The trapezium bone (greater multangular bone) is a carpal bone in 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 ...

. It forms the radial border of the

carpal tunnel In the human body, the carpal tunnel or carpal canal is a flattened body cavity on the flexor ( palmar/volar) side of the wrist, bounded by the carpal bones and flexor retinaculum. It forms the passageway that transmits the median nerve and the ...

Structure

The trapezium is distinguished by a deep groove on its anterior surface. It is situated at the radial side of the carpus, between the scaphoid and the first

metacarpal In human anatomy, the metacarpal bones or metacarpus, also known as the "palm bones", are the appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones ( wrist bones), which articulate ...

bone (the metacarpal bone of the thumb). It is homologous with the first distal carpal of reptiles and amphibians.

Surfaces

The trapezium is an irregular-shaped carpal bone found within the

. The trapezium is found within the distal row of carpal bones, and is directly adjacent to the

bone of the

thumb The thumb is the first digit of the hand, next to the index finger. When a person is standing in the medical anatomical position (where the palm is facing to the front), the thumb is the outermost digit. The Medical Latin English noun for thumb ...

. On its ulnar surface are found the

trapezoid In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are ...

and scaphoid bones. The '' superior surface'' is directed upward and medialward; medially it is smooth, and articulates with the scaphoid; laterally it is rough and continuous with the lateral surface. The '' inferior surface'' is oval, concave from side to side, convex from before backward, so as to form a saddle-shaped surface for articulation with the base of the

first metacarpal bone The first metacarpal bone or the metacarpal bone of the thumb is the first bone proximal to the thumb. It is connected to the trapezium of the carpus at the first carpometacarpal joint and to the proximal thumb phalanx at the first metacarp ...

. This saddle-shaped articulation is partially responsible for the

's opposable motion. The ''dorsal surface'' is smooth. The ''palmar surface'' is narrow and rough. At its upper part is a deep groove, running from above obliquely downward and medialward; it transmits the tendon of the Flexor carpi radialis, and is bounded laterally by an oblique ridge. This surface gives origin to the Opponens pollicis and to the Abductor and

Flexor pollicis brevis The flexor pollicis brevis is a muscle in the hand that flexes the thumb. It is one of three thenar muscles. It has both a superficial part and a deep part. Origin and insertion The muscle's superficial head arises from the distal edge of the ...

; it also affords attachment to the transverse carpal ligament. The ''lateral surface'' is broad and rough, for the attachment of ligaments. The ''medial surface'' presents two facets; the upper, large and concave, articulates with the trapezoid bone; the lower, small and oval, with the base of the second metacarpal.

Tubercle of trapezium

The tubercle of trapezium is a tubercle found on the anterior surface of the bone. It is where sometimes abductor pollicis brevis muscle attaches.

Function

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

. The trapezium is the most radial of the bones surrounding the

. It is important in thumb movement.

Clinical relevance

The trapezium is susceptible to arthritis at the joint with the

bone of the thumb, due to overuse.

History

The etymology derives from the Greek ''trapezion'' which means "a little table", from ''trapeza'' meaning "table", itself from ''(te)tra-'' "four" and ''pod-'' "foot". The name was first documented in 1840.

Additional images

File:Trapezium bone (left) - animation01.gif, Position of trapezium (shown in red). Left hand. Animation. File:Trapezium bone (left) - animation02.gif, Trapezium of the left hand. File:Trapezium bone.jpg, Trapezium bone. File:RightHumanPosteriorDistalRadiusUlnaCarpals - Trapezium bone.png, Right hand posterior view (dorsal view). Thumb on bottom. File:RightHumanAnteriorDistalRadiusUlnaCarpals - Trapezium bone.png, Right hand anterior view (palmar view). Thumb on top. File:Gray219 - Trapezium bone.png, Bones of the left hand. Palmar surface. Trapezium shown in yellow. File:Gray220 - Trapezium bone.png, Bones of the left hand. Dorsal surface. Trapezium shown in yellow. File:Ospoignet - Trapezium.png, Cross section of wrist (thumb on left). Trapezium shown in red (labelled as "''Greater Multang''"). File:Gray422 - Trapezium.png, Transverse section across the wrist and digits. Trapezium is shown in yellow (labelled as "''Greater Multang''"). File:Gray334.png, Ligaments of wrist. Anterior view File:Gray416.png, Tendons of forefinger and vincula tendina.

References

{{DEFAULTSORT:Trapezium (Bone) Skeletal system Wrist Bones of the hand Carpal bones