How is the talocrural angle defined on radiographs?

How is the talocrural angle defined on radiographs?

• A. Line drawn parallel to the tibial plafond and line through the malleolar tips.
• B. Line drawn perpendicular to the tibial plafond and another line between the tips of the malleoli.
• C. Line perpendicular to the calcaneus and line through the malleoli.
• D. Line along the tibial axis and line through the malleolar tips.

Answer: (B)

The talocrural angle is defined on AP ankle radiographs by two landmarks: a line drawn perpendicular to the distal tibial articular surface (the tibial plafond) and a line that connects the tips of the medial and lateral malleoli. The angle between these two lines reflects the ankle mortise alignment relative to the tibia.

This is the best choice because it uses a stable, consistent reference to the tibial plafond and the malleolar tips to gauge mortise orientation. Using a line parallel to the tibial plafond would not provide a reliable reference for tilt, and a line perpendicular to the calcaneus or a line along the tibial axis would measure different relationships that don’t correspond to the talocrural angle.