THE UPPER EXTREMITY.
Fracture of the Metacarpal Bones.
Apparatus.—1. A piece of gutta-percha.
2. A roller 2 inches wide.
In treating this fracture it is important to keep the broken bone in place without confining the wrist or fingers.
A pattern of the palm and dorsum of the hand is cut out of paper, which is doubled round the radial side, letting the thumb out through a hole of convenient size to clear it (see fig. 27). The piece of paper is then laid on a sheet of gutta-percha ¼ inch thick, and the requisite quantity cut off; a hole as big as a pea is next punched in the gutta-percha in the middle, about 1 inch from the lower border, or at a point corresponding to the hole in the paper for the thumb. The fragments are then pushed into place and held so by an assistant, while the surgeon softens the gutta-percha in boiling water; when thoroughly soft, he draws the thumb through the little hole punched in the gutta-percha, and moulds the splint to the palm and back of the hand, bringing the ends of the gutta-percha together at the ulnar side of the hand; the fragments are held carefully in position till the splint is set. The splint is afterwards removed and trimmed. A few holes should be punched in it after it is moulded to allow perspiration to escape. The splint may then be covered with wash-leather, and a pair of straps with buckles stitched on to keep it in place. It is worn for three or four weeks, or until the fragments are united.
Fig. 27.—Gutta-percha Glove for fractured Metacarpal Bone.
Should gutta-percha not be at hand, another plan is effectual.
Apparatus.—1. A firm ball of tow large enough to fill the palm, stitched in old linen.
2. A roller 2 inches wide.
The broken bone is first replaced; then the hand and fingers bound on to the ball by carrying the roller around them until they are all immoveably confined.
This plan has the disadvantage of confining the whole hand for the fracture of one metacarpal bone; the gutta-percha allows free use of all but the metacarpal bones.
Broken phalanges are treated by bandaging them on to a slip of wood long enough to reach into the palm; the slip must be well padded, that the somewhat concave anterior surface of the digit may accommodate itself on the flat splint. If more than one finger be injured, and the fracture be compound, the splint should then reach up the palmar aspect of the forearm and hand. Fingers should be cut in it to correspond with the fingers to be fastened to the splint.
Fracture of the lower end of the Radius.—Colles’ Fracture.—The displacement in this fracture is mainly due to the lower end of the radius and the carpus being carried backwards while the shaft projects in front.
Apparatus.—1. A straight splint of wood. A second splint, curved at its lower end.
2. Pads and cotton wool.
3. A roller 2 inches wide.
4. A sling.
5. A strip of plaster.
The objects to be attained in treating this fracture are to press the lower fragment forwards and to draw (adduct) the hand towards the ulnar side of the limb. For this purpose a straight and a curved splint are used.
No bandage should be placed under the splints in treating any fracture of the shaft of the radius or ulna, lest the broken ends be pressed into the interosseous space.
Step 1. Prepare the splints. The straight splint should reach, when the arm is bent, to a right angle with the thumb upwards, from a little below the inner condyle to the lower end of the upper fragment or shaft; the curved or pistol splint extends from the outer condyle to the joint of the first and second phalanges. The width of both splints should slightly exceed that of the forearm. The bend of the lower end of the pistol splint should be abrupt, and directed towards the ulnar border opposite the wrist, where the margin of the splint should make an obtuse angle of about 1½ right angles (see fig. 28).
Fig. 28.—Pistol Splint for fracture of the Radius near the lower end.
Pads used with these and other wooden splints are made of layers of cotton wool, carded sheep’s wool, tow, or folds of old blanket. These materials should be stitched in old linen or calico, and covered outside with oiled silk where likely to be stained with the discharge from wounds.
The pads must be thicker below than above, to keep the splints parallel along the forearm; and that of the pistol splint is thickest opposite the carpus, to push the lower fragment forwards.
Fixed deformity opposite the wrist is usually present from impaction of the fragments; moderate extension may be employed to remove this, but forcible or continued efforts give great pain and do harm, by further straining the already wrenched ligaments. After these preparations the splints are applied.
Step 2. Put a very little cotton wool in the palm and across the root of the thumb, before the roller is begun, lest it chafe the carpus in front. The curved splint, with the barrel or longer part inclined downwards below the forearm, is next attached to the back of the hand by a roller carried in figures of 8 round the hand and root of the thumb, but not above the wrist (see fig. 29). This is made fast by a pin.
Fig. 29.—Fracture of the Radius.
Step 3. Raise the straight part of the outside splint till parallel to the forearm, thus adducting the hand to the ulnar side; and fix the splint by a strap of plaster an inch wide carried round it and the forearm below the elbow.
Step 4. Apply the inside straight splint next, keeping the front of the carpus and of the lower fragment exposed. Draw the two splints together by simple spiral turns of a roller, begun just below the elbow and carried down to the lower end of the inside splint, there fasten it off.
Step 5. Put a narrow sling under the forearm between the elbow and the wrist to support the limb comfortably.
When the apparatus is finished the position of the broken fragments should be visible (see fig. 29) and not concealed by bandage. The hand should also be quite free of the sling, lest it be drawn from its proper adducted position. The fragments are in good position when the hollow on the anterior aspect of the wrist and the prominence on the corresponding posterior surface are removed.
The Gutta-percha Gauntlet is another plan of treating fracture of the lower end of the radius that may often be adopted from the first, and may always replace the wooden splints and bandage when the swelling has subsided. It was contrived by Mr. Heather Bigg, and permits the patient to use his hand to some extent while the bone is uniting.
Apparatus.—1. A piece of gutta-percha ¼ inch thick, wide enough to enwrap the metacarpus and wrist, and long enough to reach up the lower half of the forearm. Two thirds across the width, and about 1 inch from the lower end, a small round hole is punched. The sheet is then softened in hot water, and applied to the hand, the thumb being thrust through the hole punched to receive it, which rapidly enlarges when soft. The gutta-percha is then adjusted to the hand and forearm, its borders meeting at the ulnar side of the limb, rather nearer the inner border of the arm than is depicted in fig. 30.
Fig. 30.—Gutta-percha Gauntlet for Colles’ Fracture.
If the fracture is recent, it must be reduced while the splint is soft by extending the hand and holding the parts in the required position until the gutta-percha is set. Before removing the splints superfluous edges should be marked, and, when the splint is off, trimmed away with a knife. Holes must also be punched at frequent intervals that the perspiration may escape. The splint is next lined with wash-leather, and fitted with a pair of straps and buckles to keep it in place.
By this plan the fingers are left free, and some motion allowed also to the thumb. The only joints kept immoveable are those of the carpus and wrist.
Apparatus of some kind must be worn three weeks continuously; then for a fortnight longer, while it is removed every day to allow passive motion of the fingers and gradually of the wrist also to be practised. Care should be taken to warn the patient that pain and stiffness last long in these fractures, lest he blame the surgeon because he does not quickly recover full use of his arm.
Fracture of the Shaft of one or both Bones of the Forearm.
Apparatus.—1. Two straight wooden splints.
2. Pads and wool.
3. 2-inch wide roller.
4. Sling.
The treatment is the same whether one or both bones are broken. Caution has been already given against bandaging the forearm underneath the splints.
Step 1. Prepare two straight wooden splints; one to go in front of, and one behind the forearm. The posterior or outside reaches from the external condyle to the end of the metacarpus; the anterior or inside splint from a little below the internal condyle only as far as the wrist, keeping clear of the ball of the thumb. The splints should be slightly broader than the forearm, and well padded; towards the lower end the padding should be thicker than above. The forearm is bent to a right angle and the thumb put upwards.
Step 2. Reduce the fracture by gentle slow extension at the wrist; this being effected, apply the splints to the forearm, and let an assistant hold them while the bandage is rolled on.
Step 3. When a little wool has been wrapped round the hand and wrist, fasten the dorsal splint by figures of 8 carried round those parts; then draw the two splints together by simple spirals continued to the elbow (see fig. 31).
Fig. 31.—Fracture of both Bones of the Forearm.
Step 4. Support the forearm in a sling, to complete the apparatus.
The splints are worn three weeks; after this, passive motion may be practised daily, and the splints finally abandoned ten days later. But a sling is still required some ten days after the splints are laid aside.
When the ulna alone is broken, an anterior splint reaching from the inner condyle to the tips of the fingers often suffices without a second one.
When the shaft of the radius is broken high up (a rare accident) the displacement is sometimes very difficult of reduction unless the wrist be well supinated. To preserve this position it may be necessary to use a wooden angular splint, and to fix the vertical part to the arm behind the elbow, while the horizontal part is carried along the back of the forearm.
Fracture of the Olecranon.—This fracture, if seen early before effusion takes place, may be put up at once, but if delay till the joint is swollen has occurred, the limb must be kept quiet on a pillow, or on a splint in an easy position with evaporating lotions, until the effusion is absorbed, before any means can be taken to restore the position of the olecranon. Though the straight position of the elbow is usually employed, it is not essential for even very close union of the fragments.
In treating this fracture the following plan is useful.
Apparatus.—1. Straight hollow splint.
2. 2-inch rollers and finger rollers.
3. Pad, wool, and lint.
4. Strapping plaster.
5. Pins.
Step 1. Bandage the fingers; wrap the hand in cotton wool and bandage it. When the wrist is passed, fasten the bandage for a time by a pin, and straighten the arm.
Step 2. Push the olecranon down as close as possible to the rest of the ulna, and put a dossil of lint over it. Place the middle of a strap of plaster an inch wide and 16 inches long, on the lint, and carry its ends round the forearm in a figure of 8; to some extent this alone fixes the fragment.
Step 3. Continue the bandage up the forearm by reverses, keeping the elbow straight; and pass the joint by figures of 8 carried over the compress of lint and the forearm, to draw down the olecranon (see fig. 32). When this is secured, prolong the bandage to the deltoid, to confine the action of the triceps muscle.
Step 4. Pad lightly a hollow splint about 2 inches wide, reaching from the axilla nearly to the wrist, and apply it along the anterior aspect of the limb, then fix it by a second roller. This completes the apparatus.
Fig. 32.—Bringing down the Olecranon with Figures of 8.
The splints and rollers should be removed on the fourth or fifth day, that the positions of the fragments may be examined and the roller again applied to draw them closer together. After ten or twelve days, passive motion of the wrist and fingers, with pronation and supination of the radius, should be adopted, but great care is to be taken that the patient does not inadvertently bend the elbow joint while free of the splint. The splint must be worn, with the frequent removals directed above, for five weeks, by which time gentle flexion of the elbow may be practised.
Hamilton notches his splint at each border about its middle so that the notches shall be 3 inches below the tip of the olecranon (see fig. 33). He begins the bandaging by fastening his splint on to the hand and forearm, as high as the notches; here the roller is carried above the olecranon and again down to the notches; this is repeated again and again, each turn below the last, until the notches are all covered, he then continues the bandage upwards by circular turns until the top of the splint is reached.
Fig. 33.—Hamilton’s Splint for fracture of Olecranon.
Fractures of the Humerus near the Elbow.—These resemble dislocations of the ulna and radius backwards, but are distinguished from them by the ease with which the bones slip into place and again slip back from it when left to themselves; by crepitus; and, when the fracture is above the condyles, the common accident, by those projections retaining their natural relation to the olecranon. In children and youths the articulating surface of the humerus may separate from the shaft without carrying the rest of the lower epiphysis with them. In this rare accident the main distinctions from the usual fracture are, the projection of the olecranon behind the condyles; from dislocation, the absence of the hollow of the sigmoid notch, and facility of reduction.
In ordinary cases, where the deformity is reduced without much difficulty, and the injury to the joint is not severe, lateral rectangular splints of leather, hollowed wood, or wire gauze, answer very well. These are placed both inside and outside the limb, and reach from the axilla and shoulder to the wrist. They are applied in the following manner:—
Apparatus.—1. Lateral hollowed angular splints.
2. Pads and wool.
3. Rollers 2 inches wide for the arm, and 1 inch wide for the fingers.
4. Sling.
Step 1. The splints must be prepared.
Wooden and wire gauze splints are double. 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. Then apply the splints. When adjusting the inside splint, care must be taken that the internal condyle is eased from pressure by sufficient padding above and below it. Next fasten on the splints by a roller begun at their lower end, leaving the hand free, and carried up to the elbow. Before turning round that joint a soft pad must be placed in the hollow of the elbow to push the lower end of the humerus back, and the length of the arm should be measured against the unbroken one to make sure that the shortening is reduced. Extension is kept up the whole time the splint is being fixed to the arm, which is done by carrying the roller round the elbow with figures of 8 and simple spirals up to the axilla, where it is finished off.
Step 3. Lastly, the forearm is supported in a sling under the wrist, leaving the elbow free (as in fig. 35, page [52]).
After three weeks of complete immobility, passive motion should be applied to the elbow daily, during a fortnight or three weeks more in which the splint is still worn.
If the displacement returns very easily, it is better to use an L-shaped splint passing behind the arm and below the forearm. This may be made of wood, or of leather, or of gutta-percha, in the mode about to be described.
The L-shaped splint of gutta-percha, or leather, is made as follows:—
Apparatus.—1. Sheet gutta-percha ¼ inch thick.
2. A tray or wide wash-hand basin.
3. A basin of cold water.
4. A kettle of boiling water.
5. A towel.
6. A knife.
7. A sheet of newspaper.
Cut a pattern of paper reaching, while the elbow is bent and the thumb upwards, from the arm-pit down the back of the arm and under the elbow and forearm to the wrist. The sides must be brought forward to the biceps and front of the forearm as seen in fig. 34. Next cut from the sheet of gutta-percha a piece to match the pattern. Prepare the tray with the hot water, lay in it the towel, and then soften the gutta-percha by laying it in the tray and covering it with almost boiling water, adding more water as the first cools; this may be done by an assistant, while the surgeon directs another assistant to grasp the forearm and reduce the fracture. The assistant keep extension while the surgeon lifts the softened gutta-percha with the towel from the hot and plunges it a moment into cold water, then lays it on the limb, which the assistant keeps at a right angle, and the bone in place, while the splint is setting to the limb. This done, the splint is removed to be trimmed, perforated, and covered with wash-leather. It is then ready for use.
Fig. 34.—Gutta-percha Splint for fracture at the lower end of Humerus.
Leather takes so much time to set that it should not be used in recent fractures. When the bone is partly set, leather is a useful substitute for wood. It is prepared from a pattern in the same manner as the gutta-percha, but is trimmed before soaking, not after it is moulded, like gutta-percha. If possible it should have twenty-four hours soaking in water before being fitted to the limb; but when this cannot be done, immersion in hot water, into which a teacupful of vinegar has been thrown, will make the leather quite supple in a quarter of an hour. The leather splint must be worn twenty-four hours while it sets, and then be removed for covering (see Leather Splints).
Fractured Shaft of the Humerus.
Apparatus.—1. Four straight hollow splints.
2. Rollers 2 inches wide, and 1 inch for the fingers, or straps and buckles.
3. Pads and wool.
4. Sling.
When broken below the attachment of the deltoid and coraco-brachialis muscles the displacement of the bone is commonly prevented with ease; neither shoulder nor elbow-joint need be fixed, and it is not necessary to apply the splints so tightly as to risk interference with the venous circulation. If the pectoral muscles or deltoid be connected with the lower fragment, the displacement is sometimes obstinate; in such cases it is necessary to buckle the splints lightly. For this to be done, the fingers, hand, and forearm must be previously bandaged to prevent œdema; with this addition, the method of treatment is the same in both varieties of fracture.
Step 1. Select the splints; they should be hollowed, of wood, perforated sheet zinc, or wire gauze, about 2 inches broad, lightly padded, and provided with straps and buckles.
The external one reaches from the acromion to the outer condyle; the inner one from the axilla to the inner condyle; a third shorter one is placed behind the arm, and if there is much projection forwards of the lower fragment, a fourth very short one is added in front. The patient should sit on a chair while the apparatus is being put on.
Step 2. The fingers and thumb are bandaged; then, the hand and forearm, first padded with a little wool in the palm and over the wrist, are evenly bandaged to the elbow, round which the roller is carried while the joint is well flexed; this being covered in, the roller is made fast.
The first step of bandaging the hand and forearm before applying the splints is better omitted if the compression requisite to procure the natural position of the bone does not interfere with the circulation.
Step 3. An assistant grasping the elbow in one hand, pulls down the lower fragment, while he steadies the shoulder with the other. The displacement thus reduced, the surgeon applies the splints, taking care that the inside splint does not reach too high into the axilla, lest it compress the axillary vein.
In simple cases, the splints should be drawn close by straps and buckles; where the muscles are powerful, a roller should be wound round the splints instead of straps.
Fig. 35.—Fractured Shaft of the Humerus.
Step 4. A 2 inch wide roller is fastened to the arm above the elbow, and then carried round the trunk to the arm again, to steady the limb against the body.
Step 5. The hand and wrist are supported by a sling over the shoulders, the elbow being allowed to hang (see fig. 35).
This apparatus is worn three weeks, when the bandages are removed from the forearm, and the splints replaced less tightly than before. They may be substituted by a sheath of gutta-percha moulded to the arm from the acromion to the elbow, and buckled on to the limb. The arm must be supported by splints for five weeks, but passive motion of the elbow and wrist should be adopted after the third week. The wrist especially should be set at liberty as soon as possible. In treating this fracture great care is necessary that the bone be kept in accurate and close position, as the humerus is specially prone to remain un-united for many months.
Fracture of the Anatomical or Surgical Neck of the Humerus, of the Great Tuberosity, and of the Neck of the Scapula. These fractures are similarly treated.
Apparatus.—1. Paper for pattern.
2. Gutta-percha, leather, or millboard.
3. Pads. A soft thin pad, 10 inches long, 5 inches wide (a double fold of thick flannel or blanket answers very well), is wanted to line the axilla. If the cap is of leather or gutta-percha, a lining of wash-leather should be added after the splint is made.
4. Rollers, 2 inches and 1 inch wide for the fingers.
5. Scissors.
6. A tray, and kettle of hot water.
7. A towel, and basin of cold water.
8. Sling.
9. Cotton wool.
Step 1. Cut out a paper pattern of the splint on the limb to be fitted. The pattern should reach along the clavicle to the root of the neck, and over the scapula to its posterior border, and be continued down the arm to the elbow, tapering as it goes, but having its anterior and posterior margins brought sufficiently to the inner side of the arm to give the splint a good grasp of the limb in descending. The end should be left long enough to turn a couple of inches round the point of the elbow (see fig. 36). A notch must be cut at the upper end of the paper pattern to make it fit on the shoulder between the clavicle and the spine of the scapula; this should not be repeated in the gutta-percha, as that can be moulded on without; and for that reason the cap is much more serviceable when made of gutta-percha than of leather, where a notch must be cut and stitched together when the leather is set. The gutta-percha, when cut to pattern, must be softened in the manner described in making the splint for the elbow at page [50], fig. 34; then accurately adjusted to the shoulder as high as the root of the neck, and turned under the point of the elbow a couple of inches (see fig. 36), while the forearm is well raised across the chest.
Fig. 36.—Cap for fracture near the Shoulder.
When set, the splint must be removed that it may be trimmed and lined with wash-leather. If of gutta-percha, it must be perforated with small holes; if of leather, the notch at the shoulder must be stitched together. Next prepare a soft thin pad, 5 or 6 inches broad, and 8 or 10 inches long, to fill the axilla.
Step 2. Bandage the fingers and thumb separately, then, putting a little wool in the palm and round the wrist, bandage the hand and forearm to the elbow, where the bandage is fastened.
Step 3. Apply the splint. First get on the cap; then put the soft pad in the axilla, filling it out if the arm-pit is very hollow with cotton wool, and bend the elbow till the hand lies on the breast of the opposite side. Then, while an assistant holds the limb and apparatus in position, fasten them all in place by continuing the roller of the forearm in figures of 8 round the elbow until the splint is well fixed to it; and carry the roller up the arm by reverses to the axilla.
Step 4. A little wool or piece of flannel having been placed in the opposite arm-pit to prevent chafing, a spica for the shoulder is then applied (see page [16]), beginning at the root of the neck and working downwards. Careful extension is continued by the assistant all the time this bandage is being put on, until the head of the bone is well drawn into the cap.
Fig. 37.—Fracture at the upper end of Humerus. The apparatus completed.
Step 5. The arm is drawn to the side, and the forearm fixed against the chest by a roller carried round the arm and trunk and over the shoulder (see fig. 37).
After three weeks the forearm may be released, but the cap and axillary pad must be continued to be worn two or three weeks longer while the arm is well drawn to the side, and the wrist carried in a sling.
Fracture of the Great Tuberosity of the humerus is difficult to treat, on account of the tuberosity being carried backwards by the muscles and the humerus being rotated forwards. Hence the parts must be braced together with a firm cap of gutta-percha moulded on to the shoulder while soft, and while the fractured parts are held in apposition, which may be done by the fingers, or by putting on a wet roller firmly over the shoulder as a spica before the splint is set. When the splint is hard the bandage may be taken off, and the splint removed and finished ready for application. In doing this, the steps are the same as for fracture of the surgical neck of the humerus, and the necessity for fixing the arm well to the side of the body as great as in that fracture.
Fracture of the Acromion is treated very much like fracture of the clavicle, that is, the arm is well raised by a sling under the elbow, and then fastened to the side. It is not necessary to fill the axilla with a pad, as in fracture of the clavicle, for in this case the shoulder is not drawn inwards.
Fracture of the Clavicle.
Apparatus.—1. Axillary pad.
2. Roller, 3 inches wide.
3. Sling.
4. Wool.
Fractures of the clavicle nearly always leave some deformity after union; this is best avoided by keeping the patient on his back on a flat couch with the head alone supported by a cushion, and the arm fixed to the side until union has taken place. As most persons will not submit to a fortnight or three weeks’ confinement in bed for this accident, the fragments must be kept in position as nearly as possible by apparatus while the patient goes about.
The displacement of the outer fragment is inwards, downwards, and forwards. Many varieties of apparatus are employed to prevent this displacement during union; the following mode is perhaps as effectual as any other in accomplishing this object.
Step 1. Fix in the arm-pit a firm wedge-shaped pad of bedtick filled with chaff; 5 inches broad, 6 inches long, and 1½ or 2 inches thick at the thick end, or just enough to fill the axilla and throw out the humerus without compressing the axillary vein, hence the thickness varies with the hollowness of the axilla (see fig. 38). A band and buckle are stitched to the thick end, which is uppermost. When in use, this band is passed over the opposite shoulder and keeps the pad in place. A little wool should be put under the band, where it crosses the root of the neck, to prevent chafing.
Fig. 38.—Wedge-shape pad for broken Collar-bone, attached to the American ring-pad.
Step 2. The elbow is elevated by an assistant, who keeps the arm vertical and lays the fingers on the breast bone. A roller attached to the arm by a couple of turns is carried behind the back round the trunk, and over the arm above the elbow, drawing that close to the side.
Step 3. To support the elbow, the longest border or base of a three-cornered handkerchief is carried under it, one end passes in front, the other behind the body; both are then drawn tightly and crossed over the opposite shoulder, where one end is taken under the axilla, and tied in front. In giving this direction the ring-pads shown in the figures are supposed not to be at hand. Lastly, the loose corner at the wrist is folded neatly and pinned up (see fig. 39).
Fig. 39.—Apparatus for broken Clavicle finished.
This apparatus must be watched from time to time, and re-adjusted if any part slips. The sling and pad are to be worn for four weeks.
Union sometimes takes place in three weeks or less, in which case the pad may be removed so much the earlier; but a sling should be worn for a fortnight after the bandage and pad are laid aside. In children the pad must be very much thinner and shorter than that described; the sling should be replaced by a bandage carried alternately round the body, and over the opposite shoulder. After it is put on the turns should be well stitched together, and smeared over with stiff starch. In bandaging children, great care must be taken to protect with wool the parts likely to be chafed.
Figure-of-8 bandage.—Many surgeons still employ a figure-of-8 bandage carried under each axilla and crossed behind the back. Under any circumstances this is exceedingly irksome to the patient, but is least so if two silk handkerchiefs be substituted for the bandage, one being passed round each shoulder and the ends of both braced tightly together behind the back. The wedge-shaped pad may be dispensed with if the shoulders are braced back, but the elbow must still be raised and drawn to the side.
The American surgeons have a very good plan for attaching the sling to the sound shoulder. Instead of carrying the ends of the sling round the shoulder and under the axilla, they pass over the shoulder a loose but well-stuffed collar or ring-pad (see fig. 38), to which they fasten the ends of the sling in front and behind; this prevents all cutting or chafing under the armpit, and distributes the strain evenly.