Assessment of osseous corridor for transiliac-transsacral screws and clinical applications: Computational simulation study

Abstract

Background: Transiliac-transsacral (TITS) screw fixation might be necessary in some cases involving the vertical shearing injuries with transforaminal fracture and bilateral posterior ring injuries. However, the possibility of S-1 TITS screw should be preoperatively assessed because the pelvic ring injuries with sacral dysmorphism had the insufficient osseous corridors. Hypothesis: AxW(S2) may predict the possibility of TITS screw fixation and be used as the new indicator to discriminate the sacral dysmorphism. Materials & methods: The conventional CT images of eighty-two cadaveric pelvis imported into Mimics (R) software to reconstruct three-dimensional (3D) models. A 7.0 mm-sized screw was processed into a 3D model using a 3D-sensor at actual size and virtually implanted as S-1 and S-2 TITS screw using Mimics (R) software. The cortical violation around screw path was evaluated using 3D biplanar and conventional CT images. The osseous corridor widths around TITS screws were measured in the axial plane images and defined as AxW(S1) and AxW(S2), respectively. Results: Despite no cortical violation in S-2 of all models, cortical violation of S-1 TITS screw was found in 20 models. Of them, 14 models (impossible models) were identified in the 3D biplanar images, and all 20 models (CT-violation models) were identified only in CT axial plane images. AxWS(1) was < 7 mm in the impossible models and < 9.0 mm in the CT-violation models. AxW(S2) negatively correlated with AxW(S1) (R -0.450, p < 0.01). By receiver operating characteristic curve analysis to identify the CT-violation model using AxW(S2), the cut-off value of AxW(S2) was 13.32 mm (sensitivity 0.70, specificity 0.70). Discussion: By using AxW(S2), the possibility of S-1 TITS screw fixation could be predicted and safely placed without cortical violation, if AxW(S2) was less than 13 mm. Considering the negative relationship with AxW(S1), AxW(S2) should be used as a new indicator to predict safe S-1 TITS screw fixation. Level of evidence: III, controlled laboratory study. (C) 2020 Elsevier Masson SAS. All rights reserved.