Developmental dysplasia of the hip, particularly Crowe type IV, presents significant challenges in orthopedic surgery due to severe anatomical deformities and biomechanical instability. This study focuses on evaluating the biomechanical performance of a prosthesis–femur–derotation plate system designed to address these challenges. Using FEA, a comprehensive assessment of stress distribution, displacement, and safety factors was conducted under physiological loading conditions. The derotation plate was specifically engineered to stabilize the femur and restore the anatomical and biomechanical axis of the limb. Results demonstrated that the derotation plate effectively eliminated rotational and axial displacement, with a peak displacement of 0.08 mm, and maintained sufficient strength reserves, with a minimum safety factor of 3.63. The maximum von Mises stress in the plate was 76 MPa, significantly below the yield strength of the titanium alloy, ensuring long-term durability and reliability. The system as a whole exhibited favorable biomechanical properties, confirming its ability to manage high stress loads without the risk of material failure or instability. These findings underscore the potential of this novel system to improve surgical outcomes in complex cases of hip dysplasia. Future clinical trials will further validate its practical utility, providing valuable insights for advancing orthopedic implant design and patient care.

Total hip arthroplasty (THA) in Crowe type IV developmental dysplasia of the hip (DDH) is technically demanding due to high dislocation, abnormal femoral morphology, and soft-tissue contractures. Subtrochanteric shortening osteotomy (SSO) is often required to restore the anatomic hip center and prevent excessive lengthening, yet the ideal osteotomy design and fixation remain controversial. The step-cut SSO offers greater rotational stability and bone contact but is technically complex and biomechanically under-evaluated. This report describes a clinical case supplemented by computational biomechanical analysis evaluating a hybrid fixation technique using a titanium plate reinforced with ultra-high-molecular-weight polyethylene (UHMWPE) tape. In this clinical case, a 35-year-old female with bilateral Crowe IV DDH underwent staged THA with step-cut SSO at the National Scientific Center of Traumatology and Orthopedics, Astana, Kazakhstan. Approximately 4.5 cm of femoral shortening was performed per side. The osteotomy was stabilized with a locally designed titanium plate and UHMWPE tape cerclage. Both procedures were uneventful, achieving equal limb lengths, early mobilization, and complete bone union by four months. Finite element analysis (FEA) was performed to evaluate mechanical behavior under single-leg-stance loading (1000 N vertical, 200 N horizontal). The hybrid construct demonstrated favorable stress distribution: peak von Mises stress values of 137 MPa in cortical bone and 94 MPa in the plate - both below yield limits. Maximum displacement was 0.16 mm, and safety factors exceeded 2.9, confirming high rigidity. Clinically, both hips showed stable fixation, pain-free gait, and excellent functional outcomes with a Harris Hip Score of 90 for the right hip and 88 for the left hip at one-year follow-up. In this case, the combination of step-cut SSO with hybrid titanium-plate and UHMWPE-tape fixation demonstrated favorable biomechanical characteristics and successful clinical outcome. Finite element analysis supported the mechanical stability of the construct. These findings should be considered preliminary and represent a proof-of-concept observation. Further experimental and multicenter clinical studies are required to confirm the generalizability of this approach.

Hip dysplasia is a severe pathology of the musculoskeletal system which, if not diagnosed and treated in time, leads to impaired function of the hip joint. This leads to osteoarthritis, which requires surgical intervention. This report describes a case of non-union of the transverse subluxation shortening osteotomy zone combined with total hip replacement of the left hip joint. It should be noted that our report/study had some limitations, such as a short follow-up period and one patient. We believe that further research with a long follow-up period and a larger sample of patients with Crowe type DDH is needed to obtain good results. This study and patient follow-up are ongoing.Key words: Hip dysplasia, endoprosthesis, subluxation shortening osteotomy, nonunions.

Жамбас буынының дисплазиясы – бұл дер кезінде диагноз қойылмаса және емделмесе, жамбас буынының қызметінің бұзылуына әкелетін тірек-қимыл аппаратының ауыр патологиясы. Ол хирургиялық араласуды қажет ететін остеоартриткеәкеледі.Бұл мақалада 6,5 см болатын көлденең ұршықасты қысқарту остеотомиясымен сол жақ жамбас буынының цементсіз толық жамбас артропластикасы жасалған науқастың жағдайды сипатталады.Клиникалық жағдайдың ерекшелігі – остеотомия аймағында ротациялық және осьтік тұрақтылықты қамтамасыз ететін жаңадан әзірленген пластинаның қолданылуы болды. Пациенттің жағдайы әрі қарай бақылауда және тиісті ем жүргізілуде. Зерттеу мен пациенттің жағдайын қадағалау процесі әлі де жалғасып жатыр.

Dysplasia of the hip joint (DDH) is a severe pathology of the musculoskeletal system which, if not diagnosed and treated in time, leads to impaired function of the hip joint. This leads to osteoarthritis, which requires surgical intervention. This case report describes a case where a cementless total hip arthroplasty (THA) of the left hip joint with a 6.5 cm transverse subtrochanteric shortening osteotomy (SSO) was performed. A special feature was the use of a newly developed plate that provides rotational and axial stability at the osteotomy site. With further observation and management of the patient. It is worth noting that this study and follow-up of the patient is ongoing. Keywords: developmental dysplasia of the hip (DDH), arthroplasty, subtrochonteric osteotomy.