Comparison of x-ray and CT methods for assessing sacral shape variants and identifying a secure sacroiliac screw fixation corridor

Sacroiliac screw fixation is the only minimally invasive technique for stabilizing unstable posterior pelvic ring fractures. X-ray/CT methods identify sacral shape variants, which influence screw fixation feasibility at sacral segment S1. As no reliability analysis was previously published, this study analyzed four X-ray/CT-based screw corridor evaluation methods. CT datasets of 80 human pelvises (♂=47, ♀=33, x& age=56 years, x& height=173cm, x& weight=76kg) were used. CTs were post-processed using Amira 5.2 software to generate 3D models and analyzed for S1 transverse 7.3mm screw corridors using a C++ program. CT-slices and radiograph-like images were generated per each classification's requirements. Five surgeons independently assessed sacral shape and transverse screw insertion feasibility. Sensitivity, specificity, and positive/negative predictive values were calculated. C++ analysis indicated feasible screw insertion in 66 cases (82%). Sensitivities were 86% (Mendel), 75% (Routt), 74% (Carlson), and 67% (Kim). Specificities were 73% (Mendel) and 79% (Kim). Mean positive predictive value spanned from 54.6% (Mendel) to 26.2% (Carlson); negative predictive value spanned from 94.5% (Kim) to 90.4% (Carlson). No significant differences existed between surgeons. Mendel's classification provides reliable and reproducible assessment via the lateral sacral triangle, without additional CTs like Carlson or Routt or the subjectivity of Kim's method.