Biomechanical Effect Of An Interspinous Process Spacer Of Lower Lumbar: A Finite Element Analysis

Lumbar spinal stenosis disease belongs to the category of lumbar degenerative disease.Because of intervertebral disc degeneration,intervertebral disc matrix bulged,and oppressed peripheral cauda equina nerve,which resulted in low back pain.The high-risk groups are the elderly,along with increasing morbidity and younger age.Spinal fusion,regarded as "gold standard" treatment for lumbar degenerative disease,is widely used in clinical.But the study found that,after the fusion,the normal spine force line and the original structures were changed,and stress in adjacent segments increased.These lead to adjacent segment degeneration disease and become the main postoperative complications for fusion surgery.Interspinous devices make up for the inadequacy of spinal fusion.With the increased use of time,they also exposed many problems,such as postoperative prosthesis slippage,spinous fracture,etc.To provide references for design improvement,this research analyzed two types of Interspinous devices,Coflex and X-STOP.The research aimed at simulating surgery procedures with finite element method,comparingtheir different biomechanical properties in the treatment of lumbar spinal stenosis(LSS),andproviding references for design improvement and clinic application of the interspinous process spacer.A CT-scanner was used to acquire normal lumbar images.With the help of Mimics17,Geomagic Studio2012,Hypermesh12 and Abaqus6.12-1,the finite element(FE)model(the lower lumbar L3-S segments)have been constructed and verified.On this basis,the disc and ligament were adjusted to establish the mild-degenerate lumbar finite element model.X-STOP and Coflex geometry model were made using CAD and assembled with degenerative model,and then simulated the patient normal motion after surgery through finite element analysis.Biomechanics of two devices with health and degenerative models have been compared respectively,including Range Of Motion(ROM),stiffness,intervertebral disc stress in the implanted and adjacent segments,implant and vertebral body stress distribution and etc.Results showed that comparingwith degenerative model,both X-STOP and Coflex devices could restrict ROM and decrease disc pressure in extension of the implant segment,without affect ROM of bending and torsion.Besides Coflex also limit most ROM of flexion,both of X-STOP and Coflex did not have impact on adjacent levels.Coflex max Von.Mises stress appeared at corner of U shape when extension and flexion,however,X-STOP max Von.Mises stress appeared on the connection place between left win and expandor.The contact pressure with spinous of both implant appeared at extension position.This study modified existing X-STOP design in aspect of material and structure,according to Coflex and X-STOP biomechanical responses.The improved design could ameliorate contact pressure of contact surface and work normally as spacer used to be.This improvement ensure the safety of both implant and spinous.