Finite Element Analysis Of The Iliolumbar Fixation In Traumatic Spino-pelvic Dissociation

Objective The aim of this study is to establish the digital model of iliolumbar fixation by 3D reconstruction and finite element technology based on the CT data of healthy adults.To explore the optimal screw pathway of iliolumbar fixation for traumatic spino-pelvic dissociation,and analyze the biomechanical stability of our model.Methods Firstly,a healthy adult male volunteer underwent CT scanning of the lumbar and pelvis,with a slice thickness of 0.625 mm.The original data was saved in DICOM format and imported into Materialise Mimics Innovation Suite 16.0 software(Materialise,Belgium)for three-dimensional reconstruction of lumbar and pelvic.The results are stored in STL file format.Secondly,according to the previous experimental design,the safe “geometric screw pathway” was determined for the pedicle and the ilium.Then,using the translation and rotation tools,the “free screw pathway” was generated.Next,the iliolumbar internal fixation screw rod system model,with pedicle screw diameter 5.5 mm,length 50.0 mm,iliac screw diameter 6.0 mm,length 130.0 mm was produced in Solidwoks 2012 software(Dassault systems,USA).The model was imported into Geomagic studio 2014(Geomagic,USA)software for further processing.After that,the 3D model is imported into Abaqus 6.13(Simulia,USA)software for assembly,so as to realize gridding and material assignment.Finally,a load of 500 N is applied to the model,the stress distribution of von Mises was measured,and the biomechanical stability after fixation was analyzed and compared.Results The bend connecting the sacrum and vertebra is the area of stress concentration.The lumbar-iliac fixation model showed strong compression resistance.The maximum von Misses stress appeared in the L4-5 pedicle screw and the longitudinal rod.Under rotational loading,the upper longitudinal rod and the L4-5 pedicle screw bears the maximum stress.The stressstrain distribution diagram of the geometric pathway system is generated by the finite element analysis,and the corresponding mechanical parameters is calculated of the two kinds pathway system under each working condition.It is concluded that the overall displacement,the stress of the vertebra and the screw are less than that of the free pathway in the geometric pathway system.Conclusions Double vertebrae and bilateral fixation with long iliac screw may be an effective method for iliolumbar fixation,and the geometric screw pathway determined by digital analysis may be more biomechanical.