Anatomical Diversity & Bilateral Symmetry: CT-Based Native Acetabular Surface Characterization in Pakistani Adults.

Abstract

Objective: The contralateral acetabulum serves as a reliable internal anatomical reference for evaluating pelvic and hip morphology. At the population level, however, bilateral symmetry may coexist with considerable inter-individual varia-tion. This study quantified right–left differences in native acetabular morphology and characterized selected morphomet-ric variants within a multicenter adult Pakistani population.
Methodology: Retrospective cross-sectional analysis of the CT examinations was conducted from January 2023 to De-cember 2024, from three tertiary care hospital. Eligible were adults aged 18-75 years, who had both acetabula and prox-imal femora completely visible. Examinations that had fractures, prior hip surgery or arthroplasty, developmental dyspla-sia, advanced OA, destructive arthropathy, femoral-head collapse, a tumor of the pelvis, congenital deformity, substan-tial pelvic rotation, incomplete visualization or poor image quality were excluded. The maximum acetabular diameter, depth, depth-to-diameter ratio, anatomical anteversion, inclination, lateral center-edge angle and wall indices were measured with a standardized multiplanar CT assessment. The main analysis was a comparison between paired meas-urements from the right and left side. Secondary analyses involved describing sex-associated differences and the inci-dence of selected morphometric categories.
Results: Two hundred and four subjects and 408 acetabula were included in the study. The measurements of the ace-tabula of both the right and left side were comparable. Maximum diameter was 52.1±3.6 mm on the right and 51.9±3.6 mm on the left, with a mean paired difference of 0.20 mm (p=0.126). Differences were similarly small for depth (0.17 mm; p=0.141), depth-to-diameter ratio (0.18 percentage points; p=0.339), anteversion (0.31°; p=0.174), inclination (0.22°; p=0.263), and lateral center-edge angle (−0.19°; p=0.491).
Although this is bilaterally symmetrical, there was morphometric variation with 14.0 % hips with a diameter <48 mm, 22.5 % hips with a depth-to-diameter ratio (DDR) <45, 15.2 % hips with anteversion >25°, 8.3 % hips with inclination >50° and 8.6 % hips with a lateral centre-edge angle (CEA) <25°. For several variants, a significant difference between sexes was observed.
Conclusions: CT-based measurements of the acetabulum demonstrated good bilateral symmetry across all major pa-rameters. However, this symmetry was observed within a population characterized by substantial inter-individual and sex-related anatomical variation. Consequently, native morphology alone may be insufficient to define an individual’s hip anatomy, and the contralateral acetabulum may serve as a more reliable patient-specific reference.
Keywords: Bilateral symmetry, acetabulum, computed tomography, pelvic morphology, anatomical variation, hip, ante-version, acetabular depth, and center-edge angle.