in each group.Among them experimental groups(1,2,3)were instrumented with a special apparatus which was divided into 3 different static compression loads(1.8N,4.5N and 7.2N respectively);the control group was instrumented no appraratus and the sham group was loaded with the apparatus without springs(no static compression load).Positioning Co8/9and Co9/10 intervertebral space and the rats were instrumented with special apparatuses to establish intervertebral disc degeneration model.The degeneration of the discs was evaluated by magnetic resonance imaging(MRI),histology,gene expression of anabolism and catabolism after two weeks.First,we chose 3 rats randomly from each group and rats were anesthetized with intraperitoneal injections of 1% pentobarbital.After operation all rats were performed magnetic resonance imaging(MRI)of T2 images in the sagittal plane,calculated Pfirrmann classification which classify disc images into five grades.All rats were euthanized after the examination.Each group was chosen 2 rats randomly to take for HE(hematoxylin and eosin)staining and safranin o-fast green and hematoxylin staining.Calculate the method of Masuda to to assess changes in the annulus fibrosus(AF),the border between the annulus fibrosus and the nucleus pulposus(NP),the cellularity of NP,and the matrix of NP through midsagittal sections.3 additional rats were also euthanized and discs were immediately removed,in the mid-sagittal plane and parallel to the endplate direction,by using a scalpel under microscopic examination.The discs were then put into liquid nitrogen to prevent RNA degradation and reverse transcription.Finally,The relative expression levels of mRNA were counted by real-time reverse transcription(RT)-polymerase chain reaction(PCR)to calculate the difference in threshold cycles for the target gene and the reference gene using the 2-??Ct method.Results:As the loading magnitude increased,static compression produced a significantly progressive decrease in nucleus intensity on T2-weighted MRIs,a decrease of aggrecan and Type II collagen,an increase in Matrix metallopeptidase-3(MMP-3)and Matrix metallopeptidase-13(MMP-13)expressions,and a histomorphological degeneration.Conclusions:1.It's successful for our special apparatus to establish the model of intervertebral disc of the bent rat tail.2.The sham group(without the spring)can't lead to intervertebral disc degeneration in two weeks.3.We conclude that different stresses lead to different processes of degenerative changes,the concave disc degenerating more severely as stress gradually increased.