ANATOMICAL CONSIDERATIONS

The frog generally is viewed as the blood pump of the foot. However, the frog has no major blood supply. It is my (Chapman's) belief that it serves little function, if any, in forcing or acting to pump venous blood back up the leg.

The union of the horny wall and the corium of the third phalanx is formed by the laminae. In the normal foot, the bond between these laminae cannot be broken. It is only after death of these structures that they can be separated.

The sole is the horny covering or plate of horn on the bottom of the hoof. It is not usually as tough as the wall. Its origin is the solar matrix and it receives its blood supply from arteries branching from the terminal arch, drained by the subsolar venous plexus. The bond between the matrix and the sole is papillar, rather than laminar. They, too, cannot be separated in a healthy foot. Only when the foot is injured or in the case of founder, can they be torn apart.

The coronary band (coronet) produces the central laminar portion of the horny wall. The coronet is similar to the human cuticle and houses a mass of minute capillaries. The horny wall starts below the coronary band and extends downward until it reaches the sole. The wall including these laminae is extremely important, as it is responsible for bearing most of the weight of the horse.

The deep digital artery is the main blood supply to the third phalanx. It enters the hoof both medially and laterally at the bulb of the heel, passes through the foramen on either side of the semilunar crest, and forms the terminal arch. This artery is not protected by anything but the sole until it passes through the plantar foramen of the third phalanx where it anastomoses with its partner of the opposite side. If this artery or its branches which perforate the wall of the third phalanx are destroyed, the horse will also be ruined. This is why a hoof cast, improperly applied, is so dangerous. Cases are known in which the blood supply was shut off and the digital artery was destroyed.

The disposition of the vascular system of the complete hoof consists of two-thirds veins and one-third arteries. Two major vessels are the circumflex vein and circumflex artery which run along and the distal peripheral edge of the third phalanx. At no point can sharp divisions be recognized. Each part unites and becomes continuous with the other.

ETIOLOGY

Laminitis is usually a sign of some underlying disease process which commonly includes diseases of, damage to, or infections of the intestinal tract; toxemia, as following retained afterbirth; stress and trauma, such as occur with dystocia; deep necrotic wounds, resulting in septicemia; pneumonia, which is severe and often may be necrotic; drugs, especially high levels of steroids and reactions to different drugs; and finally, mechanical laminitis, such as road founder, trimming and/or shoeing which forces the horse to walk on the sole or allows the shoe to put pressure on the sole.

These conditions must be corrected before a favorable response can be expected.

The major point to consider is that not only the cause must be determined, but also the extent of the damage to the feet. Measures need to be taken to correct this damage and steps must be taken to prevent further damage.

The laminae swell in the early stages. Pressure increases between the hoof wall and the third phalanx. It is this pressure that causes the eventual necrosis, and it is this pressure that causes the rotation of the third phalanx. It is our opinion that the pressure from the deep flexor tendon is a negligible factor in rotation of the third phalanx, unless there is a pre-existing flexor deformity, or unless the heels are cut abnormally low or the toe is elevated to create a secondary flexor deformity.

The relationship between founder and flexor deformity is very complex and will be discussed later.

Pre-existing conditions seen in many laminitic horses include: overfed, overweight and under-exercised; stall confinement; being shod too young (as yearlings); having feet that are too small and flexor deformities.

DIAGNOSIS

Sometimes, the white line will appear to be bright red, and the horse will show no clinical signs of lameness. In the early stages of laminitis, the horse will be stiff and frequently will be diagnosed as a case of shoulder lameness. At the initial onset of laminitis, the vascular apparatus of the sole is not affected. It is only after laminae become damaged that the wall and third phalanx start to separate.

If rotation of the third phalanx is not present, then one can supplement the diagnosis by running the finger down the middle of the leg to the coronary band. If it encounters a depression behind the coronary band, straight vertical displacement of the bony column down through the hoof capsule (sinker) is likely. This is disastrous, as it does not show up radiographically except at the coronary band, and means that 100% of the laminae have separated. Furthermore, this straight vertical displacement is often missed. It will show only at the coronary band, anteriorly on a lateral radiograph, and will have the appearance of the hoof capsule going proximally up the leg.

Unless this sinking process is stopped, the hoof will slough. Due to the anatomy and weight of the equine species, when the bony column sinks, the coronary area of the hoof is jammed onto the coronary plexus, cutting off the blood supply to the plexus. This is tantamount to leaving a tourniquet on the leg.

We are all familiar with the typical laminitis gait of "walking on eggs" or "glued to the ground." Examination with hoof testers indicates soreness anterior to the point of the frog.

Many foundered horses we see are chronic. The condition has been coming on over a period of days, weeks or months. The signs have just been ignored or called something else, until the animal finally assumes the typical stance. Many early cases are called "stiff-gaited", "sore in the shoulders" or "stone-bruised". Many have pads under the shoe to protect the feet. Many are also on "Bute" or a similar product which will mask the clinical signs.

Some of these animals have obvious evidence of other clinical diseases such as diarrhea, colic, retained membranes or pneumonia.

The major point here is that we have to look closely at these sore, stiff or sick individuals to be aware that we may be dealing with an early case of laminitis.

Some early cases show no soreness to the hoof tester. Some appear lame only in one foot but may be lame in the other foot after a volar nerve block.

A digital pulse is always present; however, if it is pounding, this is an indication of laminitis: the greater the laminar swelling, the stronger the pulse.

X-rays of both feet are mandatory. One pedal bone usually rotates before the other. A lateral X-ray of the foot is taken to pinpoint the amount of rotation. This is important to determine the exact location to apply the support of the heart bar shoe. A helpful tip to determine the exact location for support is:

Place a thumbtack about 1 cm. back from the anterior tip of the frog before the X-ray is taken. This is used only as a point of reference.
Take lateral X-rays with the foot on a block so that the X-ray beam is parallel to the ventral border of the third phalanx.
X-rays are often negative in the early stages, but evidence of previous problems may exist such as sole bruises, pedal osteitis, or re-shaping of the third phalanx.

Early and accurate diagnosis and prompt treatment are the responsibility of the veterinarian, and will result in the majority of the horses being returned to service.

TREATMENT

Treatment begins with an accurate diagnosis and evaluation of the primary cause:

Digestive problems can span a wide range, from no obvious signs of abdominal abnormalities which respond to minimal treatment, to the other end of the spectrum where we use antibiotics, sulfas, anti-inflammatory drugs, fluids, plasma and blood.

It is important in all cases to begin with a CBC and continue treatment until it is within normal limits and all clinical signs have disappeared. I (Platt) also routinely run a SMAC 20, which helps determine which systems are involved. It is necessary to evaluate the electrolyte balance, thus giving a baseline for subsequent comparisons.

The CBC ranges from 2,500 to 25,000, with the differential counts being equally varied. I (Platt) cannot categorize laminitis based on blood values. The WBC is usually elevated in chronic cases of enteritis, and it also rises with necrosis and abscesses of the feet. Acute cases often have a depressed WBC value.

Retained membranes may result in laminitis within 24 hours. One should not wait for the signs to appear. A gas-sterilized stomach tube is used to flush the uterus with 3-5 gallons of warm tap water. The uterus is filled and siphoned until all the membranes are removed and the return water is clean. This is repeated 4-5 times daily until the water is clean. I (Platt) use very few antibiotics in such cases.

Now, attention must be directed to the feet.

When the shoes are removed, the sole is examined for bruises, blood at the white line, and soreness anterior to the frog. Nerve blocks are used, if necessary. A posterior digital block alone will not help a laminitic horse. The anterior nerve must also be blocked to anesthetize the sole.

The amount of pain is a significant clinical sign. In some cases, this pain must be controlled to some degree, but by using the least amount of drugs possible. If the laminae are tearing loose and the bone is likely to rotate, it is wrong to mask the signs with pain-killing drugs or nerve blocks. By using pain-killing drugs, the horse continues to walk and cause more tearing of laminae hastening the separation process. Two grams of phenylbutazone is the maximum dose of anti-inflammatory agent used. I (Platt) never use a nerve block for the purpose of exercise.

The shoes are removed and the sole cleaned and examined for soreness anterior to the frog. Some of the early tell-tale signs of laminitis occur visually in the form of bruises to the horny sole. This sign is usually noticed while trimming the foot, in that red spots are seen. They normally appear only in the front feet but occasionally will be seen in the hind feet as well. The reason this problem is more prevalent in the front feet is because two thirds of the weight of the horse is carried by the forelimbs; however, the hind feet are occasionally affected and require stabilization of the third phalanx.

Stabilization of the third phalanx can be accomplished with the use of the heart bar shoe. A good analogue of laminitis is trauma to the human fingernail: the nail becomes loose. A person can grow a new nail but does not have to walk on that fingernail until it can grow again! In order to enable the horse to grow a new hoof, it is necessary to stabilize the third phalanx and support the bony column. The blood supply to the sole and the third phalanx must not be restricted in the process.

As noted earlier, the frog has no major blood supply. There are a few capillaries that are protected by the thick, horny cushion of the frog; thus, considerable support can be applied to the frog without causing pressure necrosis.

In the early stages, before the hoof is deformed, the foot should be trimmed, as nearly normal as possible, to fit the pastern axis. The heel should not be lowered in order to align the third phalanx parallel to the ground. If the heel is lowered, it places more stress on the deep flexor tendon, separating the third phalanx further from the wall.

If the rotation is severe or the pain is severe in acute cases, one should remove the anterior hoof wall. This allows space for the swollen laminae. It allows drainage when the laminae are necrotic and sloughing. It also removes the pressure exerted on the coronary band by a loose hoof wall. It is not necessary to cover the tissue with acrylic. We use merthiolate under a wrap to dry out the tissue.

The sole is removed if abscessed or necrotic tissue is present. The object here is to remove anything that is not normal. Constant debridement of the sole is important. The sole is also treated with merthiolate, which creates less proud flesh than does iodine.

If a farrier is not present, which is often the case, a two-inch roll of gauze is taped to the frog. The roll is flattened and unrolled to the point where there will be even pressure on the frog and both hoof walls. Elastikon tape (two-inch) is used and will stay in place for 2-3 days. A piece of carpet, cut to fit the frog, can also be used.

The amount of support that one can apply to the frog depends on each individual case. The amount of pressure depends on the amount of rotation at the time of application and whether the sole is dropped. It is recommended that one can start by shoeing the "worst" foot first. The animal can stand on the so-called "good" foot while the farrier is working on the "worst" one; then, the foot will have some support when the horse is required to stand on it.

The heart bar shoe is prepared by the farrier. The amount of support is as critical as the point of support, and cannot be left to chance. The heart bar shoe is a precision instrument. It can cause much damage, when not applied in the proper manner. It is the only way we know to support the skeletal column of the horse. We have some support under the bone and we do not have to rely on the laminae to hold the whole horse.

STABILIZATION OF THE THIRD PHALANX WITH THE USE OF THE HEART BAR SHOE.

The heart bar of the shoe is usually made of 1/4" by 1/2" stock and is V-shaped just like the frog. This bar, on the normal light horse of today (Thoroughbred, Quarter Horse, Arabian, etc.), should extend along the frog to a point 3/8" posterior to the apex. A width of 5/8" is plenty for a hand made shoe with full fullering, as this makes removal of the shoe much easier at the time of reset. THE HEART BAR MUST NOT TOUCH THE SOLE OR BARS OF THE FOOT. If a keg shoe is to be used, it should not be a wide-webbed shoe. (A keg shoe is any manufactured, store-bought, machine-made, presized, or stamped shoe).

The shoe is shaped to the hoof wall and measurement is made to see how far forward the bar should extend along the frog. When this measurement is made, the bar is welded in place. It should be noted that anything touching the sole will hinder the blood supply to that area.

Next, the toe is rolled severely until is turned up, resembling a sled-runner. This is done to move the fulcrum of the toe posteriorly until it is nearly under the distal end of the third phalanx. This reduces the energy it takes for the deep flexor tendon to force (break) the toe over and will diminish tearing of the laminae.

It is not advisable to cut out the toe in the front of the shoe (open-toe). A full rim pad is used in most cases. This is used to clear the third phalanx off the ground when it has prolapsed through the sole. I (Chapman) use a thermoplastic casting material. It will not be attacked by iodine, copper sulfate or water. It is a very good cushioning agent.

Before being nailed on the hoof, the shoe is placed on the foot by hand and squeezed down on the frog. If the horse moves away and acts like it hurts, then there is too much support. This can be adjusted by knocking the bar down a little. If the shoe is nailed to the hoof and the horse does not want to bear weight on it or will not put the foot on the ground, too much pressure has been applied; the shoe should be removed and the bar adjusted. These shoes should never be put on a horse that is nerve blocked. The horse must be able to feel the pressure and thus indicate if the correct support has been applied.

After the foot is shod, the horse is walked to see how it reacts; then, the other foot is shod in the same manner.

Concern has been expressed to the effect that the heart bar shoe causes abscessation; however, most of the horses I (Chapman) see already have serious sepsis. After the heart bar shoe is properly applied, the sepsis clears within 90-120 days - in less severe cases, frequently within 30 to 60 days. Use of the heart bar does allow better drainage of the solar corium. Pressure on the apex of the frog does appear to cause abscesses under the frog, especially when too much pressure is applied or the angle is incorrect.

In any case of founder, if the rotation is more than three or four degrees, abscesses are likely. The shoe can be harmful if it is built or put on improperly, especially if it touches the sole. It cannot overlap the frog in any way, and the apex of the bar must never extend over the apex of the frog. It should be at least 3/8" posterior to the point of the frog. This is extremely important.

AFTER CARE

This is very important. The hemograms are continued, and constant evaluation of the internal condition, as well as the feet, is important. The shoes must be reset every 3-4 weeks, and pressure evaluated. If we are trying to return the third phalanx to its normal position, X-rays must be taken.

Difficult cases with numerous abscesses have to be re-evaluated and treated daily, and the feet have to be wrapped, soaked, etc. Proud flesh must be controlled.

It is vitally important that we understand the relationship between pain relievers and a loose hoof, so we can prescribe the amount of exercise or lack of same for each particular case.

If we use pain-relieving drugs, we can create two important problems: (1) abscesses can form without our knowledge but the early symptoms are masked, and (2) too much movement may cause the animal to tear loose damaged laminae, where they would normally be more protective.

Most cases require exercise, but each must be treated as an individual. If the whole wall is loose, then exercise is not recommended. Most need to be walked at least 10 minutes, four times a day, or maybe 5 minutes every hour.

Most horses start "stiff and sore" but improve as they continue moving. These horses do not need much forced exercise but they do need to be moved at frequent intervals. They also do best if kept in a pasture where they have to move to feed and water.

A good plane of nutrition is necessary to promote healing and a feeling of well-being. We prefer good pasture and/or alfalfa with oats or a mixed grain ration. The only supplement I recommend is methionine.

THE STRAIGHT VERTICAL DISPLACEMENT

When it is evident that the horse is affected with a straight vertical displacement, a heart bar shoe should not be used. Instead, the heart bar shoe should be simulated by using a thermoplastic casting material. This, designed for human splints, can be heated in hot water and molded into any desirable shape. A thermoplastic-material shoe, with clips, is cut in the shape of the hoof. A triangular-shaped wedge, also of thermoplastic material, is cut out to fit over the frog and bradded to the simulated shoe. The material can be 0.6 cm. to 1.8 cm. thick, depending on how flat the sole is at the time. A good average is 1.25 cm. This triangular-shaped piece must not overlap the frog in any manner.

Next, a pad of gauze, cotton or even disposable diapers is cut to fit around the wedge to pad the sole. This padding must be thicker than the frog support wedge. For example, if the wedge is 1.25 cm. thick, the padding should be 1.8 cm. thick. This is all put together, first by placing medicated gauze sponges next to the exposed laminae, then molding the thermoplastic material clips (toe, quarter, and heel) around the foot and taping the "shoe" to the hoof with elastic tape. The horse is now bearing nearly all of its weight on the frog. Palpation of the coronary area allows the finger to slide rather easily over the coronary band.

These horses will have the most severe sepsis, because of the widespread damage; the coronary plexus, it is hoped, will still be alive. All laminar vessels, laminae, venous plexus and, in many instances, the circumflex vein and the circumflex artery are destroyed. It is rare for the deep digital artery to be so damaged; however, if it is, the chance for recovery is very remote.

HOOF RESECTION

When an entire hoof resection is done, it is amazing how fast the hoof will regenerate, taking 6-1/2 to 7 months to grow a complete new hoof. Constant nursing care is essential to salvage these horses. Intermittent suppuration occurs for 20 to 90 days. The entire area must be treated as an open wound, the hoof being kept clean, bandaged and turbulated daily. Also, the use of merthiolate and iodine is indicated.

There are three basic reasons for removing the horny wall or doing a hoof-resection:

To relieve the pressure on the coronary plexus by the coronary edge of the hoof wall.
To debride any necrotic laminae entrapped between the third phalanx and the wall. This can be treated as an open wound. Systematic antibiotics are of very little value, as there is no blood supply to carry medication to this area.
When pressure is applied to the third phalanx via the apex of the frog, the anterior edge of the third phalanx will have no resistance against it, thus forcing the third phalanx back into a more normal position.
When sole abscesses occur, the feet should be turbulated daily a in hot povidone-iodine solution every other day. Epsom salts and hot water are used between, and the feet are treated and bandaged. Reducine is not recommended in any instance of severe founder where the horse is down and has decubitus ulcers. Hoofmaker and ichthammol ointment have been more effective in my experience.

Once these steps have been followed the horse should be taken off any medication such as phenylbutazone or flunixin meglumine. These drugs should be withdrawn slowly. Methionine, which exerts its maximum effect within 45 days, is fed in the grain daily at the rate of 20 Gm. per 1,000 lb. body weight. Turbulation, as noted is effective. Merthiolate should be used on the exposed areas. We have found that merthiolate has abetter drying effect and penetration. The application of a good hoof conditioner around the coronary band and heel is advised. The use of an acrylic to cover exposed tissue is not necessary.

The heart bar shoe or simulated thermoplastic heart bar shoe should be reset regularly, approximately every four weeks. This is essential to keep the correct support of the third phalanx. At each shoeing the pressure should be re-assessed and adjusted to the individual case. It is important that the feet be kept clean. Material packed up next to the sole causes extreme pain. Severely lame horses should be turned out in a pasture, if possible. A box stall is not recommended but a clean stall should be bedded with straw. Sawdust and sand are abrasive and contribute to decubitus ulcers. Each time the horse is removed from the stall it will be stiff but the farther it walks the easier it will be to move more freely. Exercise depends on the severity of the individual case. Horses which do not improve with exercise should not be forced to walk because the exercise-induced pain is a result of tearing of structures too weak to tolerate the pressure.

ALTERNATIVE DEVICES AND RELATED PROBLEMS

The heel grows faster than the toe on a foundered foot, the reason being the reduced blood supply to the anterior wall. The coronary vessels are compressed by the upward pressure of the loose anterior hoof wall. Therefore, it is important to monitor the frog support because the increased heel growth causes the heart bar to grow away from the frog, thereby losing frog support.

Flexor deformities are a new dimension that results in failure, unless diagnosed early and corrected.

Deep flexor tendon deformities are the most damaging, because the tendon is directly associated with the third phalanx. I (Platt) use inferior check ligament desmotomy to gain relief for the deep tendon. If this does not correct the problem, then tendon is cut.

All cases of severe founder go on to abscess formation. Usually one foot is worse than the other, but the degree of lameness is important because the soreness increases as the abscess forms.

The first abscess is usually anterior to the point of the frog, and the sole begins to bulge as it forms. The next location is lateral to the point of the frog, along the border of the sole and the wall. Sometimes, these are severe enough to warrant removal of the entire sole. These abscesses must be opened as they form, or they will undermine the sole and break out at the heel or work up the laminae and break out at the coronary band.

Heel abscesses are opened (if necessary) and flushed with hydrogen peroxide. If the abscess breaks at the coronary band, the wall distal to the abscess is removed and the area treated with peroxide and bandaged.

The more severe case requires removal of the hoof wall. If such is the case, a heart bar shoe is built using Orthoplast, and the foot wrapped using disposable diapers and tape. The bandage is changed daily, using merthiolate to dry out the tissues until a new hoof grows and can be shod. This takes approximately five months.

Lysis of the third phalanx can occur from osteomyelitis and loss of blood supply. The severe cases result in chronic abscesses. This problem is corrected only by surgical removal of the damaged portion of the third phalanx under general anesthesia. A tourniquet is applied at the fetlock. All abscesses are removed, including the lytic bone. A pressure wrap is applied for 48 hours to control hemorrhage. A heart bar shoe made from Orthoplast and two disposable diapers are applied to the hoof. The wound is treated daily with "sugardine" and covered with disposable diapers. "Sugardine" is a paste made from Betadine scrub and table sugar.

After the healing process has begun, it is treated with merthiolate. This is usually around 30 days following surgery.

I have "cultured" most of these lytic areas, and all of them have produced Gram-negative organisms, and the most common being E. coli. I (Platt) use systemic gentamicin on all post-surgical cases. As always, the hemograms are monitored to determine when to discontinue antibiotic therapy. These cases may be shod 60 days after surgery, with heart bar shoes.

Some comments on shoes and devices that work with very little consistency are: (1) the egg bar shoe has no stabilizing effect on the bony column, (2) the reverse shoe gives no stabilization to the third phalanx, (3) the reverse wedge pad places more tension on the deep flexor tendon thus causing more rotation, (4) the hoof cast compresses the blood supply to the venous plexus of the sole if not properly applied, and is dangerous for general use, (5) a bar shoe with the bar across the center of the shoe sometimes squeezes the deep digital artery, destroying the blood supply to the third phalanx, (6) a pad with packing under it gives no stability to the bony column and frequently causes pressure on the sole, destroying its blood supply, and (7) a shoe that raises the heel and takes the stress off the deep flexor tendon aligns all the laminae perpendicular to the ground, causing the bony column to sink.

Discussant: JAMES R. COFFMAN, D.V.M., M.S.
Mr. Chapman and Dr. Platt are to be complemented on their effective application of anatomy, farriery and appreciation of systemic disease process to bring about this improved approach to therapy of horses affected by laminitis. Two principal considerations are fundamental to a discussion of their paper.

First, prognosis of laminitis fundamentally is determined by the presence or absence of unresolved underlying problems. Dr. Platt has stated that laminitis is caused by some other problem and, that to manage it successfully, that problem must be identified and corrected. This concept might best be phrased in another way. The pathogenesis of laminitis is essentially the same in all instances; the preponderance of evidence suggests arteriovenous shunting, associated with peripheral vasoconstriction and hypercoagulation (endotoxin being a likely inciting agent). With this concept in mind, Dr. Platt's statement can then be taken at face value. Certainly laminitis commonly coexists and appears to be related to a variety of systemic disease processes, the most common being cardiovascular disorders (including verminous arteritis), gastrointestinal disorders (especially those which denude the mucosa of the bowel), chronic respiratory disease, renal disease and chronic liver disease. In chronic laminitis, gastric and colonic ulcers, chronic renal disease and diffuse lung abscesses are particularly common. Gastrointestinal ulceration may be a pre-existing problem, the aftermath of the initiating incident, or the result of chronic administration of phenylbutazone or other non-steroidal anti-inflammatory agents. Chronic renal disease frequently occurs in two forms: glomerulonephritis, as an aftermath of onset events, and medullary necrosis, as a result of phenylbutazone therapy. Diffuse or multifocal pulmonary abscesses logically would be the result of bacterial emboli emanating from septic foci in the feet via venous drainage. The presence of such unresolved problems as those described above is, in my experience, associated with a poor prognosis. However, horses with consistently normal hematology and serum chemistry values, which do not have degenerative changes in the third phalanx, have a good prognosis when shod with heart bar shoes, particularly if they have been affected for less than two months.