'THA for DDH: replacement principles and techniques - femoral side'.

Developmental dysplasia of the hip (DDH) remains a leading cause of early hip osteoarthritis and poses considerable technical challenges during total hip arthroplasty. Existing classification systems focus on the abnormal relationship between the femoral head and the acetabulum without emphasising the femoral morphological variations, which are equally significant in surgical planning. Dysplastic femora often demonstrate excessive neck anteversion, variable neck-shaft angles, reduced offset, and metaphyseal-diaphyseal mismatch with narrow intramedullary canals. These anatomical variations often compromise the abductor mechanism and alter hip biomechanics. Thorough preoperative planning is crucial and should include the evaluation of leg-length discrepancy, reconstruction of the hip centre of rotation, assessment of femoral version and canal morphology, implant selection, and consideration of femoral shortening osteotomy. Computed tomography-based planning can enhance preoperative planning in complex cases. Both cemented and cementless stems align with positive findings in DDH patients. Cemented stems enable reliable version control, decrease intraoperative fracture risk, and may be beneficial for patients with poor bone quality. In mild cases, most uncemented stems are suitable. More severe deformities necessitate specialised implant designs with conical fluted stems, which provide strong fixation and excellent long-term survivorship. Modular and custom-made options also achieve favourable outcomes in high-grade deformities. Femoral shortening osteotomies are often needed to restore biomechanics, correct abnormal version, and prevent nerve injury during reduction. The subtrochanteric osteotomy has been linked with excellent results in treating severe DDH. High-quality research is essential to deepen our understanding of proximal femur morphological abnormalities and to enhance surgical results.