Rocker arm

“ It is needless for the apparatus to extend as high up as in a fracture of the arm. What effect, in sustaining the fragments, would casts of a roller have, when applied to the body of the bone, above the place of division? Their only advantage would consist in compressing the brachial and triceps muscles, and in that way preventing their action. ”

“ In difficult crack climbing the extent to which pressure, the jamming of a leg, the touch of a calf or knee, or the twisting of a hand or forearm can be used to ease the muscular strain must be learned by practice. A fist or finger may be hooked in a smooth rift, or a foot slanted into a crack, with only friction attachment, and a slight twist to arm or leg converts either into a secure lever for lifting the weight. The clenching of the fist or the tightening of the muscles of a jammed forearm, or even the inflation of the chest, may at need serve the same purpose. ”

“ The flesh in front of the elbow will not be pinched if, the [92] forearm being fitted very accurately, the muscles of the upper arm are allowed free play, by cutting away the front of the armlet to half its height, but in this case an indirect attachment to the shoulder is essential. ”

“ A socket, fitted to the stump and articulated with the last named at the elbow.
3. The terminal appliance, intended to replace as far as possible the amputated hand and, if possible, resembling it in appearance. In the case of the upper limb the advantages that wood possesses in giving strength and accuracy of fit do not apply, and the arm and the forearm pieces are made of leather, with lateral steels articulated at the elbow: this joint is active in the case of amputations of the forearm but purely passive in amputations of the arm. ”

“ Our first thought is to suppose that a long forearm, being a weak lever, will be ill adapted for climbing. But when you look at Fig. 10, the explanation becomes plain. When a branch is seized by the hand, and the whole weight of the body is supported from it, the entire machinery of the arm changes its action. The forearm is no longer the lever which the brachial muscle moves (Fig. 10) , but now becomes the base from which it acts. The part which was its piston cord now serves as its base of fixation, and what was its base of fixation to the humerus becomes its piston cord. ”

“ 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. ”

“ And whatever arts one examines, it will be found that the natural position of the arms is not the same in each, but that in every case the arms are put into the attitude which suits best with the instrument that is used, and the work to be performed. In practicing archery, no doubt this is the best attitude of the left arm, for gingly-moid extremity of the humerus being fixed in the cavity of the ulna, in this position, throws the bones of the forearm and arm into a line, as if they constituted a single bone, and all flexion at the joint is prevented in this position. ”

“ He may, however, regain some power of flexing the forearm when it is fully pronated, the extensors of the wrist becoming feeble flexors of the elbow. There is, as a rule, no loss of sensibility, but complaint may be made of tickling and of pins-and-needles over the lateral aspect of the arm. The abnormal position of the limb may persist although the muscles regain the power of voluntary movement, and as the condition frequently follows a fall on the shoulder, great care is necessary in diagnosis, as the condition is apt to be attributed to an injury to the axillary (circumflex) nerve. ”

“ One muscle, which in ourselves forms the cushion on the shoulder, and reaches down the outside of the arm for a little distance, is called the deltoid or Δ-shaped muscle, and its especial duty is, when the shoulder-blade is fixed, to lift up the arm by its contraction. The movement is permitted because between the spots where the muscles are adherent to the blade-bone on the one hand, and to the outside of the arm-bone on the other, a distance of several inches, there is a joint like a ball and socket. ”

“ Besides these peculiarities of the hands and feet, which, moreover, are supplied in every joint with tendons and muscles of great motive power, the fore-arm is capable of turning the wrist forwards or backwards, or, as it [Pg 213] is called, rotating, and also of bending. Again, the upper arm is loosely but firmly attached to the shoulders and neck, so as to admit of great range of motion, so what with the bending and rotation of the fore-arm, and the mobility and cushioned state of the fingers, these creatures possess a wonderful apparatus, suited for extreme action and safe holding on. ”

“ CHAPTER IX ARTIFICIAL LIMBS FOR DISARTICULATION THROUGH THE SHOULDER JOINT AND AMPUTATION THROUGH THE DELTOID MUSCLE
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. ”

“ The fracture is exposed, the joint cavity opened up and cleared of clots, and silver-wire sutures passed through the fragments without encroaching upon the articular cartilage. The limb is fixed with the elbow-joint in the position of almost complete extension. Movement may be commenced at the end of a week, the angle at which the joint is fixed being changed morning and evening. During the day the flexed position should be maintained and the arm carried in a sling; during the night the limb is fixed to a pillow in the extended position. ”

“ Should the shoulder be supported, at such an elevation, as might have a constant tendency to destroy the influence of its own gravity? this is evidently prevented by the very oblique direction of the turns of the bandage. Suspending the arm in a sling, is the only way, in which that end can be attained. But does this mode always possess sufficient firmness and stability? The arm, not being here sufficiently fixed, may be constantly in motion, which, by deranging its situation, must communicate very troublesome and injurious movements to the fragments of the clavicle. ”

“ A girl should sit upright, as has been said, and in that position, when she places her hands on the cork handles, her arms should be slightly bent at the elbow. It is very common, however, to see the arms so much bent that the forearm forms almost a right angle to the upper arm. ”

“ Your arm must be raised until high overhead, the hand hanging from the wrist and dropped into your lap or down at the side, letting the elbow "give," so that the upper arm drops first, and then the fore arm and hand,—like three heavy sand-bags sewed together. The arm can be brought up to the level of the shoulder, and then round in front and dropped. ”

“ Several of the muscles in the forearm run into tendons in the wrist because if the muscle part were to extend along the wrist, this part of the arm would be large and clumsy instead of graceful and slender. ”

“ For the back stroke therefore, and that the arm may not only bend at the elbow, but also extend and straighten itself with force, other muscles, the longus, and brevis brachiæus externus, and the aconæus, placed on the hinder part of the arms, by their contractile twitch, fetch back the fore-arm into a straight line with the cubit, with no less force than that with which it was bent out. The same thing obtains in all the limbs, and in every moveable part of the body. ”

“ And see, under the big deltoid, which fits round the shoulder like an epaulette and pulls the arm up, is the scapular group, things like tidily sorted skeins, thick on the shoulder-blades, diminished to a tendon string at their insertion in the arm; their business is to pull the arm back, in opposition to the big pectoral muscle which pulls it forwards. ”

“ If we bend the forearm forcibly against the upper arm, as though to touch the shoulder with the clenched fist, we notice at once that our hand trembles, because the discharges, by means of which the contractions are produced and regulated, do not exactly answer their purpose. If we press the butt of the musket too firmly against our shoulder, or shoot with a heavy gun, we hit the mark less easily because of the trembling of our arms. ”

“ Fig. 53 represents the muscles of the arm after the skin and flesh are removed. They are all in smooth silky cases, laid over each other, and separated both by the smooth membranes that encase them and by layers of fat, so as to move easily without interfering with each other. They are fastened to the bones by strong tendons and cartilages; and around the wrist, in the drawing, is shown a band of cartilage to confine them in place. The muscle marked 8 is the extensor that straightens the fingers after they have been closed by a flexor the other side of the arm. ”

“ One, inside the arm, reaches from the axilla to the wrist, the forearm being bent to a right angle. The other extends, on the outside, from the deltoid to the wrist. They are better if provided with hinges opposite the elbow, so that their angle can be altered, if desired, in the later stage of the treatment. Splints of wood or wire gauze must be evenly and lightly padded before application.
Step 2. Bend the arm to a right angle with the thumb upwards. An assistant next reduces the fracture, and holds it in position. ”

“ The only movements that the stump can transmit [140] 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. ”

“ If the prevailing fashion be to reject the long sleeve, and to partially display the arm, let the glove advance considerably above the elbow, and there be fastened with a drawing-string, or armlet. But this should only be the case when the arm is muscular, coarse, or scraggy. When it is fair, smooth, and round, it will admit of the glove being pushed down to a little above the wrists. ”

“ Hence results, not only a tendency in the radius to approach the ulna, but also, a want of resistance in the muscles situated on the posterior and anterior sides of the fore-arm. For these muscles being, from their flatness, less compressed than the bones, give way, and do not, by forcing themselves between them, oppose the approach of the bones to each other. ”

“ If the upper arm is broken, make three splints, one long enough to reach from the shoulder to the elbow to go on the outside of the arm, one to go on the inner side of the arm, and one on the back of the arm. ”