Dual calcaneonavicular and talocalcaneal fibrous coalition

Clinical History

A 24-year-old man presented with pain and intermittent swelling at his left ankle for several years. There was no history of acute trauma. The pain was accompanied by a limitation of his physical activities. A physical examination revealed local tenderness on the dorsal side of the mid-foot and bilateral pes planus.

Imaging Findings

The radiographic examination of the left foot showed enlargement of the anterior dorsal calcaneus (arrows), referred to as the “anteater sign” (Fig. 1, curved arrow). Note C sign (Fig. 1, arrows), which is a continuous cortical contour extending from the medial aspect of talus to sustentaculum tali [1]. Middle subtalar facet is not seen.
MRI was performed, and the results revealed the nonosseous fibrous coalition.
Coronal T1 and sagittal STIR-weighted MR images showed obvious irregularity and narrowing at articulation between the calcaneus and navicular on one side and calcaneus and talus on the other side (Fig. 2-3, arrows). Marked bone hypertrophy (Fig. 4, asterisk) and associated oedema in the underlying bone are seen on both MR images (Fig. 5-6, curved arrows).

Discussion

Tarsal coalition is a condition in which two or more bones in the midfoot or hindfoot are joined and it is thought to be present in 1-2% of the population [2]. Tarsal coalitions can be either congenital (failure of embryological segmentation) or acquired [3]. Rarely may they be a part of syndromes such as hereditary symphalangism, Apert or hand-foot-uterus syndrome.
Patients become symptomatic in the 2nd decade of life with hindfoot or tarsal pain. But presentations in adulthood have been reported as is the case with our patient.
Tarsal coalition represents the bridging between the two bones of the tarsus consisting of either fibrous tissue (syndesmosis) or cartilage (synchondrosis) or osseous tissue (true synostosis) [4]. The more the coalition is due to bony bridging, the more likely and early it will cause symptoms. The vast majority (90%) of tarsal coalitions are either calcaneonavicular (± 45%) or talocalcaneal (± 45%) [4]. Calcaneocuboid, talonavicular and cubonavicular are much less common (< 10 %). Bilateral tarsal coalition is seen in almost 50% of the cases. Dual and multiple coalitions are a rare occurrence.
Conventional radiography is the first step and often sufficient to diagnose most of calcaneonavicular and talonavicular coalitions. A number of secondary radiographic signs have been described, including a talar beak, the “anteater sign” and the "C sign" [2]. The C sign may be observed in both osseous and nonosseous coalitions [4].
The diagnosis of talocalcaneal coalitions, however, generally requires cross-sectional imaging (CT or MR) for confirmation and characterization. CT offers a more precise evaluation of the extent of coalition than radiography and readily depicts associated degenerative changes. Osseous coalitions manifest with solid bone bridging on CT scans and bone marrow contiguity on MR images. In nonosseous coalitions, the joint space is reduced. MR is the best imaging tool for identification of non-osseous cartilaginous and fibrous unions. In cartilaginous coalition, signal intensity similar to that of fluid or cartilage may be present in the joint space. In fibrous coalitions, low signal intensity is present in the affected joint space on all sequences. On fluid sensitive sequences, subchondral marrow oedema may be present in the bone secondary to stress reaction [4].
Treatment options include orthotics, casting, surgical resection of the coalition or arthrodesis.
Coalitions of all types may be initially detected at CT or MR imaging examinations performed for an unrelated indication. For this reason, familiarity with the appearances of coalition on cross-sectional images is essential [4].

Differential Diagnosis List

Final Diagnosis

Dual calcaneonavicular and talocalcaneal fibrous coalition.

URL:	https://www.eurorad.org/case/13282
DOI:	10.1594/EURORAD/CASE.13282
ISSN:	1563-4086