Construction Of3-Dimensional Finite Element Model Of Inferior Tibiofibular Syndesmosis Based On CT Images

Objective According to spiral CT scan images of a normal male volunteer,s rightankle and foot,to explore how to establish finite element model of inferior tibiofibularsyndesmosis with Mimics,Free-Form and ANSYS softwares.Moreover,its validityshould be verified,so that it can reflect the mechanical characteristics of the ankle andfoot,Further more,it can provide a digital platform for the study of inferior tibiofibularsyndesmosis.Methods A healthy volunteer (30-year,170cm,60kg) was selected to establish themodel. Scanned the volunteer,s right foot from the plane20cm above the ankle downto the planta(scanning parameters:120KV,240mA,reconstruction slice thickness0.625mm,rate0.700mm/s,matrix512×512), stored the CT scan data into the CD-ROM inDicom format.Then imported the scanned data of Dicom format into Mimics10.01software,by threshold segmentation automatically or manually,to reconstruct the three-dimensional structure of a complete foot and ankle composed of all bones andsurrounding soft tissue.Finally,exported the data with point cloud format andreimported into Free-Form to form geometric model,then import the data into the finiteelement analysis software ANSYS12.0by IGES format to establish a complete finiteelement model of ankle and foot.To construct0.5mm of articular cartilage on bothsides of contact surface according to the joint space,while to use three-dimensional rodelements which were compressed only to simulate other joints cartilage.The finite element model include bones and surrounding soft tissue which were meshed withthree-dimensional10-node tetrahedral structural solid element named Solid92,ligaments were modeled according to anatomical data, using three-dimensional tensiononly2-node nonlinear link element named Link10. Finally,three-dimensional finiteelement model of inferior tibiofibular syndesmosis was established.Then took thethree-dimensional finite element model of inferior tibiofibular syndesmosis for test andload,The normal standing status of ankle joint was simulated by application a verticalload of300N on the upper section of the lower tibia while the soft tissue and the upperof tibiofibula constrained.To measure contact pressure and contact area of theplantar.Following by the same load, The plantar contact pressure distribution of thesame volunteer was measured by using the insole.The loading result of3-dimensionalfinite element model was consistent with the corresponding data by comparison.Results The3-dimensional finite element model of inferior tibiofibular syndesmosiswas built, including all bones, the main ligaments, the skin and the soft tissue. Thereare total81583elements and130865nodes in the model.The test results of the3-dimensional finite element model were taken to contrast with the actual measurement.It showed that the stress mainly distributed at the area of the heel and the1-5metatarsal in both of them when ankle joint was in neutral position under the verticalloading(maximum stress:0.240MPa,0.230MPa),substantial agreement on distributionarea,distribution trend,and numerical value.It was preliminarily verified this modelvalid.Conclusion This study has successfully constructed the three-dimensional finiteelement model of normal human ankle and foot by using Mimics,Free-Form andANSYS softwares in accordance with two-dimensional images scanned by spiralCT,and reflected the basic anatomic structures and mechanical properties of the humanankle and foot. The model was proved to be valid and could simulate various load situations of ankle for mechanical analysis.