| Background:Fracture of limbs is common in peace time and war time.according to statistics,injures of limbs accounts for77%,combined with fractures(32%) in war fractures.fractures caused by high energy usually accompany with huge soft tissue injury. Simple external fixation was advocated to fix fracture in order to transfer the wounded to reduce the occurrence of complications in medical aid station Nowadays.war injury is general open fracture.if improper treatment is used,reinjury,influence and disability are easy to lead.Proper treatment of fracture of limbs is important.the device and technique of external fixation system has been mature in clinical activities at peace time,however,there are few differences about the design and technique of external fixation system between war time and peace time,the screw of external fixation system drills into the cortical,depending on electrical drill or hand drill,complicated connection system and operation are not suit for war time and emergency time.Portable,simple and functional adjustable external fixation at peace time and war timeis badly needed,the system are provided with the doctors or soldiers in primary health care institutions to improve the level of dealing with war wound and emergency and disasters in army base.The wounded could get useful treatment between the battlefield line and base hospital,reducing the rate of reinjuring,improving the recover rate of complicated fractures,decrease infection and disability rate.In order to provide better treatment for war fracture,fractures caused by accidence in emergency and disasters or daily life,higher quality equipments and systems are developer to make a significant contribution to military medicine and relief medicine.Contents:(1Preliminary Application of Mimics14.0Software in External Fixation Utilizing software of mimics14.0to reconstruct, combinate, assign material for three dimensional model by the dates of tibia and femur in order to imput to the finite element analysis softwares(such as Abaqus,Ansys) to select appropriate material of external fixation for open fractures of tibia and femur in emergency and disasters.(2)Reconstruction of three dimensional finite element analysis model of high explosive.depending on software of mimics14.0,Pro/e,reverse engineering software(Geomagic Studio),utilizing dynamic module of the software of Ansys Workbench.according to mimic different incident angle(45°,67.5°,90°)of bullet,the speed of a bullet is1400m/s,compareing operation results with stress intensity(Mpa),total deformation(mm) and Von-mise(mm),in other words,we relyed on dynamic FEA(Finite Element Analysis) results to show biomechanical changes of different incident angle with the same velocity,established FEA(Finite Element Analysis) basements of principle and procedure of firearm wound,which would be useful to dealing with firearm wound on battlefield line and in clinical activities.(3)Biomechanical research of self tapping screw materials in external fixation system(finite element analysis).Depending on FEA experiment,we established three dimensional FEA model to compare Von-mise and Total Deformation of the self tapping screw and the tibia while drilling with six kinds of materials(titanium alloy,structural steel,stainless steel,aluminum alloy,magnesium alloy,copper alloy) and different diameter sizes to quantificate biomechanical feature of different metals to select light,portable,rigid material in order to extent application of external fixation system.(4)Three dimensional finite element analysis of general self tapping screw of external fixation system.titanium alloy self tapping screws were extensively used in clinical activities because of the advantages of high intensity and hardness,good histocompatibility,similar elastic modulus(bone).We utilized softwares of Pro/e,Geomagic Studio,Ansys Workbench to set up FEA model of tibia-screw assembly,observing results of biomechanical datas after appling force and moment loads to different sizes of diameter,to study the variation of stresses while the screw penetrated into the cortical area of the shaft of tibia quantificately,to provide basements of FEA experiments of other metal materials.(5)Threshold determination of biomechanics of self tapping screw of external fixation system.The operation of traditional self tapping scres were assisted with electrical drill,but we were determined to design the screw without the assistance of electrical drill or hand drill.According to the animal biomechanical experiment,we have measured stresses and moment of force changes and tendency of general external fixation screws while penetrated into cortical bone.(6) The design and preliminary development of portable,simple external fixation system.the current external fixation system was difficult to meet the requirements in war time or emergency and disasters (such as earthquake) caused by huge volume,complex.Thus small volume,light,cheap,portable external fixation system was badly needed.The simple and portable external fixation systemwas used on battlefield to fix the fractures temporarily to prevent reinjury caused by displacement of fractured ends in transmission,the system was convenient to the observation and care of the wound.Moreover,the operation of system could be accomplished by one man without electrical drill,that was also assistant with other internal external fixation system.The design of screw had make a breakthrough of tradional self tapping screwhead.According to refining preminary self tapping screwhead,the style of bilateral arc groove was contributed to twice self tapping,enlarge the moment of force while drilling,which could achieve the effect of hand wring tapping without the assistance of electrical drill.The design of screw clamp was fixed two screws at one timeprimitively.Moreover,the clamp was fastened by stud in the centre,however,this method required screw drilling parallelly in principle,could not allow for error of drilling angle,it was difficult to penetrate in parallel in activities.we refined the clamp,which was fixed by cap nut.15°degree error was allowed for self tapping screw to fulfill three dimentional fixation.The feature of pipe link was retractable and individualized.The pipe link ends of the external fixation was designed as ball socket to achievement the effect of three dimentional fixation by adjusting the direction.Results:(1)Utilizing software of Mimics14.0and Pro/e,based on CT scan of tibia and femur:the tibia,femur and screw had been generated4744triangles,20714triangles,4362triangles respectively.the square and volumewere5844.53mm2,32594.19mm2,18030.40mm2,106665.97mm3,2289.59mm3,3302.18m m3respectively.(2)The three dimentional FEAof high explosive revealed;stress cloud distribution displayed the maximum stress value located in cortical bone where the high speed (1400m/s) bullet emitted in different angle was138.29mm(90°),the secondary value was66.59mm(45°),the minimum value was62.56mm(67.5°). comparison of Von-mise(mm/mm)value:45°(1.43mm/mm)>90°(1.31mm/mm)>67.5°(1.22mm/mm),comparison of stress intensity(Mpa)67.5°(14447Mpa)>45°(2723Mpa)>90°(2401Mpa).(3)Comparison of biomechanical value of self tapping screw of external fixation in FEA method.1. Von-mise equivalent images have showed the maximum stress was located between the self tapping screw and tibia cortical bone,the maximum total deformation value was located in the screw tail under force loads and clockwise moment loads.2.Comparison of force loads on different metals with the same diameter:when the diameter of screw was below3.5mm,the maximum stress of metal was titanium alloy,the stress value of copper alloy, magnesium alloy, aluminum alloy were less than titanium alloy’s,the value of stainless steel and structural steel were similar.The maximum total deformation of metal was magnesium alloy,the next were aluminum alloy, titanium alloy and copper alloy,the value of stainless steel was similar as structural steel.when the diameter of screw was4mm,the stress value of stainless steel and structural steel were greater than the value of aluminum alloy and magnesium alloy;as the diameter was4.5mm,the maximum value was structural steel,the next were stainless steel and magnesium alloy.The values of total deformation were similar.This experiment revealed that the maximum stress and mimimum total deformation was titanium alloy,the feature of copper alloy was similar as ti,however, magnesium, aluminum alloy had maximum value of total deformation because of soft material,the biomechanical feature of stainless steel was similar with structural steel when the diameter of screw was less than3.5mm.The maximum stress value of metal were structural steel and stainless steel,but total deformation was similar when the diameter of self tapping screw was4mm. 3.Comparison of moment loads on different metals with the same diameter.Under the same moment loads on different metals,when the diameter of the screw was less than4mm,the biomechanical feature were similar,the maximum stress value were structural steel and stainless steel,the next were copper alloy and titanium alloy,the minimum value existed in aluminum alloy and magnesium alloy,however,the maximum total deformation material was magnesium alloy. The secondary metals were aluminum alloy, titanium alloy and copper alloy,the minimum metals were stainless steel and structural steel.When the diameter of the screw was4.5mm,the stress value of structural steel and stainless steel were greater than aluminum alloy and magnesium alloy,the maximum value materialwas structural steel,the secondary metal contented stainless steel and magnesium alloy;the maximum total deformation material was copper alloy,the next were aluminum alloy and titanium alloy,thus the value of structural steel was similar as stainless steel.This experiment revealed:when the diameter of screw was less than4mm,the material of structural steel and stainless steel had higher stress value and less total deformation value,their biomechanical were similar as copper alloy,but the metals of magnesium alloy and aluminum alloy had the minimum stress value and the maximum total deformation because of texture.When the diameter of screw was more than4mm, copper alloy had the maximum total deformation value,the biomechanical feature of stainless steel was similar as structural steel’s.4.Comparison of force loads on the same materials with the different diameters when the metals were loaded force loads,all of the materials exhibited similar characteristics,with the increase of the diameter of the screw,the peak value of Von-mise stress had dropped,thus the value of total deformation decreased.with the increase of the diameter of the screw from3mm to3.5mm,the average decline rate of total deformation value rate was10.6%,the average decline rate of total deformation value rate was37.5%. with the increase of the diameter of the screw from3.5mm to4mm,the average decline rate of total deformation value rate was36.8%,the average decline rate of total deformation value rate was70.2%.the statistical differences existed between the group(P<0.05).5.The statistical differences existed between2groups,comparing the increase of the diameter of the screw from3.5mm to4mm. with the increase of the diameter of the screw from3mm to3.5mm,the decline rates of stress value and total deformation value had a significant difference.Under the same load,the obvious decline tendency was observed with the increase of the diameter of the screw from3.5mm to4mm. Comparison of different metal,all of the metals displayed the similar biomechanical features,but fine distinction existed:with the increase of the diameter of screw from3mm to3.5mm,the maximum decline rate of metals was magnesium alloy (38.7%),the secondary one was aluminum alloy (37.7%), with the increase of the diameter of screw from3.5mm to4mm,the maximum decline rate of metals was magnesium alloy (38.8%),the minimum decline rate of total deformation was copper alloy.(4)FEA results of titanium alloy self tapping screw of external fixation:1. Von-mise equivalent images have showed the maximum stress was located between the self tapping screw and tibia cortical bone,the maximum total deformation value was located in the screw tail under force loads and clockwise moment loads.2. With the increase of the diameter of screw,the peak stress and total deformation value existed decline tendency(284.3Mpa to156.8Mpa),3mm screw>3.5mm screw>4mm screw respectively.Comparision of1000N force loads with1500N force loads,the stress value and total deformation value increased in direct ratio with the same diameter.Under the same moment force,the results of the peak stress value and total deformation:3mm screw>3.5mm screw>4mm screw,with the increase of moment force,the peak stress value and total deformation of different diameter screws had increasing tendency.(5)Threshold determination of biomechanics of self tapping screw of external fixation system revealed the stress value(1533N)appeared when the screw was penetrating into the inlayer(4.5mm) of cortical bone of tibia.The value displayed decreasing tendency as the screw drilled into marrow cavity.moment force changes had the small fluctuations(40points) with the average value(2.5N.m) of pig femur.The maximum value was3.1N.m when the screw drilled into cortical bone(6mm).in the procedure of the screw drilled,moment load value increased with the displacement(0.5mm-4mm),reached high value(3.0N.m)until inlayer of cortical bone,the value decreased when the screw penetrated into marrow cavity.Conclusion:(1)We can establish femur-screw,tibia-screw assembly rapidly,operate volume meshes and distinguish materials based on gray threshold with Mimics14.0software to set up the foundation of FEA.(2)High explosive dynamic FEA revealed collapsing force was huge in the incident angle of67.5°,we can decide damage area according to the direction of bullet in clinical activities.(3)Von-mise equivalent images have showed the maximum stress was located between the self tapping screw and tibia cortical bone,the maximum total deformation value was located in the screw tail under force loads and clockwise moment loads.(4)Animal biomechanical experiment displayed when the screw drilled into cortical bone(6mm).in the procedure of the screw drilled,moment load value increased with the displacement(0.5mm-4mm),reached high value(3.0N.m)until inlayer of cortical bone,the value decreased when the screw penetrated into marrow cavity.(5)With the improvement of self-tapping screw,clamp and pipe link,we can simplity operation proceduce,reduce cost,achieve three dimitional fixation by ball socket joint on pipe link and operate by one person. |
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