Femoral anteversion change is associated with ischiofemoral impingement after total hip arthroplasty: a retrospective CT evaluation

Objectives We evaluated the relationship between femoral anteversion (FA), FA change, and ischiofemoral impingement (IFI) and the relationship between FA, femoral offset (FO), and greater trochanteric pain syndrome (GTPS) after total hip arthroplasty (THA). Materials and methods In this retrospective study, two readers assessed FA and FO on CT images of 197 patients following primary THA with an anterior surgical approach between 2014 and 2021. FA change was calculated relative to preoperative CT, while FO change was calculated relative to preoperative radiographs and classified as decreased (>=-5 mm), increased (>= + 5 mm), or restored (+/- 5 mm). Clinical and imaging data were analyzed for IFI and GTPS after surgery. Group differences were evaluated using Student's t-test, chi-square analysis, and receiver operating characteristic (ROC) analysis. Results The change in FA was 3.6 +/- 3.3 degrees to a postoperative FA of 22.5 +/- 6.8 degrees, while FO increased by 1.7 +/- 3.5 mm to a postoperative FO of 42.9 +/- 7.1 mm. FA and FA change were higher in patients with IFI (p <= 0.006), while no significant difference was observed for patients with and without GTPS (p >= 0.122). IFI was more common in females (p = 0.023). In the ROC analysis, an AUC of 0.859 was observed for FA change to predict IFI, whereas the AUC value was 0.726 for FA alone. No significant difference was found for FO change in patients with and without IFI or GTPS (p >= 0.187). Conclusion Postoperative FA, FA change, and female sex were associated with IFI after anterior-approached THA. The change in FA was a better predictor of IFI than absolute postoperative FA alone.