Trapezium (bone)
Encyclopedia
The trapezium bone is a carpal
bone in the wrist
.
The trapezium is distinguished by a deep groove on its palmar surface. It is situated at the radial side of the carpus
, between the scaphoid and the first metacarpal bone (the metacarpal bone of the thumb). It is homologous
with the first distal carpal of reptiles and amphibians.
The etymology derives from the Greek trapezion which means "irregular quadrilateral;" literally, "a little table," from trapeza meaning table. Also, from tra- "four" and peza "foot" or "edge."
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
. This saddle-shaped articulation is partially responsible for the thumb'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; 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
; the lower, small and oval, with the base of the second metacarpal.
The tubercle of trapezium is a anatomic tubercle, where sometimes abductor pollicis brevis muscle
attaches.
Carpus
In tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do. The corresponding part of the foot is the tarsus...
bone in the wrist
Wrist
In human anatomy, the wrist is variously defined as 1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand;...
.
The trapezium is distinguished by a deep groove on its palmar surface. It is situated at the radial side of the carpus
Carpus
In tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do. The corresponding part of the foot is the tarsus...
, between the scaphoid and the first metacarpal bone (the metacarpal bone of the thumb). It is homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...
with the first distal carpal of reptiles and amphibians.
The etymology derives from the Greek trapezion which means "irregular quadrilateral;" literally, "a little table," from trapeza meaning table. Also, from tra- "four" and peza "foot" or "edge."
Surfaces
The superior surfaceAnatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
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
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
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
First metacarpal bone
The first metacarpal bone or the metacarpal bone of the thumb is the first bone of 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 metacarpophalangeal joint....
. This saddle-shaped articulation is partially responsible for the thumb'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
Abductor pollicis brevis muscle
The abductor pollicis brevis is a muscle in the hand that functions as an abductor of the thumb.-Structure:The abductor pollicis brevis is a flat, thin muscle located just under the skin. It is a thenar muscle, and therefore contributes to the bulk of the palm's thenar eminence...
and Flexor pollicis brevis; 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
Trapezoid
In Euclidean geometry, a convex quadrilateral with one pair of parallel sides is referred to as a trapezoid in American English and as a trapezium in English outside North America. A trapezoid with vertices ABCD is denoted...
; the lower, small and oval, with the base of the second metacarpal.
Tubercle of trapezium
The tubercle of trapezium is a anatomic tubercle, where sometimes abductor pollicis brevis muscle
Abductor pollicis brevis muscle
The abductor pollicis brevis is a muscle in the hand that functions as an abductor of the thumb.-Structure:The abductor pollicis brevis is a flat, thin muscle located just under the skin. It is a thenar muscle, and therefore contributes to the bulk of the palm's thenar eminence...
attaches.
See also
- Anatomical terms of locationAnatomical terms of locationStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
- Bone terminology
- FingerFingerA finger is a limb of the human body and a type of digit, an organ of manipulation and sensation found in the hands of humans and other primates....
- HandHandA hand is a prehensile, multi-fingered extremity located at the end of an arm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs...