A 13-year-old boy has a rigid flatfoot that does not correct on tiptoe standing. A calcaneonavicular coalition is suspected on plain films but the lateral and AP views are inconclusive. Which additional radiographic view is most likely to demonstrate the coalition?
- A Axial (Harris) heel view
- B Weight-bearing lateral with forced dorsiflexion
- C 45-degree internal oblique view of the foot ✓
- D Mortise view of the ankle
Correct answer: C. 45-degree internal oblique view of the foot
Explanation
The calcaneonavicular coalition lies in an oblique plane between the anterolateral calcaneus and the navicular, so a 45-degree internal oblique radiograph of the foot profiles the bar directly and is the screening view of choice. The Harris axial view images the subtalar joint and helps in talocalcaneal coalitions, not calcaneonavicular bars. CT remains the definitive study when plain films are equivocal or surgical planning is needed.
Reference: Tachdjian's Pediatric Orthopaedics, 5th ed.
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