magic104
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Navicular Syndrome
If you are not quite sure what navicular disease is, join the crowd. Veterinarians don't agree as to what it really is. They prefer to call it "navicular syndrome," which signifies that a variety of problems can cause the disease.
It is not always possible to pinpoint the exact cause of the navicular syndrome. Because there are a variety of causes, no one treatment is successful.
The navicular bone is a small bone in the foot of the horse. It is a part of the bony skeleton of the leg, sitting at the posterior aspect of the joint where the third phalanx bone articulates with the second phalanx bone. The third phalanx is often called the coffin bone in the horse because it is encased in the hoof. The second phalanx is often called the short pastern bone.
The navicular bone is held in place by ligaments which arise from the dense connective tissue of the bone surface and stretch to the adjacent bones. Along the posterior aspect of the navicular bone and curling underneath it, the deep digital flexor tendon stretches to attach firmly to the under surface of the coffin bone.
As the coffin joint flexes, the deep digital flexor tendon glides against the navicular bone. This rubbing action would cause tissue damage and pain if it were not for the bursa which is located between the tendon and the bone. In the normal state, this bursa is filled with a lubricative substance which eliminates pain and tissue damage.
Definition and causes
If it were possible to define navicular disease, it would be a simple matter to describe the cause. Navicular disease has never been adequately defined, thus the term navicular syndrome is used by veterinarians to denote this fact. From time to time various theories of development have been proposed. None of them answer all of the questions about the syndrome.
Probably the oldest idea of cause is that the navicular bone undergoes changes which bring about pathology and pain in the area. While it is true that the bone often undergoes changes which can be seen in radiographs, many cases of navicular disease have no evident bony change. A dozen years ago veterinarians generally believed that the condition could be diagnosed by careful study of radiographs of the navicular bone, and certain "tell tale" changes were "proof" of navicular disease. Now most veterinarians realize diagnosis is not that simple.
Changes in the navicular bone do occur from horse to horse, just as changes always occur in bone. Certain types of foot conformation causes more pressure to come to bear on the navicular bones, from the flexor tendon which presses hard against it. Continual heavy pressure on small bones cause them to harden up, or become more dense. As this occurs the blood supply to the inner part of the bone is shut off. A popular theory of cause of navicular disease is that ischemia (reduced blood supply) is produced and this causes more damage.
The ischemic theory was very popular a decade ago. It was thought that blood clots in the capillaries supplying the navicular area brought about the ischemia. The improvement many horses showed following treatment with drugs which improve capillary blood flow was proof enough for many. Over time, however, most veterinarians have come to believe that navicular ischemia is not the entire answer to the problem.
Another early theory of cause was that the navicular bursa was at fault. Like the bursa which causes "tennis elbow," loss of lubricating fluid and inflammation causes pain and can lead to permanent damage to the bursa. Of course this may be the only cause of the syndrome in some cases, but it is not the entire answer by any means.
Some cases of navicular syndrome are caused by pathology in the coffin joint. With today's sophisticated diagnostics, however, this situation can usually be differentiated from navicular bone pathology. Sometimes navicular bone degeneration can occur along with degenerative joint disease in the coffin joint.
There is no doubt that fracture of the coffin bone will result in navicular disease, and it does sometimes happen- but not often. A fracture is easily diagnosed with x-ray. Usually, however, there are other causes of the syndrome.
As difficult as it is to diagnose the navicular syndrome, it is even more difficult to determine if a horse is going to get navicular disease. This is why veterinarians do not generally prognosticate about a possible navicular problem when doing a pre-purchase veterinary exam. There is simply no way to tell for sure that a horse is going to have a problem.
There are predisposing factors for navicular disease. Younger horses tend to be effected more. Certain breeds of horses are more effected. This relates more to size of the feet in relation to the size of the body, than to breed. Quarter horses do have a higher incidence of the problem than other breeds. The smaller the foot on a large horse, the more likely the horse is to develop navicular disease. The activity of the horse may be an important factor.
Barrel racing, for example, puts a lot of stress on the horse's foot, and can tend to lead to navicular disease, some people believe. Contrary to the activity theory of predisposition is the genetics theory. There is at least one study which shows a genetic predisposition to navicular syndrome. This may relate to the conformation of the foot and the natural angle of the pastern. Some believe that the more upright the pastern is, the more likely the horse to develop navicular syndrome.
It is also seen in horses with vastly different foot shapes. It is a common condition in Quarter Horses, which have narrow, upright, boxy feet, small relative to their body size, as well as in European Warmblood horses, which have relatively tall narrow feet. It is also common in Thorouugbred horses, which frequently have rather flat feet with low collapsed heels. <font color="red"> </font>
Navicular Syndrome
If you are not quite sure what navicular disease is, join the crowd. Veterinarians don't agree as to what it really is. They prefer to call it "navicular syndrome," which signifies that a variety of problems can cause the disease.
It is not always possible to pinpoint the exact cause of the navicular syndrome. Because there are a variety of causes, no one treatment is successful.
The navicular bone is a small bone in the foot of the horse. It is a part of the bony skeleton of the leg, sitting at the posterior aspect of the joint where the third phalanx bone articulates with the second phalanx bone. The third phalanx is often called the coffin bone in the horse because it is encased in the hoof. The second phalanx is often called the short pastern bone.
The navicular bone is held in place by ligaments which arise from the dense connective tissue of the bone surface and stretch to the adjacent bones. Along the posterior aspect of the navicular bone and curling underneath it, the deep digital flexor tendon stretches to attach firmly to the under surface of the coffin bone.
As the coffin joint flexes, the deep digital flexor tendon glides against the navicular bone. This rubbing action would cause tissue damage and pain if it were not for the bursa which is located between the tendon and the bone. In the normal state, this bursa is filled with a lubricative substance which eliminates pain and tissue damage.
Definition and causes
If it were possible to define navicular disease, it would be a simple matter to describe the cause. Navicular disease has never been adequately defined, thus the term navicular syndrome is used by veterinarians to denote this fact. From time to time various theories of development have been proposed. None of them answer all of the questions about the syndrome.
Probably the oldest idea of cause is that the navicular bone undergoes changes which bring about pathology and pain in the area. While it is true that the bone often undergoes changes which can be seen in radiographs, many cases of navicular disease have no evident bony change. A dozen years ago veterinarians generally believed that the condition could be diagnosed by careful study of radiographs of the navicular bone, and certain "tell tale" changes were "proof" of navicular disease. Now most veterinarians realize diagnosis is not that simple.
Changes in the navicular bone do occur from horse to horse, just as changes always occur in bone. Certain types of foot conformation causes more pressure to come to bear on the navicular bones, from the flexor tendon which presses hard against it. Continual heavy pressure on small bones cause them to harden up, or become more dense. As this occurs the blood supply to the inner part of the bone is shut off. A popular theory of cause of navicular disease is that ischemia (reduced blood supply) is produced and this causes more damage.
The ischemic theory was very popular a decade ago. It was thought that blood clots in the capillaries supplying the navicular area brought about the ischemia. The improvement many horses showed following treatment with drugs which improve capillary blood flow was proof enough for many. Over time, however, most veterinarians have come to believe that navicular ischemia is not the entire answer to the problem.
Another early theory of cause was that the navicular bursa was at fault. Like the bursa which causes "tennis elbow," loss of lubricating fluid and inflammation causes pain and can lead to permanent damage to the bursa. Of course this may be the only cause of the syndrome in some cases, but it is not the entire answer by any means.
Some cases of navicular syndrome are caused by pathology in the coffin joint. With today's sophisticated diagnostics, however, this situation can usually be differentiated from navicular bone pathology. Sometimes navicular bone degeneration can occur along with degenerative joint disease in the coffin joint.
There is no doubt that fracture of the coffin bone will result in navicular disease, and it does sometimes happen- but not often. A fracture is easily diagnosed with x-ray. Usually, however, there are other causes of the syndrome.
As difficult as it is to diagnose the navicular syndrome, it is even more difficult to determine if a horse is going to get navicular disease. This is why veterinarians do not generally prognosticate about a possible navicular problem when doing a pre-purchase veterinary exam. There is simply no way to tell for sure that a horse is going to have a problem.
There are predisposing factors for navicular disease. Younger horses tend to be effected more. Certain breeds of horses are more effected. This relates more to size of the feet in relation to the size of the body, than to breed. Quarter horses do have a higher incidence of the problem than other breeds. The smaller the foot on a large horse, the more likely the horse is to develop navicular disease. The activity of the horse may be an important factor.
Barrel racing, for example, puts a lot of stress on the horse's foot, and can tend to lead to navicular disease, some people believe. Contrary to the activity theory of predisposition is the genetics theory. There is at least one study which shows a genetic predisposition to navicular syndrome. This may relate to the conformation of the foot and the natural angle of the pastern. Some believe that the more upright the pastern is, the more likely the horse to develop navicular syndrome.
It is also seen in horses with vastly different foot shapes. It is a common condition in Quarter Horses, which have narrow, upright, boxy feet, small relative to their body size, as well as in European Warmblood horses, which have relatively tall narrow feet. It is also common in Thorouugbred horses, which frequently have rather flat feet with low collapsed heels. <font color="red"> </font>