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 on an ankle radiograph is defined by the angle between a line drawn perpendicular to the tibial plafond and a line drawn through the tips of the malleoli. On an AP view, you first draw a line that is perpendicular to the tibial plafond (the bottom surface of the distal tibia), then draw a line connecting the tips of the medial and lateral malleoli. The angle where these two lines meet is the talocrural angle. This setup uses a fixed reference to the ankle joint surface and the malleoli, giving a reliable measure of the mortise’s orientation and helping assess alignment after injury. Using a parallel line to the plafond or a line through the calcaneus would not capture the same relationship, and a line along the tibial axis would reflect tibial shaft alignment rather than the ankle mortise.