Abstract: BACKGROUND: At present, there is no unified method to reconstruct the lateral wall after intertrochanteric fractures of femur. It is a common way to place reconstruction plates on the anterolateral side of the femoral intertrochanteric fracture, but there is little research on its biomechanics and clinical application.  
OBJECTIVE: To investigate the changes in biomechanical parameters of proximal femoral nail anti-rotation combined with anterolateral reconstruction plate for different types of unstable intertrochanteric fractures.
METHODS: CT scanning was used to scan the lower limb bone of a male volunteer. A three-dimensional model of the femur was established through the finite element method. According to whether the fracture line involved the medial wall, the lateral wall, the internal and external walls, and whether it was stably supported on the lateral wall, the model was divided to establish the corresponding fracture model: The lateral wall was unstable, and the medial wall was stable. The lateral wall was stable, and the medial wall was unstable. Both the internal and external walls of the model were unstable. Proximal femoral nail anti-rotation and anterolateral reconstruction plates were assembled at the same time. Ordinary nails or locking nails were used for fixation. The stress and displacement of fracture fragments and internal fixation of multiple models were compared and calculated by Abaqus.  
RESULTS AND CONCLUSION: (1) In the three types of unstable femoral trochanter models, the anterolateral reconstruction plate could improve the stability of the proximal femur, and restore the imbalance lever of the proximal femur to a certain extent. In the unstable type of lateral wall and the unstable type of medial wall, the locking nail is superior to the ordinary nail. In the type of unstable internal and external sidewalls, the difference between the locking nail and the ordinary nail could not be detected. (2) It is concluded that the placement of anterolateral reconstruction plate can significantly improve the stability of unstable intertrochanteric fracture of the femur, reduce the possibility of nail withdrawal and failure of internal fixation, and play a role in restoring the lever of proximal femur imbalance. Locking nail is better in mechanics than the ordinary nail.

Key words: lateral wall, medial wall, fracture fixation, finite element analysis, anterolateral reconstruction plate, unstable intertrochanteric fracture of femur, proximal femoral nail anti-rotation, lever fulcrum balance