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

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

s, including

humans Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

. It is the smallest bone in the

distal row 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 prov ...

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, the narrow end the palmar surface; and by its having four articular facets touching each other, and separated by sharp edges. It is

homologous Homology may refer to: Sciences Biology *Homology (biology), any characteristic of biological organisms that is derived from a common ancestor *Sequence homology, biological homology between DNA, RNA, or protein sequences * Homologous chrom ...

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 (which has two opposable thumbs on each " ...

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

palmar Palmar may refer to: Anatomy, relating to the palm of the hand * Palmar aponeurosis, deep fascia connecting and within the muscles of the palm * Palmar arches (disambiguation), various combinations of arteries in the hand and arm * Palmar art ...

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.

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