Finite element analysis of medial wall fixation of proximal femur

Objective To explore the significance of proximal femoral medial wall plating by finite element analysis of the stability after medial wall fixation of the proximal femur in all types of 6-part classification of femoral intertrochanteric fractures. Methods Finite element method was used to establish models of 7 types of 6-part classification of femoral intertrochanteric fractures which were fixated with proximal femoral nail anti-rotation (PFNA), medial wall plating (bi-cortex), PFNA+medial wall plating (uni-cortex). The boundary conditions and material properties were defined according to the data published in literature. A load of the peak hip stress was applied in simulation of a normal adult of 70 kg in weight walking. The conditions above produced the Von Mises stress diagrams and Min Principal stress distributions of the normal femur for 21 groups of internal fixation models. The stability of the model was assessed by analyzing the peak stress value of the key part and fragmental displacements in each group. Results In 7 types of fractures fixated with PFNA, the changes in stress and fragmental displacement were small for all major femoral parts while the fragmental displacement increased in the greater trochanter. In the medial wall plating, the stress increased obviously with the increase in bone fragments, especially the lateral ones, for the significant femoral parts and internal fixation, and the fragmental displacements increased greatly but the displacement was always limited for the medial fragments. In the fixation with PFNA+medial wall plating, the stress changes and fragmental displacements for significant femoral parts were the smallest of the 3 fixation methods. Conclusions Proximal femoral plating can effectively reduce stress concentration at the proximal femur and provide better support for the medial wall of the proximal femur. For unstable fractures, PFNA plus medial plating may provide rigid fixation because it better reduces stress on the femur than simple PFNA, does not increase fragmental displacements and leads to no significant abnormal changes in internal fixation structure. Key words: Femur; Fractures, bone; Fracture fixation, internal; Proximal femoral medial wall