The Effect of the Morphology of the Femur and Acetabulum in Dysplastic Hips on the Selection of Arthroplasty Femoral Implants: A Computer Tomography‐Based Study

Objectives Due to the technical challenges associated with femoral reconstruction in total hip arthroplasty for patients with developmental dysplasia of the hip (DDH), the exact indications for using femoral modular stems, despite their satisfactory clinical outcomes, remain poorly investigated. This study sought to assess the morphology of the femur and acetabulum, and to investigate the discriminative ability of femoral anteversion (FA), acetabular anteversion (AA), and combined anteversion (CA) on the selection of femoral modular stem in dysplastic hips. Methods Retrospective data were collected from multiple centers on a total of 230 cases who underwent THA due to DDH from January 1, 2020, to March 1, 2023. There were 46 males and 184 females, with an average age of 51.57 ± 14.87. Patients were stratified according to Crowe and Eftekhar classifications. FA, AA, and CA were measured using computed tomography (CT). The distribution of these indices in different grades of dysplastic hips was compared, and the correlation between these indices and the selection of femoral modular stem was analyzed. Receiver operating characteristic (ROC) and likelihood statistics were performed to investigate the discriminating and predictive value of each index in selecting modular stem. Results Two hundred and thirty hips were included in the study. FA increased as the subluxation percentage increased: type I, 21.5°; type II, 28.6°; type III, 34.9°; and type IV, 39.7°. AA was smaller in type I (16.9°) and higher in types II, III, and IV (18.9–22.6°). The area under the curve for the modular stem was 0.87 for FA, 0.86 for CA, and 0.65 for AA. The optimal cutoff values were FA > 32.6°, CA > 50.7°, and AA > 23.3°. Conclusion Excessive AA and femoral anteversion FA were observed in Crowe types II, III, and IV cases. FA and CA demonstrated strong discriminative ability and predictive value in the selection of a modular stem. The best cutoff values were ≥32.6° for FA and ≥50.7° for CA in discriminating the use of modular stem. Surgeons may contemplate the use of a modular stem when the preoperative evaluation approaches the cutoff value.