Tarsal coalition is a congenital abnormality that leads to a coalition between tarsal bones. This coalition can be bony, cartilaginous, or fibrous, with the talocalcaneal and calcaneonavicular joints commonly involved. The onset of symptoms is typically in the second decade of life and include pain, stiffness, reduced range of motion, and flatfoot deformity. Computed Tomography (CT) imaging depicts coalitions exclusively, with bony coalitions being straightforward to identify, whereas non-osseous coalitions manifest as secondary bony changes. Magnetic Resonance Imaging (MRI) shows signal changes parallel to the parent bone in cases of osseous coalition. In contrast, non-osseous coalitions exhibit variable intermediate to low signal changes, with bone marrow oedema displaying a high signal on fluid-sensitive sequences. The coalition can be located intraarticularly or extraarticularly. We present a case of an 18-year-old female who presented with right ankle pain. A CT scan of the right ankle showed an articulation between the talus and calcaneus along the medial aspect of the joint with an interspersed accessory ossicle. The extraarticular non-osseous Talocalcaneal Coalition (TCC) was diagnosed, along with the os sustentaculum located along the medial facet. In this case, we demonstrate TCC with an interspersed os sustentaculum forming an extraarticular TCC, which was detected incidentally during the evaluation of a young patient presenting with ankle pain and a visible bony deformity.
Varshney et al. (2025) studied this question.