Diseases of the Horse's Foot Part 28

THE COURSE OF THE DISEASE AND ITS PATHOLOGICAL ANATOMY.--As with most inflammations of any severity, so with this we may consider the pathological changes taking place in the foot under three headings: (a) The period of Congestion; (b) the period of Exudation; (c) the period of Suppuration.

(a) _Congestion_.--In the early stages of laminitis there is a state of engorgement of the vessels of the keratogenous apparatus generally, but more particularly the laminal portion of it. With the hoof removed at this stage the sensitive laminae are found to be swollen, dark red in colour, and affording a distinct feeling of increased thickness when pressed between the fingers, Incised, there escapes from the cut surface a large flow of dark venous-looking blood. At this stage haemorrhages of the laminal vessels occur. The escaping blood infiltrates the surrounding connective tissue, and in many cases destroys the union between the h.o.r.n.y and sensitive laminae. This change is most noticeable in the region of the toe and the commencement of the quarters, the os pedis appearing as though pushed backwards by the escaping fluid collected between the wall and the bone. In severe cases, fortunately but rarely seen, the blood so escaping continues to infiltrate, and separate the tissues until it is seen to be freely oozing at the region of the coronet. (See reported case, No. 1, p. 279.)

(b) _Exudation_.--The period of exudation marks the outpouring of the inflammatory fluid. This, even more than the haemorrhages attending the stage of congestion, tends to destroy the intimacy between the sensitive and the h.o.r.n.y laminae, leading finally to their complete separation at the region of the toe. Fig. 116 ill.u.s.trates this state of affairs after laminitis has existed for a week. The sensitive and h.o.r.n.y laminae are here shown to be distinctly separated from each other, a well-marked cavity existing between them, which cavity is greatest in extent at the toe of the os pedis. With the sensitive structures thus detached from the wall, it is evident that very much that formerly held the os pedis in normal position has been destroyed. What then happens is that the whole of the body-weight is placed upon the sole. Never intended to bear the strain thus imposed, it naturally sinks. With the sinking is a corresponding 'dropping' of the pedal bone--in fact, of the whole of the bony column. Seeing that the structures _above_ the hoof are still normally adherent to the bones, it follows that they must, as the os pedis sinks, be carried with it. As a consequence we get a marked depression at the coronet (see Fig. 117, _a_), which depression may be often noticed after the second or third week of a severe attack of the disease.

[Ill.u.s.tration: FIG. 116.--LONGITUDINAL SECTION OF A FOOT WITH LAMINITIS OF EIGHT DAYS' STANDING. The separation between the sensitive structures and the hoof is indicated by a dark line. The cavity is filled with exudate. It will be noted that as yet there is little change in the position of the os pedis.]

Here, again, though to a greater extent than that caused by the haemorrhage alone, the os pedis appears to be pushed backwards, the s.p.a.ce at the toe between the bone and the h.o.r.n.y box being closely filled with the yellow, slightly blood-stained exudate. This condition is well depicted in Fig.

117.

[Ill.u.s.tration: FIG. 117.--LONGITUDINAL SECTION OF A FOOT WITH LAMINITIS OF FOURTEEN DAYS' STANDING. _a_, The depression at the coronet caused by the dropping of the bony column within the h.o.r.n.y-box: _b_, a portion of the sensitive sole pushed downwards and forwards by the descending os pedis.]

With the descent of the os pedis we get in many cases a penetration of the h.o.r.n.y sole (see Fig. 117), leading always to serious displacement of the sensitive sole (see Fig. 117, _b_), and often to caries of the exposed bone.

The backward displacement of the os pedis may be accounted for in two ways.

Firstly, the greater vascularity of the membrane covering its front leads to a greater outpouring of inflammatory fluid in that particular position.

Here, therefore, loss of adhesion with the wall is greatest, while into the cavity so formed is poured a large quant.i.ty of a fluid that is practically incompressible. The os pedis _must_ be pushed backwards. Secondly, the manner in which the animal distributes his weight--namely, upon the heels--is calculated to aid in the bone's backward movement, for with his feet in this position tension upon the extensor pedis is relaxed, while that upon the flexor perforans is greatly increased.

(c) _Suppuration_.--Should the animal survive the pain and exhausting calls made upon his system by the accompanying fever of the foregoing conditions, the case ends either in resolution or suppuration. When suppuration occurs it is found, as a rule, at the sole, leading to almost entire separation of the sensitive and h.o.r.n.y structures. The pain, if possible, is even worse than in either of the foregoing stages, and relief for the suffering patient is only obtainable by the natural exit of the pus at the coronet, or by giving it escape with the knife at the sole. As a rule, suppuration in laminitis is rare, and then only occurs when the disease has been of some several days' duration. It has been the author's experience, however, to meet with it in a case but three days' old. This particular animal had laminitis restricted to the hind-feet. The condition was diagnosed and pus liberated at the sole of one foot during the third day of the lameness. The animal was cast on the fourth day, and pus obtained from the sole of the opposite foot.

_Complications_.--In a moderate case, carefully treated, laminitis terminates at the end of three or four days in resolution. The general symptoms of fever gradually subside, the appet.i.te returns, and the walk becomes easier. Cases thus terminating fortunately leave behind them no change of serious importance, either in the sensitive tissues or in the h.o.r.n.y envelope. Should resolution, however, be longer delayed, then the case, although eventually terminating successfully so far as soundness in gait is concerned, leaves more or less evidence behind in the shape of rings about the wall and alterations in the build of the sole.

When the happy ending of rapid resolution is denied us, then, in addition to the condition we have described as suppuration, we may meet with one or other of the following complications:

_(a) Metastatic Pneumonia_.--This complication is not uncommon, and, when occurring, more often than not ends fatally. It may be accounted for indirectly by the greater work the lungs are called upon to perform in carrying out the increased number of respirations occasioned by the general fever and pain, and directly by the poisonous materials circulating in the blood-stream.

_(b) Metastatic Colic_.--This may be either a subacute obstruction of the bowel or an enteritis accompanied by an offensive purge.

A striking case of the former is related in the _Veterinary Journal_ (vol.

xvi., p. 180) by H. Thompson, of Aspatria. Here no evacuation of the bowels occurred for three days, and the pains of laminitis were added to by the usual pains of intestinal obstruction.

The colic of enteritis is in some cases caused by the nature of the food, giving rise to laminitis. In our opinion, however, it is more often occasioned by the drastic action of the aloes nearly always resorted to in the treatment of the disorder. As does the pneumonia, the enteritis thus brought about nearly always has a fatal termination.

_(c) Gangrene of the Structures within the Hoof_.--This complication is the one most to be dreaded. It occurs as a result of the great pressure exerted by an excessive exudation, and doubtless affects first the laminae and softer structures. Once commenced, however, it rapidly extends to death of the other structures (ligament, tendon, and even bone), and gives a fatal ending to the case.

That gangrene of the tissues ("mortification" as our older writers called it) has occurred is soon made evident to the veterinarian by the symptoms shown by the patient. The agonizingly acute pains suddenly subside, the feet are placed firmly and squarely to the ground, and the animal walks with ease. Perhaps but the night before the patient is seen racked with excruciating pain; the morning sees the astounding change of apparent absolute recovery. Too well, however, the eye of the experienced veterinary surgeon sees that such is not the case. Even before proceeding to take a record of the other symptoms, he knows that it is but the commencement of the end. Methodically, however, he notes the other conditions. The pulse he finds small and imperceptible, save at the radial. The thermometer registers a subnormal temperature, the extremities are cold, and cold sweats bedew the body. To the same experienced eye the countenance of the animal is almost suggestive of what has occurred. The drawn and haggard expression, to which we have previously referred, becomes more marked, and the angles of the lips are drawn back in what has been described by some writers as a 'sardonic' grin.

We can best express what the whole look of the animal's countenance indicates to us by saying that it gives us the impression that the animal himself knows that some serious change, and a change fatally inimical to his chances of life, has taken place in his feet.

It may be that in some odd cases, although it has not yet been our lot to meet with them, gangrene may terminate in the casting off of one or more hoofs. Needless to say, there can still be but one termination to the case.

_(d) Periost.i.tis and Ost.i.tis_.--This complication is referred to by other writers under the term of 'Peditis.' It signifies, of course, that the periosteum and the bone have become invaded by the inflammatory process.

It is our opinion that these two conditions, even including an actual arthritis, always exist, even in an attack of laminitis that ends favourably. We do not claim, however, to be able to relate any means, save that of post-mortem examination, by which it may be singled out from the other changes occurring in the foot. The high fever and pain occasioned by the inroads of the inflammation into the other sensitive structures serves to effectually mask whatever evidence of it we might otherwise obtain.

It may be sometimes only small in degree, but we feel confident that inflammation, at any rate of the _outer_ layer of the periosteum, is in laminitis constant even, we repeat, in a mild case.

[Ill.u.s.tration: FIG. 118.--SHOWING CHANGES IN THE OS PEDIS WITH LAMINITIS OF LONG STANDING, (_a_, Viewed from the front; _b_, viewed from the side.) The porous condition of the bone, which is here shown, is a result of a rarefying or rarefactive ost.i.tis. This specimen also ill.u.s.trated (what the photograph cannot show) an accompanying condition of condensation of bone, or osteoplastic ost.i.tis. (For a fuller description of the changes occurring in these forms of ost.i.tis, see Chapter XI.)]

When the case is a serious one we have ample evidence to show that ost.i.tis exists, and exists in a severe form. The bones become vastly altered in shape, a process of absorption leads to the formation of large, irregular cavities within their substance, and what of the bone is left is rendered hard and ivory-like (condensed) near what was the original centre, while the edges and other portions show often a tendency to become brittle and porous.

Fig. 118 ill.u.s.trates the effects of a severe ost.i.tis in pedal bones removed from hoofs with laminitis of several weeks' standing.

_(e) Chronic Laminitis_.--The most common complication--or, perhaps, rather we should term it 'sequel'--to acute laminitis is the chronic form of the disease. For this condition we have reserved a separate section of our work. It will be found described in Section B 1 of this chapter.

_Diagnosis and Prognosis_.--One is almost tempted to state that the diagnosis of laminitis offers no difficulty. In the very early stages, however, it may, as we have already indicated, be mistaken for the oncoming of Enteritis, Lymphangitis, or even Pneumonia. The paddling of the feet may help us. If this is absent, however, nothing but a most careful examination, or, if necessary, the withholding of our opinion until the following visit will prevent a blunder being made.

Even when well established, laminitis has been mistaken for paralysis, for teta.n.u.s, for rheumatic affections of the loins, or even for some undiscovered affection of the muscles of the arms and chest. This latter is no doubt suggested to the uninitiated by the reluctance the animal shows to move the muscles _apparently_ of that region, and led the older writers to give to the disease its name of 'Chest-founder.' It is only fair to add, however, that these blunders in diagnosis are nearly always committed by persons without a veterinary training.

Thus warned, the veterinary surgeon of average ability should have no difficulty in establishing a distinction between the diseases we have enumerated as likely to be confounded with it, and the one this chapter is describing.

The prognosis in laminitis should, in our opinion, always be guarded. No advice given in a work of this description can be of any real use, for every case must be judged entirely on its merits. The severity of the symptoms, the cause of the attack, the complications, and the idiosyncrasies of the patient, have all to be taken into account. These the veterinarian must be left to judge for himself.

_Treatment_.--The treatment of acute laminitis in its early stage must be based upon the fact that we have to deal with a congested state of the circulatory apparatus of the whole of the keratogenous membrane. This fact was well enough known to the older veterinarians. It is not surprising, therefore, to learn that jugular phlebotomy was at once resorted to as the readiest means of relieving the overcharged vessels of their blood. As a matter of fact, bleeding from the jugular is still advocated by modern authorities. We cannot say, however, that we unhesitatingly recommend it.

Mechanically, of course, the removal of a large quant.i.ty of blood is bound to result in a lowering of the pressure in the vessels. The effect, however, is but transient. Blood removed in this way is again quickly returned to the vessels so far as its fluid matter is concerned, and the pressure, removed for a time, is again as great as before. With the other and more vital const.i.tuents of the blood-stream--namely, the corpuscles--restoration is not so rapid. We have, in fact, a weakened state of the system, in which it is probable it will not so successfully combat the adverse conditions the disease may induce.

With these prefatory remarks, we may advise bleeding under certain conditions. The quant.i.ty removed must be moderate (7 to 8 pints), and the pulse and other conditions must show no signs of weakness or collapse.

Local bleeding, either from the toe or the coronet, is also advised. In the former situation the sole is thinned down until a sufficient flow is obtained, while at the coronet scarification is the method adopted.

Bleeding locally, however, is far less effectual than the jugular operation. Neither must it be forgotten that wounds in these situations, more particularly at the toe, are extremely liable, especially with the existing poisoned state of the blood-current, to take on a septic character. What might possibly have remained a comparatively simple inflammation is induced by the operation itself to terminate in the more complicated and serious condition of suppuration.

Other means of combating the congested state of the membrane are princ.i.p.ally those of local applications. With many veterinary surgeons warm poulticing is still largely advocated and practised. We do not believe in it. Warmth, as a means of removing local congestion, can only be successful when applied _widely_ round the congested area, and so dilating surrounding bloodvessels and lymphatics. Applied to the congested area itself, and to that alone, it is almost worse than useless.

With the foot, both around and below it, a surrounding area is denied us.

The only vessels we are able to dilate with the warmth, and so enable them to carry off the fluid from the congested foot, are those in the limb above. That poulticing cannot be successfully there applied is self-evident. Apart from that, it is an open question whether poultices may not do actual harm in inducing suppuration in cases where, probably, it would not otherwise occur.

For these reasons we hold to the opinion that when a local application is determined on it should be a cold one. Various methods of applying cold are in vogue. Cold swabs are perhaps most in favour. They must, however, be _kept_ cold. When a suitable water-course, pond, or other expanse of shallow water is at hand, then the animal may be kept standing therein, or preferably walked about in it. When suitable apparatus is obtainable, a constant stream over each foot from a rubber hosepipe is most beneficial.

Astringent baths, containing solutions of alum, of copper sulphate, of iron sulphate, or of common salt, or composed of a mixture of two or more of the salts mentioned, may also be used with advantage. In addition to the fact that such solutions are for a time below the temperature of simple water, we have the advantage that they have also a more or less antiseptic property.

While on the subject of the relief of the congestion, we must not forget to mention a treatment which we ourselves have practised with considerable success--namely, that of forced exercise. It appears to have been first brought into prominence by Mr. Broad, of Bath, and the two terms 'Forced Exercise and Rocker Shoes' and 'Broad's Treatment' have come to be synonymous.

The Broad shoe is a shoe with a web of quite twice the thickness of the animal's ordinary shoe, and has this web gradually thinned from the toe backwards until at the heels the shoe is at its thinnest (see Fig. 119).

The excessive thickness of the shoe serves two purposes. It allows of the requisite amount of slope being given to the web, and so enables the animal readily to throw himself back on to his heels, a position in which, as we have already indicated, he obtains the greatest ease. It also minimizes to some extent the effects of concussion.

[Ill.u.s.tration: FIG. 119.--SEATED ROCKER BAR SHOE (BROAD'S) FOR TREATMENT OF LAMINITIS.]

With forced exercise, as practised by Mr. Broad, this shoe is first applied, and the animal afterwards made to walk upon soft ground, or even upon the roadway, for a half an hour to an hour and a half three times a day.

For our own part, we consider the shoe to be almost if not quite superfluous, so far as its influence upon the progress of the disease is concerned. We therefore dispense with it, and have the animal exercised in his ordinary shoes. To do this, the patient has sometimes to be severely flogged into taking the first few steps. After that progress gradually becomes easier.

It has been said to be cruel. In so far as we knowingly, and of set purpose, occasion the animal pain, cruel it undoubtedly is; but it is cruelty with an aim that is truly benevolent, and the object of our benevolence is the animal upon whom the cruelty is practised.

One word of advice is needed. The forced exercise must be commenced early.

In the later stages, when the stage of congestion has pa.s.sed from that to the acuter stages of the inflammation and the outpouring of the inflammatory exudate, then forced exercise cannot be safely commenced. The loss of adhesion between the pedal bone and the h.o.r.n.y box, which we know to be then existent, negatives its advisability.

By many it is advised to always remove the shoes. From what we have already said, it will be seen that this is not our practice. But one argument in favour of so doing appears to us to carry weight, and that is that 'dropping' of the sole is probably prevented from becoming so marked. That condition, however, is entirely dependent upon the changes occurring within the h.o.r.n.y box. It is bound to occur with the animal shod or unshod, and to reach a stage when only contact with the ground prevents its further descent. The complication then sometimes following--namely, penetration of the sole by the bone, is not prevented by having the shoes removed. It may, in fact, be thus rendered more likely.

Internal treatment consists in the exhibition of suitable febrifuges and the administration of a dose of aloes.