A Biomechanical Study Of Treatment Of Thoracolumbar Fracture By Monosegmental Compression Fusion Through Fractured Vertebra

ObjectiveTo introduce and evaluate the biomechanical features of treatment for thoracolumbar fracture by posterior monosegmental compression fusion through fractured vertebra combined with anterior allograft of cortical bone applied by a three-dimensional finite element model.MethodA youth volunteer(male,aged 20)without chronic low back pain and trauma of thoracolumbar was chosen,x-ray picture was carried out first,the spinal disorders was ruled out initally by MRI machines(Philips interaAchieva 3.0T),which was on the conduct of the thoracolumbar 1mm thick continuous scan.We use MRI pictures and Simpleware software to built a 3-D finite element model to mimic the fracture of T12-L2 and L1 vertebra,then three therapy approaches of posterior short segment internal fixation(PF),anterior bone grafting fixation(AF)and posterior monosegmental compression fusion combined with anterior allograft of cortical bone supporting(CF)were performed by 3-D finite element model.These three models were put into Ansys8.0 finite element program,axial load 500N and 10NM torque were loaded,on central compression,flexion,extension,lateral bending and torsion respectively to study the corresponding stress and straining.VonMises stress on the vertebral body and implant were calculated and load-displacement curve were obtained in the three models.ResultsVertical compression,the stiffness of CF was increased by 39.6%than the usual PF,11.3%more than AF;On flexion circumstances,CF rotation angles was decrease by 25.2%than PF,7.1%less than the AF;On right lateral bending,CF rotation angle was decreased by 39.5%than PF,46.2%less than the AF;On left and right torsion,CF rotation angle were 62.0%and 57.5%less than PF respectively,66.0%and 66.8%less than AF.The maximum stress of implants,PF appears in torsing process,the maximum was 121 Mpa;CF appears in the left bending process,the maximum was 81.4 Mpa. The maximum stress of Vertebrae,in the PF model,appeared in the process of flexing, and the maximum was 40.1 Mpa,mainly occurred in the L1 vertebral body;In the AF model,the maximum was 106 Mpa which appeared in the right side bending process, primarily in the tri-cortical implanted iliac block;In the CF model,max was 50.6 Mpa which appeared in the left bending process,mainly occurred in the left bottom of cortical plate,connecting to the left side of screws in L1 vertebrae.Conclusion1,The technique of posterior monosegmental compression fusion through,fractured vertebra combined with anterior allograft of cortical bone,in the model of vertical compression,flexion,right lateral bending and left and right torsion,stability was far more than anterior fixation or posterior short segment pedicle screw fixation methods; Posterior short segment pedicle screw fixation,in the extension process,anterior fixation in the left bending process have their own advantages in the course of stability.In general, to the thoracolumbar burst fracture,posterior monosegmental compression fusion through fractured vertebra combined with anterior allograft of cortical bone produced a stiffer construct.2,Posterior monosegmental compression fusion through fractured vertebra, compared to posterior short-segment pedicle screw fixation,anterior bone graft was increased,the risk of internal instrument failure and stress of shielding effect was reduced,this may promote the fracture healing.3,The maximum stress of bone grafting with anterior fixation was bigger than anterior allograft of cortical bone significantly,and tri-cortical iliac block was easily to collapse,it may lead to delayed kyphosis and pseudoarthrosis;In the CF model,the maximum stress of cortical bone plate appeared in the porcess of left bending,allograft bone plate was susceptive to be fracture and bending activities should be avoided.