Posteromedial subtalar coalition: imaging appearances in three cases

Abstract 

Objective. To define the imaging appearances in three cases of posteromedial subtalar coalition.

Design. Three patients who presented with hindfoot pain were found to have non-osseous coalition involving the posteromedial hindfoot. This entity is distinct from conventional middle facet coalition as the sustentaculum is uninvolved.

Results. Plain radiographs, available in two cases, demonstrated subtle irregularity of the posterior facet. MRI (three cases) demonstrated a mixed bony and cartilaginous mass lying posterior to the sustentaculum. There was trabecular oedema within the mass and adjacent talus, and narrowing of the space between the middle and posterior facets. Prominence and dilatation of the posterior tibial veins with tenosynovitis of the adjacent tibialis posterior tendon was seen. CT demonstrated the bony mass but did not detect the adjacent bony oedema.

Conclusion. Posteromedial subtalar coalition may present with hindfoot pain and stiffness. The presence of a pseudarthrosis posterior to a normal middle facet is characteristic. The abnormality can be difficult to detect on plain radiographs.