As a general rule, it may be taken that most diseases of the foot are comparatively easy of diagnosis. When, however, the condition is one which commences simply with an initial lameness, the greatest care will have to be exercised by the practitioner.
What remarks follow here should rightly be confined to a treatise on lameness. This much, however, we may state: As compared with lameness arising from abnormal conditions in other parts of the limb, that emanating from abnormalities of the foot is easy of detection. With a case of lameness before him, concerning which he is in doubt, the practitioner remembers that a very large percentage may safely be referred to the foot, and, if wise, subjects the foot to a rigorous examination.
Much may be gathered by first putting the animal through his paces. When at a trot, notice the peculiarity of the 'drop,' whether any alteration in going on hard or soft ground, and watch for any special characteristic in gait. At the same time inquiry should be made as to the history of the case; its duration; whether pain, as evidenced by lameness, is constant or periodic; the effect of exercise on the lameness; and the length of time elapsed since the last shoeing.
This failing to reveal adequate cause for the lameness in any higher part of the limb, one is led, by a process of negative deduction, to suspect the foot. If 'pointing' is a symptom, its manner is noticed. The foot is compared with the other for any deviation from the normal. In some cases the two fore or the two hind feet may differ in size. Though this may not necessarily indicate disease, it may, nevertheless, be taken into account if the lameness is not easily referable to any other member. Measurement with calipers will then be of help, and a pronounced increase in size, especially if marked in one position only, given due consideration. The hand is used upon each foot alternately to look for change of temperature, to detect the presence of growths small enough to escape the eye, and to discover evidence of painful spots along the coronet.
At this stage the method of percussion recommends itself, and in many cases no more useful diagnostic agent is to be found than the ordinary hammer. As a preliminary, the foot of the sound limb should be always tapped first. This precaution will serve to bring to light what is frequently met with - the aversion nervous animals sometimes exhibit to this manner of manipulation of the hoof. Unless this is done, the ordinary objection to interference is apt to be read as evidence of pain. No aversion to the method being shown, the suspected foot is gently tapped in various places round the wall, a keen look-out being kept for any manifestation of tenderness. This may vary from a slight resentment to each tap, indicated by a sudden lifting and setting down again of the foot, to a complete removal of the foot from the ground, and a characteristic pawing of the air that points out clearly enough the seat of pain.
Evidence of pain once given, the tapping is persisted in until, in some cases, the exact position of the tender spot is definitely located.
Failing evidence obtained from percussion, attention should next be given to the shoeing. We may add here that, even when difficulties have to be encountered in doing it, it is always a wise plan to have the shoe removed.
The nails should be removed one by one, the course they have taken, their point of emergence on the wall, and the condition of their broken ends all being carefully noted as they are withdrawn.
The removed shoe should next be examined as to the coarseness or fineness of its punching and the 'pitch' of its nail-holes, and close attention given to the shape of its bearing surface.
From that we may pass to a consideration of the underneath surface of the foot. The drawing-knife should be run lightly over the whole of its surface, the first thing to be noticed being the point of entrance of the nails as compared with the coarseness or fineness of the punching, and the staining or otherwise of the horn immediately around. We may thus be guided towards mischief arising from tight nailing apart from actual prick of the foot.
This done, more than usual care should be taken in following up any other small prick or dark spot that may show itself upon the white surface of the cleaned sole. In any case, a suspicious-looking speck should be followed up with the searcher until it is either cut out or is traced to the sensitive structures.
While this is done, we should also have noticed the condition of the horn at the seat of corn; should have noticed the shape of the heels, contracted or otherwise; and the appearance of the frog, clean or discharging.
A point to be remembered in making this exploratory paring of the foot is the peculiar consistency of the horn of the frog, and its tendency to hide the existence of punctures. In like manner, as a pin pierces a piece of indiarubber, and leaves no clearly visible trace of the hole it has made, so does a nail or other sharp object penetrate the frog, leaving but little to show for the mischief that has been done.
After all, even though we may have fully decided the foot is at fault, our case of lameness may remain obscure so far as a cause is concerned. Nothing remains, then, but to acknowledge the inability to discover it, to advocate poulticing, or some other expectant palliative measure, and to bring the case up for further examination at no distant date. Where, though we may have suspected the foot, we have not been able to definitely assure ourselves that there the mischief is to be found, a further method of examination presents itself - namely, subcutaneous injections of cocaine along the course of the plantar nerves.
The salt of cocaine used is the hydrochlorate, 2-1/2 grains for a pony, 4 grains for a medium-sized animal, and 6 grains for a large horse. A solution of this is made in boiled water (about 3 drams), and injected at the seat of the lower operation of neurectomy.
It is advisable to first render aseptic the seat of operation, and to sterilize both the needle and the syringe by boiling. A suitable point to choose for the injection is exactly over the upper border of the lateral faces of the two sesamoids, the needle being introduced behind the cord formed by the nerve and accompanying vessels, and parallel with it.
It is possible that the vein or the artery may be wounded, but such accident is of little importance. All that is necessary in that case is to partly withdraw the needle and again insert it. It is advisable to use a twitch.
When the needle is in position, the injection should be made slowly, and at the same time the point of the needle should be made to describe a semicircular sweep, so as to spread the solution over as wide an area as is possible.
Anaesthesia ensues in from six to twenty minutes, and if the cause of the lameness is below the point of injection the animal moves sound.
Regarding this method of diagnosis, Professor Udriski of Bucharest, after a series of trials, sums up as follows:
1. For the diagnosis of lameness cocaine injections are of very considerable value.
2. These injections should be made along the course of the nerves.
3. Solutions heated to 40° or 50° C. produced quicker, deeper, and longer anaesthesia than equally strong cold solutions.
4. In the sale of horses cocaine injections conceal fraud.
Cocaine being an irritant, it must be remembered that after the anaesthesia the lameness is somewhat more marked than before.
To the cocaine other practitioners add morphia in the following proportions:
As a diagnostic this mixture of the two is said to be far superior to either cocaine or morphia alone.
In connection with this subject, Professor Hobday has published, among others, the following cases illustrating the practical value of this method of diagnosis:[A]
[Footnote A: The Journal of Comparative Pathology and Therapeutics vol. viii., pp. 27, 43.]
CASE I. - Cab gelding. Seat of lameness somewhat obscure; navicular disease suspected. Injected 2 grains of cocaine in aqueous solution on either side of the limb, immediately over the metacarpal nerves.
Five Minutes. - Lameness perceptibly diminished.
Ten Minutes. - Lameness scarcely perceptible.
Case II. - Mare. Obscure lameness; foot suspected. Injected 30 minims of a 5 per cent. solution on either side of the leg just above the fetlock.
Ten Minutes. - No lameness, thus proving that the seat of lameness was below the point of injection.
Case III. - Cab gelding, aged, free clinique; Messrs. Elme's and Moffat's case. Obscure lameness; foot suspected of navicular disease; very lame. Injected 30 minims of a 5 per cent. solution of cocaine on either side of the leg over the metacarpal nerves.
Six Minutes. - Lameness perceptibly less; there was no response whatever on the inside of the leg to the prick of a pin. On the outside, which had not been injected so thoroughly, there was sensation, although not so much as in a healthy foot.
Ten Minutes. - Lameness had almost disappeared; so much so, that the opinion as to navicular disease was confirmed, and neurectomy was performed. Immediately after this operation there was no lameness whatever.
The same author also reports numerous cases among horses and cattle, dogs and cats, pointing out the toxic properties of the drug. The symptoms following an overdose are interesting enough to relate here, and I select the following case of Professor Hobday's as being fairly typical:[A]
[Footnote A: Loc. cit.]
Case IV. - Cart gelding. Free clinique; navicular disease. Injected subcutaneously over the metacarpal nerves on each side 6 grains of cocaine in aqueous solution. During the operation the animal manifested no signs of pain whatever, not even when the nerve was cut. This animal received altogether 12 grains of cocaine (3 grains were given on either side first, then fifteen minutes afterwards the same dose repeated). The effect was manifested on the system in ten minutes after the second injection by clonic spasms of the muscles of the limbs (the legs being involuntarily jerked backwards and forwards at intervals of about twenty seconds), which materially interfered with the performance of the operation. The animal was also continually moving the jaws, and was very sensitive to sounds, moving the ears backwards and forwards. This hyperaesthesia, as evinced by the movement of the ears, lasted for some considerable time after the animal had been allowed to get up.
Cocaine hydrochlorate solutions, if intended to be kept for any length of time, should have added to them when freshly made 1/200 part of boric acid in order to preserve them. Even then they are liable to spoil, and should, for subcutaneous injection, be made up just before needed for use.