Experimental Stress Analysis And Finite Element Calculation Of Intertrochanteric Fracture Of Intramedullary Nailing

Objective To compare the biomechanical properties of two screws when they are placedin different points of the neck of femur in the treatment of intertrochanteric fracture offemur utilizing proximal femoral nail(PFN).Method Three pairs of fresh femora of adults aging from55to65are taken. They aremade into AO type A1.1intertrochanteric fracture after Computed Tomography (CT)data have been gained by Philip Brilliance64CT. Fracture specimens are fixedrespectively by PFN.Experimental Stress Analysis：For the mid-blow part, two screws are placed in themid-blow1/3part of the neck of femur, while for the mid-above part, two screws areplaced in the mid-above1/3part of the neck of femur. Six strain gauges are sticked to thetwo sides of the small trochanter femoral section symmetrically. One temperaturecompensation strain gauge is sticked to the far end of the small trochanter. Whiteadhesive tapes are sticked to the relatively flat femoral surfaces which are perpendicularto the two sides of the fracture section. Straight lines are drawn on the adhesive tapeswith Mark pen. The mechanical testing machine loads the fracture model at a speed of0.5mm/s. The stress distribution of the fracture broken ends, the opening angle of thefracture broken ends, and the relationship between load and displacement are recordedrespectively.Finite Element Calculation：Three pairs of femur three dimension (3D) models areestablished in Mimics utilizing the CT data. They are made into AO type A1.1intertrochanteric fracture models respectively. The PFN3D models which wereestablished in the Catia are placed in the mid-blow1/3part and the mid-above1/3part ofthe fracture model respectively by Boolean operation. The femur and the PFN are giventhe material attributes. Finite element calculation is taken in the Abaqus simulatinghuman normal standing.Result1. The Stress Distribution of the Fracture Broken Ends. The experimental result:the stress change of the mid-blow part of the small trochanter is smaller than that of themid-over part. The results of finite element calculation: the stress beard by the mid-blowpart of the small trochanter is smaller than the stress beard by the mid-over part; theaverage value of the maximal stress beard by each PFN screw of the mid-blow part isbigger than that of the mid-over part.2. The Opening Angle of the Fracture Broken Ends.The experimental result: the opening angle of the fracture broken ends of the mid-blowpart is smaller than that of the mid-over part both during and after the procedure ofloading. The results of finite element calculation: the opening angle of the fracturebroken ends of the mid-blow part is smaller than that of the mid-over part both after theprocedure of loading.3. The Relationship between Load and Displacement. The experimental result: the displacement of the top of the head of femur of the mid-blowpart is smaller than that of the mid-over part both during and after the procedure ofloading. The results of finite element calculation: the total displacement of the top of thefemur of the mid-blow part is smaller than that of the mid-over part after the procedure ofloading.Conclusion Both in the experimental stress analysis and the finite element calculation,the performance of the mid-blow part is better than that of the mid-over part. Thus it canbe concluded that when the two screws are placed in the mid-blow1/3part of the neck offemur, the biomechanical properties are better, the structure is relatively more stable, andthe stress bearing is more reasonable. In clinical trials, it has important reference value.