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Other Terms: Metacarpal II
The metacarpal bones, like the metatarsal bones, are miniature long bones because of the presence of a medullary cavity. They are numbered one to five from lateral to medial. They all have the basic design of a rounded distal head that form the large knuckles of the hand, a narrowed shaft with longitudinally concave palmar surfaces for the attachment of interosseous muscles, and an expanded proximal base.
The term metacarpal comes from the Greek prefix meta- denoting over or beyond and karpos. The term karpos comes from the Greek word for wrist. It apparently arises from the Greek word karphos for chaff or splinters of wood. The term is a very old one and was used by Homer.
This bone articulates distally with the proximal phalanx. The articular surface is a rounded convex surface that is more narrow transversely. The smooth articular surface spreads further onto the palmar surface than it does on the dorsal surface. Proximally, the bone articulates with the trapezium, trapezoid, capitate, and the neighboring metacarpals.
The bone ossifies from two centers. A primary center arises in the shaft while a secondary center follows later in the head. The primary center appears at mid-shaft during the ninth week of prenatal life. At birth the bony shaft is developed. The secondary center appears, in order from the second to the fifth, in the heads of the metacarpals during the second year. This usually occurs earlier in females versus males. The secondary centers unite with the shaft between the fifteenth and sixteenth year in females and the eighteenth and nineteenth year in males. There can be considerable variation in these ossification times.