Tarsal coalition is a congenital fusion of two of the tarsal bones of the foot. This union can be either a complete or partial bony fusion, or a cartilaginous/fibrous fusion. Tarsal coalition will often manifest itself as chronic foot pain, and most patients will present during adolesence.

The two most common forms of tarsal coalition are:

1. calcaneonavicular (most common) - best seen on oblique view => either a direct connection (bony coalition) or close proximity with irregular joint margins (fibrous coalition) can be seen between the calcaneus and the navicular bones; on lateral view => anterosuperior aspect of calcaneus appears to extend further than normal ("beaking") towards the navicular bone.
2. talocalcaneal - more subtle on plain films - CT is often necessary to make the diagnosis; plain film (lateral) findings include talar beaking, poor visualization of talocalcaneal joint, and a C-shaped band of overlapping bone noted over the calcaneus; coronal CT views will show evidence of bony or fibrous fusion between the middle facet of the talus and the sustentaculum tali of the calcaneus.

Treatment may include surgical repair/division of the coalition.

	Talocalcaneal Coalition in an 11-year-old male. Coronal CT demonstrates an ossified coalition at the sustentacular articulation of the calcaneus with the talus.
Calcaneonavicular coalition in an 11-year old male. Top, Lateral radiograph shows the superior calcaneus to be elongated. Bottom, Oblique radiograph demonstrates fibrous coalition with close proximity and irregularity of the margins of the calcaneonavicular joint.