Early diagnosis and intervention are therefore critical to mitigating these outcomes. Various classification systems, such as those proposed by [PERSON], [PERSON], [PERSON], and [PERSON], provide a framework for diagnosing and managing DDH. Among these, the Crowe classification is the most widely adopted, especially for addressing severe cases, like Crowe type IV dysplasia [8]. Previous research has explored femoral stem designs, the stress distribution, fixation methods, and the use of modular and custom implants to address the challenges of hip reconstruction [9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24]. Studies have highlighted the importance of prosthetic stability, acetabular defect resolution, and bone grafting in total hip arthroplasty (THA) for DDH. Advances in 3D printing, uncomented arthroplasty, and titanium-based implants have further optimized surgical outcomes by improving the implant fit and load distribution. Additionally, a high hip center of rotation of the femoral head positioning and the use of modular neck prostheses have been evaluated for their long-term efficacy in maintaining joint stability and restoring limb biomechanics [23; 24; 25; 26; 27; 28; 29; 30; 31; 32]. Crowe type IV DDH is characterized by high-riding dislocated hips and severe acetabular dysplasia, presenting unique surgical challenges. THA is the treatment of choice for such complex cases, often requiring extensive soft tissue release to address longstanding contractures. Subtrochanter shortening osteotomy (SSO) is frequently employed in these procedures to restore joint congruency and limb alignment [33; 34]. This technique has proven to be effective in repositioning the femoral head within the true acetabulum without endangering the neurovascular structures. However, SSO is associated with risks, including nonunion at the osteotomy site, rotational and axial instability, and loosening of the femoral prosthesis, all of which necessitate the development of advanced fixation methods [35]. Modern fixation techniques, including the use of autogenous bone grafts, wire pins, and plates with screws, have been explored to address these complications. Biomechanical research highlights the superiority of plate and screw fixation, which not only accelerates osteotomy healing but also provides enhanced rotational and axial stability compared to traditional methods, such as cable fixation [36; 37]. Recent innovations in implant materials have further contributed to improved outcomes. Titanium, for example, is increasingly favored for its biomechanical properties, including an excellent strength-to-weight ratio, corrosion resistance, and compatibility with biological tissues [38]. Titanium plates have demonstrated superior stress distribution and reduced failure rates, making them a compelling choice for complex orthopedic applications [39]. The growing focus on computational biomechanics has further revolutionized the field of orthopedic surgery. Finite element analysis (FEA) enables detailed modeling of the stress-strain behavior of complex systems, facilitating the optimization of implant design and performance under physiological loading conditions [40,41]. By leveraging these advanced techniques, researchers and clinicians can develop innovative solutions to address the challenges posed by conditions like Crowe type IV DDH [42]. This study hypothesizes that the integration of a derotation plate in primary cementless total hip arthroplasty significantly enhances biomechanical stability, eliminates rotational and axial displacement, and promotes osteotomy fusion. The novelty of this research lies in the development and biomechanical assessment of a custom-designed derotation plate, tailored to the anatomical and functional demands of patients with Crowe type IV DDH. By combining advanced computational modeling with experimental validation, this study aims to bridge the gap between theoretical research and clinical applications. The primary objectives of this research are as follows:  
1.