Calcaneonavicular coalition

Calcaneonavicular coalition is one of the two most common subtypes of tarsal coalition, the other being talocalcaneal coalition. As with any coalition it may be osseous (synostosis), cartilaginous (synchondrosis) or fibrous (syndesmosis).

Radiographic features

This type of coalition is more easily diagnosed on plain film than talocalcaneal coalition.

Plain radiograph

Oblique view

• best at depicting calcaneonavicular coalition directly as a calcaneonavicular bar

AP view

• may also directly show the coalition
• indirect signs include 
  • the broad proximal surface of navicular: broader than the articulating talar head
  • lateral tapering of navicular

Lateral view

Indirect signs include:

• anteater sign: an elongated anterior process of the calcaneus
• reverse anteater sign: elongated lateral navicular
• talar beak
• short talar neck

CT

CT can be used to confirm the diagnosis where this was equivocal or not seen on plain films. It may also be used for surgical planning.

MRI

MRI is probably more helpful in assessing and characterising cartilaginous and fibrous coalition and allows assessment of associated bone and soft tissue oedema.

Treatment and prognosis

As with any tarsal coalition, non-operative management may allow some improvement in symptoms initially, but they usually return. Usually, surgical treatment with excision of the coalition is required.