| Objective: The tarsometatarsal joints are complicated and play an important role in the sustaining arches of foot. This study was designed to establish three-dimensional reconstruction and the finite element model of the foot from the CT data and to study finite element stress of the tarsometatarsal joints in quasi-static load. We research the anatomical structures and features of the tarsometatarsal joints and the relationship between the foot stress and the tarsometatarsal joints injury. In order to explain the mechanism of tarsometatarsal joint injury by the theory of the finite element analysis, We are hoping that this method may provide some help in the clinical diagnosis, treatment and post-evaluation.Materials and methods: A healthy female volunteer (52 years older, 164cm, 57kg) was selected to establish the model. After being scanned by spiral CT (120kv, 36mA, slice thickness 0.699mm, rate 0.707mm/s), 239 two-dimensional CT images were obtained. The images was included with the foot belong the ankle joint and about 4cm of the distal tibia, about 5cm part of the distal fibula. The CT scan data was stored into the read-write CD-ROM in DICOM files.The DICOM files were imported in MIMICS10.0. The 3-D foot-bones models were generated from skinning the original image after thresholding, region growing and smoothing three phases. Then the 3-D foot-bones models were saved as point-cloud files. Next, these files were imported in Geomagic9.0 to get entity models, which were saved as IGES files. The Geomagic9.0 is a kind of software which Transform 3D Scan Data into Accurate Digital Models. Then IGES files were imported into the finite element analysis software Ansys10.0 to get the finite element models. These finite element models including bones were meshed using 3-D 10-Node Tetrahedral Structural Solid element named SOLID92, ligaments were modeled according to anatomical data, using 3-D tension only 2-node nonlinear link element named LINK10, cartilages 3-D compression only 2-node nonlinear link element named LINK10; skin and soft tissue were meshed using element named SHELL93, LINK8. Some elements were established among the skin elements to enhance stabilization of the skin. At last, 3-D finite element model of adult foot were established.The loads were defined in this model .the areas of plantar skin of heel were fully constrained and the others areas of plantar skin were regulated its vertical displacement. Then 280N vertical downward pressure was loaded in proximal tibia .All of the loads having defined and solved, the images of equivalent stress distribution of the foot in mid-stance were obtained Following by the same loads, more force which vertical downward were loaded in top areas of instep, including the MC, IC, LC bone dorsal. The loading forces were 100N, 200N, 300N, 500N, 1000N each to simulate crushing injuries to the foot. At last the images of equivalent stress distribution of the crushing injuries to the foot were obtained.Results: The finite element models of the foot were built, including all the bones, the main ligaments, the skin and the soft tissue. There are total 72934 elements and 108855 nodes in the model, including 21 bones models, which consisted of 10266 nodes, 68110 elements and cartilages models consisted of 3805 node, 2329 elements; ligament consisted of 219 nodes 118 elements; plantar skin model consisted of 1796 nodes, 589 elements, and soft tissue models consisted of 2769 nodes, 1788 elements. The images of Von Mises stress distribution of the foot in mid-stance in normal conditions and in the crushing injuries were obtained. The study of tarsometatarsal joints finite element analysis shows that in the case of normal condition the stress in tarsometatarsal joints was gathered and the max of the stress was in plantar-front side of M2, in the crushing injuries the stress mainly concentrated during metatarsal-front side of the M1, M2, M3, and joints relative surface of metatarsal bones and tarsal bones. As force of the crushing injuries rising, stress of tarsometatarsal joints have raised. The stress of M2 was far larger than others. The max of the stress located at the base and plantar-front side of the M2. The maximum stress was 17MPa.Conclusion:1. An adult foot 3-D visual models of all foot bones were established. 2. The 3-D finite element models including the bones, major ligaments, skin and soft tissue of the foot were established. 3. The finite element analysis of the tarsometatarsal joints in normal conditions and in the crushing injuries was carried out. The images of equivalent stress distribution were obtained. As we can see from the table, we can draw a conclusion that in the stress of the tarsometatarsal joints M2 was larger than others in these conditions. The stress of M2 was focused on the base and the plantar sides. According to clinical cases of tarsometatarsal joint injury, the fractures were most likely found at the base of the M2, which indirectly reflected the accuracy of the finite element analysis in this experiment. And it may provide some theoretical basis for the study the etiology of tarsometatarsal joint injuries. |
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