| Objective :(1)CT scan was performed on the ankle of healthy volunteers to establish the finite element model of normal adults standing still with one foot through three-dimensional reconstruction and finite element pretreatment,so as to verify the validity and authenticity of the model and provide a reliable model for the biomechanical study of ankle joint injury.(2)3d finite element analysis and evaluation were conducted on different internal fixation methods of talus neck fracture,to explore the mechanical stability of different internal fixation methods and the biomechanical environment of the optimal fracture section,so as to provide reliable mechanical arguments for the selection of clinical internal fixators.(3)the talus fracture is the foot of the serious damage,and talus neck fracture is the most common type of talus fractures fracture type,screw forward after is commonly used in clinical,but its into the selection of screw Angle and postoperative restoration evaluation is still a clinical two difficulty greatly,so this experiment by measuring the healthy adult talus medial Angle and plantar side-slip Angle,for clinical into perspective and postoperative restoration evaluation standards provide detailed and reliable data.Methods :(1)the CT data of the ankle were imported into software Mimics17.0,followed by 3d reconstruction after threshold segmentation and regional growth.The Geomagic software then generated geometric models of the five bones and constructed corresponding articular cartilage,which was exported in iges format.Then,the mesh was divided in the Hypermesh software,and material assignment,ligament construction,load and interaction were set in the Abaques.Finally,the results were analyzed and calculated,and the results were compared with Anderson's experimental results.(2)the ankle joint model is built on the basis of the talus in iges format to import the Solidwork software,the structure of the talus neck fracture model,at the same time in the Solidwork by "convex platform-stretching" "helix" build half thread tension screw,such as the talus and the screw assembly,get forward forward parallel double screw and after cross fracture model of double screw,export in inp format.Finally,the internal fixation model of talus was imported into Abaques to replace the normal talus,and other applied conditions remained unchanged.Finite element analysis was conducted to explore the Von Mises stress distribution and fracture end stress distribution and displacement of lag screw under different fixation methods.(3)40 healthy adult volunteers,20 males and 20 females,were included.After CT scanning,the data of bilateral talus were obtained in DICOM format and successively imported to Mimics software.The talus was separated from the ankle joint by threshold segmentation,regional growth and manual erasure.After 3d reconstruction,the internal Angle of the talus and the inclination of the metatarsal were measured by the functions of 'point' and 'line' in 3-matic.Results:(1)the experimental model according to Anderson,experimental methods,such as the finite element analysis,the income from bone distal joint stress mainly concentrated on the upper surface,the maximum stress is 3.83 Mpa,the biggest contact area is 312.3 mm squared,talus stress mainly concentrated in the upper block outside of talus,its maximum value is 4.65 Mpa,the trend of stress and numerical consistent with Anderson,the result of the experiment,that the experiment of the finite element model has authenticity,validity and can be used for related ankle experimental research and analysis.(2)in this experiment,the maximum stress on the contact surface of talus fracture under internal fixation in the two groups was located at the bone where the fracture surface intersected with the screw,and the maximum pressure on the contact surface of fracture intersected with the screw was 5.692 mpa in the posterior and anterior cross-fixation group.The stress was the least in the posterior and anterior parallel fixation group(4.848MPa).When the talus was standing still with one foot,its displacements were all less than 1mm,and there was no significant difference in the four axial displacements of X,Y and Z,so the two fixation methods could achieve strong fixation.In the static standing state,the maximum Von Mises stress of the screws was 37.68 mpa in the forward cross fixation group after double screws.In the group of posterior and anterior parallel fixation with double screws,the screw stress was the minimum in the two groups of internal fixation,which was 30.65 mpa.(3)The left Declination angle of the male was 20.1°~32.7°(25.97°±3.29),the Inclination angle was 35.4°~44.6°(40.06°±2.49),and the right Declination angle angle was 20.9°~31.4°(26.15°±3.17),the Inclination angle is 35.5°~44.1°(39.8°±2.54).The left Declination angle of the female is 20.4°~32.1°(26.48°±3.29),the Inclination angle is 37.8°~45.7°(41.41°±2.78),and the right Declination angle is 20.6°~31.4°(26.6°±3.20).),the Inclination angle is 38.5 ° ~ 45.5 °(41.58 ° ± 2.18).The Declination angle and Inclination angle of the left and right skeletal men and women were p=0.627>0.05,p=0.115>0.05,respectively.The right Declination angle and Inclination angle of male and female were p=0.650>0.05 and p=0.095>0.0,respectively.There was no significant difference between the left and right Declination angle and the Inclination angle of the males.p=0.666>0.05,p=0.475>0.05;there was no statistical difference between the left and right sides of the female p=0.659>0.05,p=0.609> 0.05.Conclusion:(1)the 3d finite element model established in this study has good uniformity and consistency compared with Anderson and other experimental data.Therefore,the ankle finite element model established in this study has good simulation performance and reliable verification,and the results are of reference significance.When standing still with one foot,the stress of the talus was mainly concentrated around the talus neck,and its maximum value was located at the upper lateral side of the talus neck,and the maximum value was 4.65 mpa.(2)the stress of talus neck fracture increased significantly after internal fixation,and the stress was mainly concentrated in the bone below the intersection of the screw.The two fixation methods can achieve good stability,the fixation method is reliable and can be used timely.After internal fixation of talus neck fracture,the bone stress at the intersection of talus neck fracture and parallel screw was significantly better than that at the intersection of cross screw,and the mechanical properties of parallel screw fixation was significantly better than that of cross screw fixation.(3)There is no statistically significant difference in the difference between the Declination angle and Inclination angle between the male and female in this study.There is no statistically significant difference between Declination angle and Inclination angle of the talus in the same sex.The average talus Declination angle of healthy adults was 26.3 ° ± 3.18,and the average Inclination angle was 40.76 ° ± 2.53.In the talus posterior and anterior screw fixation,the angle of the nail can be referred to the angle of the contralateral talus,so that the direction of the nail is kept within a safe range,and the postoperative reduction evaluation can also be used as a reference for the talus angle. |
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