Study of the ideal insertion point and angle for the antegrade posterior column screw with the anterior approach in acetabular fracture.

Abstract

Background: For acetabular fractures of both columns, the antegrade posterior column screw (APCS) is often inserted via the anterior intrapelvic approach to stabilize both columns. Insertion of the APCS can be technically demanding due to the complex anatomy of the posterior column. Misdirection or mispositioning of the screw during surgery can result in penetrate the hip joint or damage the neurovascular structures. The purpose of this study was to detect the ideal insertion point and angles of the APCS based on anatomical landmarks that can be directly identified intraoperatively.

Methods: We retrospectively reviewed the pelvic CT of 50 adults who underwent serial slice CT imaging. Three reference plane was determined using image analysis software; (1) iliac plane (IP), which contains the anterior superior iliac spine (ASIS), the anterior margin of sacroiliac joint (AMS), and the posterior margin of pubic symphysis (PMS), (2) pelvic inlet plane (PIP), which contains the AMS of both sides, and the PMS, (3) sagittal midline plane of the pelvis (SMP). The ideal insertion point and angles of the APCS, and its maximum length were measured. The ideal insertion point was measured on the line connecting ASIS and AMS (AA line) at a distance from AMS (APCS horizontal distance) and vertical distance from AA line (APCS vertical distance). The ideal angles were measured between the screw and the PIP and between the screw and the SMP.

Results: The APCS horizontal distance was 27.4 ± 6.4 mm. The APCS vertical distance was 1.6 ± 6.6 mm. The angle between the ideal APCS and yz-plane on the outlet view (α-angle) was 5.8 ± 5.8° The angle between the ideal APCS and y-axis on the xy-plane (β-angle) was 51.6 ± 5.0° The length of the APCS was 125.8 ± 9.5 mm.

Conclusion: The ideal insertion point detected as the distance from the AMS on the AA line and the ideal insertion angles relative to the PIP and the SMP may aid in proper insertion of the APCS during surgery.