X-ray imaging and finite element analysis of the L6-S1 intervertebral disc in rats under abnormal forward-flexed posture

He Miao; Wu Gang; Zhang Xuxing

doi:10.12307/2026.359

Abstract：BACKGROUND:Our group developed a rat lumbar spine model inducing L6-S1 segmental degeneration by prolonged fixation in an abnormal forward-bending posture through a specific device.However,biomechanical evaluation of this model remains lacking. OBJECTIVE:To evaluate the biomechanical properties of L6-S1 motion segment in rats with abnormal forward bending posture through X-ray verification and finite element analysis. METHODS:This study utilized a previously established SD rat model of abnormal forward-flexed posture.Lateral X-ray images of three healthy female SD rats were taken in both restrained(unanesthetized)and relaxed(anesthetized)states to measure the L6-S1 disc angle and analyze its changes under different postures.Micro-CT data from one healthy female SD rat were used to reconstruct a 3D L6-S1 model with Mimics,Geomagic Wrap,and SolidWorks.The model was then meshed,assigned material properties,and subjected to forward flexion loading simulation in ANSYS Workbench to calculate stress distribution in L6-S1 disc structures. RESULTS AND CONCLUSION:(1)The mean L6-S1 intervertebral disc angle was(12.16±0.57)° in the relaxed posture and(1.26±0.26)° in the restrained posture.(2)Under a 10° forward-flexed posture,the maximum von-Mises stress in the superior endplate,inferior endplate,annulus fibrosus,and nucleus pulposus of the L6-S1 intervertebral disc was 10.398,19.928,6.819,and 0.104 MPa,respectively.The maximum von-Mises stress in the superior and inferior endplates was significantly higher than in the annulus fibrosus and nucleus pulposus.(3)These findings suggest that in the 10° flexion modeling posture of the L6-S1 intervertebral disc,the reduction of the L6-S1 intervertebral disc angle leads to significant changes in disc morphology and load distribution.The constructed finite element model successfully simulated the biomechanical environment of the L6-S1 intervertebral disc under abnormal forward-flexed posture in rats.The superior and inferior endplates bear higher equivalent stress in this posture,making them the structures most likely to undergo early degenerative changes.