Anatomic Study and Assembled Navigation Template-Assisted Implantation for Anterograde Transpubic Screws
Authors: Wu Chao , Shen Danwei , Deng Jiayan , Zeng Bofang , Wang Xiangyu , Li Hong , Xu Lian , Luo Min 
Published: December 2021

Abstract
Objective: Research the anatomical parameters of the anterograde transpubic screw corridor and evaluate the safety of anterograde transpubic screw placement assisted by the assembled navigation template.Methods: A total of 50 normal subjects, including 25 males and 25 females, underwent pelvic CT scanning in our hospital from January 2020 to September 2020. A 3D model of the ilium was established. The ilium was divided into zone Ⅰ, Ⅱ and Ⅲ according to Nakatani classification. The anterograde transpubic screw channel completely passes through zone Ⅰ and Ⅱ to form corridor A. The anterograde screw channel completely passes through zone Ⅰ, Ⅱ and Ⅲ to form corridor B. The diameter and length of the inner circle, the distance from the center of the inner circle to the posterior superior and to the inferior iliac spine of corridor A and corridor B were measured, respectively. A total of 9 patients underwent anterograde transpubic screw and transverse sacroiliac screw placement assisted by the assembled navigation template in our hospital, including 5 males and 4 females, were retrospectively analyzed. Operative time, blood loss, incision length and fluoroscopy times were recorded. Grading score and Matta score were evaluated after surgery.Results: In 50 normal subjects, the diameter of corridor A was 11.16±2.13 mm, and that of corridor B was 8.54±1.52mm, and the difference between the two corridors was statistically significant (P=0.000). The length of corridor A was 86.39±9.35 mm, and that of corridor B was 117.05±5.91 mm, with significant difference between the two corridors (P=0.000). The surface distance from the screw entry point to the posterior superior iliac spine in corridor A was 109.31± 11.06mm, and that in corridor B was 127.86± 8.23mm, the difference between the two corridors was statistically significant (P=0.000). The surface distance from the screw entry point to the posterior inferior iliac spine in corridor A was 91.16±10.34 mm, and that in corridor B was 106.92±7.91 mm. The difference between the two corridors was statistically significant (P=0.000). Nine patients successfully completed surgery, and a total of 18 sacroiliac transverse screws and 11 anterograde transpubic screws were inserted with the assistance of assembled navigation templates. The mean operation time of the 9 patients was 108.75±25.71 min, the blood loss was 141.11±50.21 ml, the incision length was 14±4.62 cm, and the intraoperative fluoroscopy was 17.89±4.01 times. Matta scores were excellent in 5 patients and good in 4 patients. One of the anterograde transpubic screw was in Grade 1, and 10 were in Grade 0. One S1 screw was in Grade 1, and 8 S1 screws were in Grade 0. Nine S2 screws were in Grade 0.Conclusions: Majority of the patients can accommodate anterograde transpubic screw s with diameter of 6.5 mm. Anterograde transpubic screw placement assisted by an assembled navigation template is clinically feasible, and with low cortical breaches.