Level of osteotomy is relevant to obtain better union and clinical results in patients with severe hip dysplasia operated on with total hip arthroplasty and shortening osteotomy using a cementless, rectangular femoral component.

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Total hip arthroplasty with rectangular femoral component and transverse osteotomy for patients with Crowe type 3 or 4 dysplasia yields successful results with varying radiological findings. This study aims to investigate the surgery and patient related factors associated with successful clinical and radiological results. Fifty hips of 41 patients were retrospectively examined. Length and percentage of the stem passing the osteotomy level and canal fill ratio were measured. Radiological findings such as radiolucent lines (RL) around the stem, hypertrophic callus or an identifiable osteotomy line on X-ray images were assessed. All clinical and radiological results were analyzed for any significant association. Mean stem length and percentage passing the osteotomy level were 6.4cm (± 0.7)and 51% (± 6). Presence of an identifiable osteotomy line was positively associated with the increasing length of the stem passing the osteotomy level and with a lower HHS (p < 0.05). RL around the stem were associated with a lesser reduction in VAS score (p < 0.05). Rectangular femoral stem conveniently accommodate the proximal femur in severely dysplastic hips. An upper limit for the femoral stem exists to obtain better bony union and higher HHS. RL around the stem are clinically relevant and is associated with a worse VAS score at the latest follow-up.