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ANSWER: Talocalcaneal tarsal coalition
  1. Bippan Sangha1,
  2. Julia Grebenyuk2,
  3. Teri Fisher3,
  4. Bruce B Forster2
  1. 1University of British Columbia, Vancouver, Canada
  2. 2Department of Radiology, University of British Columbia, Vancouver, Canada
  3. 3Division of Sports Medicine, University of British Columbia, Vancouver, Canada
  1. Correspondence to Dr Julia Grebenyuk, Department of Radiology, University of British Columbia Hospital, 2211 Wesbrook Mall, Vancouver, BC V6T 2B5, Canada; julia.grebenyuk{at}utoronto.ca

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Imaging findings

Anteroposterior radiograph of right ankle

No abnormality is appreciable on this anteroposterior radiograph.

Lateral radiograph of right ankle

This image demonstrates a complete C-sign with osseous bridging. There is narrowing of the posterior subtalar facet, a short talar neck and a small dorsal subtalar beak.

Sagittal fast spin echo T1, sagittal fat saturated T2 and coronal fast short tau inversion recovery magnetic resonance images

The magnetic resonance images demonstrate bone marrow oedema across the middle subtalar joint, cortical irregularity and small subchondral cysts, in keeping with fibrous coalition.

Discussion

Tarsal coalition is an abnormal union between two or more tarsal bones. The coalition can be osseous, fibrous or cartilaginous. Tarsal coalition is relatively common on autopsy, with an incidence of up to 1% of the population; although the majority of these are thought to be asymptomatic.1 Most cases of tarsal coalition occur between the calcaneonavicular and talocalcaneal joints.2 However, coalitions between almost any two adjacent tarsal bones have been reported.3 Altered joint biomechanics in the presence of union are thought to account for the symptoms.

The histopathology of tarsal coalition changes over time with gradual ossification of the fibrous bar.2 Progressive ossification limits hindfoot motion, interfering with joint mechanics, and leading to secondary inflammation that predisposes to joint degeneration. The increasing synostosis commonly leads to symptom onset in early to mid-adolescence.

Tarsal coalition can present with varying complaints. These include ankle pain, rigid pes planus, limp, peroneal tendon contracture, tarsal tunnel syndrome and …

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