The
metacarpus is the intermediate part of the
hand skeleton that is located between the
phalanges (bones of the fingers)
distally and the
carpus which forms the connection to the
forearm. The metacarpus consists of metacarpal bones.
The metacarpals form a transverse arch to which the rigid row of distal carpal bones are fixed. The peripheral metacarpals (those of the thumb and little finger) form the sides of the cup of the palmar gutter and as they are brought together they deepen this concavity. The index metacarpal is the most firmly fixed, while the thumb metacarpal articulates with the trapezium and acts independently from the others. The middle metacarpals are tightly united to the carpus by intrinsic interlocking bone elements at their bases. The ring metacarpal forms a transitional element of the semi-independent last metacarpal.
[Tubiana et al 1998, p 11] Common characteristics of the metacarpal bones
Each consists of a body and two extremities.
Body
The
body (
corpus; shaft) is prismoid in form, and curved, so as to be convex in the longitudinal direction behind, concave in front.
It presents three surfaces: medial, lateral, and dorsal.
- The medial and lateral surfaces are concave, for the attachment of the interosseus muscles, and separated from one another by a prominent anterior ridge.
- The dorsal surface presents in its distal two-thirds a smooth, triangular, flattened area which is covered in by the tendons of the Extensor muscles. This surface is bounded by two lines, which commence in small tubercles situated on either side of the digital extremity, and, passing upward, converge and meet some distance above the center of the bone and form a ridge which runs along the rest of the dorsal surface to the carpal extremity. This ridge separates two sloping surfaces for the attachment of the Interossei dorsales.
To the tubercles on the digital extremities are attached the collateral ligaments of the
metacarpophalangeal joints.
Base
The
base or
carpal extremity (
basis) is of a cuboidal form, and broader behind than in front: it articulates with the carpus, and with the adjoining metacarpal bones; its dorsal and volar surfaces are rough, for the attachment of ligaments.
Head
The
head or
digital extremity (
capitulum) presents an oblong surface markedly convex from before backward, less so transversely, and flattened from side to side; it articulates with the proximal phalanx.
It is broader, and extends farther upward, on the volar than on the dorsal aspect, and is longer in the antero-posterior than in the transverse diameter.
On either side of the head is a tubercle for the attachment of the collateral ligament of the
metacarpophalangeal joint.
The dorsal surface, broad and flat, supports the tendons of the extensor muscles; the volar surface is grooved in the middle line for the passage of the Flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface.
Articulations
Besides their phalangeal articulations, the metacarpal bones
articulate as follows:
- the first with the trapezium;
- the second with the trapezium, trapezoid, capitate and third metacarpal;
- the third with the capitate and second and fourth metacarpals;
- the fourth with the capitate, hamate, and third and fifth metacarpals;
- and the fifth with the hamate and fourth metacarpal.
Congenital disorders
The fourth and fifth metacarpal bones are commonly "blunted," or shortened, in
pseudohypoparathyroidism and
pseudopseudohypoparathyroidism.
A blunted fourth metacarpal, with normal fifth metacarpal, can signify
Turner syndrome.
In other animals
In four-legged animals, the metacarpals form part of the forefeet, and are frequently reduced in number, appropriate to the number of toes. In
digitigrade and
unguligrade animals, the metacarpals are greatly extended and strengthened, forming an additional segment to the limb, a feature that typically enhances the animal's speed. In both
birds and
bats, the metacarpals form part of the wing.
See also
Additional images
