DISSECTED EXTERNAL METACARPAL NERVE AND BRANCHES.
FIG. 62.—DISSECTED EXTERNAL METACARPAL NERVE AND BRANCHES. a, Metacarpal; b, anterior plantar; c, extra branch (probably from the internal metacarpal), conveying sensation after division of the external metacarpal.
'The operation was performed in the ordinary way, without any difficulty whatever. The wounds healed nicely, but the horse still continued to go lame. Careful examination showed that there was still sensation on the outside of the foot. Thinking that possibly there might be two external metacarpal nerves, the horse was again cast, the operation being performed slightly lower down. Only the main branch of the external metacarpal nerve could be found. A piece of this was taken out, and the horse let up. On examination, sensation was still found in the posterior part of the outside of the foot. It was very evident that there was some abnormal distribution of the nerve, as sensation was still being conveyed to that part of the foot.
'As the horse was absolutely useless, and would have to be shot unless this piece of nerve could be found, he was again thrown, and after he had been anæsthetized I determined to follow the course of the nerve down, until I found where the accessory branch came from. This I found a little below the fetlock, about 1/2 inch below the point where the anterior plantar nerve is given off from the metacarpal nerve. It was about 1/2 inch below the spot where the anterior plantar nerve passes between the artery and vein of the foot, and it was somewhat difficult to get at it.
'Fig. 62 shows the exact size and distribution of the nerves. After the separation of the accessory branch, sensation was taken from the foot, and the horse went perfectly sound.'
Stumbling.—In addition to the sequelæ we have mentioned, it is urged against the operation of neurectomy that one of the first effects of depriving the foot of the sense of touch is a tendency on the part of the animal to stumble. From the cases we have seen we cannot regard this objection as a serious one. Nevertheless, as veterinarians, with a knowledge of the physiology of the structures with which we are dealing, we must treat the objection with respect, for, after all, we are bound to allow that stumbling, and a bad form of it, would be but a natural sequence of the operation we have just performed. The real fact remains, however, that cases of stumbling, even immediately after the operation, are rare; and that even when they do occur, the animal seems easily able to accommodate himself to the altered condition, and as readily uses the comparatively inert mass at the end of his limb as he did previously the intact foot.
From the prominence we have given to the unfortunate sequelæ of the operation it might possibly be inferred that, while not giving it our absolute condemnation, we regard neurectomy with a certain amount of distrust. That we may contradict any such false impression, we state here that in many cases the operation is the only measure which will offer relief from pain, and restore to work an otherwise useless animal. In support of that we will now quote the recognised advantages of the operation.
That in many cases, when all other methods—surgical and medicinal—have failed, there is an immediate and total freedom from pain and lameness no one will deny. This, if it restores to active work an animal that would otherwise have had to have been cast aside, is ample justification for giving the operation, in spite of its many unfortunate terminations, a real place among the more highly favoured remedial measures to our hand.
'For Contracted Hoofs, viewing them in the light of idiopathic disease, or as being the immediate cause of the existing lameness in the uninflamed condition of the foot, and when consequential changes of its organism have taken place which bid defiance to therapeutic measures, neurotomy is a warrantable resource' (Percival).
'For Ringbone neurotomy has been practised with perfect success, after blistering and firing had both failed, notwithstanding the work the animal had to perform afterwards was of the most trying nature' (ibid.).
For Navicular Disease, when that malady is diagnosed, the earlier neurectomy is performed the better. The greater work given to the diseased bursa and bone, and the return of the contracted heels to the normal, brought about by the greater freedom with which the foot is used, are claimed by many to effect a cure.
Writing of navicular disease, and mentioning his belief in the possibility of the diseased bone effecting its own repair after the operation, Harold Leeney, M.R.C.V.S., says:
'The expansion of the heel, and rapid development of the frog (in this and many other cases) immediately after the operation, has not, I venture to think, attracted so much attention as it deserves, and may have something to do with those cases which appear to be actually cured, not merely made to go sound by absence of pain.'[A]
[Footnote A: Veterinary Record, vol. xi., p. 297.]
Speaking of the median operation before a meeting of the Central Veterinary Medical Society, Professor Hobday says:[A]
[Footnote A: Veterinary Record, vol. xiii., p. 427.]
'For old-standing lamenesses, when due to splints, exostoses, chronically sprained, thickened, and painful perforans and perforatus tendons, or cases of that kind which cause pain by pressing on the adjacent nerve structures, after all other known methods have failed, median neurectomy is the operation which will be most likely to give the animal a new lease of life and usefulness.'
'Of the Humanity and Utility of Neurectomy there can be no question whatever, and provided the cases are well selected, and the operation is efficiently performed, the advantages to be derived from it are most striking as well as enduring. But the disadvantages attending the loss of sensation in the foot have been brought forward on many occasions as an argument against neurectomy, and no one can deny that the foot with sensation is better than one without that faculty. But in a long experience of the operation I have never found these disadvantages outweigh the great advantages which have immediately followed it.'[A]
[Footnote A: Veterinary Journal, vol. ix., p. 178 (Fleming).]
Beyond these, the direct advantages of neurectomy, are other and more indirect advantages which claim attention.
The most astonishing among them is the fact noted by many writers of repute that exostoses (ringbones, side-bones, splints, etc.) rapidly diminish in size. This is vouched for by such well-known authorities as Zundel and Nocard.
Percival, too, mentions at some length the effect of the removal of pain on the oestral and generative functions, quoting a case of a brood cart-mare by reason of bony deposits being stayed from breeding for some years. Two months after the operation she went to work, and moved sound, her altered condition leading her to breed several healthy foals.
No operation is of any considerable value to the veterinary surgeon unless he is able to show that after it he has left his patient workable. The alleviation of pain alone, commendable as it is from a humanitarian standpoint, is of no interest to the average owner of horse-flesh, unless with it he sees his animal capable of justifying his existence by the amount of labour performed.
Criticised in this way, is the operation of neurectomy justifiable? Upon that point the opinions of many practitioners, even at the present day, differ. We have already partly answered the objections likely to be raised on this score by stating that the work afterwards allotted the animal should be fixed to suit his altered condition. It may be taken as a general rule that in all cases where the animal's usefulness depends upon his delicacy of touch, as, for example, animals used solely for hacking or hunting, his future usefulness in that special sphere of work will be done away with.
Percival himself, always a strong advocate for the operation, fully recognises this. 'Does the neurotomized horse maintain the same step as before?' he asks. 'To this important question,' he replies, 'I unhesitatingly answer no; he does not. There can be no doubt but that the horse feels the ground upon which he is treading, and that he regulates his action in consonance with such feeling, so as to render his step the least jarring and fatiguing to himself, and therefore the easiest and pleasantest to his rider.... Such impressions'—those of touch—'being in the neurotomized subject, so far as regards the feeling of the foot, altogether wanting, a bold, fearless projection of the limb in action will be the consequence, followed by a putting down of the hoof flat upon the ground, as though it were a block, creating a sensation alike unpleasant both to horse and rider.'
Emphatic as Percival is upon this point, there are, nevertheless, others who maintain with equal stoutness that the unnerved animal is positively as safe, if not safer, than the animal who has not been so treated.
'That the tactile sense in the horse's foot is useful, it would be idle to deny; but that it is absolutely essential, even to safe progression, no one who has paid attention to the results of plantar neurectomy will maintain. On several occasions for years I have hunted, hacked, and driven horses which have been deprived of sensation in their fore-feet, and never had an accident with them. Their action has not been impaired by the operation; on the contrary, it has been vastly improved compared with what it had been previous to it. And my opinion has not been single in this respect, as many competent horsemen can give like evidence after long and severe trials of neurotomized horses. The opponents of neurotomy were, probably, not aware that there is in progression a muscular as well as a tactile sense.'
This latter contention is supported by numerous cases, reported at the time when the operation of neurectomy was at the heyday of its popularity. Two I select from writings of a later period:
Recorded Cases.—1. 'Two of the finest among the many fine horses in the Second Life Guards were so lame from navicular disease, when I joined the regiment, that they were unsafe and unsightly to ride, and were therefore entered on the list to be cast off and sold. One was so crippled that it could scarcely be moved out of its stable. Peeling sorry at having to get rid of such good horses, and anxious to give another blow to the mistaken theory that unnerved animals were unsafe, I obtained the consent of my commanding officer, who patronizes practical conclusions, to perform neurotomy. This was carried out on both horses about eighteen months ago. Within a fortnight they were at their duty, absolutely free from lameness, and with first-rate action, and one of them, from being troublesome and unsteady in the ranks—probably from the pain in its feet—had become quite steady and tractable. Instead of being lame, blundering, and unsafe, both were sound, free in movement, and secure, and, the pain being abolished, they looked improved in condition.
'During the month of July the regiment attended the summer drills at Aldershot, and five days every week for a month these horses carried a weight of about 22 stones each over the roughest and most dangerous ground, nearly always at a fast pace, and for four, five, or six hours each day; and yet they never fell or blundered, and the troopers who rode them had unbounded confidence in their sure-footedness. They returned to Windsor, at the end of the month's severe test, as sound in their paces as when they left, and certainly now offer no indication whatever that they are less safe to ride than any other horse in the regiment. The effects of the relief from pain are also most marked, not only in the altered gait out of doors, but also in the stable.'[A]
[Footnote A: Veterinary Journal, vol. ix., p. 178 (George Fleming, F.B.C.V.S.).]
2. 'Some years ago I operated upon a valuable hunter, the property of a gentleman in Kildare, the animal having shown unmistakable symptoms of navicular disease for some months previously, and which had been unsuccessfully combated by the milder forms of treatment for the disease without any benefit. Although the horse went sound, the owner feared to ride him, and sent him to be sold in Dublin, where he was disposed of for a small price, and I then lost sight of him. The following Punchestown Races, to my surprise, amongst a group of horses walking round the paddock previous to saddling for an important race, I recognised my old patient, bandaged, clothed, and trained, ready to take his part in the cross-country contest, and surrounded by a host of admirers willing to back him at any price.
'Having satisfied myself that it was no other than the same animal, my first impulse was at once to find out the jockey who was to ride him, and warn him of his danger by telling him his mount was devoid of feeling in both fore-feet; but the saddling-bell had already rung, and in a few moments more the jockey emerged from the weighing-room and the next view of the horse was his tearing up the course in the preliminary, and "pulling double." I was sorry for the jockey if he felt as I did at that moment, for if he did I fear he and his horse would have parted company at the first fence, as I was certain there would be a smash before the end of the long and difficult three miles of the Kildare Hunt Cup course. It was not until I saw him again in the front rank passing the stand, in the first round, that I breathed freely, and even then I felt very guilty, and, had he come to grief badly, I don't think I should ever have operated on another horse except in such a way as would have left unmistakable traces after it.
'"The old horse wins!" screamed a thousand voices as the competitors safely cleared the last bank (now taken away for a gorse fence) the last time round, and from that moment the operation went up in my estimation a hundredfold, and I almost lost all interest in the finish (and it was a close one, with my patient a good third), resolving I would operate for the future on every animal, young and old, which showed symptoms of navicular disease.
'Neither owner nor jockey knew the horse had been operated on, and he was soon after, on the strength of his performance, sold for a good price to come to England. It is idle to think that all cases are as successful as this was, as experience soon told me; but I consider that, in careful hands, the advantages well outweigh the disadvantages of the operation, and I have selected this instance merely as a practical example.'[A]
[Footnote A: Veterinary Journal, vol. iii., p. 254 (W. Pallin, M.B.C.V.S.).]
It is solely with the object of ventilating both sides of the question that we quote the last two cases. In our opinion, the colours in which the results of the operation are there painted are far too rosy. The practitioner who has before him the task of satisfying a client as to what will or what will not be the results of an operation he has suggested will do well to weigh each side of the argument carefully, and endeavour in his explanation to strike the happy mean.
We hold, further, that the animal who has previously been accustomed to fast work, and to work entailing a large call upon the sense of touch when passing over rough and uneven ground, will be far more likely, in his neurectomized condition, to give satisfaction to his owner if put to a slower and a more suitable means of earning his living.
Under this heading we shall deal with such formations of the feet as depart sufficiently from the normal to render them serious. Faulty conformation may be either congenital or acquired, and acquired gradually as the result of slowly operating causes, or suddenly as the sequel to previous acute disease. Whether congenital or acquired, serious in its nature or comparatively of no account, the veterinary surgeon will often find that the matter of conformation is one which will have a direct bearing on many of his 'foot' cases, and, furthermore, that it is one upon which he will often be called to give advice.
Definition.—That condition of the wall in which, owing to the softness of the horn and the oblique direction of the horn fibres, the heels are unable properly to bear the body-weight, and, as a consequence, curve in beneath the sole. We give the condition first mention, not because of its greater importance, but for the reason that it is frequently the forerunner of the condition to be next described—namely, contracted feet.
Symptoms.—The extreme point of the heel is not affected unless the foot has been greatly neglected, and the condition allowed to develop. Where, however, the foot has been uncared for, curving in of the wall takes place to an alarming degree, and the heels curl underneath the foot to such an extent as to grow over the sole and the bars. By the pressure they exert on the sole corns result, and the animal is lamed.
Causes.—In the main this defect is hereditary. It is seen commonly in connection with flat-foot, and where the horn of the wall is thin and shelly.
Treatment.—In the case of weak or 'turned in' heels no suitable bearing is offered for the shoe in the posterior half of the foot. Any attempt to induce the heels to bear weight is immediately followed by their bending in. It follows from this that the best shoe to be used here is one in which the bearing is confined to the anterior half of the wall, the heels being relieved by being sufficiently pared. As might be expected, this bearing on the anterior half only of the foot is insufficient; pressure must be given the frog. This latter end is best gained by a bar shoe (Fig. 68). With it the anterior portions of the wall, the whole of the bars, and the whole of the frog may be in contact, and the heels only so pared as to take no bearing at all. A few such shoeings sees the defect remedied. In every instance paring of the sole should be discouraged, as it serves but to increase the deformity.
(a) GENERAL CONTRACTION—CONTRACTED HEELS.
Definition. By the term contracted foot, otherwise known as hoof-bound, is indicated a condition in which the foot, more especially the posterior half of it, is, or becomes, narrower from side to side than is normal.
It must be borne in mind, however, that certain breeds of horses have normally a foot which nearer approaches the oval than the circular in form, and that a narrow foot is not necessarily a contracted foot.
The contraction may be bilateral when affecting both heels of the same foot and extending to the quarters, or unilateral when the inside or outside heel only is affected.
In some cases contraction is confined to one foot, while in others it may be noticed equally bad in both. It is a matter of common knowledge that contraction is usually seen in the fore-feet, while the hind seldom or never suffer from it, a fact which, to our minds, seems difficult of adequate explanation. Zundel explains this by stating that contraction is principally observed in the fore-feet, by reason of the fact that when lameness arises from it alteration in action will more readily be detected in front than behind. Percival, on the other hand, suggests that the greater expansive powers of the hind-foot, by reason of the impetus of its action, is able to overcome any influence operating towards contraction. It may be, however, that given a cause for contraction, such as the removal of the frog's counter-pressure with the ground by faulty shoeing or excessive paring, the fore-feet, by reason of their being called upon to bear the greater part of the body-weight, are the first to suffer.
Flat feet with weak heels are those most frequently affected, and, as we have already intimated, the condition may exist with or without other disease of the foot.
Depending upon its degree, contracted foot may vary from a simple abnormality, non-inflammatory and painless, to a condition in which it becomes a veritable disease, giving rise to a bad form of lameness, and bringing about a withered and sometimes discharging and cankerous affection of the frog.
Symptoms.—In its early stages contraction is difficult of detection, and where both feet are affected may for some time go unsuspected. With only one foot undergoing change, the early stages may the more readily be marked, for in this case comparison with the other and sound foot will at once reveal the alteration in shape. If lameness in the suspected foot is present, then any lingering doubt will be quickly dispelled.
When far advanced, contraction offers signs that cannot well be missed. The converging of the heels narrows the V-shaped indentation in the sole for the reception of the frog. As a consequence of this, the frog itself becomes atrophied by reason of the continual pressure exerted upon it by the ingrowing horn of the wall and the bars. The median and lateral lacunæ of this organ, from being fairly broad and open channels, become pressed into mere crack-like openings (see the commencing of this condition in Fig. 80, and a badly wasted frog in Fig. 74A). As the case goes on, the lateral branches of the frog entirely disappear, and all that is left of the organ is a remnant of its body or cushion, now wedged in tightly between the bars. Following upon the disappearance of the frog, we find that the bars are in contact, or, in some cases, actually overlapping each other at their posterior extremities.
At this stage, perhaps, the whole condition has become aggravated by a foul discharge from the place originally occupied by the frog, and the foot, especially in the region of the heels, has become hot and tender—really a form of local and subacute laminitis.
The long-continued inflammation, although only of a low type, renders the horn of the hoof hard and dry, and only with difficulty will the ordinary foot instruments cut it. This in its turn leads to cracks and fissures in various places, but more especially in the bars and what is left of the frog. Often, too, cracks will appear in the horn of the quarters, and a troublesome and incurable form of sand-crack results.
An animal with contraction advanced as far as this, especially if confined to one foot, goes unmistakably lame. With both feet affected, he ordinarily starts out from the stable in a manner that is commonly called 'groggy.' In other words, the gait is uncertain, and feeling; and stumbling is frequent. Anyone who has had the misfortune to drive an animal with feet in this condition knows full well that every little irregularity in the road at once makes itself felt to the feet, and that the animal, as time goes on, learns to carefully avoid any suspicious-looking group of stones he may see. To drive an animal like this is to keep one's self continually on tenter-hooks, for, sooner or later, the inevitable happens, and the animal comes down.
Up to now we have described the changes of form in the hoof as seen when the contracted foot is viewed from the solar surface. With those changes as evident as we have depicted them, there will be no difficulty in detecting the alterations in the form of the wall.
In addition to a narrowing from side to side there will be noticed an abnormal straightness of the quarters, with a turning in, more or less sudden, of the heels. This effect is given in these cases by the smith maintaining the shoe of a length and width that should normally fit a foot of that particular animal's size and substance. This is probably done with the idea of deceiving anyone examining the solar surface. Viewed from this position, the width of the shoe at the heels gives the impression that it is attached to a foot of normal breadth. This deception is heightened if at the same time has been practised the process of 'opening up the heels.' That expression indicates that the bars have been removed, and the lateral lacunæ of the frog made to continue the concavity of the sole. The arch of the latter is thus made to appear of much greater extent than it really is, and the heels, by reason of their being abruptly cut off when removing the bars, also convey the false impression of being wide apart.
The practitioner unversed in the tricks of the forge will best guard against this by viewing the foot, while on the ground, from behind. From that position he will be able to detect the lowness of the quarters, and the projecting portion of the shoe, that the hoof, by reason of its sudden bending inwards, does not touch.
The 'feeling' manner of the gait before alluded to, together with the disinclination to put the foot firmly and squarely forward, will sometimes lead the examiner to over-look the contraction, and diagnose his case as one of shoulder lameness. In many cases, too, such consequent conditions as 'thrushy frogs' and 'suppurating corns' are often treated with utter disregard of the contraction that has really brought them about. But above all, the disease most likely to be confounded with simple contraction is navicular disease. More than probable it is that many cases of so-called 'navicular' have in reality been nothing more than contraction brought about by one or other of the causes we shall afterwards enumerate—cases where a due attention to the prime cause of the mischief would, in all likelihood, have remedied the lameness.
Changes in the Internal Structures.—It follows as a matter of course that the changes we have described in the form of the hoof itself carry with them alterations in the bones and sensitive structures beneath it. The tissues, as a whole, become atrophied. The os pedis becomes deformed, loses its circular shape, and gradually becomes more or less oval in contour. At the same time, its structure becomes more compact, the cribriform appearance of its anterior and lateral faces more or less destroyed, and the few remaining openings apparently increased in size. This atrophy of the os pedis is best noted at the wings.
In the plantar cushion the effects of the atrophy are noted in the smallness of the organ, in its becoming whiter in colour than normal, and more resistant to pressure.
The coronary cushion is also affected in the same way, where the changes are noted most in its posterior portions.
A further effect of the narrowing of the heels, and their consequent tendency to drop downwards, is the exertion of a continual pressure on the sensitive sole. In course of time, and especially in flat feet, this leads to the appearance of corns.
The navicular bone and bursa and the tendon of the perforans also suffer from the effects of compression. The movement of the tendon is restricted, and arterial supply to the adjacent structures rendered deficient. The tissues of the bone and bursa are insufficiently nourished, and the secretion of synovia lessened. In this way it is conceivable that navicular disease may follow the condition of simple contracted heels.
In common with the other structures, the lateral cartilages also suffer from the continual pressure. Their blood-supply is lessened, their functions interfered with, and side-bones result.
Causes.—Upon the causation of contraction a very great deal has been written, both by early veterinarians and by those of the present day. Many and widely differing opinions have been advanced, but a careful résumé of only a few will lead one to certain fixed conclusions.
We may consider the causes of contraction under two headings—predisposing and exciting.
Predisposing Causes of Contraction.—Among these we will first mention heredity, although it is possible it should not be deemed of so great account as it is by some. That the shape of certain feet, especially those with low heels and abnormally sloping walls, predisposes to contraction no one will deny. So long, however, as the animal goes unshod, so long does the foot maintain a normal condition of the heels. In other words, it is not until the tendency to contraction already there is aggravated by careless shoeing and the effects of work that it operates to any noticeable extent.
The degree of contraction will also be very largely governed by the amount of the development of the frog. With a frog of good size, low down, and taking part in the pressure of the foot on the ground, contraction will be prevented. On the other hand, an ill-developed frog, one wasted by long-continued and spreading thrush, or one robbed of its normal function by excessive paring in the forge, is a common starting-point of the condition we are considering. We have already referred to this in Chapter III., when considering the experiments of Lungwitz in this connection. What we have to bear in mind in these experiments is that the application of a pad to the frog, in such a manner that effective ground-pressure is obtained, results always in a marked expansion of the heels, and that, with counter-pressure with the ground absent, expansion occurs to little or no extent. This is proof positive of the enormous part the frog plays in maintaining an open and elastic condition of the heels—a fact so insisted on by Coleman.
It is worthy of mention, however, that loss of the frog's function does not operate to nearly so serious an extent in horses with high, upright heels as in those with the heels low and excessively sloping.
In illustrating this, Mr. Dollar, in his work on shoeing, mentions the case of a pair of trotting horses of similar age, size, and weight, each having weak fore-heels. In one case the hoofs were flat, in the other upright. The horse with the flat hoofs suffered from contraction, while the other did not.
The reason appears to be that in the animal with upright hoofs the proportion of body-weight borne by the heels is considerably less than in those with the hoofs flat and sloping.
Certain conditions of the horn-producing membranes also predispose to contraction. For example, in horses reared on marshy soils, and afterwards transferred to standing in town stables, we find that a dry and brittle condition of the horn supervenes. This we may regard as a low form of laminitis, brought about by the heat of the material upon which the animal is standing, and the congestion of the feet engendered by his enforced standing for long periods in one position, as opposed to the more or less continuous exercise when at pasture. With the hoof in this condition it loses by evaporation the moisture that normally it should contain, and, as we might expect, a certain degree of contraction of its structure is the inevitable result.
We thus see that contraction brought about in this way is not so much caused by the heat of the stable, as it is by the decreased ability of the horn to retain its own moisture.
On the other hand, it cannot be denied that excessive warmth and dryness combined tend also to an undue abstraction of moisture, even from the horn of the healthy foot; and this explains in great measure how it is that lameness, as a rule, and especially that proceeding from contracted heels, is far more frequent and of greater intensity in the hot, dry months of summer, than in the cooler and more humid atmosphere of winter. It is interesting to note, too, that an alternation of humidity and dryness is far more liable to injure the quality of the horn and tend to its contraction than the long-continued effects of dryness alone. A common illustration of this is to be found in the effects of the ordinary poultice. Everyone knows that when, after a few days' application, they are discontinued, we get as a result an abnormally dry and brittle state of the horn. This is doubtless due to the poultice removing the thin, varnish-like, and protective pellicle known as the periople, and thereby allowing the process of evaporation to act on the water normally contained in the hoof.
Exciting Causes of Contraction.—Among these, first place must undoubtedly be given to shoeing. This does not necessarily imply shoeing more than ordinarily faulty, nor a faulty preparation of the foot, but shoeing as it is generally practised. No ordinary shoe, except a few devised for the purpose, such as the Charlier or the tip, allows the frog to come in contact with the ground. This we take to be the main factor in the causation of contracted heels, especially with a predisposition already present in the foot itself. In the words of Lungwitz: 'Regarded from this point of view, there is no greater evil than shoeing. It abolishes the necessary counter-pressure, and thus interferes with expansion. Bars, sole, and frog cannot perform the functions that naturally belong to them as they would do without the shoe.'
In addition to the evil of the shoe itself, errors of practice in the forge contribute to the causation of contraction. Taking first the preparation of the foot, we find that often the heels are lowered far too much, and the toe allowed to remain too long. This can have but one effect—that of throwing a greater proportion of the animal's weight upon the heels than properly they should bear, with, what we now know to be the consequence of that, a corresponding pushing inwards and downwards of the horn; in other words, contraction.
Excessive paring of the bars, to which we have already partly alluded, is also an active agent in bringing about an inward growth of the horn of the heels and quarters. The bar, or inflexion of the wall at the heel, by means of its close contact with the frog, communicates the outward movements of that organ to the wall of the hoof. With the bar removed, the outward movements of the frog under pressure are naturally rendered of no account, and a proper and intermittent expansion of the wall denied it. The same evil follows, though to a less extent, excessive paring of the sole.
The shape of the bearing surface of the shoe is often to be blamed. Where this is concave—'seated'—and the 'seating' is carried back to the heels, it is easy to see that, when weight is on the foot, there is an ever-present tendency for the bearing edge of the wall to slide down towards the inner edge of the shoe. This tendency, operating on both the inner and outer wall simultaneously, must strongly favour contraction.
A further wrong practice is that of continuing the nailing too far towards the heels. In our opinion this is not now often met with. When it occurs its effect is, of course, to prevent those movements of expansion of the wall which we now know to be normal and most marked at the heels.
It may be remarked of the build of the shoe, or of errors in the preparation of the foot, that neither are of much moment. Neither are they. But when one stays to consider that errors of this description are practised not only once, but each time the horse goes to the forge, and that with some of them—those relating to the build of the shoe—the injury thereby brought about is inflicted not only once, but every day that particular shoe is worn, then it is not to be wondered at that, sooner or later, ill consequences more or less grave result.
Prognosis.—This will depend to a very large extent upon the conformation of the limb, and upon the previous duration of the contraction. Contraction of long standing, where atrophy of the sub-lying, soft structures and the pedal bone may be expected, will prove obstinate to treatment. Especially will this be so if the lateral cartilages have become ossified. Neither may we look for much benefit from treatment if the contraction has occurred in animals with an oblique foot axis and flat hoofs.
On the other hand, if the case is comparatively recent, if the limb is straight and the form of the hoof is upright, and if matters are uncomplicated by side-bones, or other serious alteration in the internal structures, then treatment may be rewarded with some measure of success.
FIG. 63.—TIP SHOE. The dotted portions represent the length of the branches removed.
Treatment.—The greater part of the treatment of contracted foot will almost suggest itself as a corollary of the causes we have enumerated. The normal width of the heels may be renewed, and development of the wasted frog brought about by one of three methods:
1. By restoring the pressure from below to the frog.
2. By the use of an expansion shoe.
3. By operative measures upon the horn of the wall.
1. By Restoring the Pressure from Below to the Frog.
This may be accomplished as follows:
(a) By Shoeing with Tips.—This method is advocated by Percival, by A.A. Holcombe, D.V.S., Inspector. Bureau of Animal Industry, U.S.A., by Dollar in his work on horseshoeing, and by many others.
Though requiring more care than in fitting the ordinary shoe, the application of a tip is simple. In reality, the tip is just an ordinary shoe shortened by truncating the heels.
Before applying the tip, the horn of the wall at the toe should be shortened sufficiently to prevent any undue obliquity of the hoof, and the foot should be so prepared as to allow the heels of the tip to sink flush with the bearing edge of the wall behind it.
When the foot does not allow of the removal of much horn at the toe, what is termed a 'thinned' tip is to be preferred. Its shape is sufficiently shown by the accompanying figure (Fig. 65).
With the tip the posterior half of the foot is allowed to come into contact with the ground, and the object we are striving for—namely, frog pressure, and greater facilities for alternate expansion and contraction of the heels—is thus brought about.
FIG. 64.—THE TIP SHOE LET IN THE FOOT.
FIG. 65.—THE THINNED TIP.
(b) By Shoeing with the Charlier.—The results brought about by the use of a tip may be arrived at by the application of a Charlier or preplantar shoe, or by a modified Charlier or Charlier tip.
Briefly described, a Charlier is a shoe that allows the sole and the frog to come to the ground exactly as in the unshod foot. This is accomplished by running a groove round the inferior edge of the hoof by removing a portion of the bearing edge of the wall with a specially devised drawing-knife. Into this groove is fitted a narrow and somewhat deep shoe, made, preferably, of a mixture of iron and steel, and forged in such a manner that its front or outer surface follows the outer slope of the wall.
The Charlier should have the inner edge of its upper surface very slightly bevelled, in order to prevent any pressure on the sensitive sole, and should be provided with from four to six nail-holes. These latter should be small in size and conical in shape. The nails themselves should be small, and have a conical head and neck, to fit into the nail-hole of the shoe.
THE SPECIAL DRAWING-KNIFE (FLEMING'S) FOR PREPARING THE FOOT FOR THE CHARLIER SHOE.
FIG. 66.—THE SPECIAL DRAWING-KNIFE (FLEMING'S) FOR PREPARING THE FOOT FOR THE CHARLIER SHOE.
The modified Charlier, or Charlier tip, perhaps the better of the two for the purpose we are describing, is really a shortened Charlier, and bears the same relation to the Charlier proper as the tip does to the ordinary shoe. It is let into the solar surface of the foot in exactly the same manner as its larger fellow, but it does not extend backwards beyond the commencement of the quarters. By its use greater opportunity for expansion is given to the heels than is done by the Charlier with heels of full length.
FOOT PREPARED FOR THE CHARLIER SHOE.
FIG. 67.—FOOT PREPARED FOR THE CHARLIER SHOE.
We do not here intend to deal at any length with the arguments for and against the Charlier as regards its adoption for general use. These will be found fully set out in any good work on shoeing.
The point that it is correct in theory it would be idle to attempt to evade; but that it is generally practicable, or that it offers any very pronounced advantages, as compared with the disadvantages urged against it, over the shoes in ordinary use, the limited favour it has drawn to itself, since its introduction in 1865, seems sufficiently to deny.
(c) By the Use of a Bar Shoe.—Where the frog is not excessively wasted benefit will be derived from the use of a bar shoe.
FIG. 68.—BAR SHOE.
The transverse portion at the back, termed the 'bar,' and which gives the shoe its name, is instrumental in bringing about from below that counter-pressure on the frog that we now know to be so necessary a factor in remedying contraction. When the frog, by wasting or disease, is so deficient as to be unable to reach the 'bar,' this shoe must be supplemented by a leather or rubber sole.
In the event of corn or sand-crack existing with the contraction, the shoe known as a 'three-quarter bar' is preferable (see Fig. 103). The break here made in the contour of the shoe allows of dressing the corn, and, in the case of sand-crack, removes the bearing from that portion of the wall. (d) By the Use of a Bar Pad and a Heelless or 'Half' Shoe.—The bar pad consists of a shape of rubber composition firmly fixed to a leather foundation, which shape of rubber takes the place of the 'bar' of the bar shoe.