The Hand

Robert Vragovski

What is the hand?

The hand is an organ that consists of a unique structural basis. It is powered by muscles, ligaments and bones. The hand plays a very important role in our lives. Sometimes it even replaces speech, like Winston Churchill's victory sign. This article will discuss the function, grips, movement and anatomy of this unique structure, known as the hand.

Bones of the hand

The hand consists of 27 bones (fig. 1); one more than the foot. Beginning at the wrist, it has eight carpals that connect to five metacarpal bones, which, in turn, articulate with the five digits at the metacarpal heads. The eight carpal bones lie in two rows; distal and proximal.
(i) The distal row is comprised of the trapezium, trapezoid, capitate and hamate.
(ii) The proximal row is comprised of the scaphoid, lunate, triquetral and pisiform.
The five metacarpal bones, beginning at the lateral side, are numbered from 1 to 5 and articulate distally with the carpal bones. The five digits connecting to the metacarpal heads are referred to as the phalanx, otherwise known as the fingers. Each phalanx consists of a base, shaft and head. The bones in each phalanx that allow flexible movement are termed the phalanges. The first digit, the thumb, has two phalanges. The other four digits, in order following the thumb, are the index finger, middle finger, ring finger and little finger. Each of these digits consist of three phalanges hence there are 14 phalanges in each hand.

Hand Creases

The hand also has creases on both the volar and dorsal aspects and have names. These creases help the skin fold when the hand is in extension and flexion. Movements of the hand and fingers play a major role when the hand is used, such as gripping and pointing etc. Creases are located over three areas of the hand on the palmar aspect; they are the wrist, palmar and digital creases. These creases lay on top of joint levels, but not always directly over them. The creases assist in locating the boundaries or parameters when immobilising or supporting the hand.

Function of the Hand and Forearm

The hand has many functions, it plays a vital role in our lives as discussed in the introduction, like the fingered gesture of Churchil's victory sign. The hand can be positioned or moved in many different positions or grips. The anatomical and biomechanical terms of the hand are: Pronation, Supination, Flexion, Extension, Abduction and Adduction. Movement of the hand occurs at the radiocarpal and intercarpal joints. The hand is capable of moving in flexion, extension, abduction, adduction and circumduction. Digits are also capable of these same movements.

Pronation - The bringing of the hand into palm down position.
Supination - The bringing of the palm face up.
Abduction - The movement of the hand away from the midline when placed in the anatomical position.
Adduction - The movement of the hand toward the midline when placed in the anatomical position.
Flexion - The bending movement of the wrist (palm down). Flexion is measured in degrees starting at neutral (wrist straight) 0 degrees.
Extension - The movement of the wrist where the wrist is moved toward the dorsum of the hand (cocked up). Extension is measured at neutral 0 degrees.

Grips

The hand has five different grips such as the precision grip, hook grip, pointing grip, power grip and position of rest. Its use is very important in our everyday lives; it helps us to hold things and survive from day to day.

		Precision grip is held between the opposed pads of the thumb and index finger.
		Hook grip when the fingers are flexed to resemble a hook for lifting objects.
		Pointing grip is when the index finger is extended with the other digits flexed.
		Power grip is held between the fingers and the palm. It can also be modified into a hook grip for lifting things.
		Position of Rest is the most comfortable position for the hand as it is immobilised and hence minimising stiffness in the metacarpal, phalangeal or interphalangeal joints.

Neurological Observations of the Hand

There are 3 important nerves arising from the shoulder region down to the hand.

Radial nerve supplies the muscles on the posterior aspect of the arm and forearm. To test sensation, pinch the web space between the thumb and index finger. To test motion, the thumb must be hyperextended as well as the four fingers at the MCP joints. (Damage is indicated by wrist drop or inability to extend hand at the wrist.)

Median nerve supplies most of the muscles of the anterior forearm and some of the muscles in the palm. To test sensation, pinch the distal surface of the index finger. To test motion, move thumb and fifth digit so that the finger tips touch and attempt to flex the wrist. (Damage is indicated by numbness, tingling and pain in the palm and fingers, weak thumb movements and proper flexion of the wrist.)

Ulnar nerve supplies the anteromedial muscles of the forearm and most of the muscles of the palm. To test sensation, pinch the distal pad of the fifth digit (small finger). To test motion, attempt to abduct all fingers. (Damage is indicated by an inability to flex and adduct the wrist and difficulty in spreading fingers.)

Muscles That Act on the Wrist, Hand and Fingers

Conclusion

The hand is a complex organ with a variety of functions. A thorough understanding of the musculo-skeletal system, hand creases and grips will assist the cast applicator in achieving a much more functional cast or splint.

References