To accurately describe these instruments is out of place in this article: those wishing to study this branch of the subject more fully are referred to the article by Debout,128 where drawings and descriptions of the most important appliances are given.
128 “Sur les Appareils prothetiques, etc.,” Bull. de Thérap., 1860, pp. 327-377.
Their mode of action may be considered under the following heads:
I. Advantage is taken of muscles as yet unaffected, which are made to act as splints (so to speak) to those affected, greater stability being thus given and cramp controlled when present.
Under this head may be mentioned the simple plan of placing a rubber band around the wrist, wearing a tight-fitting glove, or applying Esmarch's rubber bandage with moderate firmness to the forearm. Large cork pen-holders, by distributing the points of resistance over a larger surface, are thus much easier to hold than small, hard pen-holders.
Two of the instruments devised by Cazenave—one, consisting of two rings joined together in the same plane (to which the pen-holder is attached), and through which the index and middle fingers are thrust as far as the distal joints; and another consisting of two rings of hard rubber, one above the other, sufficiently large to receive the thumb, fore and middle fingers, which are thus held rigidly in the writing position—act in this manner, and are used when the cramp affects the thumb or fore finger.
II. The cramp of one set of muscles is made use of to hold the instrument, the patient writing entirely with the arm movement.
The simple plan of grasping the pen-holder in the closed hand, as previously described, or of thrusting a short pen-holder into a small apple or potato, which is grasped in the closed hand, occasionally affords relief and acts in this way. The instruments of Mathieu, Velpeau, Charrière, and one by Cazenave are based upon this principle. The first consists of two rings rigidly joined together about one inch apart, one above the other, through which the fore finger is thrust, and of a semicircle against which the tip of the thumb is pressed; the pen-holder is attached to a bar adjoining the semicircle and rings. Velpeau's apparatus consists of an oval ball of hard rubber carrying at one extremity the pen-holder at an angle of 45°; the ball is grasped in the closed hand, and the pen-holder allowed to pass between the fore and middle fingers. Charrière's instrument is a modification of the last, having in addition to the ball a number of rings and rests for the fixation of the fingers. The latter has also devised an instrument consisting of a large oval ball of hard rubber; this is grasped in the outstretched palm, which it fills, and is allowed to glide over the paper; the pen-holder is attached to one side. Cazenave's instrument is simply a large pen-holder with rest and rings to fix the fingers.
III. The instrument prevents the spasm of the muscles used in poising the hand from interfering with those used in forming the letters.
One of the instruments devised by Cazenave acts in this way: it consists of a small board, moving upon rollers, upon which the hand is placed; lateral pads prevent the oscillations of the arm due to spasmodic action of the supinators. The pen-holder is held in the ordinary manner.