|Latin||Os talus, Astragalus|
|Anatomical terms of bone|
The talus ( /ˈteɪləs/ ; Latin for ankle  or ankle bone  ), talus bone, astragalus ( /əˈstræɡələs/ ), or ankle bone is one of the group of foot bones known as the tarsus. The tarsus forms the lower part of the ankle joint. It transmits the entire weight of the body from the lower legs to the foot. 
The talus has joints with the two bones of the lower leg, the tibia and thinner fibula. These leg bones have two prominences (the lateral and medial malleoli) that articulate with the talus. At the foot end, within the tarsus, the talus articulates with the calcaneus (heel bone) below, and with the curved navicular bone in front; together, these foot articulations form the ball-and-socket-shaped talocalcaneonavicular joint.
The talus is the second largest of the tarsal bones;  it is also one of the bones in the human body with the highest percentage of its surface area covered by articular cartilage. It is also unusual in that it has a retrograde blood supply, i.e. arterial blood enters the bone at the distal end.[ citation needed ]
In humans, no muscles attach to the talus, unlike most bones, and its position therefore depends on the position of the neighbouring bones. 
Though irregular in shape, the talus can be subdivided into three parts.
Facing anteriorly, the head carries the articulate surface of the navicular bone, and the neck, the roughened area between the body and the head, has small vascular channels. 
The body features several prominent articulate surfaces: On its superior side is the trochlea tali, which is semi-cylindrical,  and it is flanked by the articulate facets for the two malleoli.  The ankle mortise, the fork-like structure of the malleoli, holds these three articulate surfaces in a steady grip, which guarantees the stability of the ankle joint. However, because the trochlea is wider in front than at the back (approximately 5–6 mm) the stability in the joint vary with the position of the foot: with the foot dorsiflexed (toes pulled upward) the ligaments of the joint are kept stretched, which guarantees the stability of the joint; but with the foot plantarflexed (as when standing on the toes) the narrower width of the trochlea causes the stability to decrease.  Behind the trochlea is a posterior process with a medial and a lateral tubercle separated by a groove for the tendon of the flexor hallucis longus. Exceptionally, the lateral of these tubercles forms an independent bone called os trigonum or accessory talus; it may represent the tarsale proximale intermedium. On the bone's inferior side, three articular surfaces serve for the articulation with the calcaneus, and several variously developed articular surfaces exist for the articulation with ligaments. 
For descriptive purposes the talus bone is divided into three sections, neck, body, and head.
The talus bone of the ankle joint connects the leg to the foot.
The head of talus looks forward and medialward; its anterior articular or navicular surface is large, oval, and convex. Its inferior surface has two facets, which are best seen in the fresh condition. 
The medial, situated in front of the middle calcaneal facet, is convex, triangular, or semi-oval in shape, and rests on the plantar calcaneonavicular ligament; the lateral, named the anterior calcaneal articular surface, is somewhat flattened, and articulates with the facet on the upper surface of the anterior part of the calcaneus. 
The neck of talus is directed anteromedially, and comprises the constricted portion of the bone between the body and the oval head. 
Its upper and medial surfaces are rough, for the attachment of ligaments; its lateral surface is concave and is continuous below with the deep groove for the interosseous talocalcaneal ligament. 
The body of the talus comprises most of the volume of the talus bone (ankle bone). It presents with five surfaces; a superior, inferior, medial, lateral and a posterior: 
During the 7-8th intrauterine month an ossification center is formed in the anklebone. 
The talus bone lacks a good blood supply. Because of this, healing a broken talus can take longer than most other bones. One with a broken talus may not be able to walk for many months without crutches and will further wear a walking cast or boot of some kind after that.
Talus injuries may be difficult to recognize,   and lateral process fractures in particular may be radiographically occult. If not recognized and managed appropriately, a talus fracture may result in complications and long-term morbidity. A 2015 review came to the conclusion that isolated talar body fractures may be more common than previously thought. 
A fractured talar body often has a displacement that is best visualised using CT imaging. In case a talus fracture is accompanied by a dislocation, restoration of articular and axial alignment is necessary to optimize ankle and hindfoot function. 
Dice were originally made from the talus of hoofed animals, leading to the nickname "bones" for dice. Colloquially known as "knucklebones", these are approximately tetrahedral. Modern Mongolians still use such bones as shagai for games and fortune-telling, with each piece relating to a symbolic meaning. 
The talus apparently derives from the fusion of three separate bones in the feet of primitive amphibians; the tibiale, articulating with tibia, the intermedium, between the bases of the tibia and fibula, and the fourth centrale, lying in the mid-part of the tarsus. These bones are still partially separate in modern amphibians, which therefore do not have a true talus. 
The talus forms a considerably more flexible joint in mammals than it does in reptiles. This reaches its greatest extent in artiodactyls, where the distal surface of the bone has a smooth keel to allow greater freedom of movement of the foot, and thus increase running speed. 
In non-mammal amniotes, the talus is generally referred to as the astragalus.
In modern crocodiles the astragalus bears a peg which inserts into a corresponding socket on the calcaneum, and the hinge of the ankle joint runs between the two tarsals; this condition is referred to as "croc-normal"; this "croc-normal" condition was likely ancestral for archosaurs. In dinosaurs (including modern birds) and pterosaurs, the hinge of the ankle instead is distal to the two tarsals.   Far rarer are archosaurs with a "croc-reversed" ankle joint, in which the calcaneus bears a peg whilst the astragalus bears a socket. 
In the theropod dinosaur lineage leading to birds, the astragalus gradually increases in size until it forms the entire proximal facet of the ankle articulation; additionally the anterior ascending process gradually extends increasingly proximally. In modern birds the astragalus is fused with the tibia to form the tibiotarsus. 
In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck. It is named for Atlas of Greek mythology because, just as Atlas supported the globe, it supports the entire head.
The ulna is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. It runs parallel to the radius, the other long bone in the forearm. The ulna is usually slightly longer than the radius, but the radius is thicker. Therefore, the radius is considered to be the larger of the two.
The humerus is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a rounded head, a narrow neck, and two short processes. The body is cylindrical in its upper portion, and more prismatic below. The lower extremity consists of 2 epicondyles, 2 processes, and 3 fossae. As well as its true anatomical neck, the constriction below the greater and lesser tubercles of the humerus is referred to as its surgical neck due to its tendency to fracture, thus often becoming the focus of surgeons.
In the human body, the cuboid bone is one of the seven tarsal bones of the foot.
The tibia, also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates, and it connects the knee with the ankle bones. The tibia is found on the medial side of the leg next to the fibula and closer to the median plane or centre-line. The tibia is connected to the fibula by the interosseous membrane of leg, forming a type of fibrous joint called a syndesmosis with very little movement. The tibia is named for the flute tibia. It is the second largest bone in the human body next to the femur. The leg bones are the strongest long bones as they support the rest of the body.
The fibula or calf bone is a leg bone on the lateral side of the tibia, to which it is connected above and below. It is the smaller of the two bones and, in proportion to its length, the most slender of all the long bones. Its upper extremity is small, placed toward the back of the head of the tibia, below the knee joint and excluded from the formation of this joint. Its lower extremity inclines a little forward, so as to be on a plane anterior to that of the upper end; it projects below the tibia and forms the lateral part of the ankle joint.
The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side : the first, second, third, fourth, and fifth metatarsal. The metatarsals are analogous to the metacarpal bones of the hand. The lengths of the metatarsal bones in humans are, in descending order, second, third, fourth, fifth, and first.
The ankle, or the talocrural region, or the jumping bone (informal) is the area where the foot and the leg meet. The ankle includes three joints: the ankle joint proper or talocrural joint, the subtalar joint, and the inferior tibiofibular joint. The movements produced at this joint are dorsiflexion and plantarflexion of the foot. In common usage, the term ankle refers exclusively to the ankle region. In medical terminology, "ankle" can refer broadly to the region or specifically to the talocrural joint.
In humans and many other primates, the calcaneus or heel bone is a bone of the tarsus of the foot which constitutes the heel. In some other animals, it is the point of the hock.
The radius or radial bone is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is usually slightly longer than the radius, but the radius is thicker. Therefore the radius is considered to be the larger of the two. It is a long bone, prism-shaped and slightly curved longitudinally.
In the human body, the tarsus is a cluster of seven articulating bones in each foot situated between the lower end of the tibia and the fibula of the lower leg and the metatarsus. It is made up of the midfoot and hindfoot.
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 lower extremity of femur is the lower end of the femur in human and other animals, closer to the knee. It is larger than the upper extremity of femur, is somewhat cuboid in form, but its transverse diameter is greater than its antero-posterior; it consists of two oblong eminences known as the lateral condyle and medial condyle.
The plantar calcaneonavicular ligament is a complex of three ligaments on the underside of the foot that connect the calcaneus with the navicular bone.
In human anatomy of the arm, the capitulum of the humerus is a smooth, rounded eminence on the lateral portion of the distal articular surface of the humerus. It articulates with the cupshaped depression on the head of the radius, and is limited to the front and lower part of the bone.
A malleolus is the bony prominence on each side of the human ankle.
The fourth metatarsal bone is a long bone in the foot. It is smaller in size than the third metatarsal bone and is the third longest of the five metatarsal bones. The fourth metatarsal is analogous to the fourth metacarpal bone in the hand
The second metatarsal bone is a long bone in the foot. It is the longest of the metatarsal bones, being prolonged backward and held firmly into the recess formed by the three cuneiform bones. The second metatarsal forms joints with the second proximal phalanx through the metatarsophalangeal joint, the cuneiform bones, third metatarsal and occasionally the first metatarsal bone.
The first metatarsal bone is the bone in the foot just behind the big toe. The first metatarsal bone is the shortest of the metatarsal bones and by far the thickest and strongest of them.
A calcaneal fracture is a break of the calcaneus. Symptoms may include pain, bruising, trouble walking, and deformity of the heel. It may be associated with breaks of the hip or back.
This article incorporates text in the public domain from page 266 of the 20th edition of Gray's Anatomy (1918)
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