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 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. 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. ==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. == Other animals ==

illustrated by the adaptive radiation of the metacarpal bones of mammals. All conform to the basic pentadactyl pattern but are modified for different usages. The third metacarpal is shaded throughout; the shoulder is crossed-hatched. 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. ==History==

Etymology The Greek physician Galen used to refer to the as μετακάρπιον. The Latin form more truly resembles Meta– is Greek for beyond and carpal from Ancient Greek καρπός (, "wrist"). In anatomic Latin, adjectives like , , , , and can be found. The form is more true to the later Greek form μετακάρπιος. , as in in the current official Latin nomenclature, Terminologia Anatomica is a compound consisting of Latin and Greek parts. The usage of such hybrids in anatomic Latin is disapproved by some. == Additional images ==

File:Metacarpal bones (left hand) - animation01.gif|Metacarpus of the left hand (shown in red). Animation. File:Medical X-Ray imaging VNH07 nevit.jpg|X-ray image of right hand with thumb on left. File:Metacarpal fractures.jpg|Multiple fractures of the metacarpals (aka broken hand). (Right hand shown with thumb on left.) File:Medical X-Ray imaging OCU06 nevit.jpg|X-ray image of human infant left hand. File:Hand of embryo.jpg|Micro-radiography of 8 weeks human embryo hand File:Slide1dsds.JPG|Right hand. Deep dissection. Anterior (palmar) view. File:Slide1tyty.JPG|Right hand. Deep dissection. Posterior (dorsal) view. File: Carpus.png|Bones of the hand, being the metacarpus labeled with number 3. == See also ==