Identification of a saddle point (SP) for safe sacral segment channel planning via data analysis and rapid physical...

This study introduces a novel geometric marker, derived from CT image data analysis via grey theory and prototyping verification, to enhance the planning of sacroiliac joint screw placement, aiming at optimizing safety. A dataset comprising 107 adult cases with hip thin-slice CT scans in DICOM format was collected for statistical analysis. The sacral bone model was segmented from the scanning data sets to facilitate planning for sacroiliac screw surgery. The saddle point (SP), located at the intersection of the contralateral sacral promontory and the sacral wing, was identified as the target direction for needle insertion. The entry point on the anterior convexity and posterior concavity of the ear-shaped surface was connected to the posterior superior aspect to determine the retrograde positioning of the screw channel. Utilizing a home-made software, E3D, the safe channel was visualized using three cross-sectional views with the screw channel as the axis. Adjustment of the central screw channel's position in the transverse and coronal planes facilitated its establishment. The distances between the highest (up, u) and lowest (down, d) entry points on the ear-shaped surface (ud, mm), as well as the distances between the most anterior (ahead, a) and most posterior (back, b) points (ba, mm), were measured to approximate the area (surface, s, mm²) within the four points, aiding in assessing the size of the safe range. Out of the 107 cases, two were unable to undergo sacroiliac screw placement due to sacral morphological variations (1 male and 1 female). In the remaining 105 cases (61 male and 44 female), 98.13% successfully underwent bilateral safe screw placement (53 cases on the left side and 52 on the right side). Statistical tools and grey relation analysis are applied to extract templates for data reuse and validation. The utilization of the central screw channel as the axis in the three-section view facilitated a direct three-dimensional assessment of the screw channel's safety, ensuring its containment within the bone tissue. Consequently, planning the sacroiliac screw channel with the contralateral saddle point as the target direction and the posterior superior aspect of the ear-shaped surface as the entry point is deemed safe and feasible, notwithstanding individual variations. To validate the findings, a printed sacroiliac joint prototype and a real human sacroiliac joint specimen were employed to simulate puncture insertion surgery. The results demonstrate the practicality of the newly identified marker as a crucial reference point for surgical planning. Subsequent steps will involve the statistical analysis of additional medical specimens and the execution of clinical surgeries to demonstrate its application.