To determine if there is a safe osseous corridor for trans-sacroiliac screw fixation of U-type sacral fractures using fluoroscopic landmarks. We reviewed the sacral anatomy of patients who underwent Computed Tomography (CT) investigations between October and December 2009. Agfa-IPMAX Version 5.2 software was used to determine if there was a trans-sacroiliac osseous corridor in the S1 and S2 vertebrae from one ilium to the other. 76 patients were in the study, 38 male and 38 female. Exclusion criteria were patients under 18 years old; patients with degenerate lumbar spine and lumbo-sacral junction; CT imaging slices greater than 2.5mm. We measured various parameters including the dimensions of the S1 and S2 mid-sagittal vertebral body; cross-sectional areas of the S1 and S2 corridor; location of the centre of the S1 and S2 corridor. The mean cross-sectional area for S1 and S2 corridors in males and females are 21mm2 and 15mm2 respectively. The mean cross-sectional area for the S2 corridor in males and females were 15mm2 and 11mm2 respectively. The centre of the S1 and S2 corridor is located in the centre of both S1 and S2 vertebrae. Two-thirds of males and females have a complete osseous corridor to pass a trans-sacroiliac S1 screw. The S2 corridor was present in all males but only in 87% of females. Before placement of trans-sacroiliac screws, the surgeon should review the CT sacral anatomy to determine if the trans-sacroiliac osseous corridor is present. Ethics Approval: None – Audit Interest Statement: None
