Journal of Pediatric Orthopaedics - 2026-03-23 - Journal Article
Talar Index: A New Radiologic Marker for Clubfoot Equinus.
Garg V, Agarwal A, Bhalla S, Iqbal MZ
Topics
Key Takeaway
The Talar Index identifies residual clubfoot equinus with 95.9% sensitivity and 90.5% specificity (AUC 0.929) against the lateral tibiocalcaneal angle as reference standard.
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Summary
This cross-sectional study validated the Talar Index as a radiologic marker for residual equinus in infants with idiopathic clubfoot undergoing Ponseti treatment, assessed immediately before percutaneous Achilles tenotomy. The index was compared against the lateral tibiocalcaneal angle using ROC analysis and logistic regression across 49 affected and 21 contralateral unaffected feet. The Talar Index achieved 95.9% sensitivity, 90.5% specificity, NPV of 93.4%, AUC of 0.929, and excellent inter- and intraobserver reliability (κ=0.84 and κ=0.97, respectively).
Key Limitation
The contralateral unaffected feet served as controls rather than a separate cohort of non-clubfoot infants, and the small sample of 49 affected feet limits generalizability across the full spectrum of Pirani severity scores.
Original Abstract
BACKGROUND
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.
METHODS
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.
RESULTS
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.
CONCLUSION
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 OF EVIDENCE
Level III.