PROBLEM
A 70-year-old man complains of pain in his ankle that has lasted for months. What is your interpretation of this lateral projection of his ankle?

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ANSWER
The correct diagnosis is biphasic Paget’s disease. The lucent area in the distal tibia represents the lytic phase of the disease; it shows a V-shaped margin between the lucent bone and adjacent normal bone (the blade of grass sign). The calcaneus and navicular bone show the typical coarsening of the bony trabeculae. The increased density represents the blastic phase of Paget’s.

This series of diagnostic quizzes that challenge your ability to read a variety of x-ray films is edited by Dr. Keats, alumni professor of radiology at the University of Virginia School of Medicine in Charlottesville. Emerg Med 39(9):63-64, 2007