Abstract: Objective    To measure the anatomical parameters of the innovative sacroiliac screw-sacroiliac screw passing the back of sacrum(SISPTBOS), so as to provide basis for clinical application.    Methods     The 3D CT reconstruction images of 32 cases of normal adult pelvis were analyzed to observe the range of SISPTBOS channel, by simulating placement of SISPTBOS, measuring the anatomical parameters including the length of the screw channel（L), the distance between the insertion point and the center of superior articular process of S1(M1), the distance between the exit point and the superior- posterior border of actabulium(M2), the anteversion angle between the central axis and the line parallel to the upper endplate of S1(e), the outward angle(f), the safety angle in the sagittal plane(a), the safety angle in the coronal plane(b), the minimum diameter in the sagittal plane(d1) and the minimum diameter in the coronal plane(d2).   Results    The medial boundary of the screw canal was the inner wall of the arcuate line. The lateral boundary was the posterior-lateral walls of the spinal canal of S1 and the ilium, the lower boundary was the line between the sacral hole of S1 and the ischial notch, the upper boundary was the sacral slope, surface of sacroiliac joint, and the bottom of the true pelvis. L was (11.90±1.62) cm, M1 was ((2.07±1.40) mm, M2 was (4.78±2.57) mm, e was (57.97±4.28) °, f was (54.89±5.13) °, a was (11.45±2.73) °, b was (7.46±1.34) °, d1 was (8.57±0.99)mm and d2 was (6.75±0.84) mm. There were significant differences in the anteversion angle between the central axis and the line parallel to the upper endplate of S1 (e) and the outward angle(f) between males and females (P<0.05).    Conclusions    Implanting of the SISPTBOS is feasible and safe, which may be selected by using screws with a diameter of 5.0 to 6.0 mm and a length of 9 to10 cm.

Key words: Sacroiliac joint; ,  , Sacroiliac screw; ,  , Computed tomograph; ,  , Anatomy