The inferior or wearing margin of the isolated wall must now be so trimmed that it takes no bearing on the ground when the opposite limb is held up by an a.s.sistant and full weight placed upon the foot.

For a day or two after the operation lameness is intense. This is to be treated with hot poultices or hot baths, and and soon disappears. Three to four days later a bar shoe is nailed on (taking care that the bearing of the quarters is still eased), and the hot poultices still continued. Four days later still walking exercise may be commenced, to be followed shortly afterwards by trotting. At about the twelfth day some animals may conveniently be put to work, while in other cases a fortnight, or even a month, must elapse before this can be done. When put to work early, it is wise to fill in the fissures made in the wall with hard soap, with wax, or with a suitable hoof dressing, in order that irritation of the sensitive structures with outside matter may be prevented.

This operation is soon followed by remarkable changes in the shape of the foot. At about the third week the coronet shows signs of bulging, and the upper part of the wall operated on is often so protruding as to render the foot wider here than at the ground surface. This is a sign that the case is doing well.

Should no improvement be noticed at the end of three weeks or a month, or should the grooves become filled from the bottom (which they do remarkably fast), then the incisions must be deepened, the exercise reduced, and the fomentations or poulticing repeated. So treated, many cases of side-bone lameness will be relieved, if not entirely cured, and, should the worst happen, and no alteration in the lameness is noticeable, no harm will have been done to the foot. In this connection, the originator of the treatment says: 'I may a.s.sure those induced to doubt either their diagnosis or the value of hoof section that no harm is done to the foot, even should the operation be of no value. It may do much good; it cannot do harm. The operation will never succeed until the inherent timidity of sawing or cutting into the wall is overcome. The _incisions must be deep, and of the same depth from the coronet to the ground_.'[A]

[Footnote A: _Journal of Comparative Pathology and Therapeutics_, vol.

iii., p. 313.]

It is well to remark here that the operation of hoof section cannot be expected to succeed in every case. The last man in the world to claim that for it would be its originator. Failure to relieve the lameness may be accounted for in a variety of ways. First, of course, will come errors in diagnosis. No one of us is infallible, and the lameness we have judged as resulting from side-bone may arise from another cause. There are, too, complications to be reckoned with, the existence or absence of which cannot always be definitely ascertained. Such are: Ringbone, especially that form of ringbone known as 'low'; bony deposits on the pedal bone, either on its laminal or plantar surface, or even changes in the navicular bursa.

CHAPTER XI

DISEASES OF THE BONES

A. PERIOSt.i.tIS AND OSt.i.tIS.

We head this section, Periost.i.tis _and_ Ost.i.tis, for the reason that in actual practice it is rare for one of these affections to occur without the other. The periosteum and the bone are so intimately connected that it is difficult to conceive of disease of the one failing to communicate itself in some degree to the other. Pathologically, however, and for purposes of description, it is more convenient to describe separately the abnormal changes occurring in these two tissues.

With the main phenomena of inflammation occurring elsewhere we presume our readers are aware. Briefly we may put it, that under the action of an irritant, either actual injury, chemical action, or septic infection, the healthy tissues around react in order to effect repair of the parts destroyed. Also that this reaction involves the distribution of a greater blood-supply to the part, with an abundant migration of leucocytes, and the outpouring of an inflammatory exudate, together with symptoms of heat, pain, redness, and swelling of the affected area. And that in chronic inflammations, owing to persistence of the cause, the process of repair thus inst.i.tuted does not stop at mere restoration of lost tissue, but continues to the extent of forming an abnormal quant.i.ty of such tissue as normally exists in the parts implicated.

The process of inflammation in bone is essentially the same. It takes place along the course of the bloodvessels, and is only modified in its attendant phenomena by the structure of the parts involved. Swelling, for instance, cannot take place in the centre of compact bone tissue. Otherwise, other changes occur exactly as in inflammations of other structures.

When the causal irritant has been excessively severe and the migration of leucocytes abundant, actual formation of pus may occur, the bony tissue being broken down and mingled with it, and an abscess cavity formed. In milder cases, affected and necrotic tissue is removed by a process of phagocytosis, and new tissue (this time osseous) formed in its place.

In the periosteum we may take it roughly that inflammation runs a course similar to that occurring in soft tissues elsewhere. There is but one exception, and that, as we shall mention shortly, is connected with its deeper layer.

As we know, the periosteum consists of two layers, an outer fibrous and an inner yellow elastic, and is extremely vascular. Numerous bloodvessels ramify in it, and, with their attendant nerves, break up to enter the numberless ca.n.a.ls of the Haversian system. This extreme vascularity, of course, favours abundant exudation. The exudate, however, is, as it were, shut in by the dense fibrous layer of the membrane, and the result is that in periost.i.tis it collects between the membrane and the bone, causing swelling and raising of the membrane, and giving rise to excruciating pain from pressure upon the nerves.

Should the periost.i.tis be complicated by the formation of pus, then the vessels entering and supplying the bone are, in the suppurative area, destroyed. With their destruction it may happen that we get also death of a portion of the osseous tissue. This, however, when the suppuration is abundant, cannot commonly occur, as the bloodvessels within the bone--those of the medulla--commence to supply blood to the affected part. In cases of trouble with the bones of the foot, these last few remarks have a special significance. Here we have three bones whose medullary cavity is extremely small--almost nil, in fact--which explains in some measure how easy it is when suppuration exists to get necrosis and exfoliation of, say, portions of the os pedis. Necrosis and sloughing of the periosteum itself may also happen, but as the extreme vascularity of the membrane is a fairly strong safeguard against that it is of only rare occurrence.

In connection with the deep layer of the periosteum, and forming part of it, are found numerous bone-forming cells (_osteoblasts_). These, under ordinary conditions, are relatively quiescent. Under the slightest irritation or stimulation, however, their bone-forming functions are stirred into abnormal activity, thus explaining how easy it is (especially with bones so open to receive slight injuries as are those of the foot) to get ossific deposits, the starting-point of which we are quite unable to account for.

With this brief introduction we will now describe such pathological changes as occur in the separate structures, and which we are likely to encounter in the various diseases of the foot. While so doing, we shall draw attention to such diseases as we have previously described in which the pathological conditions we are considering may be met with.

1. PERIOSt.i.tIS.

This we shall consider under _(a)_ Simple Acute Periost.i.tis, _(b)_ Suppurative Periost.i.tis, _(c)_ Osteoplastic Periost.i.tis.

_(a) Simple Acute Periost.i.tis_.--This is the periost.i.tis that follows on the infliction of a slight injury to the membrane--an injury without an actual wound and free from infective material. It is one, therefore, which we always judge as existing in those cases where we have distinct evidence or history of injury, but in which the injury has not been severe enough to lead to fracture or to the infliction of an actual wound.

Such cases may be those of lamenesses persisting after violent blows upon the foot--cases where the animal has been kicking against the stable fittings, or where the foot has been partially pa.s.sed over by the wheel of a waggon. It may be, too, that in a case of 'nail-bound' a great deal of the pain and lameness is due to a simple periost.i.tis caused by pressure of the bulged inner-layer of horn upon the sensitive structures.

Simple acute periost.i.tis may also occur in cases where an actual wound is in existence, but where such wound, fortunately, remains aseptic. We may thus have this condition accompanying ordinary cases of p.r.i.c.ked foot, of treads in the anterior region of the coronet, and of accidental injuries of other kinds.

In simple acute periost.i.tis the membrane is thicker and redder than normal, and is easily stripped from the bone. As it is pulled off it is noticed that there are numerous fibril-like processes hanging to its inner surface, and which draw out from the substance of the bone. These are simply the vessels (bloodvessels and nerves) which, loosened by the inflammatory exudate, are readily detached and drawn from the Haversian ca.n.a.ls into which they normally run. In addition to its increased redness, the membrane has a swollen and gelatinous appearance owing to its infiltration with the inflammatory discharges. Simple acute periost.i.tis may and often does end in resolution. On the other hand, it may end in suppuration or may become chronic. If the latter, then the osteoblasts of the innermost layer become active, and abnormal deposits of bone are the result.

_(b) Suppurative Periost.i.tis_.--This condition simply indicates that the inflammation is complicated by the presence of pus organisms. It is, therefore, a common termination of the simple acute form attending the infliction of a wound. The wound becomes contaminated, and the case of simple periost.i.tis is soon changed into the suppurative form. Once having gained entrance to the wound, the pus increases in quant.i.ty, and slowly runs between the membrane and the bone. This, however, it does not do to any large extent, showing rather a tendency to penetrate the outer fibrous layer and gain the outside of the membrane.

Suppurative periost.i.tis is met with in foot cases, commonly in connection with punctured foot. It occurs, too, as a complication in suppurating corn, in severe tread, in complicated sand-crack, as a result of the spread of suppurative matter in acute coronitis, and in sub-h.o.r.n.y quittor.

In ordinary cases of suppurative periost.i.tis the pus formed is yellow in colour, creamy thick, and free from p.r.o.nounced odour--the so-called 'laudable' pus of the older writers. It so happens in many cases of foot trouble, however, that putrefactive organisms gain entrance side by side with those of pus. In this case the characters of the discharge are very different. It is distinctly more fluid, is of a pink or even light chocolate colour, and extremely offensive. In these instances the pus shows a marked tendency to spread, strips the periosteum from the bone, perforates the outer layer of the membrane, and finally infiltrates the surrounding tissues.

This forms a near approach to what is known in human surgery as an _infective_ periost.i.tis, and in our subjects is nearly always met with in cases of severe p.r.i.c.k. Its rapidly spreading character makes it always a dangerous condition, and a punctured foot exuding a discharge of this nature should always be regarded as serious. The close contiguity of the joint (it can never be _far_ distant in foot cases), the spreading character of the disease, and the rapidity with which the horse succ.u.mbs to arthritis, are all factors to be taken into consideration, and to lead to a warning-note being struck when attending a case of such kind.

A further instance of infective periost.i.tis is that met with in acute laminitis. The discharge obtained from the sole in these cases very often bears the character we have just described, and when one considers the thinness of the keratogenous membrane, one is bound to admit that changes so grave occurring in it cannot fail to spread and infect the periosteum.

_(c) Osteoplastic Periost.i.tis_.--This is more particularly a chronic process, and is, as the suffix '_plastic_' indicates, a.s.sociated with bone-forming changes in the membrane. It may occur as a consequence of slight but continued irritation, often without ascertainable origin (see Case 2, p. 392), or it may be the sequel of acute disease.

In this form of periost.i.tis the membrane is again swollen and more vascular than in health, and is also easily separable from the bone. The exposed bone is generally rough, in some cases even spicular, and the inner layer of the removed membrane is rough and gritty to the touch--characters imparted to it by numerous minute fragments of bone that have been torn away with it from the more compact osseous tissue beneath.

The results of an osteoplastic periost.i.tis are frequently met with in the bones of the foot, and are described by veterinary writers under such headings as 'Pedal Exostoses,' 'Ossifying Ost.i.tis,' and 'Pedal Ossification' (see Figs. 152, 153, 154, and 155). In many of these cases the disease is purely chronic, and the original cause nearly always wanting. When the foot has been subjected to laminitis of some weeks'

duration, the same condition is also met with, being at the same time a.s.sociated with rarefactive osteoplastic ost.i.tis, conditions which we shall shortly describe. Cases we have examined have undoubtedly shown this condition of osteoplastic periost.i.tis, the rarefactive and osteoplastic changes in the bone itself, met with in older cases, occurring no doubt as a result of non-expansion of the h.o.r.n.y box. So far as we are able to ascertain, there is every reason to believe that in chronic laminitis the accompanying periost.i.tis leads to the formation of bone, and would, if it were possible, lead to increase in the size of the os pedis. If proof were wanted of this, it is only necessary to point out the increased growth at points where resistance is nil--namely, along the upper margin of the bone (see Fig. 118). However, increase in size elsewhere is prevented by the resistance of the hoof, so that, as the bone-forming process progresses, as it inevitably _must_ under the inflammatory changes going on, it is, as it were, compensated for by rarefaction or bone-absorption changes occurring simultaneously with it.

2. OSt.i.tIS.

We shall next deal with the inflammatory changes occurring in the bones themselves, and shall consider them under (_a_): Rarefying or Rarefactive Ost.i.tis, (_b_): Osteoplastic Ost.i.tis, and (_c_): Caries and Necrosis.

Inflammatory changes occurring in the medulla we may pa.s.s without consideration, for in the bones of the foot the medullary cavity is so small, and the changes taking place in it of such minor importance, that we may do this without in any way seriously prejudicing our work.

_(a) Rarefying or Rarefactive Ost.i.tis_.--By this term is indicated an inflammation of the bone attended by its absorption, the absorption being due to the action of certain cells, termed _osteoclasts_. This condition may be due to the pressure of tumours, may occur as the result of injury when a piece of bone is stripped of periosteum, or may be the result of an inflammation occurring in the periosteum elsewhere.

A piece of bone undergoing rarefactive ost.i.tis is redder than normal, and the openings of the Haversian ca.n.a.ls are distinctly increased in size. As a result a greater number of them become visible. Their increase in size is due to the inflammatory absorption of the bony tissue forming them, and in the larger of them may be seen inflammatory granulation tissue surrounding the bloodvessels. This enlargement of the Haversian ca.n.a.ls is well seen when the bone is macerated, the whole then giving the appearance of a piece of very rough pumice-stone.

This process of rarefaction or absorption of bone tissue may be confined to quite a small portion, or it may be spread over the whole of the bone, rendering it more porous than is normal, but stopping short of complete destruction of the bone tissue (a condition which is sometimes known as inflammatory osteoporosis (see Fig. 118)). In this latter case the condition is a chronic one, and the bone tissue remaining often appears to be strengthened by a compensatory process of condensation. For an example of rarefactive ost.i.tis as met with in cases of disease of the feet, we refer the reader to laminitis (see Fig. 118). The osteoplastic or condensing process that appears to exist simultaneously with it explains, no doubt, how it is that bones so affected do not more commonly fracture.

A further example of this process is ill.u.s.trated in Fig. 133. The pressure of a tumour (in this case a keraphyllocele) has led to rarefactive changes in the bone, forming a neat indentation in the normal contour of the bone which serves to accommodate the tumour.

_(b) Osteoplastic Ost.i.tis, Osteosclerosis, or Condensation of Bone_.--This, too, is essentially a chronic process. It may occur as a result of, or, as we have just shown, exist simultaneously with the condition of, diffuse rarefactive ost.i.tis. In this case there is a formation of new bone in the connective tissue surrounding the vessels in the Haversian ca.n.a.ls. As a consequence the bone affected is greatly increased in density, and many of the Haversian ca.n.a.ls by this means obliterated. The end result is an increase in size of the bones in such positions as the h.o.r.n.y box admits of it, and a peculiar ivory-like change in their consistence.

For an example of this, we again refer the reader to the changes occurring in chronic laminitis.

_(c) Caries and Necrosis_.--_Caries_ is a word which appears to be used with a considerable amount of looseness. In addition to the meaning implied by necrosis (namely, 'death' of the part), caries is generally used to indicate that there is also a condition of rottenness, decay, and stench.

It is particularly applied, in fact, when the death of the bone is slowly progressive, and is due to the inroads made upon it by putrefactive or septic matter.

_Necrosis_ of bone may be the result of any injury, such as severe blows, or p.r.i.c.ks and stabs. In such cases it would appear that it is loss of a portion of periosteum that is the starting-point. With death of a portion of this membrane the vascular supply to a portion of the bone is cut off, and necrosis ensues. It may also result from the extension of inflammatory affections of the structures adjoining it, as, for instance, the spread of the infective material in severe tread, or the encroaches made by pus in cases of quittor, suppurating corn, or complicated sand-crack.

When the necrosed portion of bone is small, and is free from infective properties, it is quite possible that it may, as is the case with small spots of necrosis in softer tissues, be removed by a process of absorption.

It must be remembered, however, that where the necrosis has occurred as a result of septic invasion this cannot be looked for, for in every case such reparative changes are worked solely by healthy tissue. If the tissues around the necrosis are engaged in dealing with organismal invasion and the poisonous products thus poured into their working area, their state of health is so weakened that they are unable to successfully combat with the two conditions simultaneously. As a consequence, the necrotic piece of bone persists, and acts as a permanent source of irritation.

It must be remembered, too, that if the dead portion of bone--even though it be free from septic matter--is very large, that it may itself act as a continual irritant, in which case it again persists, and cannot by natural means be removed.

In our cases necrosis of bone may be met with in punctured foot, in severe cases of tread, in cases of complicated crack, and in suppurating corn.

It is met with, too, in navicular disease, in the extension of irritating discharges in cases of quittor, and in cases of chronic laminitis where the solar margin of the os pedis has penetrated the sole. In this latter case the protruding portion of bone is quickly denuded of its periosteum. Its blood-supply is destroyed, and necrosis follows.