Kevin E Snyder, M.D.

February 17, 2004

Discussion

Tarsal coalition is also sometimes referred to as peroneal spastic flatfoot. It is almost always a congenital anomaly in which there is a lack of segmentation involving the bones of the foot. The form of tarsal coalition presented here, Calcaneonavicular coalition, is the most frequent type, being found in approximately 60% of cases. Talocalcaneal coalition is the second most frequent type. Males are afflicted more frequently than women, and findings of bilateral coalition are not uncommon, being present in up to 25% of cases.

While tarsal coalitions are present from birth, presentation tends to be early in adulthood, when symptoms begin to develop. Presentation in early adulthood may include pes planus, limited range of motion in the hindfoot, and spasticity of the peroneal muscles. In these cases, initial imaging is performed consisting of plain radiographs. Calcaneonavicular coalition may be occult on the standard AP radiograph. This coalition is better seen on lateral radiographs, where the "anteater" sign of a very prominent anterior process of the calcaneus is present. Even better, the coalition itself may be directly imaged on oblique images. Coalition need not consist of a complete osseous bridge. Other types of coalitions include fibrous or cartilaginous. In the absence of bony bridging, a fibrous or cartilaginous coalition can be recognized by sclerosis, irregularity and broadening at a point of an abnormally close interface between the tarsal bones, as is recognized between the calcaneus and navicular in this case.

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