FP1.7 Is the Lateral Center-Edge Angle Truly Static? A Conceptual Framework for Dynamic Acetabular Coverage

Abstract ICLB01 - The Instability Masterclass: Correcting Bone, Biology, and Bad Outcomes, Session Room 6 (BMCC Level 3), October 8, 2026, 10:30 - 12:30 Background The lateral center-edge angle (LCEA) is the static radiographic measure used to classify acetabular coverage as dysplastic (<20°), borderline dysplastic (20–25°), normal (25–40°), or over-covered/pincer (≥40°) and guides surgical decision-making. However, the pelvis tilts obliquely in the coronal plane during daily activities. We hypothesized that static LCEA does not accurately represent the coverage a hip experiences during functional loading. Methods We included 101 femoroacetabular impingement patients (38 male / 63 female; mean age 31.1 ± 11.7 years; mean BMI 26.0 ± 4.8 kg/m2). Using three-dimensional motion capture during walking, we computed a dynamic LCEA at each frame by adding coronal pelvic drop captured by motion capture during normal walk to the static radiographic LCEA. Acetabular coverage classification was compared between static and dynamic measurements during gait. Results The mean change in dynamic LCEA range during a single walking trial was 9.8° ± 2.3°. Of 101 patients, 63 (62.4%) crossed into a different acetabular coverage classification during walking compared to their static classification. Among 69 patients with normal LCEA (25.1–39.9°), 19 (27.5%) spent part of gait in the borderline dysplastic range, 1 (1.4%) reached the frank dysplastic range, and 22 (31.9%) crossed upward into the over-coverage range. Among 17 statically borderline dysplastic patients, 10 (58.8%) reached the frank dysplastic range during gait and 15 (88.2%) crossed upward into the normal range, while none crossed into the over-coverage range. Among 15 statically over-covered patients, 5 (33.3%) dropped into the normal range during gait, while none reached the borderline or dysplastic ranges. Conclusion The LCEA measured on a standing radiograph represents a single snapshot of a dynamic relationship. Clinical interpretation should account for individual pelvic kinematics, as patients near classification boundaries — at either the under- or over-coverage end — may experience dynamic reclassification despite appearing stable on static radiographs.