This study investigates the biomechanical effects of a unilateral external fixator in treating different types of femoral fractures using finite element analysis (FEA). The research focuses on three fracture types: simple oblique, AO32C3 comminuted, and 20 mm gap transverse fractures. The study aims to evaluate the stability and effectiveness of the unilateral external fixator in these scenarios. The results show that the fixation stiffness decreases significantly in the 20 mm gap fracture, leading to higher displacement, interfragmentary movement (IFM), and stress distribution at the pin-bone interface. These factors increase the risk of delayed union, pin loosening, infection, and implant failure. In contrast, the stress observed on the fracture surfaces was relatively low and controlled, indicating that bone union is still possible in all models. The study also highlights that the unilateral external fixator may provide desirable results in smaller fracture gaps but could be problematic in larger gaps. The findings suggest that surgeons and researchers should consider the biomechanical stability of fixation in different fracture types and how it affects bone union. The study uses a validated finite element model to simulate the biomechanical behavior of the external fixator under stance phase conditions. The model was validated experimentally, showing a high degree of accuracy in predicting the mechanical behavior of the femur under axial compression. The study concludes that the unilateral external fixator is suitable for smaller fractures but may not be appropriate for larger gaps. The results provide insights into the biomechanical stability of fixation in different fracture types and the potential risks associated with their treatment. The study also emphasizes the importance of considering the mechanical environment for bone healing and the need for careful selection of fixation methods in different fracture scenarios.This study investigates the biomechanical effects of a unilateral external fixator in treating different types of femoral fractures using finite element analysis (FEA). The research focuses on three fracture types: simple oblique, AO32C3 comminuted, and 20 mm gap transverse fractures. The study aims to evaluate the stability and effectiveness of the unilateral external fixator in these scenarios. The results show that the fixation stiffness decreases significantly in the 20 mm gap fracture, leading to higher displacement, interfragmentary movement (IFM), and stress distribution at the pin-bone interface. These factors increase the risk of delayed union, pin loosening, infection, and implant failure. In contrast, the stress observed on the fracture surfaces was relatively low and controlled, indicating that bone union is still possible in all models. The study also highlights that the unilateral external fixator may provide desirable results in smaller fracture gaps but could be problematic in larger gaps. The findings suggest that surgeons and researchers should consider the biomechanical stability of fixation in different fracture types and how it affects bone union. The study uses a validated finite element model to simulate the biomechanical behavior of the external fixator under stance phase conditions. The model was validated experimentally, showing a high degree of accuracy in predicting the mechanical behavior of the femur under axial compression. The study concludes that the unilateral external fixator is suitable for smaller fractures but may not be appropriate for larger gaps. The results provide insights into the biomechanical stability of fixation in different fracture types and the potential risks associated with their treatment. The study also emphasizes the importance of considering the mechanical environment for bone healing and the need for careful selection of fixation methods in different fracture scenarios.