The sustentaculum tali is a horizontal shelf that arises from the anteromedial portion of the calcaneus. The superior surface is concave and articulates with the middle calcaneal surface of the talus. The inferior surface has a groove for the tendon of flexor hallucis longus.
Several ligamentous structures attach to the sustentaculum tali:
- plantar calcaneonavicular ligament (anterior surface)
- deltoid ligament (medial surface)
- medial talocalcaneal ligament
The sustentaculum tali is typically involved in cases of tarsal coalition, specifically talocalcaneal coalition and subtalar coalition. In cases of talocalcaneal coalition, the complete C-sign can be seen on a lateral radiograph where there is bridging between the talus superiorly and the posterior portion of the sustentaculum tali inferiorly.