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 joint is classed structurally as a synovial joint, and functionally as a plane joint. Structure The talus is oriented slightly obliquely on the anterior surface of the calcaneus. There are three points of articulation between the two bones: two anteriorly and one posteriorly. The three articulations are known as facets, and they are the posterior, middle and anterior facets. At the anterior and middle talocalcaneal articulation, convex areas of the talus fits on to concave surfaces of the calcaneus. The posterior talocalcaneal articulation is formed by a concave surface of the talus and a convex surface of the calcaneus. 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. In some people the middle and anterior facets are joined giving just one articulation. The posterior facet is the largest of the three, and separated from the others by the tarsal canal. Ligaments and membranes The main ligament of the joint is the interosseous talocalcaneal ligament, a thick, strong band of two partially joined fibers that bind the talus and calcaneus. It runs through the sinus tarsi, a canal between the articulations of the two bones. There are four additional ligaments that form weaker connections between the talus and calcaneus. The anterior talocalcaneal ligament (or anterior interosseous ligament) attaches at the neck of the talus on the front and lateral surfaces to the superior calcaneus. The short band of the posterior talocalcaneal ligament extends from the lateral tubercle of the talus to the upper medial calcaneus. The short, strong lateral talocalcaneal ligament connects from the lateral talus under the fibular facet to the lateral calcaneus, and runs parallel to the calcaneofibular ligament. The medial talocalcaneal ligament extends from the medial tubercle of the talus to the sustentaculum tali on the medial surface of the calcaneus. A synovial membrane lines the capsule of the joint, and the joint is wrapped in a capsule of short fibers that are continuous with the talocalcaneonavicular and calcaneocuboid joints of the foot. Function The joint allows inversion and eversion of the foot, but plays minimal role in dorsiflexion or plantarflexion of the foot. The centre of