[Three-dimensional computed tomography analysis and clinical application of sacroiliac screw placement].

Objective To evaluate the possibility of transverse sacroiliac screw placement in different segments of the sacrum. Methods Data of 80 pelvic CT scans (slice thickness ≤1.0 mm) archived in CT department of the Third Hospital of Hebei Medical University from September 2016 to October 2017 were retrospectively collected. Mimics software was used to rebuild the pelvis three-dimensional model. According to whether the sacral 1(S1) segment could place the transverse sacroiliac screws or not, all the sacrums were divided into normal group (n=55) and dysmorphic group (n=25). Simulation the S1, sacral 2(S2) transverse sacroiliac screw placement in 3-Matic software. Analysis whether there was any difference in maximum diameter and length of S2 transverse sacroiliac screw between the normal group and the dysmorphic group. The pelvic CT data of the dysmorphic group were measured, and the optimal tilt angle and length of the oblique S1 screw were obtained. The feasibility of transverse sacroiliac screw insertion in sacral 3(S3) segment was evaluated.t-test, rank sum test, and χ2 test was used to analyze data, respectively. Results In the dysmorphic group, the largest diameter of the S1 transverse screw was (4.9±1.6)mm, and the normal group was (13.6±3.6)mm (t=-15.07, P=0.00). In the dysmorphic group, the largest diameter of S2 transverse screw was (13.8±3.0)mm, and was (12.4±2.2)mm in the normal group(t=2.11, P=0.04). There was no significant difference in the length of S2 transverse sacroiliac screw between the two groups (t=0.47, P=0.64). In the dysmorphic group, the anterior vertebral height of S1 was (23.1±4.0)mm, which was significantly higher than that of the normal group ((14.1±4.2)mm)(t=9.01, P=0.00). The angle of S1S2 in the dysmorphic group was 10.9°(3.8°, 17.6°), which was significantly larger than that of the normal group (2.0°(1.0°, 2.0°) (Z=-4.03, P=0.00). In the dysmorphic group, the incline angle of the oblique S1 sacroiliac screw was (35.6±6.2)°, the anteversion angle was (37.2±4.4)°, and the mean screw length was (90.2±4.7)mm. In the dysmorphic group, the placement rate of S3 transverse sacroiliac screw was 48.0%, and that of the normal sacral group was 9.1%. Conclusions There is often dysmorphic in the sacrum in patients with large S1 anterior vertebral height and S1S2 angle. Sacral dysmorphic patients with posterior pelvic ring injury may be treated with S1 pedicle oblique sacroiliac screws. S3 transverse sacroiliac screws should be carefully placed, especially for the absence of sacral dysmorphic in patients. Key words: Sacrum; Imaging, three-dimensional; Dysmorphic; S1 transverse iliosacral screw