carpal
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The bones of the carpus (wrist) and other
bones with which they articulate
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Any of the small bones (ossa carpi) in the wrist
(carpus) or, in the case of four-legged animals (tetrapods) in the proximal
part of the foot of the forelimb. The human hand contains eight carpals.
Each articulates on the proximal side with the radius
and ulna of the lower arm, and on the distal
side with a metacarpal.
Osteology of the carpals (Gray's Anatomy, 1918)
The eight carpal bones are arranged in two rows. Those of the proximal row,
from the radial to the ulnar side, are named the navicular (scaphoid), lunate,
triangular (triquetrum), and pisiform; those of the distal row, in the same
order, are named the greater multangular (trapezium), lesser multangular
(trapezoid), capitate, and hamate.
Common characteristics
of the carpal bones
Each bone (excepting the pisiform) presents six surfaces. Of these the volar
or anterior and the dorsal or posterior
surfaces are rough, for ligamentous attachment; the dorsal surfaces being
the broader, except in the navicular and lunate. The superior or proximal,
and inferior or distal surfaces are articular, the superior generally convex,
the inferior concave; the medial and lateral surfaces are also articular
where they are in contact with contiguous bones, otherwise they are rough
and tuberculated. The structure in all is similar, viz., cancellous tissue
enclosed in a layer of compact bone.
Bones of the proximal
(upper) row
The navicular bone (os naviculare manus; scaphoid bone)
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Left navicular bone
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The navicular bone is the largest bone of the proximal row, and has received
its name from its fancied resemblance to a boat. It is situated at the radial
side of the carpus, its long axis being from above downward, lateralward,
and forward. The superior surface is convex, smooth, of triangular shape,
and articulates with the lower end of the radius. The inferior surface,
directed downward, lateralward, and backward, is also smooth, convex, and
triangular, and is divided by a slight ridge into two parts, the lateral
articulating with the greater multangular, the medial with the lesser multangular.
On the dorsal surface is a narrow, rough groove, which runs the entire length
of the bone, and serves for the attachment of ligaments. The volar surface
is concave above, and elevated at its lower and lateral part into a rounded
projection, the tubercle, which is directed forward and gives attachment
to the transverse carpal ligament and sometimes origin to a few fibers of
the Abductor pollicis brevis. The lateral surface is rough and narrow, and
gives attachment to the radial collateral ligament of the wrist. The medial
surface presents two articular facets; of these, the superior or smaller
is flattened of semilunar form, and articulates with the lunate bone; the
inferior or larger is concave, forming with the lunate a concavity for the
head of the capitate bone.
The navicular articulates with five bones: the radius proximally, greater
and lesser multangulars distally, and capitate and lunate medially.
The lunate bone (os lunatum; semilunar bone)
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Left lunate bone
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The lunate bone may be distinguished by its deep concavity and crescentic
outline. It is situated in the center of the proximal row of the carpus,
between the navicular and triangular. The superior surface, convex and smooth,
articulates with the radius. The inferior surface is deeply concave, and
of greater extent from before backward than transversely: it articulates
with the head of the capitate, and, by a long, narrow facet (separated by
a ridge from the general surface), with the hamate. The dorsal and volar
surfaces are rough, for the attachment of ligaments, the former being the
broader, and of a somewhat rounded form. The lateral surface presents a
narrow, flattened, semilunar facet for articulation with the navicular.
The medial surface is marked by a smooth, quadrilateral facet, for articulation
with the triangular.
The lunate articulates with five bones: the radius proximally, capitate
and hamate distally, navicular laterally, and triangular medially.
The triangular bone (os triquetum; cuneiform bone)
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Left triangular bone
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The triangular bone may be distinguished by its pyramidal shape, and by
an oval isolated facet for articulation with the pisiform bone. It is situated
at the upper and ulnar side of the carpus. The superior surface presents
a medial, rough, non-articular portion, and a lateral convex articular portion
which articulates with the triangular articular disk of the wrist. The inferior
surface, directed lateralward, is concave, sinuously curved, and smooth
for articulation with the hamate. The dorsal surface is rough for the attachment
of ligaments. The volar surface presents, on its medial part, an oval facet,
for articulation with the pisiform; its lateral part is rough for ligamentous
attachment. The lateral surface, the base of the pyramid, is marked by a
flat, quadrilateral facet, for articulation with the lunate. The medial
surface, the summit of the pyramid, is pointed and roughened, for the attachment
of the ulnar collateral ligament of the wrist.
The triangular articulates with three bones: the lunate laterally, the pisiform
in front, the hamate distally; and with the triangular articular disk which
separates it from the lower end of the ulna.
The pisiform
bone (os pisiforme)
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Left pisiform bone
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The pisiform bone may be known by its small size, and by its presenting
a single articular facet. It is situated on a plane anterior to the other
carpal bones and is spheroidal in form. Its dorsal surface presents a smooth,
oval facet, for articulation with the triangular: this facet approaches
the superior, but not the inferior border of the bone. The volar surface
is rounded and rough, and gives attachment to the transverse carpal ligament,
and to the flexor carpi ulnaris and abductor
digiti quinti. The lateral and medial surfaces are also rough, the former
being concave, the latter usually convex.
The pisiform articulates with one bone, the triangular.
Bones
of the distal (lower) row
The greater multangular
bone (os multangulum majus; trapezium)
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Left greater multangular bone
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The greater multangular bone may be distinguished by a deep groove on its
volar surface. It is situated at the radial side of the carpus, between
the navicular and the first metacarpal bone. The superior surface is directed
upward and medialward; medially it is smooth, and articulates with the navicular;
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 dorsal surface is rough. The volar 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 lesser multangular; the lower, small and oval, with the base of
the second metacarpal.
The greater multangular articulates with four bones: the navicular proximally,
the first metacarpal distally, and the lesser multangular and second metacarpal
medially.
The lesser multangular bone (os multangulum
minus; trapezoid bone)
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Left lesser multangular bone
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The lesser multangular 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 volar surface; and by its having four articular
facets touching each other, and separated by sharp edges. The superior surface,
quadrilateral, smooth, and slightly concave, articulates with the navicular.
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 dorsal and volar 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 greater
multangular. The medial surface is concave and smooth in front, for articulation
with the capitate; rough behind, for the attachment of an interosseous ligament.
The lesser multangular articulates with four bones: the navicular proximally,
second metacarpal distally, greater multangular laterally, and capitate
medially.
The capitate bone (os capitatum; os magnum)
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Left capitate bone
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The capitate bone is the largest of the carpal bones, and occupies the center
of the wrist. It presents, above, a rounded portion or head, which is received
into the concavity formed by the navicular and lunate; a constricted portion
or neck; and below this, the body. The superior surface is round, smooth,
and articulates with the lunate. The inferior surface is divided by two
ridges into three facets, for articulation with the second, third, and fourth
metacarpal bones, that for the third being the largest. The dorsal surface
is broad and rough. The volar surface is narrow, rounded, and rough, for
the attachment of ligaments and a part of the Adductor pollicis obliquus.
The lateral surface articulates with the lesser multangular by a small facet
at its anterior inferior angle, behind which is a rough depression for the
attachment of an interosseous ligament. Above this is a deep, rough groove,
forming part of the neck, and serving for the attachment of ligaments; it
is bounded superiorly by a smooth, convex surface, for articulation with
the navicular. The medial surface articulates with the hamate by a smooth,
concave, oblong facet, which occupies its posterior and superior parts;
it is rough in front, for the attachment of an interosseous ligament.
The capitate articulates with seven bones: the navicular and lunate proximally,
the second, third, and fourth metacarpals distally, the lesser multangular
on the radial side, and the hamate on the ulnar side.
The
hamate bone (os hamatum; unciform bone)
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Left hamate bone
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The hamate bone may be readily distinguished by its wedge-shaped form, and
the hook-like process which projects from its volar surface. It is situated
at the medial and lower angle of the carpus, with its base downward, resting
on the fourth and fifth metacarpal bones, and its apex directed upward and
lateralward. The superior surface, the apex of the wedge, is narrow, convex,
smooth, and articulates with the lunate. The inferior surface articulates
with the fourth and fifth metacarpal bones, by concave facets which are
separated by a ridge. The dorsal surface is triangular and rough for ligamentous
attachment. The volar surface presents, at its lower and ulnar side, a curved,
hook-like process, the hamulus, directed forward and lateralward. This process
gives attachment, by its apex, to the transverse carpal ligament and the
Flexor carpi ulnaris; by its medial surface to the Flexor brevis and Opponens
digiti quinti; its lateral side is grooved for the passage of the Flexor
tendons into the palm of the hand. It is one of the four eminences on the
front of the carpus to which the transverse carpal ligament of the wrist
is attached; the others being the pisiform medially, the oblique ridge of
the greater multangular and the tubercle of the navicular laterally. The
medial surface articulates with the triangular bone by an oblong facet,
cut obliquely from above, downward and medialward. The lateral surface articulates
with the capitate by its upper and posterior part, the remaining portion
being rough, for the attachment of ligaments.
The hamate articulates with five bones: the lunate proximally, the fourth
and fifth metacarpals distally, the triangular medially, the capitate laterally.
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