FP1.8 Is the Anterior Wall Index a Reliable Surrogate of Anterior Hip Coverage? Correlation With Anterior center Edge Angle and Interobserver Reliability Study

Abstract

Abstract ICLB01 - The Instability Masterclass: Correcting Bone, Biology, and Bad Outcomes, Session Room 6 (BMCC Level 3), October 8, 2026, 10:30 - 12:30 Introduction Accurate assessment of anterior femoral head coverage is essential in hip preservation surgery. The anterior center-edge angle (ACEA), measured on false-profile radiographs, is widely used but may be affected by projectional variability and landmark identification. The anterior wall index (AWI), measured on standard anteroposterior (AP) pelvis radiographs, has been proposed as a simple and reproducible alternative. This study aimed to evaluate the correlation between AWI and ACEA, as well as interobserver reliability and measurement bias. Materials and Methods A retrospective radiographic study of 50 hips was performed. Two independent observers measured AWI on supine AP pelvis radiographs and ACEA on false-profile views using mediCAD® 2D software (Hectec GmbH, Germany). Demographic variables included age, sex, laterality, and body mass index (BMI). Statistical analysis was performed using SPSS (IBM Corp., USA). Normality was assessed with the Shapiro–Wilk test. Pearson correlation coefficient was used to evaluate relationship between AWI and ACEA. Interobserver reliability was assessed using intraclass correlation coefficient (ICC). Measurement bias was evaluated using paired Student’s t-test. Statistical significance was set at p < 0.05. Results All variables demonstrated normal distribution. A weak correlation was observed between AWI and ACEA (r = 0.16–0.30; p > 0.05), indicating limited association between both parameters. Interobserver reliability was good for AWI (ICC = 0.789; 95% CI 0.657–0.875; p < 0.001), whereas ACEA showed only moderate reliability (ICC = 0.474; 95% CI 0.230–0.662; p < 0.001). Paired t-test analysis demonstrated no significant differences between observers for either AWI or ACEA (p > 0.05), indicating absence of systematic measurement bias. Discussion The weak correlation between AWI and ACEA suggests that these parameters may reflect different aspects of anterior hip coverage. While ACEA is influenced by projectional factors and landmark selection, AWI provides a more reproducible measurement on standard AP radiographs. The higher interobserver reliability of AWI supports its robustness compared to ACEA, which demonstrated only moderate agreement. Conclusion AWI doesn’t strongly correlate with ACEA, suggesting they are not interchangeable measurements. However, AWI demonstrates superior interobserver reliability and no measurement bias, supporting its role as a consistent and reproducible parameter for assessing anterior hip coverage.