Chapter 18

WOUNDS OF THE KERATOGENOUS MEMBRANE

A. NAIL-BOUND--BIND OR TIGHT-NAILING.

_Definition_.--By the term 'nail-bound' is indicated that accident occurring in the forge in which the nail of the shoe is driven too near the sensitive structures. Although involving no actual wound, it is important to consider the condition under the heading of this chapter, in order that it may be distinguished from the graver accident of a 'prick.'

_Causes_.--Very largely the whole matter of causation turns on the correct fitting of the shoe. The points especially to be noticed in this connection are (1) the position of the nail-holes in the web of the shoe, (2) the 'pitch' of the nail-holes.

Regarding the position of the nails, it goes without saying that the first consideration when 'holing' the shoe should be to punch the holes opposite to sound horn. This remark applies especially to shelly and brittle feet, the type of feet in which tight-nailing most often occurs. The next consideration in this connection is that of punching the holes so that the nail emerges from the upper surface of the web at exactly its correct point of entrance on the bearing surface of the foot. This should be on the white line immediately where it joins the wall. From this position any marked deviation inwards ('fine-nailing,' as it is termed) is bound to give to the nail a direction dangerously near the sensitive structures.

The 'pitch' of the nail-holes should be such that the nail is guided more or less nearly to follow the line of inclination of the wall. Accordingly, the nail-holes at the toe should be 'pitched' distinctly inwards, the inward pitch lessening as the quarters are reached, until the hindermost nail-hole or two is pitched in a direction that is almost perpendicular.

Too great an inward inclination of the nail will, however, give rise to a bind.

It is probable that 'tight-nailing' results more often from fine punching of the shoe than from any fault in the pitch of the hole. Inattention to either detail, however, is apt to bring the mischief about.

Even with a correctly fitted shoe, and with a normal foot, tight-nailing may occur as a result of sheer carelessness on the part of the smith.

_Symptoms_.--Possibly the animal returns from the forge sound. It is on the following day, as a rule, that evidence of the injury is given by the animal coming out from the stable lame. In a well-marked case the foot is warmer to the hand than its fellow, and percussion over the wall will sometimes reveal the particular nail that is the cause of the trouble. Should the shoe be removed, then the fact that the hole the nail has made is far too close to the sole often points out at once the seat of the mischief.

_Treatment_. As to whether or not the shoe should be removed is very much a matter for careful discretion on the part of the veterinary surgeon. Where the foot is shelly and brittle even a good smith sometimes finds himself unable to firmly attach the shoe without verging closely on causing the condition we are now describing. The author has known cases where animals with feet of this description have almost invariably returned from the forge, or rather been found the next day, with a suspicion of tenderness. After the lapse of a day or two this has quite often disappeared, and nothing in the meantime been done with the foot. Seeing, therefore, that removal and refitting of the shoe is in this case attended with risk of breaking away portions of the brittle horn, and so rendering the foot in an even worse condition than it was before, it is policy to decline to have the shoes removed unless worse symptoms make their appearance.

In coming to this decision the veterinary surgeon must be guided by noting in the wall the points of exit of the nails. Should the nail adjoining the position already pronounced to be tender have come out at a higher point than the others, it may be assumed that at a lower position in its course through the horn it has gone near the sensitive structures without actually penetrating the horny box, and that in the course of a day or two the sensitive structures involved will accommodate themselves to the pressure thus inflicted.

If, on the other hand, symptoms of tight-nailing show themselves in an animal with good sound feet, then there is no objection to be raised against having the shoe at once removed. Should the offending nail be definitely detected, then the shoe may again be put on, and that particular nail omitted from the set.

B. PUNCTURED FOOT.

(_Pricked Foot_--_Nail-tread_--_Gathered Nail_.)

_Definition_.--Under this heading we propose describing wounds of the foot occurring in the sole or in the frog, and penetrating the sensitive structures beneath.

_Causes_.--These we shall consider under two headings:

1. Wounds resulting from the animal himself 'picking-up' or 'treading' on the offending object.

2. Cases of pricking in the forge.

Those occurring under the first heading are, of course, purely accidental. In the majority of cases, the object picked up is a nail; but similar injury may result from the animal treading on sharp pieces of wood or iron, on pieces of umbrella wire, on pointed pieces of bones, broken-off stable-fork points, sharp pieces of flint, etc. The same accident may also occur in the forge as a result of the animal treading on the stumps of nails, from treading on an upturned shoe with the stumps of nails _in situ_, or from treading on an upturned toe-clip. It may also occur from an accidental prick with the stable-fork when 'bedding up,' or from casting part of a shoe when on the road and treading on the nails, in this case left sometimes partly in and partly out of the horn.

'Serious wounds of this description are also met with in animals engaged in carting timber from plantations in which brushwood has recently been cut down. This is, of course, from treading on the stake-like points that are left close to the ground. Hunters also meet with the same class of injury when passing through plantations or over hedge banks, where the hedge has just been laid low or cut down.

'Agricultural horses also meet with severe wounds of this class from treading on an upturned harrow.'[A]

[Footnote A: _Journal of Comparative Pathology and Therapeutics_, vol. iv., p. 2.]

It has been remarked how strange it is that nails should so readily penetrate the comparatively hard covering of the foot. The matter, however, admits of explanation. One knows from common observation how easy it is to tilt a nail with its point upwards by exerting a pressure in a more or less slanting direction upon its head. This is exactly the form of pressure that is no doubt put upon the nail if the animal treads upon it when moving at any pace out of a walk. The foot in its movement forward tilts the nail up, and almost simultaneously puts weight upon it. The great weight of the animal is then quite sufficient to account for its ready penetration.

In purely country districts cases of punctured foot are of far less frequent occurrence than in large towns. In the latter, animals labouring in yards where a quantity of packing is done, or engaged in carting refuse containing such objects as we have mentioned, or broken pieces of earthenware or glass bottles, meet with it constantly.

For the manner of causation of those wounds to the foot occurring in the forge the reader may be referred to the matter under the heading of 'nail-bound.' As in that case so in this the nail may be wrongly directed by improper fitting of the shoe, by the 'pitch' of the hole, or by the position of the hole. The nails may also be wrongly directed as a result of faulty pointing, or by meeting with the stump of a nail that has carelessly been allowed to remain in the substance of the horn.

Often pricking is a result of carelessness engendered by a rush of work. Often it is almost unavoidable on account of the character of the foot that is brought to be shod. Feet with thin horn, especially a thin sole, feet with horn shelly and brittle, each in their way are difficult to shoe.

Sometimes pricking is purely accidental, as in the case of a 'split' nail. The nail as it is driven splits at its point, and continues to split down its centre, one half emerging at the correct spot on the wall, the other half bending inwards, and penetrating the sensitive structures.

_Common Situations of the Wound_.--In a case of picked-up nail the common seat of puncture is about the point of the frog, either in one of the lateral lacunæ, in the median lacuna, or the apex of the frog itself. In comparison with this puncture of the sole is rare.

Prick sustained at the hands of the smith may, of course, run in either of the following directions: (1) Directly into the position where the horny and sensitive laminæ interleave; (2) between the sensitive laminæ and the os pedis; (3) into the os pedis itself; (4) the nail may bend excessively immediately after entering the horn, and so pass either between the horny and sensitive sole; or (5) between the sensitive sole and the bone.

_Classification_.--Punctured wounds of the foot may be classified as follows:

_Simple or superficial_ when penetrating no structure of great importance. For instance, a prick that penetrates to the sensitive sole and is not driven with sufficient force to seriously injure the os pedis we may regard as simple. In the same manner a prick to the frog that, although deep, is mainly concerned with penetrating the plantar cushion may also be classed as simple.

_Deep or penetrating_ when driven with sufficient force or in such a direction as to injure structures whose penetration is calculated to give rise either to serious constitutional disturbance or to permanent lameness. In this category we may place injuries to the terminal portion of the perforans, puncture of the navicular bursa, fracture of the navicular bone and penetration of the pedal articulation, and splintering of the os pedis.

_Symptoms and Diagnosis_.--While discussing the symptoms and diagnosis, we will still continue to consider our subject under the two headings of (1) accidental 'gathering' of some foreign body, and (2) pricks inflicted in the forge.

In a few cases belonging to the former class the veterinary surgeon is fortunate in obtaining a direct history of the injury. The driver has seen the animal go suddenly lame, and has examined the foot for the cause. Either the nail has been found embedded in the horn, or the puncture it has made detected, and the matter has been reported. The foot is then explored and the full extent of the injury ascertained.

In many cases, however, it so happens that no evidence of the infliction of the injury is forthcoming. The momentary lameness occurring at the time of the prick is unreported at the time by the attendant, and the horse for a time goes sound. It is not until the changes set up by the subsequent inflammatory phenomena make their appearance, and lameness results, that attention is called to the foot. When this happens there has, as a rule, been time for pus to form around the seat of puncture--a matter of about forty-eight hours.

The horse is now brought out for the veterinary surgeon's examination, going distinctly lame. If the case is well marked there may then be noted by the man of experience many little signs pointing to the foot as the seat of the lameness. These, though well enough known to the practitioner, are nevertheless difficult to describe. It is, in fact, hard to say exactly in what they really consist, appearing to be as much a matter of intuition as of actual observation.

There is a peculiar 'feeling' characteristic in the gait. The affected foot is put forward fearlessly enough, but is not nearly so rapidly put to the ground. When at rest the foot is almost immediately pointed, and the pain at intervals manifested by pawing movements. It is this extreme liberty of the rest of the limb, as evinced during the pawing movements, that really strikes one. Shoulder, elbow, knee, and fetlock are all easily and painlessly flexed and extended. There is nothing wrong with them; it must be the foot. The short manipulation necessary to test the lameness--viz., the walk and slow trot--is sufficient to raise the animal's pulse and quicken the breathing.

All this is enough, and more than enough, to lead the veterinary surgeon to examine the foot. It is hot to the touch, and at the coronet tender to pressure, possibly in a neglected case fluctuating at the heel. Pain is evinced by the animal withdrawing his foot when percussion takes place over the affected spot. In a bad case one gentle tap is all that is needed. The animal at once snatches away his foot, holds it high from the ground, and makes pawing movements in the air. At that moment, too, his countenance is highly expressive of the pain he is suffering. Again the foot is explored, the injury found, and the pus liberated.

Regarding the manner of exploration of the foot we will take first that case in which the veterinary surgeon is called in early, and in which pus has not yet had time to form. Sometimes the merest cleaning up of the inferior surface of the foot then reveals a distinct stab either in the sole or the frog.

If the accident be recent only a little blood will be found, either liquid, or coagulated about the wound. Later there exudes from the stab a flow of yellow, serous fluid. The opening thus found should be carefully probed, and its depth and situation noted.

At other times the prick is not so readily apparent. The nail or other object has penetrated and afterwards withdrawn itself. The natural elasticity of the horn, especially that of the frog, causes it to contract upon the puncture, and to largely obliterate the hole made. What, therefore, may look to be but a simple injury to the horn alone may in reality be the only evidence of a stab complicating the sensitive structures. It thus behoves the veterinary surgeon to follow up and carefully cut out any unnatural-looking mark in the horn, more especially if the horn is discoloured, or if blood is extravasated into its fibres, or there is moisture exuding from the part.

In some cases of this description the knife in the act of paring comes into contact with the cause of the trouble. Sometimes this is a nail, sometimes a sharp and small piece of flint, so deeply penetrated as to have become quite buried. When met with in this manner, however, the foreign body is more often than not a splinter of wood deeply embedded in the cleft of the frog or in the frog itself.

The fact that multiple punctures may occur should here be remembered, and the remainder of the inferior surface of the foot thinly pared.

On withdrawal of the foreign object blood may immediately follow. Should the former have been fixed in position for some time, however, pus is nearly always found at the bottom of the wound. As a rule, its removal is comparatively easy, but one case recalls itself to the author's mind in which the extraction was a matter of considerable difficulty. The offending object was a large, flat-headed nail, some 2 inches long. This was driven fast into the os pedis, and necessitated the employment of a pair of pincers and the exertion of some amount of force to move it from its position.

In this connection it must be remembered that the penetrating object sometimes breaks off after entering the foot. The fact that this occasionally happens only serves to give point to the advice we have previously rendered--that every stab should be carefully probed, and its exact condition and depth ascertained.

In those cases where percussion has led to the positive opinion that pus really exists, then the exploration must be most searching. There may, or may not, be a suspicious-looking mark to work on. In the latter case, the veterinary surgeon must not be content with confining his paring operations to one spot. The sole should be carefully thinned all round, and the thinning cautiously proceeded with until either small, pin-point hæmorrhages denote that healthy sensitive structures have been reached, or a sudden flow of pus indicates that the injury has been definitely located.

While the symptoms remain much about the same, the diagnosis of pricks received in the forge, as compared with those occurring in the natural manner, is easy. The animal starts to the forge quite sound, and returns, perhaps, with a slight limp. The slight limp in two days' time becomes a decided lameness, and no doubt remains as to what has occurred. The mere fact of the lameness arising immediately after a visit to the forge should be sufficient in the majority of cases to lead one to a correct diagnosis.

Where the opinion has been formed that a prick has been received, then the shoe should be removed.

This operation should always be superintended by the veterinary surgeon himself. After the removal of the clinches, the nails should be drawn one at a time with the pincers, and carefully examined. Often the offending nail may thus be picked out by observing upon it blood-stains, or the moisture from inflammatory exudate or from pus. Further inflammation will also be gathered by occasionally meeting with a nail that has split.

At this stage, too, the veterinary surgeon should have noticed whether or not the smith has previously sent the animal home with what is known as a 'draw back.' He has discovered, immediately after he has done it, that he has pricked the animal. He has then withdrawn the nail, and either sent the animal back with that nail altogether missing from the set in the shoe, or with the hole filled up with a stump.

The shoe once off, the holes made by the nails in the horn should be minutely examined for the presence of hæmorrhage, inflammatory fluid, or pus exuding from them, and also for evidence of their correct placing in the foot. Should fluid matter issue from any one of them, or should it be deemed that one has approached too near the inner margin of the white line, more especially if tenderness exists around it, that hole should be followed up with a 'searcher' or small drawing-knife until diagnosis is certain.

_Complications_.--Before proceeding to discuss the complications that may arise in the case of pricked foot, we may call to mind that the anatomy of the parts teaches us that the most serious position in which a punctured wound can occur is at the centre of the foot. Here the plantar aponeurosis, the navicular bursa, the navicular bone itself, or the pedal articulation may be injured.

Anterior to this position the most serious mischief that can ordinarily result is stabbing of the os pedis.

Posterior to the position we have named, the only structure to be injured is the plantar cushion.

Anatomically, then, the inferior surface of the foot may be divided into three zones, as follows:

_A. Anterior_, extending from the toe to the point of the frog.

_B. Middle_, extending from the point of the frog to the commencement of its median lacuna.

_C. Posterior_, including everything posterior to the middle zone.

This division of the inferior surface of the foot into zones will be somewhat of a guide also when describing the complications next to follow:

_(a) Suppuration_.--This is the common complication of most wounds of the foot. When detected, it calls for immediate surgical interference in the shape of removal of the horn of the sole or the frog, as the case may be. This we shall consider further under the treatment.

_(b) Separation of the Horny Frog_.--This is a sequel to pus formation in the sensitive structures immediately beneath it, and the condition makes itself apparent by a line of separation between the horn and the skin of the heel of the injured side.

_(c) Wounding of the Plantar Aponeurosis_.--This occurs when a moderately-deep penetration of the horn of the middle zone has taken place. It is always most painful, especially when complicated by necrosis. The heel is then persistently elevated, and lameness is extreme, in some cases so severe as to cause the leg to be carried altogether.

In favourable cases the necrosed piece of tendon is sloughed off by the process of suppuration, and escapes with the discharges from the wound. There is then an abatement in the symptoms, and recovery is rapid.

Commonly, however, on account of the non-vascularity of the structure of the tendon, the necrotic spot in it tends to spread. The wound is thus led to become fistulous in character, and the pus forming within it prevented from escaping from the original opening. As a result, lameness and fever persist. There is a gradual increase in the severity of the symptoms, and later fistulous openings appear in the hollow of the heel.

_(d) Puncture of the Navicular Bursa_.--This results from a prick in exactly the same position as that last described, and means that the penetrating object has gone deeper, It may be distinguished from puncture of the plantar aponeurosis alone by the fact that there is an excessive discharge of synovia from the wound. This, as it escapes, is at first clear and straw-coloured. Later it becomes cloudy and flaked with pus, and shows a tendency to coagulate in yellowish clots.

Pain and accompanying fever is most marked, much more so than when the plantar aponeurosis alone is injured.

Should the original wound be insufficiently enlarged, or should its opening become occluded by the solid matters of the discharge, then this condition, like the last, ends in the formation of fistulous openings in the heel. These make their appearance as hot, painful, and fluctuating swellings in that position. Later they break, discharge their contents, and leave a fistulous track behind.

_(e) Fracture of the Navicular Bone_.--Penetration of the substance of the navicular bone, _without_ its fracture, adds nothing to the symptoms we have described under puncture of the bursa. That the bone has been reached by the penetrating object may be detected by probing. This, however, must be performed with care, especially if a flow of synovia is absent. Otherwise, the wound, as yet, perhaps, superficial enough to avoid penetrating even the bursa, is made a penetrating one by the probe itself.

Fracture of the navicular bone is fortunately rare.

_(f) Penetration of the Pedal Articulation and Arthritis_.--This we shall consider in greater detail in Chapter XII. It is sufficient here to state that the condition may be suspected when a hot and painful swelling of the whole coronet makes its appearance. There is at the same time a diffused oedema of the fetlock and the region of the cannon, sometimes extending upwards to the whole of the limb.

Of all the complications to be met with in punctured foot this is the one most to be dreaded. The intense pain and the high fever render the animal weak and thin in the extreme. The appetite becomes impaired, sometimes altogether lost, and the patient in many cases appears to die from sheer exhaustion. Added to this is always the extreme probability of the wound becoming purulent, and later the dread of general septic infection of the blood-stream ensuing, and death resulting from that. Even with the happier ending of resolution, anchylosis of the joint and incurable lameness is more often than not left behind. (See Suppurative or Purulent Arthritis,