Pelvic Tilt Reproducibility Using Fluoroscopy in Direct Anterior Approach Total Hip Arthroplasty

Precise acetabular component positioning depends heavily on accurately recreating pelvic tilt (PT) during total hip arthroplasty (THA). The direct anterior approach (DAA) facilitates intraoperative fluoroscopy for real-time assessment, yet the accuracy of recreating preoperative standing PT intraoperatively remains unexplored. This study evaluated the precision of intraoperative PT recreation between pre- and intra-operative antero-posterior (AP) radiographic images during DAA THA.

This retrospective cohort included 325 patients undergoing primary unilateral DAA THA by a single surgeon between July 2022 and July 2024. Sagittal PT was measured on preoperative EOS radiographs in both standing and sitting positions. There were two validated parameters, anteroposterior PT and the sacro-femoral-pubic (SFP) angle, that were then calculated for both standing as well as intraoperative fluoroscopic images. There were two blinded observers who independently performed all measurements using the intraclass correlation coefficient (ICC greater than 0.80). The primary outcome was the proportion of patients in whom intraoperative PT was reproduced within ± 7.0 and ± 14.0° of standing values, thresholds corresponding to approximately 5.0 and 10.0° of anteversion inaccuracy. The secondary outcomes assessed correlations between pre- and intra-operative alignment parameters.

Both AP PT and the Delta SFP (standing-to-sitting) angle demonstrated moderate-to-strong correlations with sagittal standing PT and Delta PT, confirming measurement accuracy before intraoperative analysis. Intraoperative fluoroscopy reproduced standing PT within ± 7.0° in 76% of patients and within ± 13.0° in 95%. However, preoperative standing and intraoperative AP PT demonstrated low correlation (r = 0.294), indicating substantial variability. The change in SFP (standing to supine) demonstrated moderate correlation with the change in AP PT (r = 0.422), further reflecting the limited precision of the PT recreation.

Visual fluoroscopic recreation of standing PT during DAA THA demonstrated moderate accuracy, with three-quarters of patients achieving clinically relevant precision. Variability in reproducing functional PT suggests that visual assessment alone may benefit from adjunctive verification to improve consistency in acetabular positioning.