ARTIFICIAL LIMBS FOR AMPUTATION THROUGH THE ARM

In this chapter we shall deal only with amputation of the arm below the upper third, i.e. with cases in which the stump is long enough to transmit movements to the artificial limb. Amputation through the deltoid muscle must be considered in association with disarticulation of the shoulder.

Below the arm socket is attached an artificial limb which represents the elbow joint, forearm, and hand.

There are two types to be described:—

1. The artificial arm proper, which has the external shape of the natural limb.

2. The worker's arm, a terminal appliance in which outward appearance is not considered.

The considerations as to the arm socket and its attachment by a shoulder cap are the same for the two types of appliance.

Attachment and Arm Socket.—The surface over the acromion and clavicle is the only point from which support can be given to an appliance for an amputation through the arm; the attachment is made by means of a shoulder cap.

The general shape of this shoulder cap and its attachment by means of a strap passed under the opposite axilla are similar to those described for appliances for amputation through the forearm.

The larger the shoulder cap the more it extends forwards over the anterior wall of the axilla, upwards over the supra clavicular fossa, and backwards over the scapula, the more secure will be the support. The appliance is heavy and has no support other than the axillary strap. The latter has a tendency to ride upwards against the axilla where it exerts a pressure which may be uncomfortable. This may be relieved by attaching a vertical strap which is buttoned to the trouser belt.

But although this extensive enclosure of the thoracic region may not hinder the movements of the stump forwards and backwards, it must obviously interfere with the movement of abduction. No doubt this movement is the less important of the two, but we ought to try to preserve it as far as possible.

In short stumps we must abandon it. But if the stump is long and consequently has no tendency to escape from the socket, even if this slips down a little, movement may be retained by two methods.

The first consists in separating the arm socket from a large shoulder cap, and inserting a joint between (see page 87); but the appliance is then heavy and cumbersome. Moreover, although abduction can thus be easily attained, thrusting and pulling movements require a light appliance, and finally it is impossible to secure rotation.

It is possible, on the other hand, by means of the other method, which consists in ending the shoulder cap at a line continued vertically upwards from the thoracic margin of the axilla. If the straps are strong and carefully adjusted the result is better than with the fitting over the scapula, so that this appliance is preferable. We here illustrate a method of fitting the straps which we consider a good one. From the posterior part of the ordinary axillary strap, a Y-shaped branch passes to the upper border of the shoulder cap above and in front of the clavicle, this makes up for the small extent of the enclosure of the shoulder.

For the worker's arm a considerable enclosure without any joint is essential, in order to secure stability.

The arm bucket, usually continuous with the shoulder cap, is made of leather strengthened with steels.

The artificial arm is often abducted from the trunk, which constitutes an inconvenience. This is sometimes due to a fault in the alignment, the arm piece not being at right angles to the shoulder cap. It is, however, more often due to the cylindrical shape given to the arm bucket which forces it away from the trunk. The inner side of the bucket should be flattened so that it may hang vertically close to the thorax.

The details of construction are different for the true artificial arm and the worker's arm.

1. Artificial Arm

The arm and forearm pieces are both made of leather. There is no object in making them to lace, the stump is enclosed in a socket in which it need not fit very tightly, because, as we shall explain, this appliance is unsuitable for heavy work.

These two parts are strengthened with steels, which are articulated by hinge joints at the level of the elbow. We have to study—

1. The position of the steels and the direction of the axis of the joint.

2. The lock to fix the elbow joint in a flexed position.

1. Position of the Steels.—The stump can transmit to the arm socket the various movements grouped under the name of circumduction, but its hold does not enable it to transmit rotation.

It is therefore undesirable—although usual—to attach the steels on the arm and forearm to the inner and outer sides of the limb. If this is done, as rotation is impossible, flexion of the forearm at the elbow can only be carried out in the sagittal plane. But this movement is only exceptionally required; the elbow being flexed to the right angle and fixed in this position by a ratchet the limb forms a hook upon which an object may be hung, provided that the forearm lies transversely in contact with the abdomen and not antero-posteriorly. Flexion should therefore be in a plane which is almost the frontal plane (20° or 30° in front of this), and not in the sagittal plane. As there is no active rotation of the arm therefore the steels must be almost in the sagittal plane (the anterior a little external, the posterior a little internal).

In certain carefully constructed appliances the arm bucket is cut transversely above the elbow and between the two parts a bayonet joint is fixed where the arm can be rotated by the sound hand, so that the direction of the elbow movement can be altered.

2. Ratchet to fix the Elbow Joint in the Flexed Position.—When at rest the forearm should hang vertically. But the hand can only be used when the elbow is flexed to an obtuse angle or a right angle, the latter position being more often used. Therefore when the patient has bent the joint to the required angle with his sound hand, he must be able to fix it in this position.

This fixation is effected by means of a ratchet attached to the outer side of the elbow, which can be locked or unlocked at will.

This ratchet consists of a flat metal plate with a prolongation upwards shaped like the handle of a fork. The end of this prolongation is attached to the arm steel by a pin joint about 3 centimetres above the axis of the elbow joint. The plate is pierced by a rectangular opening, one border of which is notched; it lies against the forearm steel, a catch projecting from which fits into the opening, this catch, situated 6 centimetres below the axis of the elbow, is of the same diameter as the notches with which it engages. The higher the notch with which engagement takes place the more nearly flexion approaches the right angle.

The width of the opening in the plate is twice the size of the catch, so that the joint works freely when the catch glides on the smooth edge and becomes fixed as soon as the catch engages in the notched border.

It is only necessary to arrange a lock, manipulated through the sleeve, to bring the smooth or the notched border in contact with the catch.

Suppose that the handle of the ratchet is prolonged behind the point at which it is hinged to the arm steel as a little lever furnished with a button, and that an elastic cord or spring is stretched from this button to a point on the postero-external border of the forearm, then if the lever points upwards and the notches are on the upper edge of the ratchet (as is the case in figure 205), the elastic, pulling the lever forwards, will press the ratchet down and make the notches engage with the catch on the forearm, if, on the other hand, the lever points downwards the elastic traction will release the notches. The reverse occurs if the notches are on the lower edge.

It is then only necessary to arrange a mechanism by means of which this little lever can turn, with a stop which arrests it above at the vertical position, below at a point 45° beyond the horizontal.

A simple mechanism of this sort is shown in figures 206 and 207. The joint surfaces of the ratchet and of the little lever each bear a shoulder, the former in front, the latter behind, extending over such a proportion of their circumference as will make them act as stops in the desired positions above and below.

A lock is thus provided which can be manipulated with the other hand.

In the particular pattern illustrated, traction is made by an elastic cord fixed to the centre of the back of the wrist and ending above in a leather strap pierced with holes which fix on the button of the lever. This arrangement allows of the adjustment necessitated by the gradual stretching of an elastic which is subjected to continuous tension.

A steel spring of this length (the whole length of the forearm) would be too heavy if it were sufficiently powerful. If it is desired to use this method the two ends of a powerful spring should be fixed, one to the button on the lever, the other to the catch on the forearm with which the ratchet engages.

The spring should always be in tension. As the distance between the joint on the arm and any point on the forearm increases as the elbow extends, it is better for the ratchet, with notches on its upper edge, to be engaged when the button points upwards and free when it points downwards. In the opposite arrangement, which is often used, the tension is considerable without being useful when the forearm is vertical, and the mechanism soon wears out.

3. Hand and Other Appliances.—The hand attached to the end of the forearm has a spring thumb which may be passive or automatic. In the latter case, if the stump is long enough to allow considerable movements of the arm, the cord works in the way described on page 87, for amputation of the forearm. If the stump is short, traction must be exerted by movement of the shoulders, rounding the back.

The hand with a mobile wrist is never used with these amputations except in certain expensive appliances, in which in addition the four fingers may be articulated, as described on page 101. For the ordinary limb these delicate mechanisms are devoid of practical utility.

It is easy to replace the hand with interchangeable appliances, but when the patient has to do hard work this is not a satisfactory method.

The arm with the ratchet at the elbow is in fact suitable for use by a clerk. But it is not either strong enough or simple enough for manual labour. In our opinion the functional and practical value of an artificial arm, particularly for amputation above the elbow, is often exaggerated, however it does exist, especially in many branches of agricultural work. For the latter the slightness of the lateral steels—and especially of the joints at the elbow—makes the appliance insufficiently strong. The necessary delicacy of the ratchet and its manipulation through the sleeve by the sound hand are additional disadvantages.

2. Worker's Arm

If our object is to fit to an arm stump an appliance which will be at the same time strong and flexible, capable of carrying out rough and even vigorous work, we must abandon the attempt to imitate the natural shape of the arm.

The movements and strength of the stump must be transmitted to the object held by means of a rigid rod at the extremity of which the appliance for gripping is fixed. It is possible to fix around this rod a show arm with a hand and a passive spring thumb for wearing on special occasions, in exactly the same way as we fit the show leg round the peg. Figures 208 and 210 will show at a glance how this is done.

But, as far as our present experience goes, this is only an accessory added for Æsthetic reasons. The true worker's arm consists of a strong metal rod fixed to the arm socket in a way that we must now study.

1. The Arm Socket.—We have already said that this must be continued into a shoulder cap of considerable extent, which may be perforated in the region of the point of the shoulder in order to render the appliance lighter. Abduction at the shoulder is thus sacrificed.

The arm socket is made of leather, open down the front and laced. By being laced it fits the stump more securely. It is strengthened by two steels which may be fixed in the frontal plane because, as we shall see, a passive rotation at the elbow joint is possible.

These steels are directly continuous below with a hemispherical steel cap, which is pierced in the axis of the limb by a hole into which is bolted the connecting piece to which the rod which represents the forearm is attached.

2. Articulation at the Elbow.—The forearm consists of simple metal tube, attached beneath the arm socket by methods which depend upon the following principles.

The only movements that the stump can transmit to the arm socket are forward and backward movements hinging about the shoulder, and abduction. The first of these movements is the only really useful one for the workman. The downward pressure exerted by active extension of the elbow no longer exists; in order to press upon an object the sound hand must be used, for it is not practicable to make use of the weight of the body thrown forward for this purpose.

In backward and forward movements—considering, for example, the use of the file—the angle at the elbow opens when the arm is thrust forward and closes when it is pulled backwards. These passive movements of the joint must not be impeded in any way, that is to say, the forearm must swing freely below the arm upon a transverse axis and it must also be able to rotate freely around a vertical axis.

These movements are secured in the ploughman's hand which was designed sixty years ago by Gripouilleau and in which the joint which we have shown as a method of attaching the mobile ring to the wrist is utilised. The forearm rod attached by a strong transverse pin swings freely in a little stirrup-shaped cap, which itself rotates around a bolt by which it is firmly fixed into the metal or wooden hemisphere which terminates the arm socket.[14]

It is clear that this complete liberty of action has its disadvantages; the elbow joint can never be made to assume a fixed position against any passive resistance; moreover, in actual practice the useful range of either of these movements is small. For this reason attempts have been made to devise methods by which they can be limited in the various worker's arms which have been designed since the beginning of the war. In all these arms the mechanism of the elbow joint is derived from that of the ploughman's arm of Gripouilleau. Unfortunately none of these mechanisms in which a pressure screw is used for fixation possess any strength. At first sight, in a new appliance they appear attractive and work well, but it is well known to all mechanics that the thread of a screw which is in constant use quickly wears and then it is impossible to tighten it.

At the extremity of an artificial arm, whether it be an arm of natural shape or a worker's arm simplified to the form of a jointed rod, any of the appliances already described for forearm amputations can be screwed on as required.

It is by the use of these appliances that Gripouilleau's old ploughman's arm, which ended in an interchangeable hook and ring, has been improved.

Apart from their actual economic value, results have been obtained by use of these terminal appliances, in many different skilled trades, which are of the greatest possible interest.

For reasons that we have indicated in describing the attachment of the elbow, the various attempts that have been made to give to the wrist a mobility that is under control have not so far led to the invention of an appliance that is both strong and durable. For this reason we consider that until something new is designed it is better to make the terminal appliance a fixed one.

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