Normal Talo-Calcaneal Index Size on Radiography
The talo-calcaneal index (TCI) is the sum of the talo-calcaneal angles measured on anteroposterior (AP) and lateral weight-bearing radiographs of the foot. It reflects the three-dimensional relationship between the talus and calcaneus, providing a composite assessment of hindfoot alignment. Accurate measurement is essential in the evaluation of pediatric and adult flatfoot deformities, clubfoot, and other hindfoot pathologies.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior, Lateral | >40¡ |
Clinical Significance
A normal talo-calcaneal index is greater than 40°, representing the combined AP and lateral talo-calcaneal angles. A reduced TCI indicates convergence of the talus and calcaneus, a hallmark of hindfoot varus deformities such as clubfoot (talipes equinovarus). Conversely, an abnormally elevated TCI may suggest hindfoot valgus or planovalgus deformity, as seen in flexible flatfoot.
The TCI is particularly valuable in pediatric populations where individual talo-calcaneal angles may be difficult to interpret in isolation. Serial measurements can help monitor treatment response following casting, bracing, or surgical correction of congenital foot deformities. Clinicians should be aware that normal values shift with age during skeletal development, and weight-bearing positioning is critical for reproducibility.
- Clubfoot (talipes equinovarus): Reduced TCI due to hindfoot varus and adductus
- Flexible flatfoot / planovalgus: Elevated individual angles contributing to increased TCI
- Tarsal coalition: Altered hindfoot mechanics affecting talo-calcaneal relationships
- Vertical talus (congenital): Markedly abnormal talo-calcaneal alignment on lateral view
- Post-traumatic hindfoot deformity: Asymmetric TCI compared to contralateral foot
Reference: Ebnezar J. Textbook of Orthopedics. Jaypee Brothers Medical Pub. (2010).
Imaging Notes
The talo-calcaneal index is measured on standard weight-bearing radiographs of the foot in both the anteroposterior and lateral projections whenever clinically feasible. On the AP view, the talo-calcaneal angle is formed between the long axis of the talus and the long axis of the calcaneus. On the lateral view, the same axes are used in the sagittal plane. The TCI is the arithmetic sum of these two angles.
Strict positioning is essential — non-weight-bearing films significantly underestimate deformity in flexible conditions such as flatfoot. In young children unable to bear weight, simulated weight-bearing or stress views may be substituted. Care should be taken to identify true talar and calcaneal long axes, as overlapping ossification centers in pediatric feet can introduce measurement error.