FP7.6 Thick MPR CT: Simulating Standing Pelvic Tilt for the Evaluation of Acetabular Coverage in Patients with Borderline Hip Dysplasia

Abstract

Abstract ICLB07 - The Digital Surgeon: Practical Tools and Navigation Basics for Your Everyday Practice, Session Room 12 (BMCC Level 3), October 8, 2026, 14:00 - 16:00 Background Treatment decisions in borderline hip dysplasia (BHD) rely heavily on small differences in acetabular coverage measurements. The reliability of radiographic parameters in this setting remains uncertain. Purpose The purpose of this study was to compare acetabular coverage measurements between standing radiographs and simulated standing CT in patients with BHD. Methods Symptomatic patients with BHD (LCEA 18°–25°) were prospectively evaluated with standing AP pelvic radiographs and CT using a low-dose protocol. Pelvic tilt on CT was adjusted to match the standing radiograph. Thick MPR reconstructions were used to assess acetabular coverage. LCEA, Tönnis angle, AWI, and PWI were measured independently by three observers. Agreement between methods was analyzed using paired t-tests and Pearson correlation. Results Seventy-two paired measurements were analyzed. LCEA was lower on radiographs compared with CT (22.5° ± 5.8° vs 24.9° ± 5.8°), with a mean difference of −2.4° ± 5.6° (p < 0.001; r = 0.53). No significant differences were observed for the Tönnis angle (p = 0.840), AWI (p = 0.412), or PWI (p = 0.130), with moderate to strong correlations across these parameters. LCEA showed the greatest inter-observer variability. Notably, AWI values were consistently higher in supine radiographs compared to standing radiographs, although this difference did not reach statistical significance (n=16 vs n=62; p>0.142) Conclusion In borderline hip dysplasia, most acetabular coverage parameters are comparable between standing radiographs and simulated standing CT. However, LCEA is consistently underestimated on radiographs and shows higher variability, which may affect surgical decision-making. Furthermore, the trend toward higher AWI values in supine positioning suggests that weight-bearing status influences coverage assessment Low-dose simulated standing CT provides a reproducible complementary assessment in cases where measurements are borderline.