If, in spite of the antiseptic irrigations, the fistula persists, then nothing remains but to resort to excision of the aponeurosis, as described on p. 222.
When Necrosis of the Lateral Cartilage is present.—In this case we may at first try the ordinary treatments of poulticing; and blistering, of antiseptic caustic injections, and of plugging. In some cases a cure is effected. Should these fail, however, and we intend to see the finish of our case, then operative measures must be determined on. This means cutting down upon the diseased cartilage, and either removing the necrosed portion, or excising the cartilage in its entirety.
The latter method is seldom practised in this country. As it is the most radical of the two, however, we shall describe it here first.
Extirpation of the Lateral Cartilage.—The operation of extirpating the lateral cartilage is by no means a new one, being introduced, according to Zundel, by the senior Lafosse in 1754. It consisted in removing a portion of the wall by grooving and stripping it, and of excising the exposed cartilage by means of a sage-knife.
As to what portion of, and how much of the horn of, the quarter should first be removed, and as to what particular direction each groove should take, opinion among the older writers varied considerably. This we know now is not an important matter, and it is sufficient to say that the first preliminary is a thinning down of the horn of the quarter with the rasp over the position occupied by the cartilage. At the present time there are two or three modifications of the operation as originally introduced. In all, however, the preliminary steps are the same. We shall therefore describe them collectively, as applying correctly to either of the three methods of operating we are about to show.
Preparation of the Subject and Preliminary Steps in the Operation.—On the day previous to the operation the horn of the wall immediately over the cartilage must be so thinned with a rasp as to yield readily to pressure of the thumb in any position. It should be so thin as to only just avoid wounding the sensitive structures below.
The whole of the foot must then be thoroughly cleansed, and rendered as nearly aseptic as possible. The use of warm water, soap, and a stiff brush is the readiest means of removing the surface dirt. Afterwards the foot should be soaked for some time in a reliable antiseptic solution, a 1 in 1,000 solution of perchloride of mercury being the most suitable. When removed from the solution the foot must be packed round with wool or tow impregnated with corrosive sublimate, and then bandaged, the whole afterwards wrapped in a thick cloth, or protected with a boot.
On the following day the animal is brought out and cast, and the foot desired to be operated on firmly secured, after the manner described on p. 81. The bandages and sublimate pads are then removed, and the skin of the coronet over the seat of operation shaved of hair. An Esmarch rubber bandage is next run up the limb, and the tourniquet applied, thus rendering the operation a nearly bloodless one.
This done, the animal is chloroformed, and an antiseptic douche played over the foot.
So far, the steps in the operation are common to all methods. There are now, however, three slightly differing modes of extirpating the cartilage, which modes vary simply according to the structures severed by the knife.