Diseases of the Horse's Foot Part 38

Perhaps the best advice we can give is to say that the whole of the cartilage must be manipulated both with the foot _on_ and _off_ the ground.

What the reason may be we do not pretend to say, but it is a well-known fact that in many instances the cartilage, with the foot bearing weight, is so rigid as to at once convey the impression that ossification has commenced or is even far advanced. And yet that same cartilage, with the foot removed from the ground, is as pleasantly yielding to pressure of the thumb as the most exacting of us could wish for. In any case, then, where doubt exists, the foot should be lifted to the knee, and the cartilage carefully examined with the foot in that position. If, then, at any spot above the normal contour of the os pedis we meet with hardness or rigidity, we are to look upon that foot with suspicion. Nevertheless, providing our conscience is sufficiently elastic, the animal may be pa.s.sed _sound_ so far as the _existence_ of a side-bone is concerned. We know, however, that with commencing rigidity we may ere long expect one, and if our opinion is asked with regard to that particular, it must be admitted that with rigidity of the cartilage once commenced it is usually not long afterwards before a fully-developed side-bone makes its appearance.

As is only to be expected, the first noticeable hardening of the cartilage is to be found near the normal bone. We may thus look for it more particularly in the lower portions of the cartilage. We think we may say, too, that in the vast majority of cases the ossification of the cartilage commences in its anterior half. It is thus brought about that often we are called upon to examine and report on the condition when we have _anteriorly_ a side-bone in course of formation, and _posteriorly_ a perfectly normal cartilage. It is to the latter half of the cartilage that dealers and others mainly, if not wholly, devote their attention. A horse with the cartilage in this transition state will therefore pa.s.s muster, and a nice little point of ethics has again to be decided by the veterinary surgeon before giving his signature to a certificate of examination of an animal in this condition.

With regard to alteration in gait, we may say at once that side-bones in heavy animals are not often the cause of lameness. In fact, where the foot is well developed, when neither the foot as a whole nor the phalangeal bones give evidence of disease, and where the pasterns are fairly oblique and well formed, this alteration of the cartilages may be looked upon as of no serious import at all. Neither is the side-bone due to blows or other injuries likely to be productive of lameness--that is, always supposing, of course, that the foot in other respects is of good shape. If lameness is met with at all, then it is where we have a foot that is in other respects unsound, with badly contracted heels and upright 'stumpy' hoof, or where side-bones have occurred in a young animal, and have already reached a large size before the horse is put to labour. In this latter case, the added effects of concussion and the evil influences of shoeing are sufficient to turn the scale. Directly the animal, previously sound, is asked to work, lameness is the result.

It follows, therefore, that side-bone in the feet of young animals is of far more serious import than when occurring in older horses. In a nag animal they const.i.tute a positive unsoundness, and lameness in this case is more often than not an accompanying symptom.

_Causes_.--To commence with, we may remark that, although met with sometimes in very early life, side-bones are seldom, if ever, congenital, and that more often than not they may be looked for in animals of three years old, or older, seldom earlier. They appear, in fact, only when the animal is shod and commences work.

This at once suggests two of the princ.i.p.al factors in their causation--namely, concussion and loss of normal function. Directly the horse is put to work he has for a great part of his time to travel upon roadways--either macadamized roads or town sets--where everything is calculated to bring concussion about. In addition to that he has the lateral cartilage itself thrown largely out of action by shoeing. We explained in Chapter III. (p. 66) that the chief function of the cartilage was to take concussion received by the plantar cushion and direct the greater part of it outwards and backwards. Now, with the animal shod, the plantar cushion does not itself, as normally it should, receive concussion.

By the shoeing the frog is lifted from the ground, and the plantar cushion, together with the cartilage, taken largely out of active work. In other words, the normal outward and inward movements of the cartilage are enormously reduced.

It is fair, we think, to take it that the mere fact of the lateral cartilage persisting _as_ cartilage is due in large measure to its constant movement. Directly, therefore, it is placed in a state of comparative idleness, then it commences to ossify, more particularly if there should at the same time be a tendency to a low type of inflammation of the parts.

Does this latter exist? We may safely say that it does. It is in this way: The secondary effect of loss of ground-pressure upon the frog and plantar cushion is to bring about contraction of the heels. With this we get compression of the parts within, with a certain amount of irritation and the exact low type of inflammatory phenomena calculated to a.s.sist in the bone-forming process.

The fact that concussion acts as a cause explains in great measure how it is that side-bones are more frequent in cart animals than in nags, and also why they should be more common in the fore-feet than in the hind. Taking, in both animals, a rough calculation as to the weight of body carried by feet of a certain size, we notice at once that the cart animal has proportionately more weight to carry than has the nag. Concussion to the foot is therefore greater. The greater part of the body-weight is borne by the fore-limbs. Concussion is therefore greater to the fore-feet than to the hind.

This, however, does not explain altogether the comparative immunity of the nag animal from this defect. He, too, must also be subject to the effects of concussion, especially when his higher and faster action is taken into account. To our minds there is only one explanation to be offered here. We point at once to the years of constant and judicious breeding of the nag.

Compare that with the relatively few minutes that have been devoted to a more careful selection of the cart animal, and we at once see a possible explanation. That the explanation holds some amount of truth is borne out by the fact that, since a greater attention has been paid to the selection of our cart animals, side-bone has grown a great deal less common.

Is side-bone hereditary? We can best answer that by saying that, some several years ago, the Council of the Royal College of Veterinary Surgeons, at the request of the Royal Commission on Horse Breeding, drew up a list of those diseases 'which by heredity rendered stallions so affected unfit as breeding sires,' and that in that list was included side-bone.

Side-bones, therefore, are hereditary. We think, however, the statement needs qualifying. It is in this way: side-bones occur only at a certain, usually well-defined, time after birth, and we might say are _never_ congenital. They occur only after the animal has been put to work, and are more or less plainly due to mechanical causes--namely, the ill effects of shoeing and concussion. The cause of their appearance, in short, is more plainly extrinsic than intrinsic, and side-bone in the horse is, as Professor McCall puts it, about as much due to heredity as is corn on the human foot.

Between these two opinions--that they are plainly hereditary, and that they just as plainly are not--it is well to strike a middle course. They are, we will say, hereditary in this way: So long as a cart animal is bred, to put it vulgarly, 'top-heavy' (that is, with a body out of reasonable proportion to the feet that have it to support), so long will the foot be subjected to a greater concussion, and so long will side-bones in such animals commence to make their appearance at about middle life.

In addition to the causes we have now mentioned, side-bones are often the result of other diseases of the foot. They thus occur as a sequel to sub-h.o.r.n.y quittor, to suppurating corn, to complicated quarter sand-crack, or to the inflammation of the parts occasioned by a p.r.i.c.k. They also arise in many instances from the effect of a p.r.i.c.k or injury to the coronet.

Among the latter we may mention treads from other animals, and treads inflicted by the animal himself with the calkin of an opposite shoe, or the repeated injury occasioned by the shafts being carelessly allowed to drop on to the foot. In severe cases of laminitis, too, the cartilages are nearly always affected. In this instance the inflammatory phenomena in the os pedis no doubt give rise to an abnormal activity of bone-forming cells.

The cartilage is invaded, and the side-bone formed (see Fig. 118).

_Treatment_.--In the ordinary way the 'treatment' of side-bone is a thing but rarely mentioned. The explanation lies, of course, in the fact that side-bones are so rarely the cause of lameness. When lameness does occur with a side-bone, and we have reason to believe that the said side-bone is the cause of the lameness, it is well before talking of treatment to question ourselves thus: 'In what way does the side-bone cause lameness?'

The now generally-accepted answer to that query is the explanation put forward several years ago by Colonel Fred Smith--namely, that the pain, and therefore the lameness, was due to the compression of the sensitive laminae between the ossified and enlarged cartilage and the non-yielding and often contracted wall of the quarters. That, in fact, const.i.tutes the basis upon which Smith's operation for side-bone (that of grooving the wall of the quarters) is founded.

Before describing the operation, however, we may say that we are now able to understand that older operators who claimed success for other methods of treatment, were to a very great extent justified in so doing.

For instance, take the combined treatments of firing and blistering, and the use of a bar shoe. Here the beneficial action of the cautery and the blister may be largely problematical. The bar shoe, however, would be almost certain to give good results. Frog-pressure with the ground would be again restored, and the contraction of the heels removed. Pinching of the sensitive structures would be diminished, and the lameness cured.

Take, again, the treatment of 'unsoling.' It was barbarous, we know barbarous, because unnecessary and easily avoidable. It was practised, however, certainly very little more than two decades ago, and practised by men of standing in the profession. Without dragging the case to light again by mentioning the names of those concerned, we may mention that not many years ago a highly respected member of the profession was, at the instigation of the Royal Society for the Prevention of Cruelty to Animals, prosecuted for practising unsoling for the relief of side-bone. Practically only one other member of the profession was able to come forward and defend the operation on the score of its utility. We see now, however, that--as does Smith's operation--unsoling does permit of the greater expansion of the heels. The contraction is done away with, the pressure on the sensitive laminae again diminished, and the lameness relieved.

Not that we are attempting to defend the operation--far from it. We simply mention it as interesting, and quote this and the use of the bar shoe (with both of which methods older operators have claimed success) merely as evidence that the operation of Smith is based on a logical foundation.

When treatment is decided on, therefore, we may first advise blistering and the use of a bar shoe. After that, should the lameness continue, and should we still judge the side-bone to be the cause of it, the operation may be advised.

As we have said before, the operation consists in so grooving the wall as to allow of the quarters widening sufficiently to relieve pressure on the parts within. In one or two previous portions of this work we have considered operations involving this procedure. Before detailing the operation here, therefore, we will first describe the instruments necessary, and the most satisfactory methods of incising the horn.

To begin with, it must be remembered that all methods of hoof section have for their object the after-expansion of the h.o.r.n.y box, and that this can only be brought about by making each groove complete from coronary margin to solar edge of the wall, and carrying it, throughout its length, _deep enough to reach the commencement of the sensitive structures_.

To this end, therefore, the operator must bear in mind the comparative thickness of the various parts of the wall, and must, in particular, remember the relative thinness of that portion of horn forming the outer boundary of the cutigeral groove, and accommodating the coronary cushion.

For the making of the incisions there is the special saw devised for this operation by Colonel F. Smith, A.V.D., and which we ill.u.s.trate in Fig. 144.

With this the wall is sawn through _until the depth arrived at is equal to what is indicated by a previous examination of the thickness of the crust as viewed from the solar surface_. Here Colonel Smith says: 'I strongly advise everyone to use a metal gauge (a thin piece of material) to introduce into the incision made by the saw, and run it up and down to ascertain whether the wall is properly divided throughout. The depth to which this should be done we know from the previous measurements of our gauge on the crust.'

[Ill.u.s.tration: FIG. 144.--SMITH'S SIDE-BONE SAW (EARLY PATTERN).]

Should the saw be of a pattern in which the set of its teeth makes only a narrow incision,[A] it should, while operating, be kept well oiled, and should be withdrawn every few seconds in order that the horn-dust lying in its teeth may be examined. If this is getting slightly blood-stained, we know, of course, that the sensitive structures are reached, and the incision has been carried far enough. In so judging the depth of the incision, however, care must be taken to see that the top of the coronary cushion is not injured with the saw, for if this is done the blood trickling into the depth of the incision will tinge the horn-dust, and give the false impression that the incision is sufficiently deep.

[Footnote A: That is Smith's older pattern. The newer pattern (Fig. 145) has the teeth so set as to make an incision wide enough to be looked into.

In this case the depth arrived at is to be judged by the appearance of the bottom of the incision.]

If the operator has had no previous experience of the use of the saw in this operation, he must also be careful to avoid placing too great a pressure on the teeth of its lower third. This is done by keeping the hand too greatly depressed. Again, this leads to wounding of the sensitive structures (this time at the lower end of the incision), and again the operator is confused by the blood thus allowed to run into the groove.

The only portion of horn difficult to operate on is that immediately under the coronet. This is best severed with a succession of downward movements, and is easier performed with Smith's later pattern of side-bone saw (Fig.

145) in which the set of the foremost teeth is reversed.

[Ill.u.s.tration: FIG. 145.--SMITH'S SIDE-BONE SAW (IMPROVED PATTERN).]

In making these grooves we must say that we think the use of the special saw may be dispensed with, and the incisions just as easily, or, at any rate, just as successfully, made with the knife. Those who select to use this instrument should choose a narrow-topped and sharp searcher, or a modern shaped drawing-knife of suitable size, such as those depicted in Fig. 46, _a_ and _b_, and they will find their work much easier if they will make the first steps in the incisions with an ordinary flat firing-iron. By the use of the latter instrument the grooves are made conveniently open along their tops, and room left for nicely finishing the more delicate manner of removing with the knife the softer horn near the sensitive structures.

Those whose leaning is towards the use of special instruments, but who, at the same time, do not care to use the saw, will find their wants supplied in the hoof plane (Smith's), Fig. 146, or the hoof chisel (Hodder's), Fig.

147. With the hoof plane the groove in the wall is made by a succession of downward sc.r.a.ping movements, while with the chisel the cut in the wall is made either from below upwards, or from above downwards, according as the foot is held forward or backward--whichever, in fact, comes most convenient.

[Ill.u.s.tration: FIG. 146.--HOOF PLANE (SMITH'S).]

When using the knife or the hoof plane it is not often that the sensitive structures are injured. In all cases, however, no matter what the instrument used, the metal gauge should be employed when the sensitive structures have been touched, and the operation obscured by blood.

[Ill.u.s.tration: FIG. 147.--HOOF CHISEL (HODDER'S).]

Our instruments at hand, the operation may be proceeded with. The first step is to ascertain the extent of the side-bone, and to determine the position of the incisions. To do this the coronet is felt with the thumb, and the anterior extremity of the side-bone noted. This is marked on the horn with a piece of chalk, and a vertical line dropped from this position to the inferior margin of the wall (Fig. 148,1). The line crosses the horn fibres obliquely, and is purposely made in that direction in order that its inferior end may be far enough back to avoid the last nail-hole. Should the side-bone reach very far forwards, it may be wise to cause this line to slant from before backwards (see dotted line _a_, Fig. 148). Unless this is done, it is found that in some feet so much of the wall is isolated at the bottom that insufficient is left to nail the shoe to.

The next line to be made is the rear one. Its correct position is ascertained by first noting the junction off the wall with the bar (see groove 2, Fig. 149); and its inferior end must be just anterior to the inflexion of the wall. This is done that we may avoid cutting the bar. The position of the lower end of the rear line thus ascertained, it is run upwards with the chalk in the direction of the horn fibres.

[Ill.u.s.tration: FIG. 148.--DIAGRAM ILl.u.s.tRATING THE POSITION OF THE GROOVES IN THE WALL IN COLONEL SMITH'S OPERATION FOR SIDE-BONE. 1,2, and 3, mark the grooves in the order in which they are made; the dotted line _a_ marks the position taken by the anterior line when the side-bone, is one reaching far forward, while the dotted lines _b_ and _c_ mark the position of the additional grooves to be made if thought necessary.]

The third line is made in such a position as to divide into two equal portions the wall between lines 1 and 2. Here, however, some operators prefer to make two, or even three, lines, adding those as at _b_ and _c_, Fig. 148; and Smith himself says that a multiplicity of lines is an advantage rather than not.

In any case, having once determined the position of the lines, they should be plainly marked out with chalk, and then viewed from a distance with the foot on the ground, in order to judge of their regularity. If we are satisfied with them, we then lightly mark them with the saw, with the hot iron, or with the knife, whichever instrument we may be intending to use.

Unless the details are methodically carried out as here described, it is probable that more of the foot will be isolated than is necessary, and that as a consequence very little is left to which to nail the shoe.

[Ill.u.s.tration: FIG. 149.--DIAGRAM ILl.u.s.tRATING THE POSITION OF THE GROOVES MADE IN THE HOOF IN COLONEL SMITH'S OPERATION FOR SIDE-BONES. 1, 2, and 3, show the grooves in the wall in the order in which they are made; 4 shows the groove made at the junction of the sole with the wall.]

The incisions are then made with the saw or the knife, with the foot held in a convenient position by an a.s.sistant. That usually found most comfortable for the first incision is with the foot held forwards and placed on an a.s.sistant's thigh in the position adopted for 'clenching up'

when shoeing, while that for the rear incision is with the animal's knee flexed, and the foot held well up to the elbow. In this, however, each operator will suit himself.

Should the preliminary steps in making the incisions be performed with the iron, it will be easiest done with the foot on the ground.

When the incisions through the wall are complete, our attention must be given to the sole. A drawing-knife is here used, and a further incision made over the white line so as to destroy the union of the sole with the wall between incisions 1 and 2, and so completely isolate the portions of wall included within the four grooves (see groove 4, Fig. 149). When this is done it should be found that the portions of the isolated wall spring readily to pressure of the thumb.