Part 20

(b) Short Stump.--The stump of an amputation in the upper third of the forearm is too short to be securely held in the forearm bucket. There is consequently a loss of power in the movements communicated, particularly in flexion, the arm of the lever being too short; in addition, the elbow joint in these cases is often a little stiff, so that flexion beyond a right angle is impossible (Figs. 136 to 138).

The chief functional difficulty depends upon the fact that, with the elbow at a right angle, the anterior surface of the forearm stump is too short to support a weight; for example, a basket held by the handle. The stump escapes partly from the bucket when the forearm extends. It is therefore well in such cases to fix the elbow at a right angle by means of a ratchet identical with that used in the artificial arm for amputation above the elbow (Fig. 138).

3. THE ARTIFICIAL HAND AND APPLIANCES

At the extremity of their forearm almost all patients wish in the first place to wear something that is shaped like a hand. Many people--and even many medical men--consider that this "artificial hand" is really useful. In actual fact, by means of fairly simple contrivances, it can be used to enable the patient to eat, to write, to put on and take off his hat, but it is out of the question for it to do real work. For that an appliance, a tool in fact, adapted for use and not for appearance is necessary.

The limb, therefore, will, as a rule, end in a hand, but for workmen this hand will be capable of being unscrewed and replaced easily by one or more appliances.

Attempts have been made to construct so called universal hands and forceps which will serve for any sort of work, but up to the present none of these inventions have given satisfaction. And the practical solution of the problem in the present state of affairs consists in devising a special appliance for a particular trade, studying carefully the movements necessary in this trade.

A workman who in the course of his occupation carries out a number of different movements may thus have several appliances, which he selects as he requires them. For example, a locksmith must be able to hammer, to file, and to drill holes in succession.

We will describe first the hand properly so called, then the appliances. The former is suitable for clerks, and it is for them that the various improved patterns that we shall describe are made. The latter are suitable for manual workers to whom should be given a hand in which the mechanism is reduced to a spring thumb grip and one or more special appliances.

These appliances will almost always be constructed to carry out the movements made by the left hand in the course of the work, because the first step in the re-education of a patient who has lost the right hand should always consist in training the remaining left hand to carry out the work hitherto entrusted to the missing right hand.

A.--THE ARTIFICIAL HAND.

The hand, which is screwed into the end of the forearm socket in such a way that it is in semipronation when the arm hangs vertical, is nearly always made of wood, but occasionally of aluminium.

Hands are nearly always made of lime wood, which has the advantage of lightness, but the fingers are fragile and easily break. Instead of using hornbeam, which is hard but heavy, as the fragility only affects the fingers, some makers have overcome this difficulty by reinforcing the fingers by what they call a "philippeau."

The finger is divided throughout its whole length by a mortise 1·5 millimetres in width, in which are glued two layers of veneering wood (mahogany, rosewood, etc., extremely hard woods, or else a layer of hornbeam).

It may be a simple show hand without any joint. This pattern is no longer used. It may be jointed in one or in several fingers. We shall first consider certain principles of construction which we can explain by describing the chief mechanisms used.

Simple Spring Grip Thumb.--The simplest and most useful articulation is that of the thumb, which when at rest is kept by means of a spring in the flexed position, with the grip against the index finger which is partly flexed (as are also the other fingers).

In many cases the patient is content with this simple mechanism. He opens the spring with the other hand and allows it to close on the object he wishes to grip (Figs. 139-145).

The thumb turns on the axle D upon a piece which fits by a tapered extremity C into a hollow cut out in the thenar eminence. The base of the thumb is rounded. The spring AB flexes the thumb.]

The model shown on page 98 is more mobile than this, in which the thumb turns on the axis AB, and is fitted directly into the thenar eminence. But in this type it will be seen that the spring CD which keeps the thumb flexed, reaches right up to the wrist, and is therefore longer and more powerful. The thumb is much stronger, and this is the mechanism usually adopted. It has the inconvenience that it requires a deep excavation of the thenar eminence, encroaching upon the root of the index finger, so that it is impossible to mount the thumb in this way when it is desired to fit a movable metacarpo-phalangeal joint to the index finger, either with a spring (Fig. 155) or without (Fig. 148).]

The Automatic Thumb.--Active opening movement can be produced by the mechanism shown in figure 146. A cord fixed behind the scapula of the opposite side by a ring which passes over the clavicle and under the axilla, extends down the posterior surface of the arm and forearm pieces, running in pulleys which keep it in place. If the patient bends the elbow and at the same time brings the arm and both shoulders forward, rounding his back, the cord is tightened and pulls the thumb into the position of abduction and extension.

This narrow grip, between the tips of the thumb and index finger only, is not always convenient. A commercial traveller or a foreman could not easily hold with it the order book, in which he has to write. But if the thumb, held by a powerful spring, is parallel to the palm of the hand and grips against the other fingers, which are stretched out and not semiflexed, the grip will be strong and convenient, especially if a mechanism is introduced between the forearm and the hand, allowing the latter to be rotated at will into any position (Fig. 148).

As in the preceding case the thumb may have either a simple grip or an automatic grip opened voluntarily by a cord from the shoulder.

The following is a very interesting method which allows a fork or pen to be held, the automatic thumb being used. The fingers are half flexed, the index being separated from the middle finger, so that the handle of a pen can be inserted between them. The grip of the thumb is not against the tip of the index finger but against the outer side of the last phalanx of the middle finger, against which in consequence the handle of the object held will be pressed (Fig. 147).

FIG. 146--Appliance with automatic thumb. The cord is fixed to a loop which passes round the sound shoulder. Abduction and forward movement of the shoulder and flexion of the elbow open the thumb.]

FIG. 147.--Hand with space between the index and middle fingers, wide enough to take the handle of a fork, which is held by pressure of the thumb against the side of the middle finger.]

The extended fingers are better placed for gripping than the partially flexed fingers, although the latter are convenient to the patient in certain ways. Ball and socket joints are inserted at the interphalangeal joints. (Details are shown in figures 152 to 154.) These are so stiff that they maintain the position in which they are placed passively, as do the joints of an artist's lay figure.

FIG. 149.--The usual pattern of hand. The grip is too small.]

FIG. 151.--The middle finger being longer than the index, the latter does not reach the surface of the table and the ball cannot be picked up.]

If the fingers are rigid and in semiflexion it is possible to articulate all the metacarpo-phalangeal joints, fitting them with a spring, which keeps them flexed, and arranging for active extension as already described for the thumb. All that is necessary is to terminate the cord by five separate strings instead of one. In certain special cases this arrangement may be useful (Figs. 155 to 157). It seems to us useless to render the interphalangeal joints automatic.