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Anteriorposterior ankle radiograph demonstrates a subtle lucent region in the lateral facet of talus (red arrow). An unequivocal wedge radiodensity is present in the adjacent soft tissue (blue arrow). There is soft tissue swelling adjacent to the lateral malleolus. Patient was referred for CT study for further characterization.
There is subchondral sclerosis of the medial facet of the talus and the corresponding medial malleolus. A well corticated triangular bone fragment is present beneath the medial malleolus. The finding is in keeping with previous impaction injury between the medial malleolus and medial facet of talus. The likely mechanism is an inversion and adduction injury. The corticated triangular bone fragment is likely to represent an old fracture. Less likely differential diagnosis would include an accessory ossicle (os subtibiale) which usually has a rounded / ovoid appearance.