Normal Talocalcaneal Index Size on Radiography
The talocalcaneal index (TCI) is the sum of the talocalcaneal angles measured on anteroposterior and lateral radiographic projections of the foot, providing a composite assessment of hindfoot alignment. On the lateral view alone, it reflects the angular relationship between the long axes of the talus and calcaneus. Accurate measurement of this index is essential for evaluating hindfoot valgus or varus deformity in the pediatric population, including conditions such as flatfoot and clubfoot.
Normal Reference Values
| Orientation | Age | Measurement |
|---|---|---|
| Lateral | Newborn | 76¡ |
| Lateral | 2 y/o | 76¡ |
| Lateral | 4 y/o | 76¡ |
| Lateral | 4-9 y/o | 45-103¡ |
Clinical Significance
The talocalcaneal index is a key tool in pediatric foot assessment because hindfoot alignment changes substantially with skeletal maturation. In newborns and toddlers, relatively high values reflect the physiologic laxity and valgus orientation of the hindfoot that is normal in early childhood. As children grow, the index narrows toward adult ranges, making age-matched reference values critical for accurate interpretation.
An abnormally increased talocalcaneal angle suggests hindfoot valgus, as seen in flexible flatfoot or vertical talus. A decreased angle indicates hindfoot varus, which is a hallmark of talipes equinovarus (clubfoot). Clinicians must correlate radiographic findings with clinical examination, as soft-tissue contracture and ossification stage can influence apparent angles.
- Talipes equinovarus (clubfoot) — decreased talocalcaneal angle
- Congenital vertical talus — markedly increased angle
- Flexible flatfoot (pes planus) — mildly to moderately increased angle
- Tarsal coalition — restricted subtalar motion with altered alignment
- Neuromuscular hindfoot deformity (e.g., cerebral palsy) — variable changes
Reference: Vanderwilde R, Staheli LT, Chew DE et al. Measurements on radiographs of the foot in normal infants and children. J Bone Joint Surg Am. 1988;70(3):407-15.
Imaging Notes
Lateral radiographs of the foot should be obtained in a true lateral projection with the patient weight-bearing when age and cooperation permit; in infants, a simulated weight-bearing or stressed lateral view is used. The talocalcaneal angle on the lateral view is measured between a line drawn through the long axis of the talus and a line along the inferior cortex of the calcaneus. Consistent positioning is paramount, as internal or external rotation artifacts can falsely alter the measured angle.
When calculating the full talocalcaneal index, the lateral angle is added to the angle obtained from the anteroposterior projection. Ossification of the hindfoot bones is incomplete in infants, so the geometric center of the partially ossified nuclei should be used as landmarks. Serial measurements over time are more informative than a single study when monitoring treatment response in deformity correction.