Biomechanical evaluation of intramedullary retrograde nail and dynamic condylar screw used in unstable distal femoral fractures

Distal femur fractures are a common problem in orthopedics. Intramedullary retrograde nails (IRN) and dynamic condylar screws (DCS) are generally used for the treatment of these fractures. In this study, it was aimed to mechanically evaluate and compare these two implants used for the treatment of distal femur fractures. In this study, an AOOTA 33C1.3 fracture was created on the intact femur obtained from computed tomography images. The fractures were fixed with DCS and IRN. Then the created models were imported into the ANSYS Workbench for finite element analysis to determine the most convenient mechanical fixation type. The distal region of the femur was loaded considering 75 kg-f, and the created models were constrained in all directions from the femoral head. The intact femur was also analyzed to compare it with the DCS and IRN fixation models. The von Mises stress, strain, and displacement results were examined to determine the damage risk. According to the results, the risk of damage is lower in the model of fixation with IRN. The normal strain distribution in the model fixed with IRN is closer to the model of an intact femur. For this reason, the risk of stress shielding in IRN fixation is less than in DCS fixation. However, the fracture lines were more stable in the fixation with the DCS. In conclusion, fracture fixation with IRN is mechanically more suitable for distal femur fractures in terms of fracture healing.