Tarsal coalitions are developmental abnormalities due to failure of tarsal segmentation. They may be associated with congenital syndromes.

Calcaneo-navicular and talo-navicular coalitions comprise 90% of all coalitions.

Clinically there is flat foot, peroneal spasm and lateral leg pain and foot pain. Commonly seen in children 8-12 years of age. Natural history is progressive pain and stiffness.

Talo-calcaneal coalitions may rarely be extra-articular, seen as the C-sign on radiographs. Ant-eater sign is the prolonged calcaneal process extending to the navicular in calcaneo-navicular coalitions.

As coalitions are not directly visualized on standard foot radiographs, awareness of secondary subtle signs is important to suspect this diagnosis. In addition to above mentioned signs, look for subchondral sclerosis, broad irregular articular surfaces (both due to secondary degeneration due to movement at non-solid coalitions), talar beak (abnormal motion at normal talonavicular joint in presence of other coalitions) or pes planus (on both weight-bearing and non weight bearing lateral views-indicating the abnormality is bony and not ligamentous). A ball and socket ankle joint maybe seen secondary to abnormal motion at ankle joint in widespread coalitions.

Solid bony coalitions demonstrate continuous bony trabeculae across the coalition, best seen on CT or MRI. Solid coalitions do not show marrow edema on MRI or degenerative changes due to lack of any motion across the coalition.

Conservative treatment includes non-steroidal anti-inflammatory drugs, cast, orthotics. Surgical treatment includes coalition resection with muscle or fat interposition. Triple arthrodesis is done if other treatment fails.