Diseases of the Horse's Foot · Chapter 51A. Periostitis and Ostitis
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We head this section, Periostitis and Ostitis, 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 instituted does not stop at mere restoration of lost tissue, but continues to the extent of forming an abnormal quantity 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 canals 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 periostitis 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 periostitis 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. PERIOSTITIS.
This we shall consider under (a) Simple Acute Periostitis, (b) Suppurative Periostitis, (c) Osteoplastic Periostitis.
(a) Simple Acute Periostitis.—This is the periostitis 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 passed 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 periostitis caused by pressure of the bulged inner-layer of horn upon the sensitive structures.
Simple acute periostitis 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 pricked foot, of treads in the anterior region of the coronet, and of accidental injuries of other kinds.
In simple acute periostitis 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 canals 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 periostitis 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 Periostitis.—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 periostitis is soon changed into the suppurative form. Once having gained entrance to the wound, the pus increases in quantity, 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 periostitis 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-horny quittor.
In ordinary cases of suppurative periostitis the pus formed is yellow in colour, creamy thick, and free from pronounced 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 periostitis, and in our subjects is nearly always met with in cases of severe prick. 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 succumbs 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 periostitis 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 Periostitis.—This is more particularly a chronic process, and is, as the suffix 'plastic' indicates, associated 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 periostitis 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 periostitis are frequently met with in the bones of the foot, and are described by veterinary writers under such headings as 'Pedal Exostoses,' 'Ossifying Ostitis,' 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 associated with rarefactive osteoplastic ostitis, conditions which we shall shortly describe. Cases we have examined have undoubtedly shown this condition of osteoplastic periostitis, 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 horny box. So far as we are able to ascertain, there is every reason to believe that in chronic laminitis the accompanying periostitis 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. OSTITIS.
We shall next deal with the inflammatory changes occurring in the bones themselves, and shall consider them under (a): Rarefying or Rarefactive Ostitis, (b): Osteoplastic Ostitis, and (c): Caries and Necrosis.
Inflammatory changes occurring in the medulla we may pass 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 Ostitis.—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 ostitis is redder than normal, and the openings of the Haversian canals 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 canals 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 ostitis 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 illustrated 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 Ostitis, 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 ostitis. In this case there is a formation of new bone in the connective tissue surrounding the vessels in the Haversian canals. As a consequence the bone affected is greatly increased in density, and many of the Haversian canals by this means obliterated. The end result is an increase in size of the bones in such positions as the horny 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 pricks 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.
Treatment.—In simple cases of periostitis, those caused by a blow but free from an actual wound, the most beneficial treatment is the continued application of cold by means of a hose-pipe or by swabs. If by these means we are successful in holding the inflammatory phenomena in check, any large formation of new bone is prevented, and the case does well.
When the case is complicated by a wound, then antiseptic measures, such as those described in the treatment of punctured foot, will at the same time have to be practised.
It must be admitted, however, that in all but the most simple cases ordinary treatment such as this is of very little use; for with only a slight exostosis in almost any position in the foot, excessive lameness presents itself and remains. In such cases nothing is left to us but the operation of neurectomy.
When the periostitis and ostitis is the result of a wound, and is complicated by caries or necrosis of the bone, the diseased portion of bone must in every case be laid bare and removed. It so happens that the majority of cases of this kind occur in positions where the diseased bone is easily got at. The lower margin of the os pedis or portions of the wings are commonly the seat of such changes. We meet with the former in cases of pricked foot, and with the latter in severe cases of tread, or as a complication in suppurating corn or in quittor. In such cases the animal must be cast and the foot secured. The wound is then followed up, the horn if necessary removed, and the bone curetted with a Volkmann's spoon; or, if showing itself as a sequestrum, removed with a scalpel and a strong pair of forceps. Care must be taken that every particle of the diseased bone is removed, and that no part of it is left to act as an after-source of irritation. With removal of the diseased portion and a strict attention to antisepsis healing soon takes place.
Reported Cases of Periostitis and Ostitis.—1. 'Figs. 150 and 151 represent the phalangeal bones of the off fore-leg of a thoroughbred horse named Osman, who was well known as a hunt steeplechaser of considerable merit in the Midland counties some twenty years ago. I may say that this horse was under my observation pretty regularly during the whole of his career, and up to the time of his death, from ruptured aorta, when eight years old. My attention was called to him as a yearling by his owner, who told me that he sometimes fancied the colt was lame. I went over to see him, and found that he was unmistakably lame on the off fore-leg. Careful examination showed no heat or enlargement anywhere. I advised rest and the colt became pretty sound, though not quite so—in fact, he never did become quite sound, and sometimes he was very lame indeed.
FIG. 150.—EFFECTS OF PERIOSTITIS ON THE PEDAL AND NAVICULAR BONES.
'Every imaginable sort of treatment was tried short of neurectomy, without avail. The curious part of the case was that there never was much heat or any apparent change of structure, nor was "pointing" a very noticeable feature. The foot always remained a good-looking one. As the horse won a good number of races he was of some value, and was seen by a good many members of the profession, who were by no means unanimous as to the cause of lameness. The favourite theory was that it was a sequence of "split pastern." A post-mortem examination showed that there was no fracture. There was no adherence of the tendon to the navicular bone nor any ulceration. The morbid changes consisted entirely of osseous deposit as shown in the photographs. The under surface of the navicular bone was much enlarged and roughened by this bony deposit, which extended on to the os pedis, causing complete anchylosis at each extremity of the navicular. The lateral cartilages were healthy. The interesting points in connection with the case are the insidious commencement of osseous disease, its extensive development, and the entire absence of any external manifestation, through its being confined entirely within the limits of the hoof.
FIG. 151.—EFFECTS OF PERIOSTITIS ON THE PEDAL AND NAVICULAR BONES.
'It should also be noted that the animal was able to undergo a severe course of training for some years, and to gallop successfully over some of the most trying courses in England. During the whole of this time he walked and galloped apparently sound, but trotted always lame, and generally dead lame.'[A]
[Footnote A: W. E Litt, M.R.C.V.S., Veterinary Record, vol. viii., p. 527.]
FIG. 152.—EFFECTS OF PERIOSTITIS ON THE OS PEDIS.
2. 'I herewith send you photographs of three cases of the above disease, occurring in the internal surfaces of the wings of the os pedis. The photos were kindly done for me by Dr. A. Lingard, Imperial Bacteriologist to Government of India. It is a cause of many cases of obscure foot lameness in India, and frequently accounts for the numerous entries on veterinary medical history sheets under the heading "Contused Foot."
'The course of the disease is as follows: The disease makes its appearance very soon after arrival in India, the animal being admitted to hospital suffering with undoubted foot lameness, generally slight. One is soon led to suspect this disease by negative symptoms of other disease being in existence. No coronary enlargement or flinching on pressure to the coronet, no shrinkage or wiring in of the heels, neither is the characteristic pointing of navicular present. In the early stages one has false hopes of recovery by finding gradual improvement for a time by fomentation and poultices, followed by irrigation and stimulants to the coronet, and perhaps the animal is discharged from hospital, to be returned after a few days worse than ever. The disease then becomes insidious and more pronounced, the nodding of the head, even at a walk, more exaggerated, and, in fact, the animal seems afraid to put his foot to the ground, and much resembles a horse with an abscess in his foot, either from prick or picked up nail. He absolutely nurses his foot. There is a certain amount of heat always present. The disease being now well developed, pressure is caused by the ends of the navicular bone, and they become involved at their points by bony deposits. The causes of this disease I attribute, firstly, to hereditary predisposition; and, secondly the exciting cause, standing confined on board ship, where no doubt pedal congestion takes place. And perhaps some subjects start it in their marches in mobs down country in Australia. Concussion may be the cause among older horses, but the specimens photographed were taken from remounts, that had either done no work or only very gentle work, in a deeply littered riding school.
FIG. 153.—EFFECTS OF PERIOSTITIS ON THE OS PEDIS.
'Treatment.—It is obvious from the position of this disease that treatment will be of no avail in producing a cure. As already stated, the disease is insidious and progressive, and it is hopeless to expect to arrest the growths once they are started. Unnerving would no doubt remove the symptom (lameness) of the disease, but an unnerved horse is not of much good for army purposes. I therefore consider that once the disease becomes firmly established it is an unfortunate and incurable one.
FIG. 154, 155—EFFECTS OF PERIOSTITIS ON THE OS PEDIS.
'Post-mortem reveals the small nodular growths on the inner surfaces of the wings of the pedal bone, and if long established the ends of the navicular bone are also involved. Exudation and gradual growth of false material around the nodules takes place, which also serves to increase pressure.'[A]
[Footnote A: Captain L.M.Smith, A.V.D., Veterinary Record, vol. xi., p. 229.]
3. 'This case was brought for my opinion. The horse was lame, and walked similar to one that had had laminitis, putting the heel down first upon the ground. I ordered the patient to be destroyed. You will note the ossification of the flexor pedis at its attachment to the pedal bone. I enclose photos of the ground, also of the articular, surfaces of the bone.'[A]
[Footnote A: F.B.Jones, M.R.C.V.S., Veterinary Record, vol. xi., p. 230.]