The trapezoid bone (lesser multangular bone) is a carpal bone in

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

s, including

humans Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

. 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 The fus ...

, 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 carpal bone 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#Characteristics, koala (which has two thumb#O ...

. 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 '' inferior surface'' articulates with the proximal end of the second metacarpal bone; 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; rough behind, for the attachment of an interosseous

ligament A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have liga ...

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