Three-dimensional Finite Element Analysis Of The Treatment Of Femoral Neck Fracture Of Young Pauwels Ⅲ With Internal Fixation With Cannulated Screws Of Different Layouts

Objective: Three cannulated screws with four different arrangements were used to compare and analyze the effect of three cannulated screws with four different arrangements on the Pauwels III femoral neck fracture model.To comprehensively evaluate the fixation characteristics of three cannulated screws arranged in different arrangements,analyze the biomechanical stability of four internal fixation methods,and provide theoretical basis and Suggestions for the clinical treatment of Pauwels III type femoral neck fracture..Methods: The volunteers were scanned with CT to collect data on the proximal femur.In Mimics20.0,the cortical bone and cancerous bone regions of the femur were isolated by setting the gray threshold,manual segmentation and region growth,and the 3d geometric model of the femur was obtained by software function.The preliminary geometric model obtained from Mimics 20.0 is imported into Geomagic Studio 12.0in STL format for surface repair,feature removal and smoothing to make the model more accurate,and finally the graph is converted to NURBS surface and the point cloud data is converted to solid model.The processed solid model was imported into Hypermesh 14.0 in SAT format,and a Pauwels type III femoral neck fracture section with Pauwels Angle of 70° was established,and cannulated internal fixation was assembled for grouping.In group a,three cannulated screws were arranged in parallel in an "inverted triangle" manner.Group b: the two screws were placed parallel to the upper part of the lesser trochanter,in the same horizontal position as the lower part of group a and at the same implantation Angle.A third screw is inserted in the greater trochanter in the direction of the fracture line perpendicular to the femoral spur.Groupc: two cannulated screws were implanted in parallel to the femoral calar level and the greater trochanter perpendicular to the fracture line.The fracture line of the femoral neck was divided into three parts on average.The second screw was parallel to the first screw and passed vertically through the junction of one third of the fracture line,located at the posterior side of the femoral neck.Group d: the two screws were placed parallel to the upper part of the lesser trochanter,in the same horizontal position as the lower part of group a and at the same implantation Angle.A third screw is inserted with the greater trochanter horizontally perpendicular to the femoral spur and perpendicular to the longitudinal axis of the femoral shaft.After grouping,fine mesh division and nonlinear material attribute assignment were performed to generate a complete finite element model for internal fixation of femoral neck fracture.Finally,the finite element software Abaqus 6.13-4 was introduced to simulate the corresponding response force of the muscles in walking gait stage.A load vector of2317 N was applied to the femoral head at an Angle of 24° on the coronal plane and15° on the sagittal plane.The load vector of 702 N ACTS on the greater trochanter at an Angle of 28° on the coronal plane and 21° on the sagittal plane with the long axis of the femoral shaft.Under the two loading conditions,the model of the distal part of the femur was constrained as the boundary condition,and the fracture surface was assumed to be completely broken and in contact with a friction coefficient of 0.2.The stress distribution of bone displacement and internal fixation in four models was analyzed and compared..Results:In the four sets of models,a hollow screw in groups a,c and d had a plastic strain due to the concentration of stress due to the large mises stress value,which reached the peak at 0.25 s under the maximum stress state.The peak displacement of femoral head in the four groups of models was a:0.707 mm,b:0.791 mm,c:1.063 mm,d:0.941 mm.The displacement peaks at the fracture line were a:0.0116 mm,b:0.070 mm,c:0.178 mm,and d:0.120 mm,respectively.The displacement trend above the fracture line in group b,c and d increased compared with that in group a,and the overall trend of the displacement difference between the two sides of the fracture line in group c was significantly improved compared with that in group a..Conclusion: Model by the finite element analysis,group b similar therapeutic effectwith a set of models,but effectively improved the internal fixation of the problem of stress concentration,by two vertical fracture line hollow nail fixed on group c Pauwels III femoral neck fracture end fracture displacement and stability has a certain effect,the result of the experiment needs further by biomechanics and clinical research..