10. What are the different forms of ring-bone? Give the causes and treatment of ring-bone.
CHAPTER XVII
DISEASES OF THE FOOT
GENERAL DISCUSSION.--The foot of the horse as generally spoken of, includes the hoof and the structures that are enclosed by it (Fig. 36). It may be divided into three parts, the insensitive and sensitive structures and the bony core. The _insensitive foot_ or _hoof_ is divided into wall, sole, frog and bars. The _sensitive foot_ is divided into vascular tissue and elastic apparatus. The vascular tissue is in turn divided into coronary cushion, laminae and velvety tissue. The elastic apparatus is divided into plantar cushion and fibro-cartilages. The _bony core_ is formed by the navicular and third digital bones. The hoof and vascular tissue in turn enclose the elastic apparatus and bony core.
[Illustration: FIG. 36.--Photograph of a model of the foot: wall; sensitive tissue; plantar cushion, inferior dark portion, sole and frog; lateral cartilage; and pedal bone.]
THE WALL forms that portion of the hoof seen when the foot rests on the ground (Fig. 37). It is covered by a thin layer of horny tissue, the _peripole,_ that coats over the wall and assists in preventing its drying out. On lifting the foot and examining its inferior surface, it is noticed that the wall at the heels is inflected under the foot and in a forward direction. This portion of the wall is termed the _bars._ Within the bearing margin of the wall and in front of the bars is a thick, concave, horny plate that forms the _sole._ At the heels and between the bars is a wedge-shaped mass of rather soft horny tissue that projects forward into the sole. This is the _foot pad_ or _horny frog._ It is divided into two lateral portions by a medium cleft.
THE CORONARY CUSHION projects into the upper border of the wall. It is covered with vascular papillae which secrete the horny fibres that form the wall. The _vascular laminae_ are leaf-like projections, the sides of which are covered by secondary leaves. _Horny laminae_, arranged the same as vascular laminae, line the wall. These two structures are so firmly united that it is impossible to tear them apart without destroying the tissue. The _velvety tissue_ covers all of the inferior surface of the foot, with the exception of the bars. As the name indicates, its surface is covered by vascular papillae that resemble the ply on velvet. It is firmly united to the horny sole which it secretes.
[Illustration: FIG. 37.--Foot showing neglect in trimming wall.]
The lateral cartilages are attached to the posterior angles of the pedal bone. They are flattened from side to side, and the portion that projects above the coronary cushion may be felt by pressing on the skin that covers it. The _plantar cushion_ is a wedge-shaped piece of tissue formed by interlacing connective-tissue fibres and fat. It is limited on each side by the lateral cartilages. Its inferior face is moulded to the frog.
THE BONY CORE formed by the last bone of the digit and the coffin bone was described briefly with the other foot bones. A very important bursa, because it is so frequently inflamed in coffin-joint lameness, facilitates the gliding of the flexor tendon over the navicular bone before it becomes attached to the inferior face of the pedal or digital bone.
SIDE-BONES.--This is a chronic inflammation of the lateral cartilages of the foot that results in their ossification (Fig. 38). This unsoundness is common in heavy horses, especially if worked on city streets. The inflammation affects the cartilages of the front feet, rarely those of the hindfeet.
_The hereditary tendency_ toward the development of side-bones is an important predisposing factor. It is not uncommon to meet with this unsoundness in young horses that have never been worked. Low, weak heels, flat, spreading feet, or any other faulty conformation of the foot are predisposing factors.
[Illustration: FIG. 38.--A very large side bone.]
The character of the work is an important _exciting cause._ Continuous work over paved streets, especially if the horse is shod with high-heeled shoes, increases the shock received by the elastic apparatus of the foot. This produces more or less irritation to the lateral cartilages, which may result in their complete ossification. Punctured wounds in the regions of the cartilage may cause it to become inflamed and changed to bone.
The following _symptoms_ may be noted. Farm horses that have side-bones seldom show lameness. This is because they are worked on soft ground and not on a hard street or road. Driving and dray horses may step short with the front feet, or show a stilty action. This may disappear with exercise.
The lameness is sometimes marked. The local diseased changes are the greatest help in the recognition of side-bones. Horses should not be passed as sound without making a careful examination of the lateral cartilages.
This examination is made by pressure over the region of the cartilage with the thumb or fingers. This is for the purpose of testing its elasticity. If it feels rigid and rough, the cartilaginous tissue has been replaced by bony tissue, and the animal should be classed as unsound.
_The treatment_ is largely preventive. Horses with side-bones should not be bred. It is not advisable to use horses with side-bones on the road or city streets. Shoeing with rubber pads may help in overcoming the concussion and relieve the lameness. Sectioning the sensory nerves going to this portion of the foot is advisable in driving horses. Rest and counterirritation relieve the lameness for a short time.
NAVICULAR DISEASE.--In navicular disease the bursa, flexor tendon, and navicular bone may become chronically inflamed. Because of the seat of the lameness, it is commonly known as "coffin-joint" lameness. This disease affects standard and thoroughbred horses more often than it does the coarser breeds. One or both front feet may be affected (Fig. 39).
_Hereditary causes_ are largely responsible for navicular disease. The tendency toward this disease probably depends on such peculiarities of conformation as narrow, weak, high heels, long pasterns and too long a toe.
The character of the work is an important factor. Hurried, rapid movements throw considerable strain on the navicular region, increasing the danger from injury. This is, no doubt, one reason for "coffin-joint" lameness being more common in driving and speed horses than in slow-going work animals. Rheumatic inflammation, bad shoeing and punctured wounds in the region of the bursa many cause it.
[Illustration: FIG. 39.--A case of navicular disease involving one front foot. The diseased foot is the smaller.]
The _first symptom_ usually noted is a tendency to stumble. When standing in the stable, the animal "points" or rests the diseased foot. Sometimes it rests the heel of the lame foot on the wall of the opposite foot. If both feet are affected, the animal may rest them alternately, or take a position with both feet well in front of the normal position. The inflamed structures are so covered by other tissues that it is difficult to detect the local inflammation, or cause the animal to flinch by applying pressure over the region. As the disease becomes more advanced, the lameness becomes permanent. The limb is carried forward stiffly and rapidly and the animal stumbles when travelling over rough ground. In time, because of the little weight thrown on the posterior portion of the foot, the quarters may become higher, contracted and more upright and the frog smaller. If one foot is diseased, it becomes smaller than the opposite foot.
The following _preventive measures_ may be recommended. We should not use animals having faulty conformation of the feet for breeding, because the offspring of such individuals have an inherent tendency toward navicular and other foot diseases. Animals that have "coffin-joint" lameness should be allowed to run in pasture as much as possible, because natural conditions help to keep down the inflammation and soreness and promote a more healthy condition of the foot. In shoeing the horse it is best to shorten the toe and raise the heel. It is advisable in the more favorable cases to cut the sensory nerves of the foot. This operation destroys the sensation in the foot, and should not be performed on feet with weak heels, or that are wide or spreading.
[Illustration: FIG. 40.--An improperly shod foot; note the manner in which the wall is cut away at the toe.]
CONTRACTED QUARTERS.--This condition of the feet is characterized by the foot becoming narrow in its posterior portion. One or both of the quarters may be affected. It is principally observed in the forefeet.
The _causes_ of contraction of the foot may be classed as _predisposing_, _secondary_ and _exciting_. It may accompany chronic diseases of the foot, such as navicular disease and side-bones. Weak heels is the principal predisposing factor. Any condition that tends to prevent the hoof from taking up moisture, or causes it to lose moisture, may cause the horn to lose flexibility and contract. This is one of the reasons why horses that are worked continuously in cities, or used for driving, frequently develop contracted feet. Ill-fitting shoes, excessive rasping of the wall and bars, and allowing the shoes to stay on the foot for too long a time are responsible to a very large degree for this disorder of the foot (Fig. 40).
The following _local symptoms_ may occur: The wall of the foot at the quarters may appear drawn in at its superior or inferior portion. Sometimes one or both quarters are perpendicular, or nearly so. The foot then appears too narrow at the heel, too elongated and less rounded than normal. The changes in the appearance of the inferior surface of the hoof vary. The changes here may be so slight that they are not noticed. In well advanced and neglected cases the arch of the sole is increased, the frog is narrow and atrophied and the bars high and perpendicular. Corns may accompany the contraction. The foot may feel feverish. The animal may manifest the pain in the feet when standing at rest by pointing and changing their position.
When lameness is present, it may resemble that occurring in inflammation of lateral cartilages and navicular disease.
_Preventive treatment_ is of the greatest importance. This consists in giving the feet an opportunity to take up moisture when they are exposed to abnormal conditions and become feverish. Under such conditions, it is advisable to occasionally remove the shoes and turn the animal into a pasture or lot. It is best to do this in the fall or winter when the ground is wet. If this can not be practised, the shoes should be removed and a poultice of ground flaxseed and bran, equal parts, applied to the feet for a period of eight or ten hours, daily for a week or two. A plank trough six inches deep, two feet wide and as long as the stall is wide may be filled with a stiff clay, and the horse made to stand with its front feet in the clay bath for ten or twelve hours daily. When grooming the horse, the foot should be cleaned with a foot-hook and washed with clean water. Hoof ointments should be avoided so far as possible. The importance of fitting the shoe to the foot, avoiding the too free use of the rasp and hoof knife and resetting or changing the shoe when necessary can not be overestimated.
Shoeing the animal with a special shoe is sometimes necessary. It is not advisable to attempt the forcible expansion of the quarters. Lowering the heels by careful trimming of the wall and sole and permitting frog pressure may be all the special attention required.
SAND-CRACK.--A fissure in the wall of the foot running in the same direction as the horny fibres, or a seam in the wall resulting from the healing of the fissure is termed sand-crack. The position and extent of the fissure or seam vary. It may involve the wall of the _toe_ (toe-crack) (Fig. 41) or _quarter_ (quarter-crack) (Fig. 42). It is _superficial_ or _deep_, according to the thickness of the wall involved; _complete_ or _incomplete_, depending on whether it extends from the bearing margin of the wall to the coronary band or only a portion of the distance; _simple_, when the horny tissue only is involved; and _complicated_, when the sensitive tissue beneath becomes injured and inflamed. Cracks of long standing usually have thick, rough margins.
_The causes_ of this unsoundness are poor quality of horn, improper care and injuries. Sand-cracks commonly occur in hoofs that are dry and brittle and have thin walls. In young horses incomplete cracks due to the wall becoming long and breaking off in large pieces are common. Unequal distribution of weight, the result of unskilled shoeing, or any other condition that may cause the foot to become unbalanced, using the foot rasp too freely, and such diseases as quittor, corns and contracted quarters subject the animal to this form of unsoundness. Any injury to the coronary cushion that secretes the fibres of the horny wall may result in either toe- or quarter-crack. Treads and barb-wire cuts are common injuries to the region of the coronet.
_The preventive treatment_ consists in preserving a healthy condition of the horn by giving the foot the necessary care and attention in the way of proper trimming and shoeing, and providing it with the necessary moisture by means of foot-baths, wet clay and poultices. Quarter-cracks respond to treatment more quickly than toe-cracks. The treatment is practically the same for both. This consists in preventing motion in the margins of the fissure so far as possible.
[Illustration: FIG. 41.--Toe-cracks.]
[Illustration: FIG. 42.--Quarter-crack caused by barb-wire cut.]
_The treatment for fissures_ in the region of the toe and quarter is as follows: The wall should be cut away along the margins of the crack until it is quite thin; and extra nail holes should be made in the shoe, and a nail driven into the bearing margin of the wall a little to each side of the fissure. The wall at the toe should be shortened and the toe of the shoe rolled if the animal's work permits the use of this kind of a shoe.
The margins of a quarter-crack and the wall just posterior and below it should be cut away until quite thin. The bearing margin should then be trimmed so that it does not rest on the shoe. A bar shoe that does not press on the frog may be used. Light blisters to the region of the coronet help in stimulating the growth of the horn. Rest is advisable.
CORNS.--This term is applied to injuries to the foot caused by bruises or continuous pressure to the posterior portion of the sole. This condition is common in the forefeet.
_The predisposing causes_ are faulty conformation that favors pressure from the shoe on the sole between the bars and wall and weak heels. Corns are commonly met with in feet having contracted quarters. The principal _external causes_ are wrong methods of shoeing and allowing the shoes to remain on the feet for too long a period.
_A common symptom_ of corns is lameness. In order to relieve the pressure over the inflamed part, the animal stands with the foot slightly flexed at the fetlock. The lameness is not characteristic. It is only by a local examination of the foot, made by pressing on the sole or cutting away the horn, that we are able to form a positive diagnosis.
We describe the _diseased changes_ by using the terms _dry_, _moist_ and _suppurative corns_. In the _dry corn_ we find the horn stained and infiltrated with blood. In the _moist corn_ the hoof may be colored the same as in the former, but in addition there is a space between the vascular and horny tissue that is filled with a serous-like fluid. If this collection of fluid becomes infected with pus organisms and is changed to pus, it is then termed a _suppurative corn_. Sometimes the pus pushes its way upward and backward between the sensitive laminae and the wall, and makes its appearance at the margin of the coronary band in the region of the quarters or heels. This usually occurs when the tissues beneath the horny frog become bruised or the sensitive tissue pricked by a nail. It is commonly termed "gravelled." Pus rarely breaks through the thick horny tissue, but follows the wall and breaks through the skin where it meets with the least resistance. Corns may be considered a serious unsoundness in driving horses.
_The treatment_ is largely preventive. Trimming the foot and fitting the shoe properly are important preventive measures. The practice of cutting away the bars and sole or "opening up the heels," as it is commonly termed, should be condemned. This method of trimming the foot instead of preventing corns is a very common factor in producing them. The shoe should not be too short or too narrow. It should follow the outline of the wall and rest evenly on its bearing margin. If this is practised, weakening the wall by cutting off that portion allowed to project beyond the shoe is unnecessary.
Feet that have low heels and large, prominent frogs should be shod with shoes thick at the heels. The best line of treatment for a horse that is subject to corns is to remove the shoes and allow the animal to run in a pasture. If this is impossible, poulticing the feet or standing the animal in moist clay will help in relieving the soreness. Excessive cutting away of the horny sole is contra-indicated. Suppurative corns should be given proper drainage and treatment.
LAMINITIS, "FOUNDER."--This is an inflammation of the sensitive or vascular stricture of the foot. The inflammation may be acute, subacute or chronic.
Stockmen frequently use a classification for laminitis based on the causes.
Feed, road and water founder are common terms used in speaking of this disease. The inflammation is usually limited to the front feet.
_The causes_ of laminitis are overfeeding, sudden changes in the feed, drinking a large quantity of water when the animal is overheated, overexertion, exhaustion and chilling of the body by standing the animal in a cold draft. It may be associated with such diseases as rheumatism, influenza and colic.
_The symptoms_ vary in the different forms of the disease. Pain is the most characteristic symptom. The sensitive or vascular structure of the foot has an abundant supply of sensory nerves, and, as it is situated between the hoof and the bony core, the pressure and pain resulting from the inflammation are severe.
In the _acute form_ general symptoms are manifested. The appetite is impaired, the body temperature elevated and the pulse beats and respirations quickened. If the inflammation is severe, the animal prefers to lie down. This is especially true if all four feet are inflamed. In most cases the horse stands with the forefeet well forward and the hind feet in front of their normal position and under the body. The affected feet are feverish and very sensitive to jarring or pressure. Moving about increases the pain in the feet, and it may be very difficult to make the animal step about the stall.
In the _subacute form_ the symptoms are less severe. The irregularity in the gait is especially noticeable when the animal is turned quickly. The local symptoms are less marked than in the acute form and the general symptoms may be absent.
_The chronic form_ is characterized by changes in the shape and appearance of the hoofs (Fig. 43). The wall shows prominent ridges or rings, the toe may be concave, thick and long and the sole less arched than usual, or convex. The degree of lameness varies. It is more noticeable when the horse is moved over a hard roadway than if moved over soft ground. One attack of laminitis may predispose the animal to a second attack.