In human anatomy, the metacarpal bones, or "palm bones", collectively the metacarpus, are the appendicular bones that form the intermediate part of the hand between the phalanges (fingers) and the carpal bones (wrist bones), which articulate with the forearm. The metacarpal bones are homologous to the metatarsal bones in the foot.
Structure
thumb|300px|Left hand shown with thumb on left.
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 is somewhat more mobile while the fifth metacarpal is semi-independent.
Each metacarpal bone consists of a body or shaft, and two extremities; the head at the distal or digital end (near the fingers), and the base at the proximal or carpal end (close to the wrist).
Body
The body (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 (basis) or carpal extremity is of a cuboidal form, and broader behind than in front. It articulates with the carpal bones and with the adjoining metacarpal bones while its dorsal and volar surfaces are rough, for the attachment of ligaments.
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File:Gray219 - Metacarpus.png|Metacarpus (yellow). Insertions are shown in red. Left hand, anterior (palmar) view.
File:Gray220 - Metacarpus.png|Metacarpus (yellow). Insertions are shown in red. Left hand, posterior (dorsal) view.
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Clinical significance
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.
Blunted metacarpals (particularly the fourth metacarpal) are a symptom of nevoid basal-cell carcinoma syndrome.
Fracture
The neck of the fifth metacarpal is a common location for a boxer's fracture, but all parts of a metacarpal bone (including head, body and base) are susceptible to fracture. During their lifetime, 2.5% of individuals will experience at least one metacarpal fracture. Bennett's fracture (base of the thumb) is the most common. Several types of treatment exist ranging from non-operative techniques, with or without immobilization, to operative techniques using closed or open reduction and internal fixation (ORIF). Generally, most fractures showing little or no displacement can be treated successfully without surgery. Intraarticular fracture-dislocations of the metacarpal head or base may require surgical fixation, as fragment displacement affecting the joint surface is rarely tolerated well. The Latin form more truly resembles Meta– is Greek for beyond and carpal from Ancient Greek καρπός (, "wrist").
In anatomic Latin, adjectives like , , , , and