Impact of Cup Anteversion and Hip-Spine Relationship on Femoral Neck Notching in Dual Mobility Total Hip Arthroplasty.

Background: Dual-mobility cups (DMCs) are increasingly used in total hip arthroplasty (THA) because of their low dislocation rates. However, a unique complication associated with DMCs is femoral neck notching (FNN), which is believed to result from impingement between the metal liner and the femoral stem neck. The risk factors for FNN, however, remain poorly understood. This study aimed to identify the risk factors associated with FNN in patients undergoing THA with DMCs. Methods: This retrospective analysis included 766 patients who underwent THA with DMCs between 2013 and 2023. Patients with follow-up durations of less than 1 year and those with mixed-manufacturer components (i.e., an acetabular cup and a femoral stem from different manufacturers) were excluded. Cup positioning angles and the presence of FNN were assessed using standard radiographs. Spinopelvic alignment was evaluated in a subgroup of 204 patients using EOS imaging. Results: FNN was identified in 24 of 766 patients (3.1%). Among these, 14 patients underwent EOS imaging, compared with 190 patients without FNN. Patients with FNN demonstrated significantly higher cup anteversion (31.4° ± 6.1°) than those without FNN (15.2° ± 4.8°, p < 0.0001). Logistic regression analysis showed that increased cup anteversion was significantly associated with FNN, with an odds ratio of 1.62 (95% confidence interval: 1.32-2.27, p < 0.0001), identifying it as the primary risk factor for FNN formation. Conclusions: Cup anteversion was identified as a significant risk factor for FNN following THA with DMCs. These findings suggest that careful attention to cup positioning may help reduce the incidence of FNN in DMC-THA. Level of Evidence: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.