| Bone: Talus bone | |
|---|---|
 |
|
| Subtalar Joint | |
| Latin | Os trigonum, Astragalus |
| Gray's | subject #63 266 |
| MeSH | Talus |
- See talus for other meanings of the word
The talus bone or astragalus is a bone in the tarsus of the foot that forms the lower part of the ankle joint through its articulations with the lateral and medial malleoli of the two bones of the lower leg, the tibia and fibula. Within the tarsus, it articulates with the calcaneus below and navicular in front. Through these articulations, it transmits the entire weight of the body to the foot.[1]
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. Additionally, it is also unique in that it has a retrograde blood supply, i.e. arterial blood enters the bone at the distal end.[citation needed]
Contents |
Structure
 |
 |
|
|
Left talus, from above and below.
|
||
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.[1]
The body features several prominent articulate surfaces: On its superior side is the trochlea tali flanked by the articulate facets for the two malleoli.[1] 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.[2] 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". 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.[1]
During the 7-8th intrauterine month an ossification center is formed in the talus.[1]
Evolution
The talus is apparently derived 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.[3]
The shape of the talus bone in the 47-million year old fossil known as Ida indicates that this species is possibly linked directly to humans, according to paleo-primatologist Philip Gingerich.[4] However, a full cladistic analysis has not been conducted to test this theory. Therefore, even though probable, it has not actually been proven to fully satisfy critics[5]
Use as dice
Due to the way that the talus bone of a hoofed animal is shaped, it can land in one of four positions. This fact led to the bone assuming a role as a form of die in games of chance and gambling, such as Knucklebones. [6]
Additional images
 Lateral view of the human ankle, including the talus |
 Bones of the right foot. Dorsal surface. |
 Bones of the right foot. Plantar surface. |
 Left talus, medial surface. |
 Left talus, lateral surface. |
 Skeleton of foot. Medial aspect. |
 Skeleton of foot. Lateral aspect. |
 Capsule of left talocrura articulation (distended). Lateral aspect. |
 Coronal section through right talocrural and talocalcaneal joints. |
 Oblique section of left intertarsal and tarsometatarsal articulations, showing the synovial cavities. |
Notes
- ^ a b c d e Platzer (2004), p 216
- ^ Thieme Atlas of Anatomy (2006), p 406
- ^ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. p. 207. ISBN 0-03-910284-X.
- ^ "Common Ancestor Of Humans, Modern Primates? 'Extraordinary' Fossil Is 47 Million Years Old". Science Daily. May 9, 2009. http://www.sciencedaily.com/releases/2009/05/090519104643.htm. Retrieved June 2009.
- ^ Switek, Brian (May 19, 2009). "Poor, poor Ida, Or: "Overselling an Adapid"". Science Blogs. http://scienceblogs.com/laelaps/2009/05/poor_poor_ida_or_overselling_a.php. Retrieved June 2009.
- ^ Smith, William (1891). A Dictionary of Greek and Roman Antiquities. J. Murray. p. 799. http://books.google.com/books?id=3uYtAAAAIAAJ&pg=PA799.
References
- Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme. ISBN 3-13-533305-1.
- Thieme Atlas of Anatomy: General Anatomy and Musculoskeletal System. Thieme. 2006. ISBN 1-58890-419-9.
External links
- Illustration at orthoinfo.aaos.org
- Fractures of the Talus at mdmercy.com
- lljoints at The Anatomy Lesson by Wesley Norman (Georgetown University) (posterioranklejoint)
|
|||||||||||||||||||||||||||||||||||||||||||
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
