The talus, also known as the ankle bone, is the second largest and the most proximally situated bone of the tarsal bones of the foot. This irregularly shaped bone forms a link between the foot and the leg via the ankle joint, and it also plays a significant role in the stability of the ankle.
It articulates with tibia and fibula superiorly, and with the calcaneus and the navicular bone inferiorly. The posterior articular surface for the calcaneus is found on the inferior surface of the talus. This posterior articular surface is one of three articular facets for the articulation of the calcaneus found on the inferior aspect of the talus; the other two being the middle and anterior calcaneal surfaces.
Up to about 70% of the surface of the talus is covered in articular cartilage. This includes the posterior articular surface for the calcaneus, which is also covered by articular cartilage and is separated from the middle calcaneal surface by a deep groove known as the sulcus tali. When the talus articulates with the calcaneus, this deep groove forms the roof of the sinus tali which is a small cavity situated between the talus and the calcaneus, on the outside of the ankle.
The articulation of the talus with the calcaneus and the navicular bone forms the talocalcaneal joint and the talocalcaneonavicular joint respectively. These two joints are collectively known as the subtalar joint.
Displaced talar neck fractures are particularly significance, especially when they result in the interruption of blood supply to the talar body, as this can cause avascular necrosis and nonunion.
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