arranged in two rows, those in the more proximal
row articulating with radius and ulna. Between
the two is the intercarpal articulation.
The bony conformation and ligamentous attachments
are such as to prevent both lateral
and dorsal-volar translations but to allow participation
in the major wrist motions (Fig. 2).
In each of the digits, the anatomical design
is essentially the same, with exceptions in the
thumb. Metacarpals II through V articulate
so closely with the adjacent carpal bones of the
distal row that, although they are capable of
some flexion and extension, independence of
motion is very limited. The metacarpal shafts
are arched to form the palm, and the distal
ends are almost hemispherical to receive the
concave curvature of the proximal ends of the
first phalanges.
The metacarpophalangeal joint exhibits a
pattern seen also in the interphalangeal joints.
As shown schematically in Figure 3, the virtual
center of rotation lies approximately at
the center of curvature of the distal end of the
proximal member. The lateral aspects of the
joint surfaces are narrowed and closely bound
with ligaments, so that lateral rotation is
small in the metacarpophalangeal joints and
lacking entirely in the phalangeal articulations.
Hence, the latter are typical hinge
joints. The thumb differs from the other digits
first in that the second phalanx is missing and,
second, in that there is greater mobility in the
carpometacarpal articulation.