Pedicle-lengthening Osteotomy For Lumbar Facet Joints Biomechanical Influence And Finite Element Analysis

ObjectiveLumbar pedicle lengthening is a minimally invasive technique for the treatment of lumbar spinal stenosis.Its clinical prospect is good,but there are few reports on the biomechanical effects and finite element analysis of facet joints.In this paper,the finite element method was used to analyze the biomechanical effects of lumbar pedicle lengthening on facet joints in order to obtain the maximum lengthening length of pedicle for clinical reference.MethodsCT images of a healthy lumbar spine volunteer were taken,and the finite element model of L3-L5 normal lumbar spine was established using Mimics,Geomagic,Solidworks,Anysis and other software.Based on the normal lumbar spine model,the postoperative model of L4 pedicle extension was established,and pressure was applied to the upper surface of L3 vertebra at 400 N perpendicular to the horizontal plane,simulating the gravity of normal lumbar vertebrae.The lower surface of L5 vertebrae was fixed.By establishing postoperative models with different extension lengths,the stress changes of L4/5 facet joints and the stress distribution nephogram and the corresponding stress-strain curves of L3/4 facet joints under left rotation condition with torque of 5Nm were analyzed respectively,and the curves of stress extremum of the articular process at L3/4 changing with the length of pedicle lengthening were obtained.ResultsIn the lumbar pedicle lengthening operation,when the operative segment was L4,the stress of the L3/4 small joint increased while the stress of the L4/5 decreased with the increase of the lengthening length by 5Nm torque,and the maximum stress was 9.13 MPa when the pedicle was lengthened by 3.8mm.Subsequently,the stress of the L3/4 facet joint decreases,and the corresponding stress-strain curve and the curve of the stress extreme value of the facet joint change abnormally with the extension length.This indicates that under this torque,when the length of pedicle extension is 3.8mm,the stress on the facet joint of the upper adjacent level L3/4 was the greatest.Once the length of pedicle extension exceeds 3.8mm,irreversible consequences such as joint degeneration may occur.ConclusionIn order to reduce or avoid the change of abnormal stress in facet joints,which may lead to facet joint degeneration or poor surgical effect,the maximum extension distance of lumbar pedicle lengthening was 3.8mm when the torque loading was 5Nm.It is still necessary to choose the minimum length required to achieve the purpose of decompression based on the severity of lumbar spinal stenosis in clinical practice,so as to achieve better surgical outcomes.