Congenital tarsal coalition: multimodality evaluation with emphasis on CT and MR imaging.

Congenital tarsal coalition is a diagnosis that is often overlooked in young patients who first present with foot and ankle pain. Calcaneonavicular and talocalcaneal coalitions are encountered most frequently; fusion at other sites is much less common. Tarsal coalitions may be osseous, cartilaginous, or fibrous. Calcaneonavicular coalitions are readily detected on oblique radiographs. Radiographic confirmation of talocalcaneal coalition is more difficult than for fusion at other locations, although several secondary radiographic signs may indirectly suggest the diagnosis. Computed tomography (CT) and magnetic resonance (MR) imaging are invaluable for assessment of tarsal coalitions because they allow differentiation of osseous from nonosseous coalitions and because they depict the extent of joint involvement as well as secondary degenerative changes, features of vital importance in surgical planning. Short-inversion-time inversion recovery MR images may reveal bone marrow edema along the margins of the abnormal articulation, an important clue to the diagnosis. Moreover, CT or MR imaging may be required to confirm the diagnosis of talocalcaneal coalition when radiographic findings are equivocal. Because the diagnosis of tarsal coalition is often not entertained by the clinician ordering a CT or MR imaging examination, multiplanar imaging of the ankle and hindfoot is required.