♘امیرحسین♞
♘ مدیریت انجمن اسب ایران ♞
Introduction
The foot of the horse is a very unique structure that undergoes a tremendous amount of strain and stress. The foot is the foundation of the horse and a structure is only as strong and stable as its foundation. Hence, the old adage “No Foot, No Horse.” The foot is the most common area of forelimb lameness because of the amount of stress to which the equine foot is exposed. Thus it is necessary to have knowledge of the foot, clinical conditions associated with the foot and ways to avoid and treat the more common foot problems.
Anatomy of the Foot
The foot structure is primarily composed of three bones: the third phalanx or coffin bone, the second phalanx or short pastern bone and the distal sesamoid or navicular bone. The short pastern and coffin bones support weight while the navicular bone serves as a fulcrum for the deep digital flexor tendon. The joint between the first and second phalanges is the proximal interphalangeal or pastern joint, and the joint between the second and third phalanges is the distal interphalangeal or coffin joint.
Besides the bones, there are numerous soft tissue structures within the hoof. The deep digital flexor tendon courses down the back of the limb and angles around the navicular bone to attach to the back of the coffin bone. The navicular bursa is a fluid-filled pouch that sits between the navicular bone and the deep digital flexor tendon and helps cushion and protect the bone and tendon. The navicular bone also has three ligaments attaching it to the second and third phalanges. There are two large collateral ligaments attaching the second and third phalanges. Any combination of these structures may be injured and a source of lameness.
There are also numerous external structures of the foot with which one should be familiar. The coronary band is where the skin and hair intersect with the hoof wall. The hoof wall grows from the coronary band at a rate of approximately 0.25 inches per month. On the bottom of the foot, there is the sole, frog, white line and bars. All of these structures are important and vital to the overall health of the equine foot.
Conformation
The relationship of how the foot is related to the limbs and how the limbs are related to the body determines the conformation of the horse. Genetics and growth will determine the limb conformation. However, the foot can be influenced throughout the horse’s life by trimming and shoeing. Horses will often toe-in and toe-out which will affect whether the horse travels straight or paddles out or wings in. Only when the horse is very young should attempts be made to correct these types of defects. Generally, the mature horse limb conformation should not be altered, as this is the angle with which the bones, tendons and ligaments have developed.
Foot conformation is extremely important in maintaining the health of the foot and the soundness of the horse. Ideally, the horse will have a large round front foot and a similar-sized more elongated hind foot. The sole needs to be concave, which allows for foot expansion and absorption of concussion each time the foot hits the ground. Normally the horse’s foot should land heel first and the heels of the foot subsequently expand. Thereafter, the pressure is moved from the walls of the foot to the frog, which further absorbs concussion as well as helps move blood through the foot and back up the leg.
There is no one ideal foot angle for the horse. The angle of the front hoof wall should parallel the pastern angle of the horse. Thus, if a horse has an upright shoulder and pastern angle then the hoof conformation needs to be upright. If the horse has a long sloping pastern, then the foot will also have a longer sloping angle. When there is an abrupt angle change in the pastern/foot angle, there will be abnormal forces exerted through the foot.
Shoeing
Proper foot care is the cornerstone of maintaining a sound horse. A good farrier is instrumental in keeping the horse’s feet balanced and well-supported. The farrier will trim the foot so that it is at a proper angle as well as balanced inside and outside. When a shoe is applied it needs to be the proper size and positioned so that the toe is rolled, since the horse cannot wear the toe down when protected by the shoe. Additionally, the shoe needs to be wider than the hoof in the heels, and the nails should not be placed back in the heels but only in the toe region. This allows for a good support structure for the heels of the foot to expand onto the shoe and therefore absorb concussion. Since the foundation of the horse is everything, a good farrier is a necessity and a tremendous asset.
Lameness Examination
Whenever a horse exhibits lameness, a thorough examination should be performed. More often than not, a good examination will be a beneficial investment, as it will lead to a more correct and faster diagnosis and usually a quicker return to soundness. The examination begins with a comprehensive physical examination, including palpation of the limbs, hoof tester examination and joint manipulation. The horse is then examined at motion to determine the severity of the lameness and which limb or limbs are affected. Localization of the lameness is performed with the use of local anesthetic deposited around nerves and/or within joints. Since the horse does not have muscle below the knee (carpus) or hock (tarsus), the nerves in the lower limbs only serve a sensory function and do not control motion. Therefore, local anesthetic can be used below these points to desensitize regions and determine if those locales are the source of the lameness. From the level of the knee or hock and above, local anesthetic is primarily only placed in joints as motion may be affected if deposited around nerves.
Once the lameness has been localized, the etiology of the lameness needs to be identified if possible. Many different diagnostics are available including nuclear scintigraphy, CT and MRI, but the most common are radiographs and ultrasound. It is critical that good, detailed, comprehensive radiographic studies be performed. When radiographing the foot, a minimum of five views should be taken to allow for a complete evaluation of all of the bony structures within the foot.
Conditions of the Foot
Navicular Disease/Syndrome
Problems with the navicular bone are common but are also overly feared. Conformation can lead to increased stress in the foot especially in the heel region and possibly predispose to the development of degenerative changes of the navicular bone. Horses with small feet and narrow heels do not absorb and distribute concussion as well and are predisposed to developing foot lameness. Additionally, a broken foot/pastern axis (especially if the toe is long and the heels are short) will place a tremendous amount of stress on the navicular region.
The clinical signs of navicular disease/syndrome include usually bilateral forelimb lameness, although one foot is usually more significantly affected. Often times the horse will exhibit pain during a hoof tester examination when the instruments are placed across the central one-third of the frog to the opposite heel. The lameness is localized to the heel region with local anesthetic. If needed, further information and localization of the lameness may be possible with the use of intra-articular anesthesia of the coffin joint and /or navicular bursa.
The cornerstone of treatment of navicular disease/syndrome is corrective shoeing. Despite the severity of radiographic signs, shoeing recommendations will be similar. The foot needs to be at an appropriate angle. Often that requires a wedge pad to make the foot more upright. The toe should be shortened and rolled to hasten break-over, which is the point that the foot can come off the ground. The longer the foot stays on the ground and the horse’s body weight moves forward, the more pressure that will be applied to the heel region of the foot. In an effort to promote heel expansion, the shoe should extend behind the heels and be slightly wider than the heels. This type of shoeing should be performed every five to six weeks. It is the rare horse that can actually go eight weeks between shoeings even without lameness.
Further treatment includes blood flow-enhancers and anti-inflammatory medications. The most common medications used to stimulate blood flow are isoxsuprine and aspirin. It is not exactly known how isoxsuprine may enhance blood flow, but several studies have shown that approximately 50% of horses with heel pain will improve with its administration. Isoxsuprine is a very safe economical medication with little reason not to attempt its use. Aspirin is used similar to its use in heart disease human patients; it changes the way blood blows, making it easier to move through blood vessels. Phenylbutazone is the most common anti-inflammatory medication used. It is important that these horses become comfortable, move with a better stride and begin to land heel-first to enhance blood flow. Another means to deliver anti-inflammatory medications more directly is sterile injection into the coffin joint and/or navicular bursa. If possible, these horses are maintained in work if comfortable. They are at least encouraged to move around by turning out every day.
The prognosis of horses afflicted with navicular disease/syndrome is generally favorable. Most of these horses will return to full athletic use. Usually, corrective and appropriate shoeing will have to be continued for the horse’s career. Occasionally, the chronic use of isoxsuprine is necessary for long-term comfort. If the response to oral medications and corrective shoeing is insufficient, then synovial injections of hyaluronic acid and corticosteroid is used to direct a more potent anti-inflammatory locally. In those cases where conservative therapy is ineffective, the horse’s occupation can be changed or a palmar digital neurectomy can be performed. Neurectomies can be very successful; however, they do not change the disease process but only change the horse’s perception of the disease process. Additionally, the nerves usually will regrow and the procedure is only temporary; the odds are definitely favorable for the surgery to be successful for several years.
Fractured Navicular Bone
Although a fracture of the navicular bone can also be classified as navicular disease/syndrome, it is worth a separate mention as the clinical signs and treatment vary. Instead of a slowly increasing bilateral lameness, the horse with a fractured navicular bone will have an acute onset consistent lameness that may be severe. The lameness is a unilateral lameness. Most of these horses will want to land toe-first instead of heel-first.
If necessary, the lameness is localized to the heel region. Good-quality radiographs are needed to assess the presence and severity of the fracture. It is important to know that a line in the navicular bone is a fracture and not a separate center of ossification, called a bipartite navicular bone. The opposite forelimb navicular bone can also be radiographed for a comparison. If the same line is present in the opposite limb, then it is a bipartite navicular bone and not a fracture.
Treatment of a fractured navicular bone also requires corrective shoeing, but it differs from shoeing for navicular disease/syndrome. The heel is elevated using a wedge pad to make the foot a little more upright than normal to decrease the tension of the deep digital flexor tendon across the navicular bone. The toe is kept short and rolled. Usually a bar shoe with clips at the medial (inside) and lateral (outside) quarters is used to help stabilize the foot. The horse will be shod this way for usually at least four to six months. Stall rest is initially required, and once the horse appears comfortable on the foot then hand walking will be commenced. The duration of stall confinement is usually 60 to 90 days with another 60 to 90 days of small paddock confinement. Additionally, phenylbutazone, isoxsuprine and aspirin are prescribed to reduce inflammation and promote blood flow respectively.
The prognosis with a fractured navicular bone is variable depending on the severity of the fracture but is relatively guarded for soundness. A significant amount of time is given to allow for healing. However, a palmar digital neurectomy is often necessary to help the horse maintain an athletic career.
Fractured Coffin Bone (Third Phalanx)
Fractures of the coffin bone are more common than fractures of the navicular bone. They can occur in multiple areas within the bone, and this will often determine the severity of clinical signs. In general, if the fracture is near the center of the bone and extends into the joint, then the horses will be more lame and the long-term prognosis may be reduced. Clinically, these horses also appear acutely with a unilateral foot lameness. The lameness is often significantly worse when the horse is circled in one direction versus the other. There may or may not be sensitivity with hoof testers in the region of the fracture.
The diagnosis is made with high-quality radiographs of the bone. Often, special oblique views are needed to identify the fracture. If the lameness is severe, then it is recommended that survey radiographs be taken of the suspected area prior to performing any peripheral nerve blocks as this may cause further damage to the fractured bone. Occasionally, slight hairline fractures may be very difficult if not impossible to observe on initial radiographs; radiographs are repeated in three to four weeks, as fractures will widen in the initial healing stages and they are more detectable radiographically at this stage.
The treatment of a fractured coffin bone is similar to a fractured navicular bone, but the duration is longer. A bar shoe with medial and lateral quarter clips is applied and often some type of impression material is placed between a pad and the sole of the hoof to give the coffin bone more generalized support. This special type of shoe is often used for one year. These horses are confined to a stall for 90 to 120 days with hand walking if comfortable. They are then allowed access to a small paddock for another 90 to 120 days. If they are doing well, they are then returned to a gradual exercise program. Phenylbutazone is administered as needed and occasionally the blood flow enhancers are used. A joint cartilage protectant medication is prescribed if the joint is involved. Rarely, if the fracture is into the joint and involves the midline of the coffin bone, a lag bone screw can be placed into the bone across the fracture line in an effort to enhance and expedite healing. This is a difficult operation with numerous possible complications and therefore is only used if absolutely necessary.
Most horses with fractures of the coffin bone have a good prognosis. Usually the fracture heals with a fibrous union and never quite disappears on the radiographs, but it is strong enough to withstand the normal stress. The only types of fractures with a poorer prognosis are the central fractures involving the joint. Occasionally these fractures will lead to secondary arthritis of the coffin joint and chronic lameness.
Laminitis (Founder)
The lamina in the equine foot connect the coffin bone to the inside of the hoof. There is sensitive lamina that covers the coffin bone that interlocks with the insensitive lamina on the inside of the hoof wall. There are numerous causes for the lamina to swell and therefore weaken the attachment of the coffin bone to the hoof wall. Generally, because of blood supply the most severely affected region is the lamina between the front edge of the coffin bone and the front hoof wall. As that area weakens, the deep digital flexor tendon continues to pull on the back of the coffin bone and usually rotation of the coffin bone is the end result. If the entire lamina becomes affected, then the support for the coffin bone is compromised everywhere and the coffin bone sinks within the foot without rotation. Sinking is considerably more rare and has a significantly worse prognosis.
Most horses with laminitis will exhibit a relatively classic stance. They want to stand with their hind legs up underneath themselves and prefer to have their front feet out in front of them and land on their heels. They will be reluctant to move and will shuffle with quick steps when forced to move. The feet will usually feel hot and have an increased pulse because of the inflammation present. It may be difficult to pick up the feet, as the horse will not want to bear weight on an affected foot. If it is possible to apply hoof testers to the soles, there is usually a painful response in the toe region.
A tentative diagnosis is commonly made based on the clinical signs. To determine the presence and severity of laminitis, radiographs must be taken. It may be necessary to “block” the feet with local anesthetic to get the horse properly positioned for radiographs. If good-quality radiographs are taken, the degree of rotation or presence of sinking can be detected, as well as the thickness of the sole, length of toe and heel and if there are any gas pockets or gas lines present which signify an abscess.
Laminitis is a medical emergency that requires immediate and often aggressive therapy. A delay in treatment can significantly reduce the prognosis for the horse. Initially, if the horse is shod then the shoes are removed. Anti-inflammatories such as phenylbutazone and intravenous DMSO are given to try to aggressively decrease the laminar swelling present between the hard coffin bone and hoof wall. Blood flow-enhancers such as isoxsuprine, acepromazine and even topical nitroglycerine patches are often used. Excessive toe is removed and the angle of the foot should be appropriate for that horse. The sole is supported with either Styrofoam or cotton or a frog support pad. The horse should be kept in a clean, dry stall with adequate bedding to encourage lying down to decrease the force exerted through the front feet. If abscesses are present, then they must be addressed with drainage and care.
Once the initial laminitis becomes stabilized and the horse is more comfortable, then corrective trimming and shoeing will be instituted. This will usually take at least seven to 10 days. Any excess toe should be trimmed and rasped. The coffin bone will have to be repositioned to its normal angle by trimming down excess heel; however, this may need to be performed gradually as you don’t want to put excessive tension on the deep digital flexor tendon too quickly. Often, some type of frog support pad or pad with impression material is used to direct more support under the frog to share the load with the hoof wall.
If the degree of rotation is severe or the horse is refractory to medical treatment of laminitis with rotation, then surgery to reduce the pull of the deep digital flexor tendon may be indicated. The deep digital flexor tendon can be transected in the standing horse in the mid-cannon region. This will temporarily reduce the constant tension of the tendon on the coffin bone. The decrease in tendon pull will usually reduce the pain acutely. For longer-term success, every effort needs to be made to realign the coffin bone with corrective trimming and shoeing, as the tendon will heal over the next several months and tension will be reestablished.
The degree of rotation, severity of clinical signs and response to initial therapy will affect the prognosis. In general, the long-term prognosis with laminitis is guarded. Horse are prone to recur as there has been damage to the structure attaching the front coffin bone to the hoof wall and this attachment will never return to original strength. In severe cases, the blood supply may also be compromised to the point that repeated abscessation is a possibility. When undertaking the treatment of a severe laminitic case, the horse owner must be committed for prolonged treatment. It takes lots of patience, time and nursing care to return these horses to comfort, and it is unfair to the horse to begin therapy and then decrease that commitment to the therapy at a later date. Additionally, an extremely capable farrier may be required for continued corrective shoeing for the life of the horse.
Summary
Lameness is the largest cause of economic loss in the equine industry. The most common location of forelimb lameness is the foot. There is a greater chance for a successful outcome if the lameness is addressed at its onset and a complete examination and workup is performed. Since the foot is the foundation of the horse, foot problems are best avoided if possible. That is best achieved with the horse having good limb and foot conformation to start, and then maintaining good conformation and support with good shoeing.
The foot of the horse is a very unique structure that undergoes a tremendous amount of strain and stress. The foot is the foundation of the horse and a structure is only as strong and stable as its foundation. Hence, the old adage “No Foot, No Horse.” The foot is the most common area of forelimb lameness because of the amount of stress to which the equine foot is exposed. Thus it is necessary to have knowledge of the foot, clinical conditions associated with the foot and ways to avoid and treat the more common foot problems.
Anatomy of the Foot
The foot structure is primarily composed of three bones: the third phalanx or coffin bone, the second phalanx or short pastern bone and the distal sesamoid or navicular bone. The short pastern and coffin bones support weight while the navicular bone serves as a fulcrum for the deep digital flexor tendon. The joint between the first and second phalanges is the proximal interphalangeal or pastern joint, and the joint between the second and third phalanges is the distal interphalangeal or coffin joint.
Besides the bones, there are numerous soft tissue structures within the hoof. The deep digital flexor tendon courses down the back of the limb and angles around the navicular bone to attach to the back of the coffin bone. The navicular bursa is a fluid-filled pouch that sits between the navicular bone and the deep digital flexor tendon and helps cushion and protect the bone and tendon. The navicular bone also has three ligaments attaching it to the second and third phalanges. There are two large collateral ligaments attaching the second and third phalanges. Any combination of these structures may be injured and a source of lameness.
There are also numerous external structures of the foot with which one should be familiar. The coronary band is where the skin and hair intersect with the hoof wall. The hoof wall grows from the coronary band at a rate of approximately 0.25 inches per month. On the bottom of the foot, there is the sole, frog, white line and bars. All of these structures are important and vital to the overall health of the equine foot.
Conformation
The relationship of how the foot is related to the limbs and how the limbs are related to the body determines the conformation of the horse. Genetics and growth will determine the limb conformation. However, the foot can be influenced throughout the horse’s life by trimming and shoeing. Horses will often toe-in and toe-out which will affect whether the horse travels straight or paddles out or wings in. Only when the horse is very young should attempts be made to correct these types of defects. Generally, the mature horse limb conformation should not be altered, as this is the angle with which the bones, tendons and ligaments have developed.
Foot conformation is extremely important in maintaining the health of the foot and the soundness of the horse. Ideally, the horse will have a large round front foot and a similar-sized more elongated hind foot. The sole needs to be concave, which allows for foot expansion and absorption of concussion each time the foot hits the ground. Normally the horse’s foot should land heel first and the heels of the foot subsequently expand. Thereafter, the pressure is moved from the walls of the foot to the frog, which further absorbs concussion as well as helps move blood through the foot and back up the leg.
There is no one ideal foot angle for the horse. The angle of the front hoof wall should parallel the pastern angle of the horse. Thus, if a horse has an upright shoulder and pastern angle then the hoof conformation needs to be upright. If the horse has a long sloping pastern, then the foot will also have a longer sloping angle. When there is an abrupt angle change in the pastern/foot angle, there will be abnormal forces exerted through the foot.
Shoeing
Proper foot care is the cornerstone of maintaining a sound horse. A good farrier is instrumental in keeping the horse’s feet balanced and well-supported. The farrier will trim the foot so that it is at a proper angle as well as balanced inside and outside. When a shoe is applied it needs to be the proper size and positioned so that the toe is rolled, since the horse cannot wear the toe down when protected by the shoe. Additionally, the shoe needs to be wider than the hoof in the heels, and the nails should not be placed back in the heels but only in the toe region. This allows for a good support structure for the heels of the foot to expand onto the shoe and therefore absorb concussion. Since the foundation of the horse is everything, a good farrier is a necessity and a tremendous asset.
Lameness Examination
Whenever a horse exhibits lameness, a thorough examination should be performed. More often than not, a good examination will be a beneficial investment, as it will lead to a more correct and faster diagnosis and usually a quicker return to soundness. The examination begins with a comprehensive physical examination, including palpation of the limbs, hoof tester examination and joint manipulation. The horse is then examined at motion to determine the severity of the lameness and which limb or limbs are affected. Localization of the lameness is performed with the use of local anesthetic deposited around nerves and/or within joints. Since the horse does not have muscle below the knee (carpus) or hock (tarsus), the nerves in the lower limbs only serve a sensory function and do not control motion. Therefore, local anesthetic can be used below these points to desensitize regions and determine if those locales are the source of the lameness. From the level of the knee or hock and above, local anesthetic is primarily only placed in joints as motion may be affected if deposited around nerves.
Once the lameness has been localized, the etiology of the lameness needs to be identified if possible. Many different diagnostics are available including nuclear scintigraphy, CT and MRI, but the most common are radiographs and ultrasound. It is critical that good, detailed, comprehensive radiographic studies be performed. When radiographing the foot, a minimum of five views should be taken to allow for a complete evaluation of all of the bony structures within the foot.
Conditions of the Foot
Navicular Disease/Syndrome
Problems with the navicular bone are common but are also overly feared. Conformation can lead to increased stress in the foot especially in the heel region and possibly predispose to the development of degenerative changes of the navicular bone. Horses with small feet and narrow heels do not absorb and distribute concussion as well and are predisposed to developing foot lameness. Additionally, a broken foot/pastern axis (especially if the toe is long and the heels are short) will place a tremendous amount of stress on the navicular region.
The clinical signs of navicular disease/syndrome include usually bilateral forelimb lameness, although one foot is usually more significantly affected. Often times the horse will exhibit pain during a hoof tester examination when the instruments are placed across the central one-third of the frog to the opposite heel. The lameness is localized to the heel region with local anesthetic. If needed, further information and localization of the lameness may be possible with the use of intra-articular anesthesia of the coffin joint and /or navicular bursa.
The cornerstone of treatment of navicular disease/syndrome is corrective shoeing. Despite the severity of radiographic signs, shoeing recommendations will be similar. The foot needs to be at an appropriate angle. Often that requires a wedge pad to make the foot more upright. The toe should be shortened and rolled to hasten break-over, which is the point that the foot can come off the ground. The longer the foot stays on the ground and the horse’s body weight moves forward, the more pressure that will be applied to the heel region of the foot. In an effort to promote heel expansion, the shoe should extend behind the heels and be slightly wider than the heels. This type of shoeing should be performed every five to six weeks. It is the rare horse that can actually go eight weeks between shoeings even without lameness.
Further treatment includes blood flow-enhancers and anti-inflammatory medications. The most common medications used to stimulate blood flow are isoxsuprine and aspirin. It is not exactly known how isoxsuprine may enhance blood flow, but several studies have shown that approximately 50% of horses with heel pain will improve with its administration. Isoxsuprine is a very safe economical medication with little reason not to attempt its use. Aspirin is used similar to its use in heart disease human patients; it changes the way blood blows, making it easier to move through blood vessels. Phenylbutazone is the most common anti-inflammatory medication used. It is important that these horses become comfortable, move with a better stride and begin to land heel-first to enhance blood flow. Another means to deliver anti-inflammatory medications more directly is sterile injection into the coffin joint and/or navicular bursa. If possible, these horses are maintained in work if comfortable. They are at least encouraged to move around by turning out every day.
The prognosis of horses afflicted with navicular disease/syndrome is generally favorable. Most of these horses will return to full athletic use. Usually, corrective and appropriate shoeing will have to be continued for the horse’s career. Occasionally, the chronic use of isoxsuprine is necessary for long-term comfort. If the response to oral medications and corrective shoeing is insufficient, then synovial injections of hyaluronic acid and corticosteroid is used to direct a more potent anti-inflammatory locally. In those cases where conservative therapy is ineffective, the horse’s occupation can be changed or a palmar digital neurectomy can be performed. Neurectomies can be very successful; however, they do not change the disease process but only change the horse’s perception of the disease process. Additionally, the nerves usually will regrow and the procedure is only temporary; the odds are definitely favorable for the surgery to be successful for several years.
Fractured Navicular Bone
Although a fracture of the navicular bone can also be classified as navicular disease/syndrome, it is worth a separate mention as the clinical signs and treatment vary. Instead of a slowly increasing bilateral lameness, the horse with a fractured navicular bone will have an acute onset consistent lameness that may be severe. The lameness is a unilateral lameness. Most of these horses will want to land toe-first instead of heel-first.
If necessary, the lameness is localized to the heel region. Good-quality radiographs are needed to assess the presence and severity of the fracture. It is important to know that a line in the navicular bone is a fracture and not a separate center of ossification, called a bipartite navicular bone. The opposite forelimb navicular bone can also be radiographed for a comparison. If the same line is present in the opposite limb, then it is a bipartite navicular bone and not a fracture.
Treatment of a fractured navicular bone also requires corrective shoeing, but it differs from shoeing for navicular disease/syndrome. The heel is elevated using a wedge pad to make the foot a little more upright than normal to decrease the tension of the deep digital flexor tendon across the navicular bone. The toe is kept short and rolled. Usually a bar shoe with clips at the medial (inside) and lateral (outside) quarters is used to help stabilize the foot. The horse will be shod this way for usually at least four to six months. Stall rest is initially required, and once the horse appears comfortable on the foot then hand walking will be commenced. The duration of stall confinement is usually 60 to 90 days with another 60 to 90 days of small paddock confinement. Additionally, phenylbutazone, isoxsuprine and aspirin are prescribed to reduce inflammation and promote blood flow respectively.
The prognosis with a fractured navicular bone is variable depending on the severity of the fracture but is relatively guarded for soundness. A significant amount of time is given to allow for healing. However, a palmar digital neurectomy is often necessary to help the horse maintain an athletic career.
Fractured Coffin Bone (Third Phalanx)
Fractures of the coffin bone are more common than fractures of the navicular bone. They can occur in multiple areas within the bone, and this will often determine the severity of clinical signs. In general, if the fracture is near the center of the bone and extends into the joint, then the horses will be more lame and the long-term prognosis may be reduced. Clinically, these horses also appear acutely with a unilateral foot lameness. The lameness is often significantly worse when the horse is circled in one direction versus the other. There may or may not be sensitivity with hoof testers in the region of the fracture.
The diagnosis is made with high-quality radiographs of the bone. Often, special oblique views are needed to identify the fracture. If the lameness is severe, then it is recommended that survey radiographs be taken of the suspected area prior to performing any peripheral nerve blocks as this may cause further damage to the fractured bone. Occasionally, slight hairline fractures may be very difficult if not impossible to observe on initial radiographs; radiographs are repeated in three to four weeks, as fractures will widen in the initial healing stages and they are more detectable radiographically at this stage.
The treatment of a fractured coffin bone is similar to a fractured navicular bone, but the duration is longer. A bar shoe with medial and lateral quarter clips is applied and often some type of impression material is placed between a pad and the sole of the hoof to give the coffin bone more generalized support. This special type of shoe is often used for one year. These horses are confined to a stall for 90 to 120 days with hand walking if comfortable. They are then allowed access to a small paddock for another 90 to 120 days. If they are doing well, they are then returned to a gradual exercise program. Phenylbutazone is administered as needed and occasionally the blood flow enhancers are used. A joint cartilage protectant medication is prescribed if the joint is involved. Rarely, if the fracture is into the joint and involves the midline of the coffin bone, a lag bone screw can be placed into the bone across the fracture line in an effort to enhance and expedite healing. This is a difficult operation with numerous possible complications and therefore is only used if absolutely necessary.
Most horses with fractures of the coffin bone have a good prognosis. Usually the fracture heals with a fibrous union and never quite disappears on the radiographs, but it is strong enough to withstand the normal stress. The only types of fractures with a poorer prognosis are the central fractures involving the joint. Occasionally these fractures will lead to secondary arthritis of the coffin joint and chronic lameness.
Laminitis (Founder)
The lamina in the equine foot connect the coffin bone to the inside of the hoof. There is sensitive lamina that covers the coffin bone that interlocks with the insensitive lamina on the inside of the hoof wall. There are numerous causes for the lamina to swell and therefore weaken the attachment of the coffin bone to the hoof wall. Generally, because of blood supply the most severely affected region is the lamina between the front edge of the coffin bone and the front hoof wall. As that area weakens, the deep digital flexor tendon continues to pull on the back of the coffin bone and usually rotation of the coffin bone is the end result. If the entire lamina becomes affected, then the support for the coffin bone is compromised everywhere and the coffin bone sinks within the foot without rotation. Sinking is considerably more rare and has a significantly worse prognosis.
Most horses with laminitis will exhibit a relatively classic stance. They want to stand with their hind legs up underneath themselves and prefer to have their front feet out in front of them and land on their heels. They will be reluctant to move and will shuffle with quick steps when forced to move. The feet will usually feel hot and have an increased pulse because of the inflammation present. It may be difficult to pick up the feet, as the horse will not want to bear weight on an affected foot. If it is possible to apply hoof testers to the soles, there is usually a painful response in the toe region.
A tentative diagnosis is commonly made based on the clinical signs. To determine the presence and severity of laminitis, radiographs must be taken. It may be necessary to “block” the feet with local anesthetic to get the horse properly positioned for radiographs. If good-quality radiographs are taken, the degree of rotation or presence of sinking can be detected, as well as the thickness of the sole, length of toe and heel and if there are any gas pockets or gas lines present which signify an abscess.
Laminitis is a medical emergency that requires immediate and often aggressive therapy. A delay in treatment can significantly reduce the prognosis for the horse. Initially, if the horse is shod then the shoes are removed. Anti-inflammatories such as phenylbutazone and intravenous DMSO are given to try to aggressively decrease the laminar swelling present between the hard coffin bone and hoof wall. Blood flow-enhancers such as isoxsuprine, acepromazine and even topical nitroglycerine patches are often used. Excessive toe is removed and the angle of the foot should be appropriate for that horse. The sole is supported with either Styrofoam or cotton or a frog support pad. The horse should be kept in a clean, dry stall with adequate bedding to encourage lying down to decrease the force exerted through the front feet. If abscesses are present, then they must be addressed with drainage and care.
Once the initial laminitis becomes stabilized and the horse is more comfortable, then corrective trimming and shoeing will be instituted. This will usually take at least seven to 10 days. Any excess toe should be trimmed and rasped. The coffin bone will have to be repositioned to its normal angle by trimming down excess heel; however, this may need to be performed gradually as you don’t want to put excessive tension on the deep digital flexor tendon too quickly. Often, some type of frog support pad or pad with impression material is used to direct more support under the frog to share the load with the hoof wall.
If the degree of rotation is severe or the horse is refractory to medical treatment of laminitis with rotation, then surgery to reduce the pull of the deep digital flexor tendon may be indicated. The deep digital flexor tendon can be transected in the standing horse in the mid-cannon region. This will temporarily reduce the constant tension of the tendon on the coffin bone. The decrease in tendon pull will usually reduce the pain acutely. For longer-term success, every effort needs to be made to realign the coffin bone with corrective trimming and shoeing, as the tendon will heal over the next several months and tension will be reestablished.
The degree of rotation, severity of clinical signs and response to initial therapy will affect the prognosis. In general, the long-term prognosis with laminitis is guarded. Horse are prone to recur as there has been damage to the structure attaching the front coffin bone to the hoof wall and this attachment will never return to original strength. In severe cases, the blood supply may also be compromised to the point that repeated abscessation is a possibility. When undertaking the treatment of a severe laminitic case, the horse owner must be committed for prolonged treatment. It takes lots of patience, time and nursing care to return these horses to comfort, and it is unfair to the horse to begin therapy and then decrease that commitment to the therapy at a later date. Additionally, an extremely capable farrier may be required for continued corrective shoeing for the life of the horse.
Summary
Lameness is the largest cause of economic loss in the equine industry. The most common location of forelimb lameness is the foot. There is a greater chance for a successful outcome if the lameness is addressed at its onset and a complete examination and workup is performed. Since the foot is the foundation of the horse, foot problems are best avoided if possible. That is best achieved with the horse having good limb and foot conformation to start, and then maintaining good conformation and support with good shoeing.