Finite element analysis of the impact of screw insertion distal to the trochanter minor on the risk of iatrogenic subtrochanteric fracture.

Iatrogenic subtrochanteric fractures are rarely encountered after cannulated screw fixation of femoral neck fractures; however, when they do occur, there can be several complications. Many orthopedic surgeons have concerns about the potential for iatrogenic subtrochanteric fractures after screw fixation distal to the trochanter minor; therefore, some surgeons are typically reluctant to perform this procedure. This study focused on the risk of an iatrogenic subtrochanteric fracture after treating femoral neck fractures with cannulated screws. The main purpose of the study was to understand iatrogenic subtrochanteric fractures and evaluate the effects on these fractures of an inverted triangular-shaped configuration for placement of the cannulated screws. A femur bone with an femoral neck fracture at a 40° incline to the horizontal plane was generated along with a representation of a three-dimensional finite element model, and three inverted triangular-shaped configurations for placement of the cannulated screws were investigated using finite element analyses. Statistical results indicated that the occurrence risk of ISF increases when the screw is located distal to the trochanter minor. Moreover, the risk of occurrence of intertrochanteric fracture increases when the screw is located medial to the trochanter minor because of local concentrated stress on the surface of the screw canals. To avoid the vulnerability of the subtrochanteric region, it was found that proximal placement of the screws using the inverted triangular-shaped configuration could yield better results. In addition, the results of this study provide suggestions on improved screw configurations.