Abstract: BACKGROUND: At present, there is a main kind of operation, which is represented by the proximal femoral nail antirotation, to treat femoral intertrochanteric fractures, but some sequelae still occur such as internal fixation loosening, failure, and nail withdrawal. We designed a new femoral neck spiral blade system to solve this problem, so we analyze the mechanical structure by the finite element method that can be regard as the theoretical basis for the system.
OBJECTIVE: To compare the mechanical properties of the new femoral neck spiral blade system and the proximal femoral nail antirotation in the treatment of femoral intertrochanteric fracture by the finite element method.
METHODS: Based on the finite element model of the femur, the A1.2 and A2.2 femoral intertrochanteric fracture models were established according to the AO fracture classification principle of 2018 edition. The models were fixed with the proximal femoral nail antirotation and the new internal fixation system, applying an axial load of 700, 1 400, and 2 100 N above the femoral head. The mechanical characteristics of the two internal fixation methods were respectively compared and analyzed by observing the maximum equivalent stress and the maximum deformation of each group.
RESULTS AND CONCLUSION: (1) The maximum equivalent stress of the new internal fixation group under different compressive loads was smaller than that of the proximal femoral nail antirotation group. (2) In the A1.2 fracture model, under different compression loads, the deformation of the new internal fixation system was smaller than that of the proximal femoral nail antirotation group, and the average value of difference between the two was 1.113 mm; the result of the A2.2 type fracture model was the same as that in the A1.1 with an average value of difference of 2.017 mm between the two. (3) In the A1.2 fracture model, under different compressive loads, the maximum deformation of the spiral blade fixed by the new internal fixation system was smaller than that of the proximal femoral nail antirotation group, and the average value of difference between the two was 1.062 mm; the result of the A2.2 type fracture model was the same as that in the A1.1 with an average value of difference of 1.891 mm between the two. (4) The results indicate that the new femoral neck spiral blade system has a lower internal fixation stress value compared to the proximal femoral nail antirotation, and a smaller displacement value of the femur after fixation and internal fixation. It can more effectively fix fractures and prevent the spiral blade from retracting or cutting out in the femoral neck. 

Key words: new femoral neck spiral blade system, femoral intertrochanteric fracture, finite element analysis, equivalent stress, compression load, mechanical property, biomechanics