Chapter 42

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.

### Introduction

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.

###### Figure 42–1.

Positions of function (A) and 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 ...

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