Navicular Disease | 1999

Q. My horse was diagnosed with Navicular Disease. What is Navicular Disease and his there anything I can do for my horse?

Definition: Navicular Disease has been recognized since the 18th century as a cause of chronic lameness involving the front legs of horses. However, a lot of research has been done as to the cause and the development of the disease but there is no one thought as to the exact cause or the development of this disease in the horse.

Cause: There appears to be two main fields of thought as to cause.

  1. That Navicular Disease is a disease where the blood supply to and/or from the navicular bone is disrupted. When the horse places his weight on a limb, the bone column pushes down on the foot's sensitive structures. The blood is then 'squeezed' from the foot. If there is damage to the vasculature to and from the navicular bone the blood cannot evacuate properly. This causes an increase in the blood pressure within the navicular bone, causing pain.
  2. That Navicular Disease is a degenerative disease, similar to arthritis. Changes in the navicular bone bear considerable similarities to degenerative joint disease of the pastern and small hock joints.

It seems most likely that abnormal biomechanical stresses are the basis for the disease. Horses with long toes/low heels or horses that spend their life in 'soup bowl' stalls are out of balance and place lots of stress on the navicular area of the foot.

Signs: Horses with Navicular Disease usually have a chronic progressive lameness, which may be intermittent in the early stages of the condition. Horses will often improve with short rest periods, only for the lameness to return when the horse resumes more frequent exercise. Owners usually complain about the horse "not moving out" or being "tied up in the shoulders".

The lameness of Navicular Disease is characterized by a shuffling forelimb gait, the foot landing toe first, a shortened length of the stride and aggravation of the lameness upon sudden turning. Lunging or trotting the horse in a tight circle will aggravate the lameness when the affected leg is on the inside.

Treatment: Treatment falls into three categories;

  • Pain alleviation with a neurectomy
  • Treatment with drugs
  • Corrective shoeing and hoof trimming

Pain alleviation and treatment with drugs are the veterinarian's responsibility.

Corrective shoeing and hoof trimming can be as simple as balancing the foot, putting on a shoe with the correct amount of extension, backing up a toe, egg bar shoes with or without wedge pads and rocker toe shoes. Balance is the key to successfully shoeing a 'navicular horse'.

Your farrier and vet should get together and start the process of drug therapy and therapeutic shoeing. If your horse does not respond to one type of drug or shoeing don't be afraid to ask for changes. Sometimes a slight change in the shoeing can make a big difference to the horse.

I would caution you to go slowly. Don't make multiple changes at the same time. If you introduced a new drug and a new type of shoeing at the same time you would not know whether he is responding negatively or positively to the drugs or the shoeing.

Prognosis: Prognosis is good for those horses that do not actually have Navicular Disease but have been diagnosed as having pain in the rear of the foot. For horses with navicular problems the prognosis is poor. Severe cases will require surgery to sever the post digital nerve. (neurectomy)

However, before you lay a wreath over your show schedule there are some things you need to have checked out. There are many things that mimic the clinical signs of Navicular Disease. They can cause pain in the back half of the foot, respond to hoof testers, force the horse to land toe first and react positively to a palmer digital block.

Part II

The back half of the horse's foot is a "diagnostic nightmare". Many Veterinarians diagnose Navicular Disease when they block the palmer digital nerve and see an improvement in the lameness, then take X-rays and see radiographic changes in the navicular bone.

Here's a list of problems you need to rule out before you label your horse navicular.

  1. Cracks. Look closely at the outside of your horse's feet. Are there cracks in the quarters or heel area? A crack may trap sensitive tissue between the horn, during weight bearing, causing pain. Once the crack is stabilized you will notice a vast improvement in your horse's movement.

    Check the bars on the bottom of the horse's feet. A bar crack can often go undetected and cause a great deal of discomfort to the horse. If you see a crack bring it to the attention of your farrier.

  2. Sheared Heels. Horses that do not have ideal conformation will have one side of the hoof bearing more weight than the other. Uneven weight distribution will cause the hoof wall bearing the most weigh to be pushed upward giving the horse an uneven coronary band. Pick up the foot and look down the foot like your farrier does to check level. If the coronary band is higher on one side of the bulbs than the other he may have sheared heels. Sheared heels will result in tearing of the digital cushion and create heel pain.
  3. Corns. A corn is a bruising of the sole between the bars and hoof wall and creating heel lameness. Like Navicular Disease the horse tends to land toe first, is lame at a trot on hard surfaces and lame on tight turns. Hoof testers on the heels will give a positive response. A palmer digital block gives the horse relief.
  4. Corns can be caused by:

    1. A shoe being left on for too long where the hoof wall overgrows the shoe and the shoe is resting on the area between the bars and hoof wall.
    2. A shoe that is too short or too tight. The shoe should always cover the buttresses of the foot and never rest on the sole.
    3. Horses that wear heels caulks too long. On hard surfaces the heel caulks put pressure right over the seat of the corns.
    4. Pads that are riveted on to the shoe where the rivet applies pressure over the seat of the corn.
    5. A large horse with big feet shod with too light a shoe. Too light a shoe will not support the heels on a heavy horse causing tearing and bruising.
  5. Contracted Feet. When the foot is contracted to the point where the foot is wider at the coronary band, at the quarter, than it it's at the bearing surface the sensitive structures of the foot become compressed. This may create heel soreness and can mimic navicular symptoms.
  6. Crushed Heels. On a normal foot the angle of the heels should be the same as the angle on the front of the hoof capsule. If the heel angle is lower, then heels can be said to be underrun. When the horn rolls under pressure can be put on the sensitive laminae, bruising the laminae and causing a corn.
  7. Puncture wounds. In the heel area of a horse's foot is the digital or plantar cushion. The digital cushion is a wedged-shaped, fatty and has little blood supply or nerve supply. It is designed to absorb shock and cushions the bones. Because the digital cushion has a low nerve supply puncture wounds in the sulci of the frog can appear as a low-grade heel lameness that may mimic navicular problems. The frog is more supple than the rest of the foot and a puncture foot may go unnoticed.
  8. Bruising. Bruising of the sensitive sole and frog. Bruising of the coronet at the heel. Cross firing injuries to the inside heel or over-reaching injuries to either heel.
  9. Thrush. Deep-seated thrush especially in the central sulcus of the frog will create soreness in the heel area. Shoeing cannot resolve this problem. Good horse husbandry is required to prevent thrush from becoming an issue at all.
  10. Separation of the white line at or behind the quarters, with or without infection. Bare foot horses or horses whose feet are not dressed properly will have flares. Flares are nothing more than hoof wall torn from its connection to the sensitive laminae.
  11. Foot imbalance. Overloading of a heel because of an imbalance in the foot or because of an uneven footfall. The may be caused by improper hoof preparation by the farrier or poor conformation of the horse.
  12. Inactivity. Lack of circulation because of inactivity (prolonged stabling). Horses that are kept in small areas, stalls, for long periods of time can develop circulatory problems. Although it is a myth that the frog is the pumping mechanism, movement is necessary for good foot/leg circulation.
  13. Suspensory Ligament of the Navicular. Tearing of the suspensory ligament of the navicular bone at its attachment to the Navicular bone will cause lameness. Without the diagnostic aid of an MRI these soft tissue injuries will go un diagnosed.
  14. Navicular bursitis. Inflammation of the Navicular bursa will cause heel pain. The treatment is a combination of drugs, from the vet, and balanced shoeing from the farrier.

No wonder many posterior hoof problems are labeled Navicular Disease and we see so many 'cures' for the syndrome.

An accurate diagnosis of the Navicular syndrome requires: experience, a keen eye, judicious use of the hoof testers, flexion and extension tests, local anesthetic, an eye for balance, an accurate history, good quality radiographs, and you could still be left guessing.

Because there are so many causes of pain in the posterior half of the foot, there is no single shoeing method that is likely to be effective.

To be able to give an accurate prognosis and treat the condition effectively, the diagnosis must be accurate, and the corrective or therapeutic shoeing must be designed to correct the condition causing the pain.