EP1.96 Assessment of Intrinsic Pelvic Morphological Variations: An Imaging-Based Study in Patients with Developmental Dysplasia of the Hip and Normal Controls

Abstract Objective We identified the presence of intrinsic pelvic morphological variations but found a lack of specific evaluation parameters. Current indices primarily assess spinopelvic relationships. Methods Individuals with normal hip anatomy and patients with bilateral developmental dysplasia of the hip (DDH) were enrolled. Standing anteroposterior and lateral pelvic radiographs were obtained. On the AP view, the distance between the inferior margins of the bilateral sacroiliac joints (a) and the vertical distance from the sacroiliac line to the pubic symphysis (b) were measured to calculate the a/b ratio. Pelvic height (c) and width (d) were measured to compute the c/d ratio. On the lateral view, the APP angle, PT angle, SS angle was measured. Additionally, four newly defined angles were measured to quantify the intrinsic pelvic deformity: the Anterior Superior Iliac Spine - Ischial Spine - Pubic Symphysis angle (ASP angle), the Anterior Superior Iliac Spine - Hip Center - Pubic Symphysis angle (ACP angle), the Posterior Superior Iliac Spine - Anterior Superior Iliac Spine - Ischial Spine angle (PAS angle), and the Posterior Superior Iliac Spine - Anterior Superior Iliac Spine - Hip Center angle (PAC angle). Statistical analyses included interaction analysis, univariate linear regression, and multivariate linear regression. Results A total of 220 participants were included: 65 male DDH patients, 65 female DDH patients, 45 male controls, and 45 female controls. Both univariate and multivariate linear regression analyses revealed that the APP angle was associated not only with traditional parameters (PT, SS) but also with the PAS and PAC angles. Conclusion While traditional spinopelvic sagittal balance parameters provide a fundamental assessment of pelvic tilt, they do not fully capture the complexity of pelvic morphology. The custom parameters defined in this study (PAS, PAC, etc.) demonstrate an independent influence of intrinsic pelvic osseous structure deformity on functional pelvic alignment.