FIXED HAND ADAPTATIONS
In thrusting or striking actions and the like,
the hand may assume fixed and rigid postures
while functioning with the arm in support.
These represent nonspecialized functions in
which the hand serves merely as an adapted
"end of the arm." The various forms include
the flat-of-hand, the clenched fist, the knuckle
and digital support postures, and so on.
WRIST MECHANICS
The wrist joint, composed of the radiocarpal
and intercarpal articulations (Fig. 1), has an
elliptical rotation field with the major axis in
the dorsal-volar excursion, the minor in the
ulnar-radial. No significant torsion occurs.
Bunnell (4) gives the angular excursions about
the radiocarpal and intercarpal articulation as
shown in Table 4.
The rotation within the carpal bones during
these movements is too complicated for brief
treatment. Not only do the rotations occur
at several articulating surfaces, but the virtual
axes of rotation lie distal to the contact surfaces
owing to gliding motions in the convexconcave
structure of the joints. Idealization of
the motions into those of a simple lever, rotating
about a fixed center, as implied in diagrams
such as Figure 2, can be justified only
as a convenient approximation.
The muscles traversing the wrist include
those inserting into the carpus and metacarpus
and those mediating flexion and extension of
Fig. 8. Volar intrinsic muscles of the hand. For
nomenclature, see Table 2.
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the phalanges. The latter contribute to t