False-Profile Radiograph Sourcil-Edge and Bone-Edge Measurements Correlate to Different Weightbearing Regions of the Acetabulum: A 3-Dimensional Analysis

Abstract

Background: The acetabular sourcil is commonly interpreted as a reliable radiographic representation of the weightbearing dome of the acetabulum, despite limited modern data. Assessment of weightbearing acetabular coverage has been described using both the sourcil edge and bone edge as anatomic landmarks, leading to confusion and potential misguidance in surgical decision-making and thus compromised patient outcomes.

Purpose/hypothesis: The purpose of this study was to characterize the 3-dimensional (3D) anatomic correlates of the sourcil-edge and bone-edge radiographic measurements on false-profile radiographs. It was hypothesized that the sourcil edge would represent anterolateral coverage and the bone edge would represent anterior coverage.

Study design: Descriptive laboratory study.

Methods: A total of 80 hips were grouped by large or small differences between bone-edge and sourcil-edge anterior center-edge angles, based on upper and lower quartiles of discrepancy. Three-dimensional surface mesh models and digitally reconstructed radiographs were generated from hip computed tomography scans. Sourcil-edge and bone-edge anterior center-edge angles were identified on digitally reconstructed radiographs and registered to the 3D models with fiducial markers. Intersections of bone-edge and sourcil-edge projection lines with the acetabular rim were obtained from the 3D models.

Results: The bone-edge and sourcil-edge projections intersected the acetabular rim at clockface means of 2:05 ± 0:22 and 1:12 ± 0:25, respectively. The 3D models consistently demonstrated that, in both large- and small-discrepancy groups, the sourcil edge corresponded to the acetabular area just posterior to the anterior inferior iliac spine (AIIS) projection, and the bone edge corresponded to the weightbearing region inferior to the AIIS. Additionally, in large-discrepancy hips, the bone edge corresponded to more prominent acetabular coverage in the region inferomedial to the AIIS when compared with the small-discrepancy hips.

Conclusion: On false-profile radiographs, the sourcil edge corresponds to superior femoral head coverage, and the bone edge corresponds to anterosuperior coverage. Radiographs with a large discrepancy between sourcil-edge and bone-edge measurements demonstrate acetabular rim prominence in the region of the AIIS.

Clinical relevance: Characterizing the anatomic weightbearing regions of the acetabulum represented on false-profile radiographs facilitates improved clinical and intraoperative decision-making in hip preservation surgery, including acetabuloplasty and periacetabular osteotomy.

Keywords: 3-dimensional reconstruction; acetabulum; anterior center-edge angle (ACEA); digitally reconstructed radiographs; false-profile radiographs; hip preservation.