Finite Element Analysis Of Pedicle Screw Fixed In Fractured Vertebra In Different Ways

With the rapid development of transportation and construction industry, thepatients with fractured lumbar are increasing. Therefore, experts and scholars on theresearch of fractured lumbar are more and more. Added spinal internal fixation widelyused in clinic and research on spinal biomechanics rapid developing, especially theinvention and clinical application of pedicle screw, the treatment of fractured lumbarhas been a great deal of progress. At present, short segmental internal fixation viafractured vertebra is an approved way of treated fractured lumbar. But as a result ofdifferent forms after vertebral body fractured, the nailed way of pedicle screw and thebiological mechanics performance of vertebral body after nailed are different. Thispaper is to discuss the biomechanical performance of the lumbar and pedicle screwsthrough the finite element model of pedicle screw fixing fractured vertebra indifferent ways. Thus it can provide certain mechanics theory basis for the clinicaltreatment of fractured lumbar.In this paper, we use Mimics, Abaqus and Catia software to establish the finiteelement model of lumbar and pedicle screw fixation system，then give the vertebralbody material properties using Mimics based on lumbar spine CT image grayscalevalue. At the same time, we give the disc high elastic material properties and ligamentasymmetric spring unit. Thus we can establish the finite element model of lumbarwith high precision. This paper established several finite element model: validationgroup model, control model without pedicle screw fixation system fixed, andexperimental group with pedicle screw fixation system fixed in different ways. Thevalidation group model is used to verify the validity of the model, the control groupand experimental group model are used to analyze and compare the mechanicsperformance of lumbar and pedicle screw system. Through the finite element analysis we know that the axial stiffness andstability of fractured lumbar increased obviously through different placement ofpedicle screws. But the axial stiffness and stability of fractured lumbar between thethree experimental group with different placement of pedicle screw are almost same.For pedicle screw fixation system, its bearing capability is different as the differentfixed ways. If the applied load is too large, the connecting rod of pedicle screwfixation system and the root of screw in vertebra adjacent injured vertebra in B groupunder antexion situation are easy to fracture; the connecting rod of pedicle screwfixation system and the root of screw in below vertebra adjacent injured vertebra in Bgroup under extension situation are easy to fracture; the connecting rod of the leftpedicle screw fixation system and the root of the left screw in below vertebra adjacentinjured vertebra in C group under left bending situation are easy to fracture; theconnecting rod of the right pedicle screw fixation system and the root of the rightscrew in below vertebra adjacent injured vertebra in C group under left bendingsituation are easy to fracture. In addition, the experimental group compared with thenormal control group, the stress in annulus fibrosus of intervertebral disc between L2and L3as well as between L3and L4reduces a lot. The maximum stress of the L2～L3and the L3～L4intervertebral disc appears in the front of f annulus fibrosus whenthe lumbar is under antexion and extension situation; The maximum stress of theL2～L3and the L3～L4intervertebral disc appears in the left part of fibrous ringwhen the lumbar is under left bending situation; The maximum stress appears in theright part of fibrous ring when the lumbar is under right bending situation.Through the study of this paper, we can draw the conclusion that the nailedway of group D is better. Thus it will provide a certain biomechanics theory basis forthe clinical treatment of fractured lumbar spine.