Bones of Hand

Bones of the Hand
There are eight carpal bones, made up of two rows of
four (Figs. 9.51 and 9.52). The proximal row consists of
(from lateral to medial) the scaphoid, lunate, triquetral,
and pisiform bones. The distal row consists of (from lateral
to medial) the trapezium, trapezoid, capitate, and
hamate bones. Together, the bones of the carpus present
on their anterior surface a concavity, to the lateral and
medial edges of which is attached a strong membranous
band called the flexor retinaculum. In this manner, an
osteofascial tunnel, the carpal tunnel, is formed for the
passage of the median nerve and the flexor tendons of the
fingers.
The bones of the hand are cartilaginous at birth. The
capitate begins to ossify during the first year, and the others
begin to ossify at intervals thereafter until the 12th year,
when all the bones are ossified.
A detailed knowledge of the bones of the hand is
unnecessary. The position, shape, and size of the scaphoid
bone, however, should be studied, because it is commonly
fractured.
The Metacarpals and Phalanges
There are five metacarpal bones, each of which has a base,
a shaft, and a head (Figs. 9.51 and 9.52).
The first metacarpal bone of the thumb is the shortest
and most mobile. It does not lie in the same plane as
the others but occupies a more anterior position. It is also
rotated medially through a right angle so that its extensor
surface is directed laterally and not backward.
The bases of the metacarpal bones articulate with the
distal row of the carpal bones; the heads, which form the
knuckles, articulate with the proximal phalanges (Figs. 9.51
and 9.52). The shaft of each metacarpal bone is slightly
concave forward and is triangular in transverse section. Its
surfaces are posterior, lateral, and medial.
There are three phalanges for each of the fingers but
only two for the thumb.