## 4 Discussion  
The results of this study provide critical insights into the biomechanical performance of the prosthesis-femur-derotation plate system, specifically its ability to withstand physiological loading conditions while maintaining structural stability. The findings confirm the robustness and reliability of the derotation plate, validating its role in addressing the challenges associated with subtrochanterior shortening osteotomy in complex cases of hip dysplasia, particularly Crowe type IV. Previous studies have highlighted the importance of proper implant design in achieving optimal biomechanical stability in total hip arthroplasty for severe hip dysplasia [43; 44]. The von Mises stress distribution analysis highlighted critical stress concentrations at the femoral head, prosthesis-bone interface, and locking screw holes of the derotation plate. The maximum stress values remained significantly below the yield strength of the materials used, particularly the titanium alloy of the plate. This demonstrates the mechanical efficiency of the design in managing high loads without the risk of failure. The uniform stress distribution observed in the plate further supports its durability and suitability for long-term clinical use. Similar findings have been reported in finite element studies analyzing osteotomy fixation and implant stability [45; 46]. Figure 7: Radiograph of the hip joints of a patient with Crowe type IV dysplasia of the left hip joint: (**a**) before surgery, (**b**) three months after surgery. A displacement analysis revealed that the derotation plate exhibited minimal displacement under applied loads, with values considerably lower than those at the prosthetic head. This underscores its role in stabilizing the femur and mitigating rotational and axial displacements. The minimal displacement not only ensures mechanical stability but also contributes to promoting osteotomy healing by reducing micro-movements that could otherwise delay bone union. These findings align with previous research that emphasized the importance of displacement control in osteotomy fixation [47; 48]. The safety factor evaluation demonstrated that all components of the system, including the derotation plate, maintained a sufficient margin of mechanical safety. The minimum safety factor for the plate, at 3.63, reflects its ability to handle peak stress loads without the risk of material failure. However, the lower safety factor values observed in the bone (1.24) warrant attention, as they indicate areas of potential vulnerability, particularly under extreme loading conditions. Future studies could explore methods to enhance bone strength in these regions, possibly through preoperative planning or additional fixation techniques. Similar biomechanical assessments of orthopedic implants have stressed the need for careful safety factor evaluations to minimize implant-related complications [49]. The focused analysis of the derotation plate revealed that the highest stress concentrations occurred at the screw holes, a finding that highlights the importance of precise screw placement to minimize localized stress peaks. The observed stress levels in this study, however, remained well within safe limits, reaffirming the reliability of the plate's design and material selection. Compared to traditional fixation methods, such as cable fixation or less rigid plate designs, the derotation plate used in this study demonstrated superior biomechanical performance. Its ability to uniformly distribute stress and control displacement offers a significant advantage in reducing complications, like nonunion, rotational instability, and implant loosening. Studies analyzing osteosynthesis techniques in hip arthroplasty have similarly reported that rigid fixation systems provide improved mechanical outcomes compared to conventional methods [43; 46]. The implications of this research extend beyond the specific case of [PERSON] type IV hip dysplasia.