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

Abstract

BackgroundTransiliac–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 S1 TITS screw should be preoperatively assessed because the pelvic ring injuries with sacral dysmorphism had the insufficient osseous corridors. HypothesisAxWS2 may predict the possibility of TITS screw fixation and be used as the new indicator to discriminate the sacral dysmorphism. Materials & methodsThe conventional CT images of eighty-two cadaveric pelvis imported into Mimics® 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 S1 and S2 TITS screw using Mimics® 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 AxWS1 and AxWS2, respectively. ResultsDespite no cortical violation in S2 of all models, cortical violation of S1 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. AxWS1 was<7mm in the impossible models and<9.0mm in the CT-violation models. AxWS2 negatively correlated with AxWS1 (R -0.450, p<0.01). By receiver operating characteristic curve analysis to identify the CT-violation model using AxWS2, the cut-off value of AxWS2 was 13.32mm (sensitivity 0.70, specificity 0.70). DiscussionBy using AxWS2, the possibility of S1 TITS screw fixation could be predicted and safely placed without cortical violation, if AxWS2 was less than 13mm. Considering the negative relationship with AxWS1, AxWS2 should be used as a new indicator to predict safe S1 TITS screw fixation. Level of evidenceIII, controlled laboratory study.