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.

Objective To establish a reliable unstable pelvic fracture model with sacral plexus stretch injury in goats and to detect electrophysiological signals when pelvis is shifted in different orientations and distance.Methods Twenty-four goats were divided into three groups of 8 animals each:pelvic longitudinal displacement was induced in group A,pelvic lateral displacement in group B,and pelvic dorsal displacement in group C.Animal left L6 and S1 nerve root and initial segment of sciatic nerve were exposed to connect stimulating and receiving electrodes respectively.Left pelvis was shifted at the speed of 0.25 mm/s to produce the model of unstable pelvic fracture with sacral plexus stretch injury.Electrophysiological signals of L6 and S1 were recorded when the placement of pelvis was 0,0.5 and 1.0 cm respectively.Results With pelvic displacement,the threshold potential,maximum stimulus potential and incubation period were gradually increased,but the peak-to-peak value became smaller gradually.When the pelvis displaced 0.5 cm at different orientations,group A showed improved threshold potential and incubation period (P ＜0.05),decreased peak-to-peak value (P ＜0.05),and no significant change in maximum stimulus potential(P ＞0.05);group B only showed lowered peak-to-peak value with no significant variations in other electrophysiological signals (P ＜ 0.05);group C had no significant variations in all electrophysiological signals (P ＞ 0.05).When the pelvis displaced 1.0 cm at different orientations,groups A and B showed improved threshold potential,maximum stimulus potential and incubation period (P ＜ 0.05) and lowered peak to peak value (P ＜ 0.05);group C showed higher incubation period with no significant variations in other electrophysiological signals(P ＜0.05).Between groups,the amplitude of variation in electrophysiological signals was the most in group A and the least in group C.Conclusion After unstable pelvis fracture in goats,sacral plexus stretch injury is the most serious in longitudinal displacement of the pelvis.

Objective: To investigate the anatomical features of the safe zone for sacral lateral mass screw placement and find the safe trajectory, so as to provide reference for clinical application. Methods: The three-dimensional computed tomography scan materials of sacrococcygeal vertebrae in 60 patients admitted to the Liaocheng People's Hospital of Shandong Province were analyzed by Mimics software to establish three-dimensional models. There were 33 males and 27 females, aged 25-78 years, with an average age of 45.7 years. After the safe zone was separated from sacral lateral mass model, a maximum cylinder was placed into the safe zone according to its anatomical feature. The cylinder was established as safe trajectory. Anatomical data were measured, including the length and diameter of screw trajectory, the distance between the entry point and the middle jaw, and adjacent upper and lower foramen, as well as the intersection angle between the screw direction and sagittal plane, between the screw direction and the adjacent upper end plate. Results: The restriction factor of screw size on S₁, S₂ lateral mass was transverse diameter, while the restriction factor on S₃, S₄ was the distance between adjacent intervertebral foramen. The maximal length of screw from S₁ to S₄ was 30 mm, 35 mm, 30 mm, 14 mm respectively, while the maximal diameter was 12 mm, 9 mm, 5 mm, 5 mm respectively. The best entry point of S₁ mass screw was lateral to the zygopophysis. The best entry point of S₂-S₄ mass screw was located at the midpoint of a line connecting the lateral edge of adjacent posterior sacral foramen approximately about 2 cm from median sacral crest. The leaning angles of screw was increased successively, and the sagittal plane was slightly inclined. There were significant differences between male and female groups in the leaning angle in S₂ [male: (35.8±1.2)°, female: (37.9±3.7)°] and the distance between entry point and median sacral crest [male: (20.5±1.0)mm, female: (19.1±1.4)mm](P<0.05), while there was no significant difference in other parameters (P>0.05). Conclusions Cylindrical bony channel which is feasible for screw placement can be found in the lateral mass of sacrum. Individualized measurement can provide reference for application of lateral mass screw.