Capitate bone - WikiHQ

thumb|Capitate of the right hand on X-ray (labeled C)

The capitate bone, also known as os magnum, is a bone in the human wrist found in the center of the carpal bone region, located at the distal end of the radius and ulna bones. It articulates with the third metacarpal bone (the middle finger) and forms the third carpometacarpal joint. The capitate bone is the largest of the carpal bones in the human hand. It presents, above, a rounded portion or head, which is received into the concavity formed by the scaphoid and lunate bones; a constricted portion or neck; and below this, the body.

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 hand. The capitate is found within the distal row of carpal bones. The capitate lies directly adjacent to the metacarpal of the ring finger on its distal surface, has the hamate on its ulnar surface and trapezoid on its radial surface, and abuts the lunate and scaphoid proximally.

Surfaces

The proximal surface is round, smooth, and articulates with the lunate bone.

Function

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

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.

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 ' 'having a head', from - '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.

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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.