The capitate bone is a bone in the human

wrist In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; "The wrist contains eight bones, roughly aligned in two rows, known as the carp ...

found in the center of the carpal bone region, located at the distal end of the

radius In classical geometry, a radius (plural, : radii) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', ...

and

ulna The ulna (''pl''. ulnae or ulnas) 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. That is, the ulna is on the same side of t ...

bones. It articulates with the third

metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...

bone (the middle finger) and forms the third carpometacarpal joint. The capitate bone is the largest of the

carpal bones The carpal bones are the eight small bones that make up the wrist (or carpus) that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, t ...

in the human

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "h ...

. It presents, above, a rounded portion or head, which is received into the concavity formed by the scaphoid and

lunate bone The lunate bone (semilunar bone) is a carpal bone in the human hand. It is distinguished by its deep concavity and crescentic outline. It is situated in the center of the proximal row carpal bones, which lie between the ulna and radius and the h ...

s; a constricted portion or neck; and below this, the body.''

Gray's Anatomy ''Gray's Anatomy'' is a reference book of human anatomy written by Henry Gray, illustrated by Henry Vandyke Carter, and first published in London in 1858. It has gone through multiple revised editions and the current edition, the 42nd (Octo ...

'' (1918). See infobox. The bone is also found in many other mammals, and is homologous with the "third distal carpal" of reptiles and amphibians.

Structure

The capitate is the largest carpal bone found within the

. The capitate is found within the distal row of carpal bones. The capitate lies directly adjacent to the

of the ring finger on its distal surface, has the hamate on its ulnar surface and

trapezoid A quadrilateral with at least one pair of parallel sides is called a trapezoid () in American and Canadian English. In British and other forms of English, it is called a trapezium (). A trapezoid is necessarily a convex quadrilateral in Eu ...

on its radial surface, and abuts the

lunate Lunate is a crescent or moon-shaped microlith. In the specialized terminology of lithic reduction, a lunate flake is a small, crescent-shaped flake removed from a stone tool during the process of pressure flaking. In the Natufian period, a lu ...

and scaphoid proximally.

Surfaces

The ''proximal surface'' is round, smooth, and articulates with the

. The ''distal surface'' is divided by two ridges into three facets, for articulation with the second, third, and fourth metacarpal bones, that for the third being the largest. The ''dorsal surface'' is broad and rough. The ''palmar surface'' is narrow, rounded, and rough, for the attachment of ligaments and a part of the adductor pollicis muscle. The ''lateral surface'' articulates with the lesser multangular by a small facet at its anterior inferior angle, behind which is a rough depression for the attachment of an interosseous ligament. Above this is a deep, rough groove, forming part of the neck, and serving for the attachment of ligaments; it is bounded superiorly by a smooth, convex surface, for articulation with the scaphoid bone. The ''medial surface'' articulates with the hamate bone by a smooth, concave, oblong facet, which occupies its posterior and superior parts; it is rough in front, for the attachment of an interosseous ligament.

Variation

The capitate bone variably articulates with the metacarpal of the index finger. However, its normal articulation is with the middle finger.

Development

The ossification of capitate starts at 1 – 5 months.

Function

The carpal bones function as a unit to provide a bony superstructure for the

. They allow movements of the wrist from side to side (medial to lateral) as well as up and down (anterior to posterior). H. A. Harris wrote in the ''British Medical Journal'' in 1944 that "the strength of construction of the hand in a man is concentrated in the radius, thumb, and index and middle fingers." Therefore, the capitate is larger to support the strength and stress that the middle finger undergoes.

Clinical significance

A capitate fracture accounts for 1.3% of all wrist fractures. Isolated fractures of the capitate comprise only 0.3% and are often non-displaced. This is since the capitate is at the centre of the carpal region and is therefore quite well protected. Capitate fractures occur together with fractures of another carpal bone, the scaphoid. Various mechanisms for fractures of the capitate have been postulated. Adler et al. described three mechanisms—the first is direct trauma to the dorsal surface of the bone, the second is fall on the palm with the wrist in forced extension and the third is fall on the forcefully flexed hand; the second being the most frequent and the third rarest. In the case of an acute capitate fracture where there is x-ray evidence of excellent alignment of the fracture fragments, the attending doctor will immobilise the wrist in a plaster or lightweight wrist brace. Once the cast has been removed the patient begins physiotherapy to regain the range of movement of the wrist joint and strength in the muscles involved. If x-rays show that the capitate fracture fragments are out of alignment, surgery is indicated. A surgeon can use small compression screws or K-wires to unite the two pieces of bone. The headless compression screw has advantage over the K-wire as it provides compression across the fracture site and allows early motion. It may be the case that the ligament between the сapitate and the scaphoid bone is also injured; if so, this would be repaired at the same time. Because the capitate has a poor blood supply there are sometimes complications with the healing process. This may manifest itself as a diffuse ache in the wrist upon activity, and can persist for many months. This is due to a breakdown of the capitate caused by the lack of blood supply and healing (avascular necrosis). Nonunion has been reported as the most common complication; 19.6% to 56% in isolated capitate fractures. Early diagnosis is key to preventing this.

Etymology

The name of the bone derives from '' la, capitātus'' 'having a head', from '' la, capit-'' 'head'.

Additional images

File:Capitate bone (left hand) - animation01.gif, Position of capitate bone (shown in red). Left hand. Animation. File:Capitate bone (left hand) - animation02.gif, Capitate bone of the left hand. Close up. Animation. File:Capitatum_ant.jpg, Capitate bone of the left hand. Ulnar surface (little-finger-side surface) File:Capitatum_post.jpg, Capitate bone of the left hand. Radial surface (thumb-side surface) File:RightHumanPosteriorDistalRadiusUlnaCarpals - Capitate bone.png, Right hand posterior view (dorsal view). Thumb on bottom. File:RightHumanAnteriorDistalRadiusUlnaCarpals - Capitate bone.png, Right hand anterior view (palmar view). Thumb on top. File:Gray219 - Capitate bone.png, Capitate bone shown in yellow. Left hand. Palmar surface. File:Gray220 - Capitate bone.png, Capitate bone shown in yellow. Left hand. Dorsal surface. File:Gray422 - Capitate bone.png, Transverse section across the wrist (palm on top, thumb on left). Capitate bone shown in yellow. File:Ospoignet - Capitate bone.png, Cross section of wrist (thumb on left). Capitate shown in red.

References

Sources

* Saladin, Kenneth S. "The Skeletal System." Anatomy and Physiology. 7th ed. New York: McGraw-Hill, 2015. N. pag. Print. * Harris, H. A. "Fractures Of The Carpal Bones." The British Medical Journal 2.4367 (1944): 381. JSTOR. Web. 28 Nov. 2016. {{Authority control Skeletal system Wrist Bones of the hand Carpal bones