The navicular bone is one of the seven bones which make up the tarsus of the Ankle and Foot. It is located on the medial aspect of the foot, next to the cuboid bone, anterior to the head of the talus and posterior to the cuneiform bones. It is one of the five bones of the midfoot.
The navicular is a small irregular bone with its shape being described as pyriform. Its posterior surface is concave and there are two faint ridges anteriorly to correspond with the articulation with the three cuneiform bones. There is a large protuberance on the inferomedial aspect of the navicular bone called the navicular tuberosity  which is often simple to palpate in the area directly anteroinferior to the medial malleolus.
The acetabulum pedis is the common name for the talocalcaneonavicular joint and forms the subtalar articular complex along with the posterior talocalcaneal joint. It has some of the morphological characteristics of a ball and socket joint which led to its name. The skeletal structures included are the posterior articular surface of the navicular bone, and the anterior and middle articular surface of the calcaneus that articulate with the head and the anteromedial surface of the talus. These bones are stabilized by the plantar calcaneonavicular ligament (spring ligament) on the medial aspect and the lateral calcaneonavicular ligament (a component of the bifurcate ligament) on the lateral aspect.
Muscle and Ligamentous AttachmentsThe only muscle attachment on the navicular is the tendon of the tibialis posterior. This a muscle located within the deep compartment of the posterior aspect of the tibia and the tendon extends inferiorly around the medial malleolus to insert on the navicular tuberosity. 
The superomedial calcaneonavicular ligament originates from the anteromedial margins of the sustentaculum tali on the talus bone. From there, it extends in an anterodorsolateral direction to the posterior aspect of the navicular and also attaches to the posterior tibial tendon 
The inferior calcaneonavicular ligament arises from the superior portion of the coronoid fossa, anterior to the sustentaculum tali. Its insertion is on the lateral, plantar aspect of the navicular, just lateral to the superomedial calcaneonavicular ligament insertion. The inferior calcaneonavicular ligament performs as one of the main static stabilizers of the longitudinal arch of the foot.
The bifurcate ligament is a Y-shaped structure originating at two separate origins: The lateral calcaneonavicular ligament and the medial calcaneocuboid ligament. The lateral calcaneonavicular ligament originates from the lateral side of the anterior talar articular surface, anteromedially from the sinus tarsi. these fibres form a durable band that facilitates the lateral foot stabilization.
There are several clinical conditions which involve the navicular directly. The navicular is often subject to developing stress fractures and can lead to Navicular stress syndrome. Müller Weiss syndrome is a spontaneous adult onset osteonecrosis of the navicular bone which may be picked up radiographically. In children, there is also a similar condition, although distinct from Müllers Weiss syndrome called Koehlers syndrome.
One common association is the abnormality called Accessory Navicular Bone,
The navicular is also used clinically within the Navicular Drop Test which may be used as a measure of foot pronation.
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