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Background: Operative strategies to overcome the anatomical anomalies in patients with osteoarthritis secondary to developmental dysplasia of the hip remain controversial. The objective of this study was to determine the outcomes of total hip replacement with a grit-blasted cementless threaded cup and a cementless straight stem in patients with developmental dysplasia.Methods: Ninety-three patients with developmental hip dysplasia who had been treated with a total of 121 cementless total hip arthroplasties were clinically assessed at a mean of 9.3 years. The acetabular reconstruction was done with a cementless threaded cup, which was medialized to ensure that at least one thread was anchored in the bone in order to achieve good primary stability. All radiographs were analyzed retrospectively.Results: Kaplan-Meier survivorship analysis, with radiographic evidence of aseptic loosening as the end point, predicted a survival rate of 97.5% for the acetabular component and 100% for the femoral stem at 9.3 years. The average Harris hip score for the unrevised hips improved from 34.0 points preoperatively to 84.1 points at the latest follow-up evaluation. The average total volume of polyethylene wear at the time of final follow-up was 73.6 mm3.Conclusions: These wear and loosening rates demonstrate that very good results were achieved in this relatively young patient population when the hip joint center had been properly restored, even when a small cup with a thin polyethylene liner had been used.Level of Evidence: Therapeutic study, Level IV (case series [no, or historical, control group]). See Instructions to Authors for a complete description of levels of evidence.