Bones of Hand

The wrist, or carpus, is composed of eight carpal bones, arranged in proximal and distal rows of four. These small bones give flexibility to the wrist. The carpus is markedly convex from side to side posteriorly, and concave anteriorly. Augmenting movement at the wrist joint, the two rows of carpal bones glide on each other; in addition, each bone glides on those adjacent to it.

From lateral to medial, the four carpal bones in the proximal row are the:

• Scaphoid (Greek skaphé, skiff, boat): a boat-shaped bone that articulates proximally with the radius, and has a prominent scaphoid tubercle; it is the largest bone in the proximal row of carpals.

• Lunate (Latin luna, moon): a moon-shaped bone between the scaphoid and the triquetral bones; it articulates proximally with the radius and is broader anteriorly than posteriorly.

• Triquetrum (Latin triquetrus, three-cornered): a pyramidal bone on the medial side of the carpus; it articulates proximally with the articular disc of the distal radio-ulnar joint.

• Pisiform (Latin pisum, pea), a small, pea-shaped bone that lies on the palmar surface of the triquetrum.

From lateral to medial, the four carpal bones in the distal row are the:

• Trapezium (Greek trapeze, table): a four-sided bone on the lateral side of the carpus; it articulates with the 1^st and 2^nd metacarpals, scaphoid, and trapezoid bones.

• Trapezoid: a wedge-shaped bone that resembles the trapezium; it articulates with the 2^nd metacarpal, trapezium, capitate, and scaphoid bones.

• Capitate (Latin caput, head): a head-shaped bone with a rounded extremity is the largest bone in the carpus; it articulates primarily with the 3^rd metacarpal distally, and with the trapezoid, scaphoid, lunate, and hamate.

• Hamate (Latin hamulus, a little hook): a wedge-shaped bone on the medial side of the hand; it articulates with the 4^th and 5^th metacarpal, capitate, and triquetral bones; it has a distinctive hooked process, the hook of the hamate, that extends anteriorly.

The proximal surfaces of the distal row of carpal bones articulate with the proximal row of carpal bones, and their distal surfaces articulate with the metacarpals.

The metacarpus forms the skeleton of the palm of the hand between the carpus and the phalanges. It is composed of five metacarpal bones (metacarpals). Each metacarpal consists of a base, shaft, and head. The proximal bases of the metacarpals articulate with the carpal bones, and the distal heads of the metacarpals articulate with the proximal phalanges, and form the knuckles of the hand. The 1^st metacarpal (of the thumb) is the thickest and shortest of these bones. The 3^rd metacarpal is distinguished by a styloid process on the lateral side of its base.

Each digit (finger) has three phalanges except for the first (the thumb), which has only two; however, the phalanges of the first digit are stouter than those in the other fingers. Each phalanx has a base proximally, a shaft (body), and a head distally. The proximal phalanges are the largest, the middle ones are intermediate in size, and the distal ones are the smallest. The shafts of the phalanges taper distally. The terminal phalanges are flattened and expanded at their distal ends, which underlie the nail beds.