Five Surgical Modes For Three Kinds Of Pauwels Femoral Neck Fractures By Finite Element Method

Objective:(1).To build three different types of Pauwels femoral neck fracture in numerical models by computational technology of Reverse Engineering,and to validite Finite Element Model(FEM)by examination of cadaveric femoral head;(2).To create internal fracture fixations and hemiarthroplasty FEM by fastening three types of Pauwells femoral neck fracture with four kinds of internal fixations and femoral head replacement separately,and to solute these models in a software namely Ansys14.0.(3).To analyze the distribution of Von Mises stresses and displacements of these models by AnSys in order and to comprehensively evaluate the biomechanical features on each kinds of surgical method for providing a theoretical basis for clinical applications.Method:Twenty specimens in-patients were randomly selected from The First Affiliated Hospital of GuangZhou Medical University during 2010~2016.The inclusive criteria were patients aged 25-60 years whose femurs without bony damage of tumor?fracture or malformation regardless of gender preferance.Images of 20 normal human-femoral randomly scanned by 64-MSCT and saved in format of *.DICOM.The images were then imported into medical image processing software called Mimics-17.0,so as to rebuild 3D simulative model of dorsal femur,and exported in format of *.STL.They were then imported into Geomagic Studio-12.0,then,simulative osteotomy were carried out in directions of 30°? 50°?70°horizontally,forming three types of Pauwells models and an osteotomic hemiarthroplasty model based on the criteria of clinical surgery.After the process of ?detection of curvature?demotion contour line?Structural surface?Structural grid?fitting curve?,NURBS curve surfice is fitted.These models were then input onto interactive CAD/CAM software namely UG-8.0 in order for solid model sewed up by a function called ?suture?.The four three-dimensional(3D)models of internal fixation were drawn by 3D graphic software namely ProE-5.0(Wildfire version)respectively: Dynamic hip screw(DHS)?Dynamic hip screw(DHS)+ a lag screw(LS)? three lag screws(3 LS)? Proximal femur locking plate(PFLP).The femoral prostheses were created by reversive reconstruction of CT scanned images after femoral head replacement.The foregoing facilities of fracture models ?fixatures and femoral prostheswere to be exported onto a pre-FEA software namely Hypermesh-11.0 separately,and assembled to internal fixations as:(a)Dynamic hip screw(DHS)?(b)Dynamic hip screw + 1 lag screw(DHS+LS)?(c)Three lag screws(3-LS)?(d)Proximal femoral locking plate(PFLP),and(e)Femoral head replacement(FHR).Finite element models will be built after operative Boolean Operation?entity division meshing?attributing properties and materials in Mimics?applying constraint and load.Finally,these FEM will be executed by FEA software namely AnSys for solution: to analyze the Von Mises of stresses and displacements for each surgical method,and to compare the advantages and disadvantages of each therapic method of any types of Pauwells fracture.Results:We successfully build three types of Pauwels fracture models in 3D,and create four kinds of internal fixations as well as virtual operation based femoral head replacement by which the Von mises of stress and displacement can be solved and observed by Ansys.For Pauwels-?,the general stresses are:(a)105.6170?(b)65.4406?(c)43.5766?(d)43.6657?and(e)43.8583(unit :Mpa);the general displacements are :(a)0.7297?b.0.5863?c.0.7536?d.0.5687?and e.0.6232(unit :mm).For Pauwels-?,the general stresses are: a:179.3238?b:80.3592?c:62.9291?d:53.1107?and e.43.8583(Mpa);the general displacements are : a:0.9258?b:0.6222?c:0.8878?d:0.6259 ?and e.0.6232(mm).For Pauwels-?: the general stresses are: a.248.5948?b.98.4781?c.68.6780?d.60.4346?and e.43.8583(Mpa);the general displacements are: a.1.0834 ? b.0.6616 ? c.0.7879 ? d.0.5682 ? and e.0.6232(mm).According to comprehensive analysis,it is presented that the Von mises stress of surgical method of femoral head replacement subjected to femoral neck fracture is the smallest among five surgical methods for all three kinds Pauwels fracture,but its general displacements are indifferent from each other.While the peak values of Von Mises stress for 3-LS and PFLP are smaller than that of the rest fixations,the smallest general displacement is DHS+LS.Conclusion:(1).Standarized by comparison of displacement and stress individually,the femoral head replacement is evaluated to be the best of all kinds Pauwells fractures.(2).If internal fixation is chosen for these Pauwells fractures,conclusions are as these:(a).For Pauwels-?,3LS or PFLP is preferable,DHS+LS is optional for second choice,whereas the DHS alone is not recommended.(b).For Pauwels-?,FFLP is the first choice,while the DHS+LS is superior to the 3LS.(c).For Pauwels-?,the stapler and stronger PFLP is the most recommended operation.The rest three fixions are not good for choice.