Dressage Today | 2000

Your horse has been 'off' lately so you call your local veterinarian. The vet watches your horse move. Your horse is landing on his toe, avoiding his heels. He is more lame on hard surfaces and tight turns. He reacts to hoof testers in the heel area. The vet blocks the back half of the horse's foot (palmer digital block.) and then trots and turns him on a hard surface. Your horse seems to move better. X-rays are taken and then the next day you get the news. Your horse has navicular changes!

Before you lay a wreath over your show schedule there are some things you need to have checked out. There are many problems that can cause pain in the back half of the foot and that respond positively to a palmer digital block.

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 a heel lameness. Like navicular 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.

Corns can be caused by:

1. A shoe being left on for too long where the hoof wall outgrows 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 and never rest on the sole.
3. Horses that wear heels calks too long. On hard surfaces the heel calks 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. Collapsed heels that move inward when weight is applied to the foot. This bruises the sensitive issues in the area of the seat of the corn.
6. Tearing of the wall just behind the quarters. This occurs with horses that have a dramatic flare behind the quarters causing tearing of the sensitive laminae.
7. 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 of the sensitive laminae in the seat of the corns.
4. 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 creates heel soreness and can mimic navicular symptoms.
5. 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.
6. 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 suppler than the rest of the foot and a puncture foot may go unnoticed. Infection in the bulb of the heel.
7. 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.
8. Thrush. Deep seated thrush especially in the central sulcus of the frog.
9. Separation of the white line at or behind the quarters, with or without infection.
10. Foot imbalance. Overloading of a heel because of an imbalance in the foot or because of an uneven footfall.
11. Inactivity. Lack of circulation because of inactivity (prolonged stabling).
12. Coffin Bone. Fracture to the wing of the pedal bone. Osteitis (inflammation) of the wings of the pedal bone. Tearing of the attachment of the lateral cartilage to the pedal bone. Inflammation of the deep digital flexor tendon at its attachment to the coffin bone.
13. Quittor. Quittor (infection of the lateral cartilage).
14. Suspensory Ligament of the Navicular. Tearing of the suspensory ligament of the navicular bone at its attachment to the Navicular bone.
15. Navicular bursitis. , Or inflammation of the Navicular bursa.
16. Flexor Surface Damage to the flexor surface of the Navicular bone, especially in horses with broken back hoof pastern axis.
17. Adhesions of the deep flexor tendon to the Navicular bone and/or other parts of the sheath of the flexor tendon.

No wonder many posterior hoof problems are labeled Navicular Disease. No wonder there is 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 anaesthetic, 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.

The back half of the 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.

The limitations of using this procedure are:

1. There are almost 30 different conditions that cause pain in the back half of the hoof (that may respond to palmer digital nerve blocks).
2. Many horses with no signs of lameness or soreness have radiographic changes on X-rays.