Accuracy of S2 Alar-Iliac Screw Placement Under the Guidance of a 3D-Printed Surgical Guide Template

OBJECTIVE: To evaluate the safety and accuracy of S2 alar-iliac (S2AI) screw placement guided by a 3-dimensional (3D)-printed surgical guide template. METHODS: The data of 27 patients treated with S2AI screws were analyzed. S2AI surgical guide templates were designed and printed, and S2AI screw placement was completed intraoperatively with the guide templates. Postoperative computed tomography was performed to measure screw path parameters, namely the sagittal angle (SA), the transverse angle (TA), the horizontal distance (HD) between the entry point of the screw and the median sacral crest, and the vertical distance (VD) between the entry point of the screw and the lower edge of the first posterior sacral foramen. Screw placement was graded according to the Oh grading criteria. RESULTS: A total of 54 S2AI screws were placed. The screw grades were as follows: 52 screws were considered grade 0, 2 were grade 1, none were grade 2, and none were grade 3. Thus grade 0 accounted for 96.3% of the screws. When the preoperatively planned SA (32.3° ± 2.0°), TA (42.1° ± 3.9°), HD (5.1 ± 1.1) mm, and VD (19.0 ± 2.4) mm were compared with the corresponding postoperative SA (31.9° ± 3.8°), TA (42.5° ± 4.0°), HD (4.9 ± 1.1) mm, and VD (19.1 ± 2.3) mm, no significant differences were identified (P > 0.05). CONCLUSIONS: S2AI screw placement assisted by a 3D-printed surgical guide is safe and accurate.