what is the subtalar joint

In human anatomy, the subtalar joint, also known as the talocalcaneal joint, is a joint of the foot. It occurs at the meeting point of the talus and the calcaneus.

The talus is oriented slightly obliquely on the anterior surface of the calcaneus.

There are two points of articulation between the two bones: one anteriorly and one posteriorly:

At the anterior talocalcaneal articulation, a convex area of the talus fits on a concave surface of the calcaneus.
The posterior talocalcaneal articulation is formed by a concave surface of the talus and a convex surface of the calcaneus.

There are three articulating facets between the talus and the calcaneus, delineated as the anterior, middle and posterior facets. The sustentaculum tali forms the floor of middle facet, and the anterior facet articulates with the head of the talus, and sits lateral and congruent to the middle facet. The posterior facet is the largest of the three, and separated from the others by the tarsal canal.