“…Various recommended angles of trajectory had been reported by previous studies, ranging from 8.3° to 34.5° in the sagittal plane, and 32.1° to 42.5° in the axial plane, which made the spine surgeons confused. 5 , 6 , 9 , 11 , 17 , 18 , 19 We thought that several factors might contribute to the variations of S2AI trajectory angles, such as etiology, race, the spatial position of the pelvis, and so on. The trajectory of S2AI screw goes through the sacrum, the sacroiliac joint space, and the ilium.…”