Geometric Match Assessment Of Three Intramedullary Nailing Systems(PFNA、PFNA-Ⅱ、InterTan)for Chinese Proximal Femurs And Finite Element Analysis Of Intertrochanteric Fracture Fixed With Three Different Kinds Of Proximal Femoral Intramedullary Nail

Background:With the modernization process,there having an unprecedented development in transportation industry and construction business,which makes the orthopedics face new challenges clinically and urgently needs to be explored in depth. As the society ages,the incidence of intertrochanteric fracture is rising year by year. Intertrochanteric femoral fracture occurs from the base of femoral neck to small protuberance level,It is difficult to achieve anatomical reduction and failure in internal fixation,these lead to the incidence of the nonunion、the malunion and the disability is rising during the treatment of intertrochanteric fracture because of its characteristic anatomy. All of these seriously affect the life quality of these patients and urgently needs to be explored in depth. The scholar diagnosed patients by means of the common radiological examination in the past,After that,the scholar pay more attention to whether the surgical technique was skilled and whether the internal implant selection was appropriated and the analysis of efficacy.However,they rarely made further investige of the reason which lead to surgery failed and efficacy declined. Many researchers had pointed out that individual differences in anatomical and biomechanical factors play a crucial role to pathogenesis,treatment and prevention of the intertrochanteric fracture pationets, however,to tackle the problem of individual differences in anatomical and biomechanical changes after fixation as well as wether the intramedullary nail were match chinese people,we must adopt scientific,accurate and repeatable method.In foreign countries people study by measurement of specimens, X-ray CT or MRI. Measurement of specimens is restricted by the quantity of specimens,and the cost is high. Although X-ray measurement is easy to carryout,during the process of X-ray film,due to the impact of many factors,it is difficult to get the standard lateral X-ray film wllich can be used to comparable analysis.In addition,because the boundary between cortical bone and cancellous bone in X-ray film is uncertainty,which will also affect the accuracy measurement of the medullary cavity of proximal femoral.And CT,MRI was arranged in two-dimensional layer-by-layer images,anatomical landmark is not clear, which often miss some important information.The technology of Three-dimensional digital reconstruction can reconstruct the original space from two-dimensional layer-by-layer images,and show objects in three-dimensional images.This method is missing less information,and the object can be observe from any angle and direction.Thus digital technology can provide a new idea and technique for the proximal femoral medullary cavity study.To studies on the changes of femoral trochanter biomechanics after internal fixation operation, In the past,studies on proximal femoral mainly used traditional experimental means of biomechanical tests.But the disadvantage of this method is the complexity of experimental means, and when carried out a variety of operating conditions,the experiment is often costly,time-consuming and low efficiency.Moreover, because it can not directly test in humans,it is difficult to accurately reflect the stress distribution after application different load.On the other hand, the femoral intertrochanteric have specific anatomical characteristics,it is difficult to accurately reflect the real situation with simple mechanical methods by standard anatomy.In order to solve this problem, in recent years,with the improvement of digital technology,more and more researchers use numerical analysis methods,namely,based on the theory of traditional mechanical analysis,numerical analysis methods such as finite element method (finite element method, FEM) and so on, for linear and nonlinear stress and deformation analysis.It can be simulated using a variety of intertrochanteric fracture by FEM, making biomechanical studies on bones’complex geometric structures,boundary conditions and material nonuniformity of the femoral intertrochanteric issues have possible solutions.For the treatment of intertrochanteric fractures,especially in elderly patients,proximal femoral nail antirotation,(PFNA) could effectively improve the stability as well as prevent rotation and collapse,it also could make resist cutting-out area significantly increased and have a greater advantage in patients with osteoporosis.When the PFNA came to the Asian market,some scholars reported that it could resulting in failing of the surgery because PFNA will lead to the splitting of the intraoperative lateral cortex of proximal femur in patients.Some scholars found that hip pain which lead to hip joint limit were higher in femoral intertrochanteric fracture patients who were fixed with PFNA. Asian scholars specificated that the design of the PFNA in the part of proximal which were applicable to the anatomical characteristics of Europe were not applicable to Asian populations in earlier years.So the Asian type PFNA (PFNA-II) were made,however, whether it matched with the femur anatomy of Asian and complications after operation were rarely reported in the literature since it was used.Furthermore,the intramedullary fixation systems were constantly improved, the Inter Tan which the nail proximal trapezoidal cross-sectional and the combination of nail and joint locking for nailing the "Z" word effect were designed as a new proximal femoral nail,whether it was suitability for chinese anatomical features remain to clinical report and experimental study.Based on previous studies,3D model and3D FE model of Chinese proximal femurs were reconstructed on a collection of the CT data,the anatomical measurement (femoral neck、neck shaft angle、anteversion angle,etc.) was carried out about anatomical parameter in proximal femur.To construct3D models of common clinical intramedullary nail (PFNA、PFNA-Ⅱand InterTan) and then they were introduced into3D model and3D FE model of proximal femur,and to obtain morphologic parameters of intramedullary nailing appropriate for proximal femur fractures in this population by assessing the geometric match between3kinds of intramedullary nailing and Chinese proximal femurs;to explore the biomechanical properties of intertrochanteric fracture fixed with3kinds of intramedullary nailing through finite element analysis (FEA). Combining measured data and analysis results, receives the data of suitable for Chinese population of idealized internal fixators system(PFNA-III),to provide theoretical support for improving surgical curative effect of intertrochanteric fracture in countrymen,and provide universal ideas for selection and development of intramedullary fixation system on treatment of intertrochanteric fracture in this population.Obiective:1.Based on normal adult proximal femur CT image data,using three-dimensional reconstruction of digital technology,reconstruct proximal femur in the software of MimiCS10.0,measure anatomical data of proximal femoral (include seven groups of data,diameter of femoral medullary cavity,etc.) and then describe the morphological characteristics of proximal femoral in countrymen.2.To obtain morphologic parameters of intramedullary nailing appropriate for proximal femur fractures in Chinese population by assessing the geometric match between3kinds of intramedullary nailing(including PFNA、PFNA-II and InterTan) and Chinese proximal femurs.3.Combining measured data and analysis results,receives the data of suitable for Chinese population of idealized internal fixators system(PFNA-Ⅲ).4.3D FE model of Chinese population proximal femurs were reconstructed on a collection of the CT data,to construct3D models of common clinical intramedullary nail (PFNA、PFNA-Ⅱ and InterTan) and then they were introduced into3D FE model of proximal femur,to explore the biomechanical properties of intertrochanteric fracture fixed with3kinds of intramedullary nailing through finite element analysis (FEA)Methods:1.One hundred and twenty Chinese femurs were scanned by computed tomography.3D models of Chinese femur were reconstructed on a collection of the CT data using Mimics10.01software.Parameters of intramedullary nailing designed for proximal femur fractures were measured on the3D models.3D models of internal fixation of the proximal femur with3kinds of intramedullary nailing,Proximal Femoral Nail Antirotation (PFNA),PFNA-II and InterTan, were reconstructed using proE4.0software.The3D models of3intramedullary nailing systems were imported into the Mimics software to match the3D models of Chinese femur.The geometric match between the3nailing systems and Chinese proximal femurs was assessed by observing the relative positions between the nail and the lateral wall of femur as well as between the nail and the top of greater trochanter.2.The tip of the greater trochanter was labeled as A,the medial axis of femoral shaft was labeled as L1, the inner diameter of middle point to the lesser trochanter was labeled as d,the inner diameter of canal20mm above the d was labeled as d+20, the inner diameter of canal40mm distal to the lesser trochanter was labeled as L2,the L1and L2were intersected at O point,a line across A parallel with L2and was intersected at B point with L1, the angle (AOB) was labeled as medio lateral angle between the line OA and L1. The measurements covered d+20、d、d+20(the inner diameter of canal20mm distal to the lesser trochanter)、isthmus width and canal、the angle (AOB)、BO、AO(results can be calculated by following formula)(Figure1) L-BO=L-AO×sin (90°-∠AOB),or L-AO=L-BO/COS (∠AOB)Fig1:schematic diagram of anatomical data of proximal femoralCombining measured data and results,receives the data of suitable for Chinese population of improved internal fixators system PFNA(PFNA-Ⅲ),and to verify morphologic parameters of intramedullary nailing appropriate for proximal femur fractures in this population by assessing the geometric match between3kinds of intramedullary nailing and Chinese proximal femurs.3.One healthy volunteer was selected,male,28years old,the man with hip disorders were excluded by X-ray examination.Both hips were scanned with CT(GE’s16-row CT, America),Scanning Requirements Patients with supine on the CT bed central, rotating pairs of lower limbs to take a neutral position.The ambit is the plane of knee jointtothetip of the greater trochanter.Scanning condition:120kV,65～150mA,Scanning parallleters:The time of scanning one slice is200ms,the thickness of each slice was0.625mm,the data of seanning images are conserved in PC by DICOM,total of421pictures.Using the right proximal femur data as sample.All the CT images were imported into the Mimics13.0and segmentation was undertaken.Three dimensional model of intact femur was established by setting thresholding and modifying the morphology.and the output from STL files,then the files were introduced into software Geomagic10.0to smooth processing.3D FE model of the Tronzo-Evans I,Tronzo-EvansIV and Tronzo-Evans V intertrochanteric fracture with different fixations waere developed.The different fixations were compared for von Mises distribution, and the von Mises distribution of the femur.Results1.To measure the data based on the samples of120Chinese population proximal femurs.(table2)2.The average protrusion of the nail into the lateral femoral cortex was significantly thicker in PFNA (1.51mm) than in PFNA-II (0.12mm) and InterTan (0.33mm)(P<0.05).The average extension distance of the nail beyond the top of the proximal femur was significantly shorter in InterTan (0.25mm) than in PFNA (3.47mm) and PFNA-Ⅱ (4.11mm)(P<0.05).3.Based on the data mesured above,the diameter of main nail of PFNA-III is16mm,proximal length is62mm,twisted point is95mm from the top and the bend angle is6°.The results showed that the average thickness of the nail protruded into lateral femoral cortex is1.76mm(SD.)in PFNA,0.12mm in PFNA-II and0.18mm in PFNA-III.There was significant diffierence between PFNA and the other two kinds of midified nail(p<0.05).Meanwhile, the distance beyond the top of proximal femur is0.25mm in PFNA-III,3.47mm in PFNA and3.11mm in PFNA-II.4.Finite element simulation showed that the von Mises distribution with Tronzo-Evans I intertrochanteric fracture have little differences among these three kinds of nails, but with Tronzo-Evans Ⅳ and Tronzo-Evans V intertrochanteric fracture the InterTan was more even.The von Mises distribution on the frmur shaft contacted with tip of the nail was higher in Tronzo-Evans Ⅴ than Tronzo-Evans I and Tronzo-Evans IV intertrochanteric fracture.The highest stress concentration area on the nail is located in the medial caudal passage of the blade through the nail. Higher maximum von Mises stress in the implantwas found in the InterTan,followed by PFNA-Ⅱ and PFNA. Interestingly,Large area of high von Mises stress values were also recorded at the proximal PFNA.Conclusions1.PFNA-II,as an improvement of PFNA,has evidently reduced intraoperative invasion to the lateral wall of femur,but does not solve the problem of proximal length. InterTan,with evidently reduced invasion to the lateral wall of femur and an appropriate proximal length,has a better anatomic match for the Chinese femur. 2.Both the PFNA-Ⅱ and PFNA-Ⅲ performed less disturbance to lateral wall of the proximal femur.And the length of the nail protruding from the proximal greater trochanter decreased significantly in PFNA-Ⅲ. However,we still need to make the finite element analysis(FEA) of them to identified the most suitable nail for Asian.3.The fracture fixed with InterTan exhibited fine fixation stability, especially for Tronzo-Evans V intertrochanteric fracture was more suitable than PFNA and PFNA-Ⅱ.The uneven distribution of stress in PFNA with proximal femur may caused by the mismatch in morphology between PFNA and Asian femur.