The trapezoid bone (lesser multangular bone) is a

carpal bone 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 ...

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

s, including

humans" \n\n\n\n\nThe robots exclusion standard, also known as the robots exclusion protocol or simply robots.txt, is a standard used by websites to indicate to visiting web crawlers and other web robots which portions of the site they are allowed to visi ...

. It is the smallest bone in the distal row of carpal bones that give structure to the palm of the hand. It may be known by its wedge-shaped form, the broad end of the wedge constituting the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

, the narrow end the palmar surface; and by its having four articular facets touching each other, and separated by sharp edges. It is homologous with the "second distal carpal" of reptiles and amphibians.

Structure

The trapezoid is a four-sided

found within the

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 ...

. The trapezoid is found within the distal row of carpal bones.

Surfaces

The '' superior surface'', quadrilateral, smooth, and slightly concave, articulates with the

scaphoid The scaphoid bone is one of the carpal bones of the wrist. It is situated between the hand and forearm on the thumb side of the wrist (also called the lateral or radial side). It forms the radial border of the carpal tunnel. The scaphoid bone i ...

. The '' inferior surface'' articulates with the

proximal Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position ...

end of the

second metacarpal bone The second metacarpal bone (metacarpal bone of the index finger) is the longest, and its base the largest, of all the metacarpal bones.''Gray's Anatomy'' (1918). See infobox. Human anatomy Its base is prolonged upward and medialward, forming a ...

; it is convex from side to side, concave from before backward and subdivided by an elevated ridge into two unequal facets. The ''

'' and '' palmar surfaces'' are rough for the attachment of ligaments, the former being the larger of the two. The '' lateral surface'', convex and smooth, articulates with the trapezium. The '' medial surface'' is concave and smooth in front, for articulation with the

capitate The capitate bone 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 carpomet ...

; rough behind, for the attachment of an interosseous

ligament A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal l ...

Function

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

Clinical Significance

Isolated fractures of the trapezoid are rare, representing 0.4% of the total, thus being the least common of all carpal fractures. This is due to the bone being in a fairly protected position. Distally, it forms a stable, relatively immobile joint with the second metacarpal, radially and proximally it forms strong ligaments with the trapezium and the capitate ulnarly, scaphoid respectively. However, injury can occur through axial force applied to the second metacarpal base. Subluxations, such as ones caused by delivering a blow, are not uncommon. Direct trauma to the bone can also cause fracture. Due to its rarity, standard treatment has not been established. A wide range of treatments are possible, including rest, surgery and casting.

History

The etymology derives from the Greek ''trapezion'' which means "irregular quadrilateral," from ''tra-'' "four" and ''peza'' "foot" or "edge." Literally, "a little table" from ''trapeza'' meaning "table" and ''-oeides'' "shaped."

Additional images

File:Trapezoid bone (left hand) - animation01.gif, Position of trapezoid bone (shown in red). Left hand. Animation. File:Trapezoid bone (left hand) - animation02.gif, Trapezoid bone of the left hand. Close up. Animation. File:Trapezoid bone.jpg, Trapezoid bone. File:RightHumanPosteriorDistalRadiusUlnaCarpals - Trapezoid bone.png, Right hand posterior view (dorsal view). Thumb on bottom. File:Gray220 - Trapezoid bone.png, Trapezoid shown in yellow. Left hand. Dorsal surface. File:Gray219 - Trapezoid bone.png, Trapezoid shown in yellow. Left hand. Palmar surface. File:Gray422 - Trapezoid bone.png, Transverse section across the wrist (palm on top, thumb on left). Trapezoid bone shown in yellow (labelled as "''Lesser Multang''"). File:Ospoignet - Trapezoid bone.png, Cross section of wrist (thumb on left). Trapezoid shown in red (labelled as "''Lesser Multang''").

References

{{DEFAULTSORT:Trapezoid Bone Skeletal system Wrist Bones of the hand Carpal bones