Does the distal screw location in the Biplane double-supported screw fixation technique affect the risk of subtrochanteric fractures after femoral neck fixation? A finite element analysis

Research indicates that in the traditional method of cannulated screw fixation for femoral neck fractures, placing the distal screw beyond the lesser trochanter increases the risk of subtrochanteric fractures. In the Biplane double-supported screw fixation technique (BDSF), the lowest screw needs to be inserted at a high inclination angle, making its entry point further from the lesser trochanter. This could increase the risk of iatrogenic subtrochanteric fractures and compromise the stability of the fracture fixation structure. However, there is currently a lack of research on this issue. Using BDSF technology to treat Pauwels III femoral neck fractures, we established finite element analysis models with three different distal screw insertion positions (models a, b, c). We determined a range on the lateral cortex midline of the femoral shaft that meets all the requirements for distal screw insertion using BDSF technology. The distal screws were inserted at three positions within this range: upper, middle, and lower, marked as A, B, and C, respectively. Model a: fracture fixation model with insertion point at (A) Model b: fracture fixation model with insertion point at (B) Model c: fracture fixation model with insertion point at (C) Under the same load conditions, finite element analysis was performed on the displacement of the internal fixation and femur, the stress distribution, and the stress distribution in the subtrochanteric region for the three models. Among the three models we studied, there was no statistically significant difference in the stress magnitude in the subtrochanteric region.Model b had the lowest peak stress values for both the femur and the internal fixation, with displacement values of the femur and internal fixation being close to the minimum. Overall, implanting the distal screw in the middle of the reasonable range of screw placement can provide better stability. From the perspectives of the maximum displacement of the femur and internal fixation, the maximum stress, and the stress distribution in the subtrochanteric region, implanting the distal screw from the middle position can provide better stability for the fracture ends without increasing the risk of subtrochanteric fractures.