Hemipelvis Index as a Diagnostically Significant Radiographic Criterion for Assessing Pelvic Ring Asymmetry

Abstract

Background: Interpretation of pelvic radiographs still relies largely on the qualitative, subjective assessment of the radiologist, and no universal quantitative measure of side-to-side pelvic symmetry is available in routine practice.
Aim: To develop and validate an original radiographic parameter, the hemipelvis index (HI), for the objective quantitative assessment of pelvic ring asymmetry and to determine its diagnostic accuracy in detecting pelvic ring injuries.
Methods: This retrospective study included 224 patients examined between 2023 and 2026. The control group comprised 154 patients (76 men, 78 women) without pelvic pathology, who were used to establish normative values. The main group comprised 70 patients with pelvic fractures of varying severity. The target subgroup for index validation included 30 patients, in whom the HI was calculated on standardised anteroposterior pelvic radiographs as the relative difference between the vertical dimensions of the right (R) and left (L) hemipelvis, measured between the most cranial point of the iliac crest and the most caudal point of the ischial tuberosity: HI = (R – L( / (R + L)/2 × 100%. Diagnostic performance was assessed by receiver operating characteristic (ROC) analysis, with calculation of the area under the curve (AUC), 95% confidence intervals (CI), sensitivity, specificity and the Youden index.
Results: The hemipelvis index showed good discriminative performance: the AUC was 0.920 (95% CI: 0.851–0.988; p < 0.001). The optimal cut-off value, determined by the maximum Youden index (J = 0.757), was 3.23%. At this threshold, sensitivity was 86.7% (95% CI: 69.3–96.2%) and specificity was 87.7% (95% CI: 81.4–92.4%).
Conclusion: The hemipelvis index is a simple, reproducible and easily applicable quantitative radiographic marker that demonstrates high diagnostic performance in detecting pelvic ring injuries and may be used as an additional criterion at the stage of initial plain radiography.