Inter-rater Reliability of Sacral Ratio Measurements in Patients with Anorectal Malformations

Background: Anorectal malformations (ARMs) are a spectrum of congenital anomalies with varying prognosis for fecal continence. The sacral ratio (SR) is a measure of sacral development that has been proposed as a method to predict future fecal continence in children with ARM. The aim of this study was to quantify the inter-rater reliability (IRR) of SR calculations by radiologists at different institutions. Materials and methods: x-Rays in the anteroposterior (AP) and lateral planes were reviewed by a pediatric radiologist at each of six different institutions. Subsequently, images were reviewed by a single, central radiologist. The IRR was assessed by calculating Pearson correlation coefficients and intraclass correlation coefficients from linear mixed models with patient and rater-level random intercepts. Results: Imaging from 263 patients was included in the study. The mean inter-rater absolute difference in the AP SR was 0.05 (interquartile range, 0.02-0.10), and in the lateral SR was 0.16 (interquartile range, 0.06-0.25). Overall, the IRR was excellent for AP SRs (intraclass correlation coefficient [ICC], 81.5%; 95% confidence interval, 75.1%-86.0%) and poor for lateral SRs (ICC, 44.0%; 95% CI, 29.5%-59.2%). For both AP and lateral SRs, ICCs were similar when examined by the type of radiograph used for calculation, severity of the ARM, presence of sacral or spinal anomalies, and age at imaging. Conclusions: Across radiologists, the reliability of SR calculations was excellent for the AP plane but poor for the lateral plane. These results suggest that better standardization of lateral SR measurements is needed if they are going to be used to counsel families of children with ARM.