Tarsal coalition is an abnormal connecting bridge of tissue between two normally-separate tarsal bones. The term 'coalition' means a coming together of two or more entities to merge into one mass. The tissue connecting the bones, often referred to as a "bar", may be composed of fibrous or osseous tissue. The two most common types of tarsal coalitions are calcaneo-navicular (calcaneonavicular bar) and talo-calcaneal (talocalcaneal bar), comprising 90% of all tarsal coalitions. There are other bone coalition combinations possible, but they are very rare. Symptoms tend to occur in the same location, regardless of the location of coalition: on the lateral foot, just anterior and below the lateral malleolus. This area is called the sinus tarsi.