Talocalcaneal coalition is one of the two commonest sub-types of tarsal coalition, the other being calcaneonavicular coalition. It accounts for 45% of all tarsal coalitions, and although all three facets of the talocalcaneal joint can be involved, the middle facet is most common.
As with any coalition it may be bony, cartilaginous or fibrous. Talocalcaneal coalition often requires cross-sectional imaging for accurate diagnosis.
Plain film findings include:
talar beak sign
- best seen on the lateral ankle radiograph
- prominent beak at the anterior aspect of the talus
Secondary radiographic features that suggest the diagnosis include close apposition of the middle facet of the talocalcaneal (subtalar) joint or non-visualisation of the middle articular facet 1,4. Sclerosis around the articular margins of the talocalcaneal joint may also occur.
At CT, coronal reformts are usually the best to appreciate the coalition. Bony coalition is seen as a complete bar of bone between the talus and calcaneus. In non-osseous coalition, there is usually irregularity of the articular surface, narrowing of the joint space and subchondral sclerosis.
MRI is more helpful for assessment of cartilaginous or fibrous coalitions and also demonstrates bone marrow and soft-tissue oedema.
Increased radionucleotide uptake at the site of the coalition may occur due to altered biomechanics at the joint, although this is a non-specific finding.
- 1. Crim JR, Kjeldsberg KM. Radiographic diagnosis of tarsal coalition. AJR Am J Roentgenol. 2004;182 (2): 323-8. AJR Am J Roentgenol (full text) - Pubmed citation
- 2. Taniguchi A, Tanaka Y, Kadono K et-al. C sign for diagnosis of talocalcaneal coalition. Radiology. 2003;228 (2): 501-5. doi:10.1148/radiol.2282020445 - Pubmed citation
- 3. Lateur LM, Van hoe LR, Van ghillewe KV et-al. Subtalar coalition: diagnosis with the C sign on lateral radiographs of the ankle. Radiology. 1994;193 (3): 847-51. Radiology (abstract) - Pubmed citation
- 4. Greenspan A. Orthopedic imaging, a practical approach. Lippincott Williams & Wilkins. (2004) ISBN:0781750067. Read it at Google Books - Find it at Amazon
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