Sustentaculum tali
Located on the medial aspect of the calcaneus, is the sustentaculum tali - a bony shelf which provides structural support for the talus and an attachment point for the plantar calcaneonavicular, or spring ligament. It can be identified by rolling your thumb superiorly and inferiorly over the medial calcaneus approximately one fingerbreadth below the apex of the medial malleolus.