| BackgroundDue to its special anatomical features and its important role in human movement and weight bearing,the femoral neck has always been a research hotspot in the field of orthopedics and sports medicine.The femoral neck is prone to fracture,especially in the case of osteoporosis in the elderly.Slight injury can cause fracture,while in the young and middle-aged patients,most of them are high-energy injuries.Therefore,the incidence of femoral neck fractures is relatively high,and the condition is relatively complicated.Although the treatment of femoral neck fracture is various,there are many complications in the treatment.So far,it has not been well solved,which has become clinically the problem of treatment.The femoral neck fracture has long been considered to be an "unresolved fracture".At present,the choice of treatment methods for femoral neck fractures has basically reached a consensus,but it has not been promoted,especiallyin the choice of internal fixation,because it is affected by many factors including age,fracture type,mental factors,doctor’s treatment level,etc.The treatment of femoral neck fracture mainly includes internal fixation,hemi-hip or total hip arthroplasty and conservative treatment.At present,the main point of treatment for femoral neck fractures is that closed internal fixation is the first choice for non-displaced femoral neck fractures.For patients with displaced femoral neck fractures,if the age is less than 65 years,internal fixation is preferred;For patients with displaced fractures,if the age is more than 65 years,hip replacement is preferred;hemi-hip arthroplasty can be selected within the 5-year survival rate of super-aged patients.However,some scholars believe that as long as patients older than65 or even 60 years of age can be treated with artificial joint replacement regardless of the type of fracture,the reason is that the current arthroplasty and artificial joint prosthesis progress and long-term follow-up survival can reach 30 years or even higher.At present,there are many internal fixation methods available.The most commonly used are cannulated screw,dynamical hip screw(DHS),and proximal femoral plates.There are many methods for classification of femoral neck fracture.Pauwels classification and Garden classification are commonly used in clinical practice.Pauwels classification is divided into 3 types according to the angle between the fracture line and the horizontal line.The angle of Pauwels type I fracture is less than 30°,the angle of Pauwels type IIfracture is 30° to 50°,and the angle of fracture of Pauwels type III fracture is greater than 50°.The angle of the fracture line is related to the stability of the fracture.The greater the degree,the bigger the shear stress on the fracture end,the more unstable the fracture.The Garden classification was proposed by Professor Garden of the Royal Preston Hospital in the United Kingdom in 1961.It is one of the most commonly used types of femoral neck fractures.Garden type I refers to an incomplete fracture,Garden II is a complete fracture,and there is no obvious displacement of the fracture end.The Garden III fracture is a complete fracture,the fracture end is partially displaced,and the Garden IV fracture is a complete fracture,and the fracture end was completely displaced.For type III and IV fractures,to reduce the risk of fracture nonunion or femoral head necrosis,anatomical reduction of the fracture ends must be followed by cannulated compression screw or other internal fixation.At present,medical biomechanical research mainly includes corpse specimens in vitro experimental research and computer finite element biomechanical research.Finite element analysis(FEA)is a theoretical method of biomechanical research.It can simulate geometric models of various structures,imparting biomaterial properties to various tissues,and can reflect the overall trend of biomechanical properties.Therefore,it can be used as a good complement of specimen experimental mechanics research.With the advancement of computer hardware and softwaretechnology,the application of FEA in biomechanical research has become more and more extensive.More studies have shown that the number of screws and their spatial configuration will affect their biomechanical stability and the prognosis of fractures,However,there are few reports on the biomechanical study of single-head or double-head compression screw fixation and whether two screws can be used for treatment of femoral neck fracture.At present,there is no method for modeling internal fixation using the method of three-dimensional(3D)scanning technology in finite element analysis.Objectives:In this study,Using computer software technology to establish fracture finite element models and to calculate the displacement of the femoral head,the stress distribution of the femoral neck and screws,and to provide a theoretical basis for the selection of screw types and the spatial arrangement of screw implant in the clinical treatment of femoral neck fracture.At the same time,it is compared with the results of the cadaver specimens to verify the validity of the finite element model and provide a basis for other simulations in the later period.Then,according to the clinical application follow-up results,the efficacy of two types of screws for treatment of femoral neck fracture was analyzed.Methods:1.Establishment of a 3D model of the proximal femurThin-layer(1-mm slice thickness)computed tomography(CT)was performed on the proximal femur of a healthy adult volunteer.Scanning from the upper femur,about 218 slices two-dimensional CT images were obtained.Data was saved as the DICOM(Digital Imaging and Communications in Medicine)format,Thereby,the original DICOM data was imported into the Mimics software to be sequentially arranged.Grayscale images including soft tissues and backgrounds such as bone tissue and muscles can be obtained in the interface.The image is preprocessed to improve its resolution and smoothness.Using the selection tool provided by Mimics software to carry out the regularization of the bone marrow cavity.According to the different density and the gray value on the image of the tissue are different,data of femur tissue is extracted.The software’s self-extracting function and erasing filling function are used to gradually improve the image quality of the tissue.A rough model of the bone tissue was obtained and saved as a STL file.The STL file is imported into Unigraphics 8.0(UG)software,and the surface is fitted and smoothed to form a three-dimensional solid model of the femur,which is convenient for subsequent processing and finite element model establishment and analysis.2.Acquisition of screws 3D modelsThe screws selected in this experiment are the commonly used AO screw and the double-head screw of General Care Corporation.They areinversely modeled by 3D laser scanning technology to be ready for the assembly of the fracture internal fixation model.3.Model AssemblyThe model of femoral neck fracture(Pauwels 60°,III degree)was established in UG 8.0 software.The model assembly was completed according the spatial configurations of the two types of screws,which were implanted in the above model with in an inverted triangle,with 2 horizontal and vertical distributions.In the same configuration model of the different screws,the screws have a common axis to ensure that they have exactly the same position and length.This modeling method greatly improves the accuracy of the experiment,is more realistic and reliable,and reduces the error of manually drawing the internal fixation 3D model.4.Establishment and analysis of finite element model of proximal femurThe assembled model was imported into Ansys 17.0(Inc.,Canonsburg,PA,USA)software for finite element calculations.The proximal femoral fracture model was meshed,and all models were made of solid 185 units,especially,the mesh was refined around the contact surface between the bone and the screw and the fracture block of the femoral neck fracture.The loading method of this model was fixed at the bottom of the femur,and the coupling node at the top of femur head was loaded.Loading was performed slowly to 600 N at the top of the femoral head and was then submitted toLS-DYNA for quasi-static calculation.The mechanical properties of the six internal fixation models were comprehensively analyzed by three indicators:(1)displacement of femur head;(2)stress distribution position and stress peak of femur head,neck and lateral wall of femur;(3)stress distribution position and stress peak of screws.5.Clinical researchRetrospective analysis of 25 cases of femoral neck fractures from October 2015 to June 2017 in the Department of Orthopaedics,the First Affiliated Hospital of Chongqing Medical University.According to Garden classification,there were 15 cases of Garden I and II fractures,7 cases of Garden III fractures and 3 cases of Garden IV fracture.The eligible patients were classified into observation group(12 cases,group A)and control group(13 cases,group B).Group A were fixed with DhCCS and group B were fixed with OCCS.The statistical indexes were:(1)Intraoperative blood loss,(2)Operation duration,(3)Postoperative fracture healing time,(4)Postoperative function scores of the hip joint.Results:1.The results of FEAIn this study,the proximal femoral CT data were used to establish a finite element model of femoral neck fracture(Pauwels 60°,III degree)screw fixation with Mimics,UG,Ansys software,etc.,which had a high geometric similarity with normal human body.Moreover,the studyinnovatively used 3D laser scanning reversely modeling the screws,and then model assembles were performed in UG software,which solved the manual error caused by the previous hand-drawn modeling.The displacements of the femoral heads of the six models were as follows: the displacement of the DhCCS horizontal fixation group,vertical fixation group and three DhCCS fixation group was 0.0890 mm,0.1479 mm and0.0646 mm,respectively;The displacement of the OCCS horizontal fixation group,vertical fixation group and three OCCS fixation group was0.1259 mm,0.2131 mm and 0.0767 mm,respectively.The stress distribution features of the six groups were as follows: The stress on the bone surface at the fracture end of the DhCCS fixation group was lower than that of the OCCS group.The maximum stress peak of the DhCCS horizontal fixation group,vertical fixation group and three DhCCS fixation group were109.2MPa,126.5MPa and 96.2Mpa,respectively.The maximum stress peak of the OCCS horizontal fixation group,vertical fixation group and three OCCS fixation group were 121.5Mpa,137.3Mpa and 113.3MPa,respectively.It could be seen from the stress cloud diagram that the stress distribution at the femoral head and neck section of the DhCCS fixation group was more dispersed,and the corresponding stress distribution of the OCCS group relatively concentrated.The stress distribution of the DhCCS fixation group was obvious on the lateral wall of the femur,while the stress distribution of the OCCS group was not obvious.The stress distribution onthe screw mainly concentrated on the screw at the fracture end,.The stress on the screw of the OCCS group was larger than that of the DhCCS group,and the stress of the vertical fixation group was larger than that of the horizontal fixation group.The stress distribution in the horizontal fixation group was larger in the front screw and smaller in the rear screw.The stress distribution in the vertical groups concentrated on the upper screw.The maximum stress peak on the screws of the DhCCS horizontal fixation group,vertical fixation group and three screws fixation group were88.3Mpa,167 Mpa and 80.2Mpa,respectively;The maximum stress peak on the screws of the OCCS horizontal fixation group,vertical fixation group and three screws fixation group were 122.3Mpa,183.5Mpa and103.7Mpa,respectively.The results of the study were compared with that of the cadaver specimens experimental biomechanics,which proved the feasibility of modeling and can accurately and completely simulate the stress characteristics of femoral neck fractures,which was conducive to biomechanical analysis.2.Clinical application results(1)Intraoperative blood loss: Except for a case of difficult to reconstructive femoral neck fracture with open reduction and fixation,the other 24 patients were treated with closed reduction.Therefore,the intraoperative blood loss was less than 10 ml.(2)Operation duration: Thetime of the two screws fixation groups in the observation group and the control group was 30 minutes and 33 minutes,respectively(only one case in each group).The average operation time of the three screws in the observation group and the control group was 42 minutes and 45 minutes,respectively.There was a significant difference in the operation time between the two screws fixation groups and the three screws fixation groups(P<0.05).(3)Postoperative fracture healing time: The average healing time of the fractures in the observation group and the control group was 4.3 months and 5.2 months,respectively,and there was a statistical difference between the two groups(P<0.05).(4)Evaluation of hip function:According to the Harris score method,the excellent and good rate of the group A and B reached 91.6% and 76.9%,respectively.There was a significant difference between the two groups(P < 0.05).Conclusion:(1)The fixation biomechanical stability of DhCCS was better thanthat of OCCS.(2)The biomechanical stability of 2 horizontal fixation was better than that of vertical fixation.(3)The biomechanical stability of 2 horizontal DhCCS fixation showed no obvious difference with three OCCSs.The horizontal fixation of2 DhCCS was sufficient to provide the same mechanical strength as the three OCCSs.(4)There was no significant difference between the three-screw groups.This was consistent with the biomechanical research results of mainstream scholars.(5)The 2 vertical OCCS group had the worst biomechanical effect in this study.(6)Clinical results also showed that the DhCCS group was superior to the OCCS in the fracture healing time and hip function score.About the operation duration,the two screws fixation groups were significantly less than three screws fixation groups.Therefore,DhCCS has better biomechanical stability than OCCS.Clinically,DhCCS can be used to treat femoral neck fractures.DhCCS is more suitable for noncomminuted and stable femoral neck fractures to obtain the first-stage healing of fractures.If the femoral neck is small,a nondisplaced or slightly displaced fracture may be treated with two horizontal fixations. |
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