Normal Talocalcaneal Angle Size on Radiography
The talocalcaneal angle (Kite's angle) is the angle formed between the long axes of the talus and calcaneus on weight-bearing or simulated weight-bearing foot radiographs. It reflects the relationship between these two hindfoot bones and is a key index of hindfoot alignment in pediatric patients. Accurate measurement is essential for diagnosing and monitoring congenital and developmental foot deformities.
Normal Reference Values
| Orientation | Age | Measurement |
|---|---|---|
| Anteroposterior | Newborn | 27-56¡ |
| Anteroposterior | 2 y/o | 26-50¡ |
| Anteroposterior | 4 y/o | 24-44¡ |
| Anteroposterior | 4-9 y/o | 15-56¡ |
Clinical Significance
The talocalcaneal angle decreases with age as the pediatric foot matures and the hindfoot aligns. A decreased angle on the anteroposterior (AP) view suggests hindfoot varus and is a hallmark finding in clubfoot (talipes equinovarus), where parallelism of the talus and calcaneus produces angles as low as 0–10°. Conversely, an increased angle indicates hindfoot valgus, as seen in flatfoot deformities and vertical talus.
Interpretation must always be age-matched, as normal ranges narrow considerably between newborn and school age. Bilateral comparison is also recommended, since asymmetry may be more clinically significant than an absolute value slightly outside the reference range.
- Clubfoot (talipes equinovarus): markedly reduced angle with talar-calcaneal parallelism
- Congenital vertical talus: increased angle with fixed hindfoot valgus
- Flexible flatfoot: mildly increased angle, typically corrects with weight-bearing changes
- Tarsal coalition: may alter hindfoot mechanics and angle
- Metatarsus adductus: angle usually preserved; distinguish from clubfoot
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
The talocalcaneal angle is measured on the anteroposterior (AP) radiograph of the foot. A line is drawn through the long axis of the talus (bisecting the talar head and neck) and a second line along the lateral border of the calcaneus; the angle between these two lines is recorded. In infants and non-ambulatory children, a simulated weight-bearing (plantar-flexed) AP projection is used. True weight-bearing views are preferred in older children to reflect functional alignment.
Consistent positioning is critical — even minor rotation of the foot can significantly alter the measured angle. Both feet should be imaged in the same projection to allow reliable bilateral comparison. The lateral view talocalcaneal angle (Böhler-related assessment) provides complementary information about sagittal alignment but is measured separately.