## 5 Conclusions  
This study demonstrated the biomechanical efficiency and reliability of the prosthesis-femur-derotation plate system in treating Crowe type IV dysplastic covarthrosis. Through finite element analysis, the derotation plate proved to be an effective solution for stabilizing the femur, maintaining axial alignment, and preventing rotational movement during subtrochanter shortening osteotomy. By restoring the anatomical and biomechanical axis of the limb, the system addresses critical challenges in complex hip reconstruction. The von Mises stress analysis confirmed that all components of the system, including the derotation plate, remained well within their respective material strength limits. With a maximum stress of 76 MPa localized at the screw holes, the titanium plate demonstrated superior load-carrying capacity, significantly below its yield strength (900-1100 MPa). Additionally, the prosthesis and bone experienced maximum stresses of 122 MPa and 167.2 MPa, respectively, further verifying the system's resilience under physiological loading conditions. A displacement analysis revealed that the prosthetic head had the highest movement at 0.1451 mm, while the derotation plate exhibited minimal displacement of 0.08 mm, ensuring stability and effective load distribution. This result underscores the plate's capacity to minimize micro-movements at the osteotomy site, which is crucial for promoting bone healing and maintaining structural integrity during early postoperative recovery. The safety factor evaluation highlighted the robustness of the system, with the derotation plate maintaining a minimum safety factor of 3.63, indicating sufficient strength reserves. Although the bone exhibited a lower safety factor of 1.24, the overall system stability remained uncompromised, ensuring reliable performance under clinical conditions. The findings validate the system's superior biomechanical performance compared to traditional fixation methods, offering an optimized solution for treating complex hip dysplasia. By evenly distributing stress, reducing displacement, and providing enhanced fixation stability, the derotation plate improves surgical outcomes while mitigating risks, such as rotational instability and nonunion. This research emphasizes the importance of advanced computational modeling, such as finite element analysis, in optimizing implant design and improving clinical efficacy. The quantitative data provided by this study serve as a foundation for further clinical investigations and experimental validation under dynamic and cyclic loading scenarios. Conceptualization, D.O. and K.A. ; methodology, M.A., R.Z., and T.B. ; software, B.A. and N.B. ; validation, R.Z., B.G. ([PERSON]), and B.G. ([PERSON]); formal analysis, B.A. and N.B. ; investigation, D.O., M.A., K.A., and B.S. ; resources, D.O., T.B., A.B., and B.S. ; data curation, R.Z. and N.B. ; writing--original draft preparation, D.O., K.A., and N.B. ; writing--review and editing, D.O., N.B., and B.G ([PERSON]). ; visualization, B.A. and N.B. ; supervision, D.O. and K.A. ; project administration, D.O. and K.A. ; funding acquisition, D.O. All authors have read and agreed to the published version of the manuscript. This work was funded by grant funding for scientific and scientific-technical projects for the years 2023-2025 under the following topic: AP19678825 \"Improvement of surgical treatment of dysplastic covarthrosis using a new derotational device\". The study was conducted in accordance with the Declaration of Helsinki (1975, revised in 2013). The protocol was reviewed and approved by the Local Ethics Committee on Bioethics of the RSE on REM \"National Scientific Center of Traumatology and Orthopedics named after Academician [PERSON]\" of the Ministry of Healthcare of the Republic of Kazakhstan (Approval Code: No. 4; Approval Date: 9 November 2022). Written informed consent was obtained from all participants prior to their inclusion in the study, ensuring compliance with ethical standards and the confidentiality of all patient-identifiable data.