Anatomical study on isocentric C-arm three-dimensional imaging navigated percutaneous double screw fixation of pubic symphysis diastasis

Abstract

Objective With the isocentric C-arm (Iso-C) three-dimensional computerized navigation system, cadaveric pelvic specimens were used to imitate double screw fixation of the symphysis pubic. Practicability and safety of the screw trajectory were examined postoperatively by local cadaveric dissections and imaging tests. Methods Pelvic specimens were harvested from 8 male and 7 female adult cadavers. Double screw placement in symphysis pubic was performed using the Iso-C three-dimensional navigation and entry point and safety trajectory was achieved. With the detailed local dissection postoperatively, distances from screw entry and exit points to unilateral structures (spermatic cord, femoral artery and vein, femoral nerve, obturator artery and vein, obtrurator nerve, and so on) were measured respectively. After complete removal of surrounding soft tissues of the specimen with only bony structure kept, the entry angle and length were calculated. Accuracy of double screw fixation of symphysis pubic was further checked using X-ray and CT. Results Entry point of the first screw was at the junction of unilateral pubic tubercle and transitional site of superior pubic ramus. Mean angle of the first screw with the horizontal plane was (7.7±1.9)° in men and (8.1±1.7)° in women. Mean angle between the first screw and coronal plane was (7.8±1.8)° in men and (7.7±2.0)° in women. Entry point of the second screw was in the same place in the contralateral pubic tubercle. Mean angle between the second screw and horizontal plane was (30.6±4.0)° in men and (30.8±3.4)°in women. Mean angle between the second screw and coronal plane was (9.1±3.0)°in men and (9.2±3.3)°in women. Conclusions With the three-dimensional computerized navigation system, the bony channels of double screws implanted in the symphysis pubic are achieved and reliable. Percutaneous double screw fixation is feasible to treat the pubic symphysis diastasis. Key words: Pubic symphysis diastasis; Bone nails; Anatomy, regional; Surgery, computer-assisted