Study On The Biomechanical Mechanism Of Degenerative Lumbar Scoliosis Using Finite Element Method

Objective:This study aimed to use finite element(FE)method to investigate the role of psoas major muscle as well as the effects of facet joint orientation and intervertebral disc degeneration in six lumbar motions including flexion,extension,left and right lateral bending,left and right rotation.It was expected to provide some ideas for the establishment of musculoskeletal model,furthermore to investigate the link between the facet joint orientation,disc degeneration and degenerative lumbar scoliosis in biomechanical way.Method:To establish the lumbar FE model,a lumbar spine of a healthy volunteer was firstly scanned,and the obtained CT images were imported to the 3D modeling software Simpleware to extract the lumbar model.Then,based on the original model,the psoas major muscle was incorporated,and the new model was employed to construct three facet joint orientations(F45,F50,F55)of the L3/4 lumbar segment.Two models with degenerated intervetebral disc in L3/L4 and L4/L5 were also established respectively.All the FE models were imported into the FE software ABAQUS to perform simulations under the mentioned six motions.Result:(1)Compared with the original lumbar spine model,the model with psoas major muscle decreased the intervertebral disc stress in the flexion and extension movements.The intervertebral disc stress and the facet contact force in the lateral bending movement were both greatly decreased,but there was a weak change in the rotation motion.(2)In the L3/L4 segment,F55 model showed higher intervertebral disc stress and facet contact force in the flexion moment,while F45 model showed a higher stress on posterior lumbar and intervetevral disc under extension and rotation motions.(3)Disc degeneration resulted in the higher stress on the nucleus pulposus.The stress on the side of height reduction was higher than the figure on the other side.The facet joint contact force on the degenerated segment was left-right asymmetry.In the five motions except flexion,the facet joint contact force of the D4 intervertebral disc degeneration model was higher than the figures in the disc degeneration model of D3.Conclusions:Under flexion and lateral bending motions,the psoas major muscle can reduce the lumbar force by its own contraction to prevent the disc and facet joint from excessive displacement.This mechanical behavior should not be ignored in the lumbar finite element simulation.Different facet joint orientations dominate the stress in different motions.Especially in the flexion movement,the sagittal facet joint orientation makes the disc and facet more vulnerable.Moreover,early intervertebral disc degeneration results in the asymmetry of the facet joint force bearing.The present study could be useful to understand the mechanism of the degenerative lumbar scoliosis and be applied in the treatment of the clinical patients.