Radiographic parameters and feasibility analysis of dual sacral-2 alar-iliac screw fixation using three-dimensional digital technology.

Objective: The purpose of this study was to evaluate the feasibility and the trajectories of dual sacral-2 alar-iliac (S2AI) screw fixation with three-dimensional digital technology simulation analysis.

Methods: The pelvic computed tomography scan data of 60 (30 men and 30 women, age: 25-86 years) individuals were selected and reconstructed. The trajectories of dual S2AI screws were plotted using three-dimensional reconstruction software. A cylinder with a radius of 5 mm was selected to simulate screw placement. If screw placement based on the cylinder with 5 mm radius failed, selected a cylinder with a radius of 4.5 mm or 4 mm. Dual S2AI trajectories were simulated, the maximum length and width of the trajectories were ensured, and their parameters were precisely measured. All parameters were measured in the three-dimensional image, including distance parameters, radius and angles.

Results: The placement of dual S2AI screws on the same side could be achieved in all individuals. No significant differences were found between the male and female regarding the head inclination angle, abduction angle, and total length or thread length of screws in the same position (P > 0.05). LH (the shortest distance from the greater sciatic notch to the cross-section of the screw trajectory) were17.52 ± 3.96 mm and 14.18 ± 2.92 mm in L1, 28.19 ± 2.58 mm and 25.54 ± 4.15 mm in L2, 16.09 ± 4.08 mm and 14.71 ± 3.94 mm in R1, 26.90 ± 3.76 mm and 24.59 ± 2.85 mm in R2 in male and female models, respectively. The shortest distance from the greater sciatic notch to the cross-section of the screw trajectory differed significantly between the sexes (P < 0.05).

Conclusion: Using a radius of 4 mm (minimum diameter of S2AI screw) as a standard, it is feasible to place two S2AI screws on the same side for the Chinese adult. Screw placement can be achieved by trisecting the lateral process of S1-S2, with one screw inserted in the bottom third and the other in the upper third. Furthermore, preoperative three-dimensional digital technology simulation analysis can effectively simulate the dual S2AI screws trajectories on the same side, and they can provide accurate data for clinical applications.