Symptoms and Diagnosis. - In the early stages of navicular disease the symptoms are obscure. Pointing of the affected limb is the first evidence the animal gives. This, however, more often than not, goes unnoticed, and the first symptom usually observed by the owner or attendant is the lameness. Even this is such as to at first occasion no alarm, being intermittent and slight, and only very gradually becoming marked. In a few cases, however, lameness will come on suddenly, and is excessive from the commencement. It is the lameness, slow in its onset, intermittent in its character, and gradual in its progress, however, that is ordinarily characteristic of navicular disease.

The animal is taken out from the stable sound, with just a vague suspicion, perhaps, that he moved a bit stiffly. While out he is thought by his driver or rider to be going feelingly with one foot or with both. Even this is not marked, and the driver has some difficulty in assuring himself whether or no he really observed it, or whether it was but imagination.

On the return home the limb is examined, and nothing abnormal is to be found. The leg is of its normal appearance, and neither heat nor tenderness is to be observed in it or in the foot. On the following day the animal again is sound, and the lameness of the previous day is put down to a slight strain or something equally simple. The patient is then, perhaps, rested for a day or two. When next he is worked he again moves out from the stable sound, but again during the going gives the driver the unpleasant impression that something is amiss; and so the case goes on. One day the owner fears the animal is becoming seriously enough affected to warrant him in calling in his veterinary surgeon; the next he is confidently assuring himself that nothing is wrong.

Perhaps the animal is now rested for a week or two, or even for a month or two, hoping that this will put him sound. Immediately on commencing work, however, the same symptoms as before assert themselves, and the veterinary surgeon is called in.

With a history such as we have given the veterinarian's suspicions are aroused. He has the animal trotted, and may notice at this stage that there is an inclination to go on the toes, that the lame limb or limbs are not put forward freely, and that progression is stilty and uncertain; it is such, in fact, as to at once suggest the possibility of corns being present.

In some cases there is just the suspicion of a limp with one limb, and this only at intervals during the trot. At one moment the veterinarian is positive that he sees the animal going lame; at another he is just as confident he sees him coming towards him sound.

Nothing is found in the limb - neither heat, tenderness, nor swelling. There is nothing in the gait (either a limited movement of the radius, or a circular sweep with the leg) to indicate shoulder or other lameness, and the veterinary surgeon, by eliminative evidence, is bound to conclude that the trouble is in the foot.

The foot is then examined - pared, percussed, pinched, and in other ways manipulated - but nothing further is forthcoming. In such a case the veterinary surgeon is wise to declare the abortive result of his examination, to hint darkly of his suspicions, and to suggest a second examination at some future date. It may be that two, three, four, or even more, such examinations are necessary before he can justly pronounce a positive verdict.

Later he is enabled to do this by an increase in the severity of the symptoms, and by the changes that take place in the form of the foot. The lameness is now more marked, and the 'pointing' in the stable more frequent. With regard to the latter symptom, it has been seriously discussed whether the horse with navicular disease points with the heel elevated or with it pressed to the ground. In either case, of course, the limb is advanced; but while some hold that the phalangeal articulations are flexed and the heel slightly raised, in order to relieve the pressure of the perforans tendon on the affected area, and so obtain ease, there are others who hold that the heel is pressed firmly to the ground in order to deaden the pain. It may be, and most probably is, that both are right; but, in our opinion, there is no doubt whatever that pointing with the heel elevated is by far the most common.

The lameness is now excessive, and is especially noticeable when the animal is put to work on a rough or on a hard ground. Even now, however, heat of the foot or tenderness is so slight as to be out of all proportion to the alteration in gait.

With the case thus far advanced, evidence of pain may be obtained by pressing with the thumb in the hollow of the heel. Evidence of pain may also be obtained by using the farrier's pincers on the frog. These methods, however, are never wholly satisfactory, as a horse with the soundest of feet will sometimes flinch under these manipulations.

Extreme and forcible flexion of the corono-pedal articulation also sometimes gives evidence of tenderness. In this case the foot is held up, the animal's metacarpus resting on the operator's knee, and the toe of the hoof pushed downwards with some degree of force.

The same movement of the joint is given by causing the animal to put full weight upon the diseased limb, a small wedge of wood being first placed under the toe. In this manner the pressure of the perforans tendon upon the bursa is greatly increased, and the animal is caused to show symptoms of distress.

The lameness may also be increased, and diagnosis helped, by paring the heels, so as to leave the frog prominent and take the whole of the body-weight. The same end is also obtained by applying a bar shoe. This was originally pointed out by Brauell, and is quoted by Zundel and by Möller.

The changes in the form of the hoof may now be noticed. These are largely dependent on the fact that more or less constantly the patient saves the heel. The horn of the walls in this region, and the horn of the frog, is thereby put out of action and induced to atrophy. The hoof gradually assumes a more upright shape, and the heels contract. We thus get a hoof which is visibly narrowed from side to side, with a frog that is atrophied and often thrushy, and with a sole that is abnormally concave, hard, and affected with corns.

When occurring in the hind-feet - a condition that is rare, but which has been noticed by Loiset, and quoted by Zundel - the animal is stiff behind, walks on his toes, and gives one the impression that he is suffering from some affection in the region of the loins.

One such case is reported by an English veterinary surgeon, and we quote it here:

'A gray gelding, and a capital hunter, the property of a gentleman in this neighbourhood, became lame in the near fore-foot after the hunting season of 1859. The lameness was believed to be due to navicular disease. The operation of neurectomy was ultimately had recourse to. The horse subsequently did his work as well as ever, and was ridden to hounds regularly till the end of the year 1861, when he went lame of the off fore-foot. From this date he also showed very peculiar action behind, and was at times lame of both hind-limbs without any apparent cause.

'In the year 1862, from the groom's indiscreet use of physic, super-purgation was brought on which caused the animal's death. On a post-mortem examination being made, the horse was found to have navicular disease of all four feet. It is worthy of note that this horse had always "extravagant" action behind, but was a remarkably quick and good jumper.'[A]

[Footnote A: F. Blakeway, M.R.C.V.S., Veterinarian, vol. ii., p. 21.]