Left hand anterior view (palmar view). Trapezoid bone shown in red.
The left trapezoid bone.
articulates with four bones:|
second metacarpal distally
trapezium bone laterally
|Latin||os trapezoideum, os multangulum minus|
The trapezoid bone (lesser multangular bone) is a carpal bone in tetrapods, including humans. It is the smallest bone in the distal row. 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 with the "second distal carpal" of reptiles and amphibians.
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 carpal bones function as a unit to provide a bony superstructure for the hand. :708
Isolated fractures of the trapezoid are rare, representing a 0.4% of the total, thus being the least common of all carpal fractures. This is because it’s 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. Thus subluxations, such as ones caused by delivering blow are not uncommon. Direct trauma to the bone can also cause fracture.
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."
- Position of trapezoid bone (shown in red). Left hand. Animation.
- Trapezoid bone of the left hand. Close up. Animation.
- Trapezoid bone.
- Right hand posterior view (dorsal view). Thumb on bottom.
- Trapezoid shown in yellow. Left hand. Dorsal surface.
- Trapezoid shown in yellow. Left hand. Palmar surface.
- Transverse section across the wrist (palm on top, thumb on left). Trapezoid bone shown in yellow (labelled as "Lesser Multang").
- Cross section of wrist (thumb on left). Trapezoid shown in red (labelled as "Lesser Multang").
|Wikimedia Commons has media related to Trapezoid bone.|
- Drake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell; illustrations by Richard; Richardson, Paul (2005). Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. ISBN 978-0-8089-2306-0.
- Sadowski, RM; Montilla, RD (2008). "Rare isolated trapezoid fracture: a case report". Hand (N Y). 3: 372–4. doi:10.1007/s11552-008-9100-8. PMC 2584218. PMID 18780025.