Diseases of the Horse's Foot Part 30

The inferior or solar surface of the foot also offers certain changes for our consideration. The first thing that strikes one is the convexity of the sole. This, as we have already pointed out, is due to descent of the os pedis, and the highest point of the convex portion is that immediately in front of the apex of the frog. Here the horn is sometimes found to be quite yielding to the finger, is excessively thin, and is more or less granular and inclined to break up under manipulation. As a consequence, any rough use of the drawing-knife, or an accidental wounding with sharp flints or stones, leads to exposure of the sensitive structures and local gangrene.

With the horn of the sole thus deteriorated by reason of excessive and continued pressure upon the parts secreting it, it is not surprising to find that, in many cases, actual penetration of it with the os pedis occurs. It is the anterior portion of the inferior margin of the bone that makes its appearance, and shows itself as a small semicircular white or dark gray line on the sole.

[Ill.u.s.tration: FIG. 123.--SOLAR ASPECT OF FOOT WITH CHRONIC LAMINITIS, SHOWING ITS ABNORMAL OVAL SHAPE FROM BEFORE BACKWARDS, AND THE EXCESS OF HORN GROWING FROM THE WHITE LINE IN THE REGION OF THE TOE.]

Exposure of the bone is soon followed by its necrosis, in which case the wound takes on an ulcerating character. From it there is a discharge of pus, black in colour and offensive in smell, and, protruding from the opening, are excessive granulations of the remains of the sensitive sole.

The 'white line,' so apparent when a normal foot is cleaned with the knife, can no longer be sharply distinguished from the surrounding horn, while in some cases the horn composing it takes on an abnormal growth at the toe (see Fig. 123). This adds still further to the abnormal lengthening of the antero-posterior diameter of the foot already mentioned.

In other cases horn in this position is altogether wanting, and in its place is a well-defined cavity, into which the blade of a knife can be readily pa.s.sed. This cavity is bounded in front by the original wall of the hoof, and is here lined by a degenerated and hypertrophied growth of the h.o.r.n.y laminae. Posteriorly the cavity is bounded by the front of the os pedis, and is lined by a thin growth of horn secreted by the keratogenous membrane covering the bone. Superiorly the cavity is quite narrow, and extends to near the lower surface of the coronary cus.h.i.+on, while inferiorly, at its open portion, it is often 1/2 inch to 1 inch wide.

Laterally it extends on each side of the toe to the commencement of the quarters.

[Ill.u.s.tration: FIG. 124.--LONGITUDINAL SECTION OF A FOOT WITH LAMINITIS OF THREE WEEKS' STANDING. On the anterior face of the cavity, in front of the os pedis, are thickened h.o.r.n.y laminae. Due to the sinking of the bony column, the os pedis has perforated the h.o.r.n.y sole.]

Exploration with a director, or with the blade of a scalpel, removes from the opening a dry detritus. This is composed of the solid const.i.tuents of the escaped blood, the dried remains of the inflammatory exudate, and broken-down fragments of cheesy-looking horn. The size to which the cavity may sometimes extend is ill.u.s.trated in Fig. 124. The thickened h.o.r.n.y laminae forming the anterior boundary of the cavity are here depicted, together with commencing perforation of the h.o.r.n.y sole by the os pedis. It is this cavity which, when opened at the bottom and discharging its mealy-looking contents, is known as seedy-toe, for a further description of which see p.

293.

The lameness occurring with chronic laminitis does not always persist. As time goes on the sensitive structures accommodate themselves to the altered form and conditions of the h.o.r.n.y box. In certain situations--namely, where pressure is greatest--the softer structures become atrophied, and sometimes even wholly destroyed; while in other positions the changes in form of the hoof tend to increase in size of its interior, with a consequent diminution of pressure upon, and increased growth of the structures within it.

_Pathological Anatomy_.--In detailing the changes to be observed in chronic laminitis, we take up the description where we left it when dealing with the pathological anatomy of the acute form. The alterations to be met with are best observed by taking a foot so diseased and making of it two sections--one longitudinal, from before backwards; the other horizontal, and in such a position as to cut the os pedis through at its centre.

These sections will expose to view the cavity formed by the pouring out of the exudate, and its full extent may be noticed by examining the sections alternately. Taking the horizontal section first, it will be seen that the hollow s.p.a.ce extends wholly round the toe, and as far back as the commencement of the quarters. In the latter position one is able to observe laminae still in their normal positions and condition. At the toe, however, the h.o.r.n.y and secretive laminae are widely separated, and the s.p.a.ce between them filled with a yellow, semi-solid material, the remains of the inflammatory exudate and new horn secreted by the keratogenous membrane.

The laminae, both h.o.r.n.y and sensitive, are greatly enlarged. This is a hypertrophy, resulting from the continued effects of the inflammation, and leads in time to the formation of laminae quite three or four times their normal size. It is this hypertrophy of the laminae and the pressure of the exudate that causes the bulging and increased growth of the horn at the toe (see Fig. 125), and contributes towards the oval formation of the foot we have mentioned before.

[Ill.u.s.tration: FIG. 125.--LONGITUDINAL SECTION OF A FOOT WITH LAMINITIS OF SEVERAL YEARS' DURATION.]

In the longitudinal section the first thing noticeable is the change in position of the bones, more especially in that of the os pedis. The circ.u.mstances we have mentioned before--pressure of the exudate upon it in front and tension of the perforans on it behind--have caused it to a.s.sume a more upright position than is normal, so much so that in a bad case the front of the bone becomes quite vertical. This vicious direction the other bones of the digit follow (see Fig. 125).

Consequent upon the displacement of the bone, the plantar cus.h.i.+on, by reason of the continued pressure thus put upon it, becomes atrophied, while its hinder half is, as it were, squeezed into taking up a position more posterior and higher in the digit than normally it should. The horn-secreting papillae covering its inferior face thus become directed backwards sooner than downwards, in which way we account in some measure for the noticeable increase of horn at the heels.

_Treatment_.--Chronic laminitis is incurable. Treatment must therefore be directed towards the palliation of such conditions as are present, with the object of rendering the the animal better able to perform work. When perforation of the sole has occurred, with the attendant formation of pus and necrosis of the os pedis, it is doubtful whether treatment of any kind is advisable. There are on record cases of this description, where careful curetting of the exposed and necrotic portions and the after application of antiseptic dressings, held in position by a plate shoe or a leather sole, has been followed by good results, and the animal restored for a time to labour. In our opinion, however, early slaughter is the most economical course to adopt, and certainly the wisest advice to give to the ordinary client.

When perforation of the sole is absent, and when serious alteration in the shape of the h.o.r.n.y box has not occurred, then the most simple treatment is to put the animal straight away to slow work, with the feet protected by suitable shoes.

Here, again, the most useful shoe is the Rocker Bar (Fig. 119). The broad web and deep seating gives ample protection to the convex sole, and with the ease in distributing his weight that this shoe affords the animal is able to perform slow work on soft lands with some degree of comfort.

Should the growth of the horn at the toe and at the heels be unduly excessive, then our attention may be directed towards reducing it to some approach to the normal. This is accomplished by removing with the rasp and the knife those portions indicated by the dotted lines in Fig. 127. Here it will be seen that the bulk of the horn removed is that protruding at the toe. After this the animal should again be suitably shod. In this connection it should be noted that the fact of the animal walking largely on the heels tends to a forward displacement of the shoe. This must be prevented by providing each heel of the shoe with a clip, after the manner shown in Fig. 128; or, in the case of a bar shoe, supplying it with a clip at the centre of the bar.

[Ill.u.s.tration: FIG. 126.--DIAGRAM ILl.u.s.tRATING THE ABNORMAL GROWTH OF HORN AT THE TOE AND HEELS OF THE FOOT WITH CHRONIC LAMINITIS.]

[Ill.u.s.tration: FIG. 127.--THE SAME FOOT AS IN FIG. 126. The dotted lines show the excess of horn removed preparatory to shoeing.]

Among other treatments to be noted we may mention one or two to be found chiefly in Continental works on this subject.

The method of Gross consists in thinning down with a rasp about 1-1/2 inches of the horn of the wall immediately below the coronet, the thinned portion extending from heel to heel. The groove made is filled with basilicon ointment,[A] and the coronet stimulated with a cantharides ointment, In this way there is induced to grow from the coronet a new wall of nearly normal dimensions.

[Footnote A: Basilicon ointment is made by heating together resin 8 parts, beeswax 8 parts, olive oil 8 parts, and lard 6 parts. Allow to cool without stirring.]

By other operators (Bayer, Imminger, Meyer, and Gunther) this treatment has been modified by enlarging upon it and removing the whole of the advent.i.tious horn.

[Ill.u.s.tration: FIG. 128.--THE SHOE WITH HEEL-CLIP.]

This is done by means of the drawing-knife and the rasp, the ugly-looking pumiced foot being carefully cut and trimmed until, so far as outward appearances are concerned, it is perfectly normal. This done, the whole foot is treated with a suitable hoof ointment, and a shoe applied that affords protection to the sole without imposing pressure upon it. The shoe indicated is either an ordinary shoe with an unusually broad and well-seated web, or the seated Rocker Bar of Broad. With either it is well to additionally protect the sole by means of a leather or rubber pad and tar stopping, or by using the Huflederkitt described on p. 148. In every case the nails must be kept well back in order to avoid the weakened and degenerated horn at the toe, and to take advantage of the greater growth of horn at the heels.

The wisdom of thus removing the whole of the advent.i.tious horn may be questioned. Although a foot of a nearly normal shape is obtained, it must be remembered that the grave alterations within it are unchanged, and that in certain positions the operation must have carried us nearer the sensitive structures than is advisable.

All other treatments failing, the operation of neurectomy has been advised.

This we do not think wise. One would imagine that, with degenerative processes already going on in the foot, the tendency to gelatinous degeneration, always to be looked for in neurectomy, would be increased.

This, as a matter of fact, is the case, and is borne out by the statements of those who have tried this method of treatment. In many cases the lameness even is not got rid of. Even where it is, the operation is afterwards followed by a great tendency to stumble, by sloughing of the hoof, or by a marked increase in the advent.i.tious horn, and a consequent greater deformity of the foot.

Sooner than risk neurectomy, it seems to us wiser to give a trial to the operation advocated by M.G. Joly, namely, that of ligaturing one of the digital arteries on each affected foot. This operation is performed in the same position as is the higher operation of plantar neurectomy, and may be either internal or external. The vessel is exposed, and a double ligature, preferably of silk, placed on it. The artery is then divided between the two ligatures. The immediate effect of the operation is to cause a considerable diminution in the arterial pressure, and so lessen the intensity of the ost.i.tis in the os pedis. Its consequences are not so serious as those of neurectomy, and it decongests tissues which neurectomy congests.

In cases related by M. Joly this operation, practised both in conjunction with removal of the excess of horn and without it, has resulted in a marked improvement in the gait, the animal going to work one month after the treatment, and remaining sound for some time afterwards.

2. SEEDY-TOE.

_Definition_.--A defect in the horn of the wall, usually at the toe, but occurring elsewhere, resulting in loss of its substance in either its internal or external layers (see Figs. 129, 130, and 131).

_Causes_.--The most common factor in the causation of this defect is undoubtedly disease of the sensitive laminae. We have, in fact, just given an excellent example of the formation of a seedy-toe in the sections of this chapter devoted to laminitis (see pp. 265 and 286). The cavity here formed by the outpouring of the inflammatory exudate and the separation of the sensitive and h.o.r.n.y laminae persists. It becomes filled with the dried remains of the exudate and perverted secretions from the h.o.r.n.y and sensitive laminae (see p. 287). As yet, however, the cavity is closed below, and its existence only surmised. Later, with successive visits to the forge, the layer of solar horn forming its floor is cut away, and the cavity exposed to view. Its mealy-looking contents are removed, and the case reported by the smith.

Although occurring in this way with an acute attack of laminitis, it must be remembered that seedy-toe may arise without previous noticeable cause.

The first intimation the owner has is a report from the forge that seedy-toe is in existence. To refer to cases so arising a probable cause is far from easy. At one time it was believed to be due to parasitic infection of the horn. Others have blamed the pressure of the toe-clip, excessive hammering of the wall, or pressure from nails too large or driven too close. Others, again, say that seedy-toe may result from a p.r.i.c.k in the forge, from hot-fitting of the shoe, from standing on a dry and sandy soil, or from the use of high calkins on the front shoes. In these cases--cases with an insidious onset--we are inclined to the opinion that the disease of the horn commences from below, and that the sensitive laminae become implicated later. Holding this view, one must account for the commencing disease of the horn by giving, as causes, firstly, those factors (as, for instance, alternate excessive dampness and dryness) leading to disintegration of the horn tubules; secondly, the penetrating into and between the degenerated tubules of parasitic matter from the ground; and, thirdly, the final breaking up of the horn, and spread of the lesion under the invasion thus started.

[Ill.u.s.tration: FIG. 129.--DIAGRAM ILl.u.s.tRATING POSITION OF SEEDY-TOE (INTERNAL). 1, The horn of the wall; 2, the horn of the sole; 3, the cavity of the seedy-toe; 4, the os pedis; 5, the keratogenous membrane.]

_Symptoms_.--Lameness sometimes attends seedy-toe, and sometimes does not.

This is an important point to be carried in mind by the veterinary surgeon who is accustomed in his practice to have many animals pa.s.s through his hands for examination as to soundness. An animal with advanced seedy-toe--a condition const.i.tuting serious unsoundness--may walk and trot absolutely sound, and may give no indication, either in the shape of the wall or the condition of the sole, that anything abnormal is in existence. Later, however, after the veterinary surgeon has pa.s.sed him, the purchaser lodges the complaint that the horse has a bad seedy-toe, which, so he is told, must have been there for some time. In this case, culpable though he may appear, there is every excuse for the veterinary surgeon.

Once the cavity is opened at the toe in the neighbourhood of the white line, then diagnosis is easy. A blunt piece of wood, the farrier's knife, or a director may be easily pa.s.sed into it, sometimes as far up as the coronary cus.h.i.+on (see Fig. 129). Issuing from the opening is seen occasionally a little insp.i.s.sated pus; more often, however, the dry, mealy-looking detritus to which we have before referred. This form of the disease we may term 'Internal Seedy-Toe.' for, plainly enough, it has had its origin in chronic inflammatory changes in the keratogenous membrane.

[Ill.u.s.tration: FIG. 130.--EXTERNAL SEEDY-TOE COMMENCING AT THE PLANTAR BORDER OF THE WALL.]

[Ill.u.s.tration: FIG. 131.--EXTERNAL SEEDY-TOE COMMENCING ON THE ANTERIOR FACE OF THE WALL.]

Disease of the horn and loss of its substance may, however, also commence from without. A report on this condition, under the t.i.tle of 'External Seedy-Toe,' is to be found in vol. xxix. of the _Veterinary Journal_, from which we borrow Figs. 130 and 131.

In Fig. 130 it will be seen that the disease commences at the plantar surface of the toe, and extends upwards and inwards. The same condition may also appear anywhere between the coronet and the ground, gradually extending into the substance of the wall, as shown in Fig. 131. According to the writer, Colonel Nunn, the progress of the disease in this latter case appears to be faster in a downward than in an upward direction. This, however, is more apparent than real, as the rate of growth of the horn downwards detracts from the progress of the disease upwards, although it spreads over the horn at the same rate.

Before concluding the symptoms, we may again allude to the fact that, although usually occurring at the toe, the same condition may be met with in other positions--namely, at either of the quarters. In appearance and in other respects it is identical with that occurring at the toe.

When the animal is lame and the existence of seedy-toe is surmised, or when the cause of the lameness is altogether obscure, a little information may perhaps be gathered from noting the wear of the shoe. If the animal has been going lame for any length of time as a result of disease in the sensitive laminae, then the shoe will be greatly thinned at the heels, and the toe but little worn.

_Treatment_.--As with diseased structures elsewhere, the most rational treatment, when possible, is that of excision. The entire portion of the wall forming the anterior boundary of the cavity is thinned down with the rasp and afterwards removed with the knife, wholly exposing the hypertrophied, but usually soft layer of horn covering the sensitive structures. These hypertrophied portions are also removed, and every particle of the dust-like detritus cleaned away. After-treatment consists in dressing the parts with a good hoof ointment, protecting them, if necessary, with a pad of tow and a stout bandage. It may be that the removal of a large portion of the wall may for some time throw the animal out of work. Acting on Colonel Fred Smith's suggestion, this may be avoided by having made a thin plate of sheet-iron, slightly larger in circ.u.mference than the portion of horn removed, and shaped to follow the contour of the foot. This made, it is sunk flush with the wall by hot-fitting it, and kept in position by several small steel screws fixed into the sound horn, just as in the treatment for sand-crack (see p. 174). This will serve the useful purpose of maintaining in position any dressing that may be thought necessary, of acting as a support to the horn left on each side of the portion removed, and of keeping the exposed structures free from dirt and grit.

Practical points to be remembered in fitting plates of this description to the feet are: The plate must never quite reach the shoe, or it will partic.i.p.ate in the concussion of progression, and so loosen the screws that hold it in place. For the same reason, that portion of the sole adjoining the piece of horn removed must have its bearing on the shoe relieved. The screws holding the plate should be oiled to prevent rusting, and should take an oblique direction in order to obtain as great a hold as possible on the wall.

When excision is deemed unwise or unnecessary, treatment should be directed towards maintaining the cavity in a state of asepsis. To this end it should be thoroughly cleaned of its contents, and afterwards dressed with medicated tow. The ordinary tar and grease stopping is as suitable as any.

This, together with the tow, is tightly plugged into the opening and kept in position by a wide-webbed shoe. Instead of the tar stopping and the tow, there may be used with advantage the artificial hoof-horn of Defay (see p.

152). Before using this the cavity should again be thoroughly cleaned out, and should in addition be mopped out with ether. The latter injunction is important, as unless the grease is thus first removed, the composition will fail to adhere to the horn. With the cavity thus cleaned and prepared, the artificial horn, melted ready to hand, is poured into it and allowed to set.