Talocalcaneal coalition

Last revised by Dr Henry Knipe on 18 Nov 2021

The talocalcaneal coalition is one of the two most common subtypes of the tarsal coalition, the other being the 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 commonly involved.

Talocalcaneal coalitions can be classified according to their location into the following subtypes 2:

  • anterior facet type
  • middle facet type
  • posterior facet type
  • extra-articular: with or without os sustentaculi

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 3,4:

  • C-sign
    • best assessed on a lateral ankle radiograph
    • posterior continuity of the talus and sustentaculum tali
    • sensitivity: 50%
    • specificity: 90%
  • 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-visualization of the middle articular facet 1,5. Sclerosis around the articular margins of the talocalcaneal joint may also occur.

At CT, coronal reformats are usually the best to appreciate the coalition. The bony coalition is seen as a complete bar of bone between the talus and calcaneus. In a non-osseous coalition, there is usually irregularity of the articular surface, narrowing of the joint space and subchondral sclerosis. CT can also nicely demonstrate the presence of an os sustentaculi.

MRI is more helpful for the assessment of cartilaginous or fibrous coalitions and also demonstrates bone marrow and soft-tissue edema.

On bone scan, increased radionuclide uptake at the site of the coalition may occur due to altered biomechanics at the joint, although this is a non-specific finding.

The talocalcaneal coalition was first described by the Hungarian anatomist Emil Zuckerkandl in 1877 2.

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Cases and figures

  • Case 1
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  • Case 2
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  • Case 3
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  • Case 3
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  • Case 4
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  • Case 4
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  • Case 5
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  • Case 6: fibrous
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  • Case 7: on 3D VR
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  • Case 8
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  • Case 9
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  • Case 10
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  • Case 11
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  • Case 12: bony fusion
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  • Case 13
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  • Case 14
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  • Case 15: fibrous
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  • Case 16
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  • Case 17: annotated images with normal comparison
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  • Case 18: cartilaginous
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  • Case 19: bony
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  • Case 20: extra-articular with os sustentaculum
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