Normal Talonavicular Coverage Angle Size on Radiography
The talonavicular coverage angle is a radiographic measurement describing the alignment between the talar head and the navicular on the anteroposterior (AP) foot view. It quantifies the degree to which the navicular is properly centered over the talar head. Accurate measurement is essential for evaluating hindfoot malalignment, pes planus, and guiding both conservative and surgical management.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior | <7¡ |
Clinical Significance
A normal talonavicular coverage angle is less than 7° on the AP projection. Values exceeding this threshold indicate lateral uncovering of the talar head by the navicular, a hallmark of hindfoot valgus and acquired or congenital flatfoot deformity. The greater the angle, the more severe the abduction deformity of the midfoot.
Elevated talonavicular coverage angles are commonly encountered in the following clinical scenarios:
- Adult-acquired flatfoot deformity (posterior tibial tendon dysfunction)
- Pediatric flexible pes planus
- Tarsal coalition with secondary hindfoot valgus
- Neuropathic (Charcot) arthropathy of the midfoot
- Post-traumatic hindfoot malalignment
A key pitfall is ensuring true AP positioning of the foot, as rotational error can artificially alter the apparent coverage angle. The measurement should always be interpreted alongside the talus–first metatarsal (Meary's) angle and the calcaneal pitch for a comprehensive assessment of arch morphology.
Reference: Gould N. Evaluation of hyperpronation and pes planus in adults. Clin. Orthop. Relat. Res. 1983;(181):37-45.
Imaging Notes
The talonavicular coverage angle is measured on the weight-bearing anteroposterior radiograph of the foot. Two lines are drawn: one along the articular surface of the talar head and one along the proximal articular surface of the navicular. The angle subtended between these lines represents the degree of lateral talar head uncovering. Weight-bearing views are strongly preferred, as non-weight-bearing films underestimate deformity severity in flexible flatfoot.
Ensure the foot is positioned flat on the cassette with the beam directed perpendicular to the plantar surface. Bilateral comparative views are helpful when asymmetric deformity is suspected, and the measurement should be correlated with the lateral projection for a complete biomechanical profile of the foot.