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The radiological diagnosis of extra-articular posteromedial talocalcaneal coalition

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Extra-articular posteromedial talocalcaneal coalition (EA-PM TCC) accounts for approximately one-third of TCC, but its radiographic features are not well-described. The current study aims to compare the radiographic features of EA-PM TCC with normal ankles and with the commoner forms of TCC.

Materials and methods

A retrospective review of cases of TCC over 12 years for whom radiographs, CT, and/or MRI study were available. Radiographs were assessed by 2 radiologists for the presence of the C-sign, talar beak, dysmorphic sustentaculum, absent middle facet, and prominence of the posterior subtalar joint. TCC was classified by a third radiologist based on CT/MRI findings into 3 groups: no TCC, EA-PM TCC, and other TCCs. The radiographic findings for the 3 groups were compared.


The study included 50 patients, 28 males and 22 females with a mean age of 21.1 years (range 8–70 years). In 15 patients, both ankles had been imaged, resulting in a total of 65 cases. In 17 ankles, no TCC was identified, while 15 ankles were classified as EA-PM TCC and 33 as having other types of TCC. There were no statistically significant differentiating radiological features between the groups with no TCC and EA-PM TCC apart from prominence of the posterior subtalar joint, while only the C-sign allowed identification of patients with other types of TCC.


The study suggests that EA-PM TCC cannot be diagnosed based on the classical indirect radiological signs of TCC, but can be identified by prominence of the posterior subtalar joint.

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Correspondence to Michael Khoo.

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The study was approved by the Research and Innovation Centre of The Institute of Orthopaedics, with no requirement for informed patient consent.

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The authors declare that they have no conflict of interest.

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Phyo, N., Pressney, I., Khoo, M. et al. The radiological diagnosis of extra-articular posteromedial talocalcaneal coalition. Skeletal Radiol 49, 1413–1422 (2020).

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