For reasons

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.

[Illustration: FIG. 201.]

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.

[Illustration: FIG. 202.]

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.

[Illustration: FIGS. 203 and 204.–Shoulder fitting of small
extent allowing abduction.]

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.

[Illustration: FIG. 205.–Elbow ratchet.]

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.

[Illustration: FIGS. 206 and 207.–The elbow ratchet and mode
of action of its lock.]

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.

[Illustration: FIGS. 208 and 209.–_Worker’s arm and show
arm._

The worker’s arm consists of a metal rod which swings backwards and
forwards at the elbow and also rotates upon the arm socket. To the
end of this rod an appliance can be screwed (a ring and hook are here
shown). Around the worker’s arm a show arm with a hand (Fig. 209) can
be fixed. They are shown in place in Figure 210.]

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.

[Illustration: FIG. 210.–Show arm in position.]

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]

[14] Wood, which was used by Gripouilleau, has been given up.

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.

So far as function is concerned these operations are identical; a
short arm stump is incapable of transmitting movements to the socket
of the artificial limb.

That is to say, our appliance will be a purely passive one, and
at the present time it is useless to attempt to make any sort of
worker’s arm. We must aim simply at supplying a limb which imitates
the external shape of the arm, with an elbow joint which can be locked
with a ratchet. At most it is possible by a movement of the opposite
shoulder to work an automatic thumb by means of a cord, as a rule,
however, a simple spring thumb is preferred.

Nothing need be added to what has been said in the previous chapter
about the elbow joint or the hand.

In the fitting of an attachment over the shoulder the amputation
through the deltoid presents an actual advantage. For in this case the
shape of the point of the shoulder is preserved, and the attachment
carried out as described on pages 87 and 130 fixes the appliance very
securely.

If the entire humerus has been removed a very extensive enclosure of
the front and back of the chest is essential and in order that the
axilla may be in close contact with the top of the limb it is a good
thing to stretch across this space a layer of some firm material.

These appliances can be used to steady a piece of paper upon which
the patient is writing, to carry a parcel which is not too heavy
with the elbow flexed, to grip an article with the thumb. A workman
who is being re-educated for some occupation which is possible
for a one-armed man, will usually–unless he is going out for
pleasure–leave his artificial arm at home in the cupboard.

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