_Differential Diagnosis_.--Navicular disease may be mistaken for ordinary contracted foot. It will be remembered, however, that in the early stages of navicular disease contraction is absent, and that it is only when the disease in the bursa is of long standing that contraction comes on. With ordinary contracted foot, too, careful paring and suitable shoeing soon sees a diminution in the degree of lameness, and a return to the normal in shape (see Treatment of Contracted Foot, p. 125). With navicular disease, however, such shoeing as is beneficial in the treatment of contracted foot (notably the various methods of giving to the frog counter-pressure with ground) soon brings on an aggravation of the lameness.

It is, perhaps, even more likely to be confounded with contraction when we have with the contraction a state of atrophy and thrush of the frog. With a frog in this condition pressure will give rise to pain, and navicular disease be erroneously judged to be present. In such a case we must rely wholly upon either extreme flexion or extreme extension of the joint to guide us, when, if contraction _only_ is the offending condition, no symptom of pain will be shown.

Navicular disease may also be confused with rheumatic affections, with sprain of the posterior ligaments of the first interphalangeal articulation, and with sesamoid lameness. Mistakes are sometimes made, too, especially with a hasty observer, in confounding it with shoulder lameness.

In rheumatism the constant changing of the seat of pain, the sometimes elevated temperature, and the appearance of symptoms of heat, tenderness, and swelling in the affected area should guide one to a right conclusion.

In sprain of the posterior ligaments of the coronet and in sesamoid lameness, nothing but a careful examination and manipulation of the parts will ward off error, for in each of these cases there is 'pointing' and resting of the limb, and considerable disinclination to put weight firmly upon it. If at the same time manipulation gives distinct evidence of pain, all doubt may be set at rest.

Roughly speaking, sesamoid lameness is a condition of the gliding surface of the sesamoids, and the face of the tendon playing over them, similar to that found in navicular disease. All symptoms of pointing, the constant maintaining of the limb in a state of flexion, and a feeling manner of progression are again all present. It is plain from this that in all cases where an animal with a gait at all suggestive of navicular disease is brought for our examination, the manipulation of the limb should be thorough. The character of the lameness is almost sure to deceive us; and it is not until we are able to obtain local symptoms pointing to the one or the other of the conditions we have enumerated that a decisive opinion may be given. In sesamoid lameness the local symptoms are those of heat and pain in the fetlock on palpation, and a swelling of the affected parts, such swelling being at first slight, yielding, and barely distinguishable, and afterwards larger, bony and hard, and more marked. Later still there is distinct evidence of 'knuckling' over at the fetlock and inability to fully flex it.

In cases of shoulder lameness the gait alone should be sufficient to render liability of error small, for with nearly every case there is a manifest inability to 'get the limb forward', and this is best seen at a side view when the animal is trotting past the observer. When trotting towards one, there is a further and unmistakable symptom common to most shoulder lamenesses that serves to distinguish it at once, and that is the peculiar 'sweeping' outwards with the affected limb.

Lastly, with either of the conditions we have just mentioned, it is the exception to get contracted foot follow on. With navicular disease it sooner or later makes its appearance.

_Prognosis_.--The prognosis of navicular disease (once diagnosed with certainty) must almost of necessity be unfavourable. The facts that the disease has made serious progress before it is really noticeable, that the situation of the parts prohibits operative interference, and that the disease is one of a chronic and slowly progressive type, all point to an unfavourable termination.

_Treatment_.--We have seen from the pathology of this disease that it may commence either as a rarefactive ost.i.tis, or as a synovitis and tenositis in connection with the bursa. With the former condition in existence, or when this and the synovitis has led to erosion of the cartilage, treatment is probably of no avail, on account of the more chronic nature of these two conditions. When, however, the condition is simply that of synovitis or tenositis, a more or less acute condition, we may a.s.sume that suitable treatment and a long rest will bring about resolution.

The first indications in treatment are those of what we may term 'nursing'

the foot. It should have sufficient rest, should be placed so as to minimize as far as possible compression of the parts, and should have its posterior half treated so as to render it softer and less liable to concussion.

The period of rest required cannot be satisfactorily advised, and the pract.i.tioner is wise who makes it a long one. Best should be advised, in fact, long after symptoms of lameness have disappeared and recovery is judged to have taken place.

Compression of the parts may be somewhat minimized, if the animal be kept in the stable, by allowing the floor upon which the front-feet are to stand to be slightly sloping from behind forwards. The same effect, though not so marked, is obtained by removing the shoes, and considerably lowering the wall at the toe, while allowing that of the heels to remain. It may here be remarked that it is a good practice to allow the shoes to remain on, and this even when the animal is at gra.s.s. They should, however, be frequently removed, and the foot trimmed as we have directed.

With the foot thus trimmed so as to most suitably adjust the angles of the articulations, it should next be thoroughly pared and rasped in its posterior half, so as to render the horn of the sole and the frog and the horn of the quarters as thin as possible. The heels, however, should not be excessively lowered, _if at all_. We now have the foot in a soft condition, and easily expanded. It should, if possible, be kept so; and this may be done either by the use of poultices, by tepid baths, or by standing the animal upon a bedding that may easily be kept constantly damp. Such materials as tan, peat moss, or sawdust, are either of them suitable.

All this, of course, calls for keeping the animal in the stable. It is far better, however, more especially if a piece of marshy land is at hand, to turn him out in that. A moderate amount of exercise is beneficial rather than not, and the feet are thus constantly kept damp without trouble to the attendants.

The second indication in the treatment is that of applying a counter-irritant as near to the diseased parts as possible. Regarding its efficacy we must confess to being somewhat sceptical. The treatment has been constantly practised and advised, however, and we feel bound to give it mention here. A smart blister may, therefore, be applied to the whole of the coronet, and need not be prevented from running into the hollow of the heel.

Instead of blistering the coronet (or in conjunction with that treatment), the counter-irritant may be applied by pa.s.sing a seton through the plantar cushion or fibro-fatty frog. Setoning the frog appears to have been introduced by Sewell. In many cases great benefit is claimed to have been derived from it, especially by English veterinarians of Sewell's time, and by others on the Continent. Percival, however, was not an advocate for it, and, at the present day, it is a practice which appears to have dropped out of use altogether.

[Ill.u.s.tration: FIG. 164.--FROG SETON NEEDLE.]

To perform this operation a seton needle of a curved pattern is needed (see Fig. 164). This is threaded with a piece of stout tape dressed with a cantharides, h.e.l.lebore, or other blistering ointment, and then pa.s.sed in at the hollow of the heel, emerging at the point of the frog. The course the needle should take will be understood from a reference to Fig. 165.

The seton may be pa.s.sed with the horse in the standing position. Previously the point of the frog should be thinned, and the animal should be twitched.

After-treatment consists simply in moving the seton daily, and dressing it occasionally with any stimulating ointment, or with turpentine.

If, in spite of these treatments, the disease persists, then nothing remains but neurectomy.

D. DISLOCATIONS.

The firm and rigid manner in which the bones of the pedal articulation are held together renders dislocation of this joint an exceedingly rare occurrence, and then it is only liable to happen under the operation of great force. In the literature to our hand we have only been successful in discovering one reported instance, and, strange to say, in this, a well-marked case, the cause was altogether obscure. We quote the case at the end of this section.

[Ill.u.s.tration: FIG. 165.--DIAGRAM SHOWING THE COURSE TAKEN BY THE NEEDLE WHEN SETONING THE FROG. This is shown by the dotted curved line _a, b_.

1, The navicular bone; 2, the plantar cushion; 3, the os pedis; 4, the perforans tendon.]

A partial dislocation of this articulation is the condition met with in 'b.u.t.tress Foot.' In this case the fracture of the pyramidal process, and the consequent lengthening of the tendon of the extensor pedis, allows the os coronae to occupy upon the articulatory surface of the os pedis a more backward position than normally it should.

It is quite probable, too, that slight lesions of the other restraining ligaments and tendons of the articulation may bring about a similar though less marked condition. We may be quite sure of this--that whenever such lesions (as, for example, sprain and partial rupture of the lateral ligaments) do occur, and the normal position of the opposing bones is changed, if only slightly, that great pain and excessive lameness must be the result, and this with but little to show in the foot. Many of our cases of obscure foot lameness might, if capable of demonstration, turn out to be cases of sprain and partial dislocation of the pedal articulation.

_Recorded Case_.--'The animal, a trooper of the 8th Hussars, was found on the morning of April 17 unable to bear any weight on the limb (the near hind). Cause not known--the heel-rope I thought at first; but on investigation I found the heel-rope had been on the other leg.

_Diagnosis_.--Dislocation of the left os coronae from the articulating surface of the os pedis in a backward direction.

'Every devisable means were unsuccessful in reducing the limb to its natural position. The horse was thrown, and a strong rope, with four men pulling at it, was fastened round the hoof, whilst I put my knee to the back of the pastern, using all possible force, with one hand to the foot and the other to the fetlock, but all to no purpose. Next day other means were tried. First by throwing the horse and placing him on his belly, with the fore-legs stretched out forwards, and the hind-legs backwards. This I did so as to get the injured limb placed as nearly flat on the ground as possible, with its anterior aspect downwards. Then a very heavy man, with his boots off, was made to jump on the back of the pastern, where the prominence showed most; and afterwards, when these means failed, a strong piece of wood, well covered with leather, was placed (where the hollow of the heel ought to have been) on the most prominent part, and hit several times with a heavy hammer; but all efforts were futile.

'_Prognosis_.--Unfavourable. During the latter operations I had a very strong pressure applied to the hoof, and the horse firmly fastened in every way, and it appeared as though no amount of force would ever reduce the dislocation.

'_Tautological_.--The case was destroyed on April 30, being of no further use to the service.

'_Post-mortem_.--The os coronae was found to have slipped out of the articulating cavity of the os pedis, backwards and past the lateral ligaments. These last-named structures prevented the bone being forced forward into its proper position, being firmly locked over the lateral prominences. The capsular ligament was considerably lacerated and inflamed, causing slight effusion and swelling about the region of the coronet.'[A]

[Footnote A: T. Flintoff, A.V.D., _Veterinary Journal_, vol. xix., p. 74.]

_Treatment_.--After the forcible means of reduction related by Mr.

Flintoff, we may add that when they are successful, they should be followed by suitable bandaging of the parts, and rest. The first is effected by applying plaster of Paris and linen, and the second by having the animal put in slings.

THE END