A tarsal coalition is a congenital condition which most commonly manifests itself in adolescence but may also become problematic in adulthood. The underlying problem is a failure of complete separation of the tarsal bones (the bones of the hindfoot area).

The most common types are the calcaneonavicular coalition and the subtalar coalition (the anatomic location of where the bones have failed to separate completely). The foot is usually flat and this flatfoot position will not correctly restore the normal arch of the foot when the foot is lifted off the ground because of the rigidity of the foot. The foot remains in a flat position at all times.

Many patients may have this condition but will not have any pain. In some patients, however, the abnormal bone or tissue connecting these bones may begin to rub against each other irregularly. This most commonly occurs during adolescence as these tissues mature, or after a traumatic injury to the foot disrupting the connections between these bones that the body had created.

Treatments involve immobilization to allow the two edges of the bone to again stabilize each other or if this treatment fails, removing the coalition (surgically removing the bone connecting the involved bones). If arthritis between the joints is present and severe, then a fusion (gluing together) of the involved joints may be necessary.