## 3 Results  
The FEA provided an in-depth evaluation of the biomechanical performance of the prosthesis-femur-derotation plate system under physiological loading conditions. The analysis revealed key insights into stress distribution, displacement, and safety factors, confirming the mechanical reliability and robustness of the system components. The von Mises stress analysis highlighted the stress distribution across the system, focusing on critical load-bearing areas. The results of this analysis are visualized in Figure 3, which demonstrates stress concentrations at the femoral head, the prosthesis-bone interface, and the derotation plate. The maximum stress of \(167.2\) MPa was observed at the femoral head due to the concentration of vertical and horizontal forces. The prosthesis-bone interface experienced a stress value of \(122\) MPa, while the derotation plate showed a peak stress of \(76\) MPa. These values are well below the yield strength of their respective materials, ensuring safe operation under normal and extreme loading conditions. The uniform stress distribution across the derotation plate further demonstrated its capability to handle biomechanical loads effectively without the risk of mechanical failure. The displacement analysis provided further insights into the relative movement of the system elements under loading conditions. Figure 4 highlights the displacement distribution within the system. The maximum displacement of \(0.1451\) mm occurred at the prosthetic head, while the derotation plate exhibited minimal displacement, with a value of \(0.08\) mm. This underscored the plate's stabilizing role in the system and its ability to control rotational and axial movements effectively. These results highlight the plate's contribution to maintaining the mechanical integrity of the osteotomy site and ensuring the long-term stability of the system. Figure 3: Von Mises stress distribution (MPa): (**a**) stress on the femur under physiological loading, with maximum stress at the femoral head, (**b**) stress at the prosthesis–bone interface, showing concentrations in the prosthetic head region, (**c**) stress on the derotation plate, with maximum stress near the screw holes. The safety factor evaluation provided a comprehensive assessment of the mechanical reliability of the system. The distribution of safety factors across the system components is visualized in Figure 5, which emphasizes the robustness of the derotation plate. The minimum safety factor of 3.63 was observed in the plate, while the bone and endoprosthesis exhibited safety factors of 1.24 and 2.26, respectively. These results underscore the importance of precise screw placement and material selection in minimizing stress concentrations and ensuring the long-term durability of the implant. A focused analysis of the derotation plate revealed its stress concentrations under load. Figure 6--von Mises stress on the derotation plate (MPa)--shows the highest stress, 76.02 MPa, localized around the screw holes. This value is significantly lower than the yield strength of  
Figure 4: Displacement of system elements (mm): (**a**) displacement of the femur under applied physiological loading, with maximum values observed at the prosthetic head, (**b**) displacement distribution at the prosthesis–bone interface, showing the highest displacement at the prosthetic head region, (**c**) displacement of the derotation plate, with minimal values concentrated near the plate body and screws, indicating its stabilizing role. The arrows in the figure represent the applied loading directions in the finite element analysis. Figure 5: Safety factor of the system: (**a**) safety factor distribution for the femur under applied loading, with the minimum value of 1.24 observed near the cortical bone, (**b**) safety factor at the prosthesis–bone interface, showing a minimum value of 2.26 near the prosthetic neck region, (**c**) safety factor of the derotation plate, with a minimum value of 3.63 localized near the screw holes, indicating sufficient strength reserves.