Both in industry and in the home, the hand is the most commonly
injured part of the body. Disorders of the hand rarely jeopardize
life but can significantly affect the ability to function.
The prime functions of the hand are feeling (sensibility) and
grasping. Sensibility is most important on the radial sides of the
index, middle, and ring fingers and on the opposing ulnar side of
the thumb, where one must feel and be able to pinch, pick up, and
hold objects. The skin on the ulnar side of the small finger and
its metacarpal, upon which the hand usually rests, must register
the sensations of contact and pain to avoid burns and other trauma.
Mobility is critical for grasping. The upper extremity is a cantilevered
system extending from the shoulder to the fingertips. It must be
adaptable to varying rates and kinds of movements. Stability of proximal
joints is essential for good skeletal control distally.
The specialization of the thumb has allowed humans to have superior
aptitudes for defense, work, and dexterity. The thumb has exquisite
sensibility and is a highly mobile structure with well-developed
adductor and thenar (pronating) musculature. It is the most important digit
of the hand, and every effort must be made to preserve its function.
The position of function of the upper extremity
favors reaching the mouth and perineum and achieves a comfortable, forceful,
and unfatiguing grip and pinch. The elbow is held at or near a right angle,
the forearm neutral between pronation and supination, and the wrist extended
30 degrees with the fingers flexed to almost meet the opposed (pronated)
tip of the thumb (Figure 42–1A).
This is the desired position of the extremity if stiffness is likely
to occur, and it should be maintained when joints are immobilized
by splinting, arthrodesis, or tenodesis.
Positions of function
rest (injury) (B).
Opposite to the position of function is the position of
rest, in which the flexed wrist extends the digits, making
grip and pinch awkward, uncomfortable, weak, and fatiguing (Figure 42–1B). The forearm is usually
pronated, and the elbow may be extended. This habitus is assumed,
without intention, after injury, paralysis, or the onset of a painful
stimulus. For that reason, it is also called the position
of the injury. Immobility in this position jeopardizes function.
All references to the forearm and hand should be made to the
radial and ulnar sides (not lateral and medial) and to the volar
(or palmar) and dorsal surfaces. The digits are identified as the
thumb, index finger, middle finger, ring finger, and small finger.
The skin is an elastic ...