| ObjectiveWith the development of material science,biomechanics,treatment of intertrochanteric fractures has also made a lot of progress.A variety of internal fixation devices has been made.While intramedullary nail fixation is mainstream of treatment in intertrochanteric fractures,but the occurrence of failure of internal fixation is still exist.This research retrospective analysis of clinical data,fracture reduction quality,tip apex distance,and other indicators in femoral intertrochanteric fractures patients after intramedullary nailing fixation,and try to explore the risk factors of occurrence of internal fixation failure.The finite element analysis has been used to evaluate the mechanical properties of the internal fixation devices,and to guide the design and improvement of medical devices.In this study,improved proximal femoral nail was designed based on the theory of proximal femoral "triangular fixation".Adjust the screw blade on the basis of the PFNA-II and the angle of the main nail,while increase one proximal tension screw to design a modified proximal femoral nail.Through the finite element analysis method to compare the physiology under load of modified proximal femoral nail and PFNA-II fixation of Evans IV type unstable intertrochanteric fracture.To test the rationality of the design and provide a theoretical basis and research ideas for the clinical application of the new equipment.MethodsThe patients of The First Affiliated Hospital of Guangzhou University of Chinese Medicine with the diagnosis and treatment of intertrochanteric fracture with closed reduction and intramedullary nail fixation were selected.Inclusion criteria and exclusion criteria were set.Collected the age,sex ratio,fracture side,fracture classification,reduction quality,internal fixation type,tip apex distance and fixation failure and other clinical data.Chi square test was used to compare the differences of clinical data between the patients with internal fixation failure group and non-failure group.The risk factors of the failure of internal fixation were analyzed by logistic regression.A healthy elderly male volunteer was selected and a full slice of the right femur was scanned with spiral CT.CT image data were introduced into Mimics 14.1 software.The cortical bone,cancellous bone and bone marrow cavity were separated according to the difference of gray value of different tissues,and the model was generated by three-dimensional model generation by threshold and pixel repair,regional growth and elimination of isolated points.The model of the femur was introduced into the reverse engineering software Geomagic Studio 10.0 for smoothing the meshing.Then,the model was introduced into Abaqus 12.0 for preloading experiments to verify that the model of this study was reliable and effective.The femur model was then introduced into Solidwork 2010 software to simulate Evans type ? fractures for osteotomy to establish Evans ? type intertrochanteric instability fracture model.Three-dimensional reconstruction of PFNA-? and modified proximal femoral nail was obtained from the data of PFNA-? intramedullary nail in SolidWorks 2010 software.The Evans? femoral intertrochanteric fracture model and two intramedullary nail models were introduced into SolidWorks 2010 to assemble the modified proximal femoral nail and PFNA-? internal fixation model.The location of the intramedullary nail in the femur is based on the operational criteria provided by Synthes company,and the blade screw is located in the middle posterior position of the femoral head.The fracture fixation model was then introduced into the finite element analysis software Abaqus 12.0 for analysis.Three-dimensional finite element analysis was carried out by referring to the material assignment,boundary condition and loading condition in the literature to simulate the peak time of adult biped standing position and gait cycle joint bearing.The stress distribution and stress peak of the internal fixation under the same load were obtained.The stress distribution and stress value of the femur,the displacement and sub displacement of the internal fixation model were compared to know the biomechanical properties of two different types of intramedullary nailing in the treatment of unstable intertrochanteric fractures in the elderly.ResultsA total of 107 patients of intertrochanteric fractures treated with closed reduction and intramedullary nail fixation were included,45 males and 62 females with an average age of 75.07 ± 6.16 years(65 years to 90 years),with fixation failure group(n = 10)and non-failure group(n = 97).There was no significant difference in sex ratio,fracture side,fracture classification,internal fixation and osteoporosis between the internal fixation failure group and the internal fixation non-failure group(P>>0.05).Age,the quality of fracture reduction,tip apex distance differences were statistically significant between the two groups(P<0.05).Logistic regression showed that tip apex distance greater than 25mm was most important risk of internal fixation failure.Three-dimensional finite element models of femoral intertrochanteric fractures fixed with modified proximal femoral nail and PFAN-II intramedullary nail were established.Under the two physiological loads,the stress concentration of the two internal fixation models was located at the junction of the main nail and neck screw.The internal fixation stress of the modified proximal femoral nail was slightly higher than that of PFNA-II in static and dynamic loading situtation,with the stress peaks were 228.OMpa,214.4Mpa and 618.3Mpa,575.4Mpa respectively.The femoral stress value was higher in modified proximal femoral nail fixation model,with the stress peaks were 113.4Mpa,95.8Mpa and 150.8Mpa,125.8Mpa respectively.The proximal femoral displacement of the modified intramedullary nail fixation model was slightly smaller than that of the PFNA-II group,displacement were 5.01 mm,5.37 mm and 5.18 mm,5.59 mm respectively.ConclusionThere was a high incidence of internal fixation after intramedullary nail fixation in intertrochanteric fractures.Those patients with elder age,poor reduction quality,the tip apex distance greater than 25mm had the higher risk of internal fixation failure.The tip apex distance was an important factor in predicting the failure of intramedullary nail fixation.In the clinical operation,doctors should pay more attention to ensure tip apex distance is less than 25mm,and try to reduce the possible failure of internal fixation.The finite element analysis method can simulate and verify the biomechanical properties of the new instrument,and has the advantages of comprehensive mechanical performance test and good reproducibility.Modified proximal femoral nail in the fixed unstable femoral intertrochanteric fractures have good stability.Considering the clinical situation,there was difficult to make the tension screw and the blade screw contact.In this study,a closed triangular structure between the resistance screw,the blade screw and the intramedullary nail can' t be made.The upper tension screw,which is close to the stress point,had high stress concentration.Finite element analysis is a simulation of the actual situation,trying to simplify the complex problem.There still need traditional vitro experimental biomechanics research to verify and evaluation the performance of the modified proximal femoral nail. |
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