Middle subtalar osseous coalition with associated fusion of the sinus tarsi: a previously undescribed type of tarsal coalition.

Tarsal coalitions affect up to 13% of the population and may cause chronic ankle and hindfoot pain. Coalitions can be subdivided as osseous, cartilaginous, or fibrous types. The most common type of tarsal coalition involvesthe talocalcaneal joint, where it usually affects the middle subtalar joint. In this article, we describe a previously unpublished form of talocalcaneal coalition with osseous coalition at the level of the middle subtalar joint with associated fusion of the sinus tarsi.