Talar Index: A New Radiologic Marker for Clubfoot Equinus.

Abstract

Residual equinus is an important indicator for deciding the need for tenotomy and checking for recurrence of clubfoot deformity. This study aims to validate a novel, radiologic marker-the Talar Index-for objective assessment of residual equinus in clubfoot. A cross-sectional observational study was conducted on infants with idiopathic clubfoot treated using the Ponseti protocol, assessed just before percutaneous Achilles tenotomy. The validity of the talar index was tested against the unaffected feet. A positive talar index was defined as the presence of residual equinus. Receiver operating characteristic (ROC) analysis and logistic regression were performed between positive talar index and lateral tibiocalcaneal angle and sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. Interobserver and intraobserver reliability of the talar index was assessed using Cohen's kappa. A total of 70 feet (49 affected and 21 unaffected) were evaluated. The talar index correctly identified residual equinus in 94.3% of feet, with a sensitivity of 95.9% and specificity of 90.5%. There was a strong association between a positive talar index and increased tibiocalcaneal angle (AUC: 0.929, P=0.001). Sensitivity, specificity, PPV, and NPV of the positive talar index were found to be 84%, 90.5%, 77.9%, and 93.4%, respectively. Logistic regression showed a significant model fit (P<0.001, R²=0.82). Inter (κ=0.84) observer and intra (κ=0.97) observer reliability was excellent. The talar index is a valid, reliable, and easily interpretable radiologic marker for assessing residual equinus in clubfoot. Its simplicity and high diagnostic accuracy make it particularly suitable for routine clinical use, including in resource-limited and high-volume settings. Level III.