Digital Measurement and Safety Parameter Analysis of the Infra-Acetabular Screw Pathway

Objective: To evaluate acetabular anatomy using digital technology, determine the limiting parameters for inferior acetabular screw insertion in Chinese patients, and explore the clinical value of this surgical approach. Methods: We collected CT data from 100 adult pelvic plain scans performed at the Affiliated Hospital of Xinjiang Medical University between 2020 and 2023. Three-dimensional models were reconstructed using Mimics software. The mid-pubic axial projection area was identified at the pelvic inlet. Simulated screw insertion procedures measured the following parameters: the medial distance (OA) and anterior distance (AP) from the entry point to the apex of the iliopubic eminence, as well as the angles formed by the screw axis with the pelvic coronal and sagittal planes. Results: The mean subacetabular screw pathway length was 101.51 ± 4.87 mm in males and 91.63 ± 3.64 mm in females. The maximum screw diameter was 5.39 ± 1.25 mm in males and 4.55 ± 0.89 mm in females. The medial distance from the entry point to the iliac crest apex was 11.09 ± 2.70 mm in males and 11.47 ± 3.46 mm in females; The anterolateral distance was 8.22 ± 3.68 mm in males and 7.32 ± 2.66 mm in females. The angle between the screw axis below the acetabulum and the coronal plane was 55.20° ± 5.40° in males and 53.30° ± 6.30° in females. The angle with the sagittal plane was 12.60° ± 9.80° in males and 2.60° ± 8.80° in females. Except for the sagittal plane angle, OA, and AP values, all other parameters showed significant gender differences (P < 0.01). Among the 100 pelvic models collected in this study, 47 cases had a minimum screw insertion channel diameter ≥5 mm; while 5 cases had a minimum screw insertion diameter <3.5 mm (1 male, 4 females). Conclusion: This study demonstrates gender-dependent differences in both screw length and maximum diameter within the subacetabular approach. We recommend preoperative 3D reconstruction simulation to determine safe and effective maximum channel parameters for subacetabular screw placement.