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The talus (; Latin for ankle or ankle bone), talus bone, astragalus (), 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 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 joi ...
. It transmits the entire weight of the body from the lower legs to the foot.Platzer (2004), p 216 The talus has joints with the two bones of the
lower leg The human leg, in the general word sense, is the entire lower limb of the human body, including the foot, thigh or sometimes even the hip or gluteal region. However, the definition in human anatomy refers only to the section of the lower limb e ...
, the
tibia 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 (the other being the fibula, behind and to the outside of the tibia); it connects ...
and thinner
fibula 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 i ...
. These leg bones have two prominences (the
lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...
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 The navicular bone is a small bone found in the feet of most mammals. Human anatomy The navicular bone in humans is one of the tarsal bones, found in the foot. Its name derives from the human bone's resemblance to a small boat, caused by th ...
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 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 ( cuboid, medial, intermediate, and ...
; 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. In humans, no muscles attach to the talus, unlike most bones, and its position therefore depends on the position of the neighbouring bones.


In humans

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,Lee F. Rogers (1992
Radiology of skeletal trauma - Volume 2
p.1463
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 The flexor hallucis longus muscle (FHL) is one of the three deep muscles of the posterior compartment of the leg that attaches to the plantar surface of the distal phalanx of the great toe. The other deep muscles are the flexor digitorum longus an ...
. Exceptionally, the lateral of these tubercles forms an independent bone called
os trigonum An accessory bone or supernumerary bone is a bone that is not normally present in the body, but can be found as a variant in a significant number of people. It poses a risk of being misdiagnosed as bone fractures on radiography. Wrist and hand ...
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.


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.Gray's Anatomy (1918) 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 plantar calcaneonavicular ligament (also known as the spring ligament or spring ligament complex) is a complex of three ligaments on the underside of the foot that connect the calcaneus with the navicular bone. Structure The plantar calcan ...
; the
lateral Lateral is a geometric term of location which may refer to: Healthcare *Lateral (anatomy), an anatomical direction * Lateral cricoarytenoid muscle * Lateral release (surgery), a surgical procedure on the side of a kneecap Phonetics *Lateral co ...
, 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.


Neck

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 interosseous talocalcaneal ligament forms the chief bond of union between the talus and calcaneus. It is a portion of the united capsules of the talocalcaneonavicular and the talocalcaneal joints, and consists of two partially united layers ...
.


Body

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: * The superior surface of the body presents, behind, a smooth trochlear surface, the trochlea, for articulation with the
tibia 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 (the other being the fibula, behind and to the outside of the tibia); it connects ...
. The trochlea is broader in front than behind, convex from before backward, slightly concave from side to side: in front it is continuous with the upper surface of the neck of the bone. * the inferior surface presents two articular areas, the posterior and middle calcaneal surfaces, separated from one another by a deep groove, the sulcus tali. The groove runs obliquely forward and lateralward, becoming gradually broader and deeper in front: in the articulated foot it lies above a similar groove upon the upper surface of the calcaneus, and forms, with it, a canal (sinus tarsi) filled up in the fresh state by the interosseous talocalcaneal ligament. The posterior calcaneal articular surface is large and of an oval or oblong form. It articulates with the corresponding facet on the upper surface of the calcaneus, and is deeply concave in the direction of its long axis which runs forward and lateralward at an angle of about 45° with the median plane of the body. The middle calcaneal articular surface is small, oval in form and slightly convex; it articulates with the upper surface of the sustentaculum tali of the calcaneus. * The medial surface presents at its upper part a pear-shaped articular facet for the medial malleolus, continuous above with the trochlea; below the articular surface is a rough depression for the attachment of the deep portion of the deltoid ligament of the ankle-joint. * The lateral surface carries a large triangular facet, concave from above downward, for articulation with the lateral malleolus; its anterior half is continuous above with the trochlea; and in front of it is a rough depression for the attachment of the anterior talofibular ligament. Between the posterior half of the lateral border of the trochlea and the posterior part of the base of the fibular articular surface is a triangular facet which comes into contact with the transverse inferior tibiofibular ligament during flexion of the ankle-joint; below the base of this facet is a groove which affords attachment to the posterior talofibular ligament. * The posterior surface is narrow, and traversed by a groove running obliquely downward and medialward, and transmitting the tendon of the Flexor hallucis longus. Lateral to the groove is a prominent tubercle, the posterior process, to which the posterior talofibular ligament is attached; this process is sometimes separated from the rest of the talus, and is then known as the os trigonum. Medial to the groove is a second smaller tubercle.


Development

During the 7-8th
intrauterine The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uter ...
month an ossification center is formed in the anklebone.


Fracture

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 Displacement may refer to: Physical sciences Mathematics and Physics * Displacement (geometry), is the difference between the final and initial position of a point trajectory (for instance, the center of mass of a moving object). The actual path ...
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.


As dice

Dice were originally made from the talus of hoofed animals, leading to the nickname "bones" for dice. Colloquially known as "
knucklebones Knucklebones, also known as scatter jacks, snobs, astragalus, tali, dibs, fivestones, jacks, or jackstones, among many other names, is a game of dexterity played with a number of small objects that are thrown up, caught, and manipulated in va ...
", these are approximately
tetrahedral In geometry, a tetrahedron (plural: tetrahedra or tetrahedrons), also known as a triangular pyramid, is a polyhedron composed of four triangular faces, six straight edges, and four vertex corners. The tetrahedron is the simplest of all the ...
. Modern
Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...
ns still use such bones as
shagai Shagai ( mn, шагай, ), chükö ( ky, чүкө, ), asyk/ashyk/oshuq ( kk, асық, ; tr, aşık; ug, ھوشۇق; tg, ошуқ, ), gachuha (Manchu : ) refers to the astragalus of the ankle of a sheep or goat. The bones are collected a ...
for games and
fortune-telling Fortune telling is the practice of predicting information about a person's life. Melton, J. Gordon. (2008). ''The Encyclopedia of Religious Phenomena''. Visible Ink Press. pp. 115-116. The scope of fortune telling is in principle identical wi ...
, with each piece relating to a symbolic meaning.


In other animals

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 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 i ...
, 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
artiodactyl The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing poster ...
s, 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 In humans and many other primates, the calcaneus (; from the Latin ''calcaneus'' or ''calcaneum'', meaning heel) 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. ...
, 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
dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s (including modern birds) and
pterosaur Pterosaurs (; from Greek ''pteron'' and ''sauros'', meaning "wing lizard") is an extinct clade of flying reptiles in the order, Pterosauria. They existed during most of the Mesozoic: from the Late Triassic to the end of the Cretaceous (228 ...
s, 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.


Additional images

File:Talus - inferior view.jpg, Talus - inferior view File:Ankle.PNG, Lateral view of the human ankle, including the talus File:Gray272.png, Left talus, medial surface File:Gray273.png, Left talus, lateral surface


See also

* Squatting facets *
Knucklebones Knucklebones, also known as scatter jacks, snobs, astragalus, tali, dibs, fivestones, jacks, or jackstones, among many other names, is a game of dexterity played with a number of small objects that are thrown up, caught, and manipulated in va ...
, a dice game using astragali *
Shagai Shagai ( mn, шагай, ), chükö ( ky, чүкө, ), asyk/ashyk/oshuq ( kk, асық, ; tr, aşık; ug, ھوشۇق; tg, ошуқ, ), gachuha (Manchu : ) refers to the astragalus of the ankle of a sheep or goat. The bones are collected a ...


Notes


References

* *


External links


Anatomy of the talus by Maurice Laude, Laboratory of Anatomy and Organogenesis, Amiens Medical School


* ()
Illustration at orthoinfo.aaos.org
{{Portal bar, Anatomy Skeletal system Bones of the lower limb Bones of the foot Tarsal bones