Many of the older authors, and with them writers of the present day, declare that unless this is done the ordinary injection is likely to fail in a great many instances where it would otherwise have been successful.

Where a counter-opening is thus made it is found that it very readily closes with granulation tissue, and the purpose for which it was made defeated. This may be avoided by the use of a seton. In preference to the seton, however, we ourselves would advise that the opening be kept free by the occasional use of a sharp-edged director or a fine scalpel.

An interesting modification of the practice of making a counter-opening is that related by Veterinary-Captain S.M. Smith.[A] In point of severity it runs a middle course between the making of a simple counter-opening and the removal of a wedge-shaped portion of the coronary band and the wall, a method which we shall later describe.

[Footnote A: _Veterinary Record_, vol ii., p. 157.]

To perform this operation, the animal is cast and chloroformed. The foot is fixed and the parts thoroughly cleansed. The horn of the wall is then sawed through in a direct line from the coronary margin to the solar edge, the saw-line running exactly over the seat of the sinus.

A strong scalpel is now introduced at the coronary opening, with its cutting-edge outwards, and is gradually pa.s.sed down the opening made by the saw. In this way the sinus is completely destroyed, and from end to end converted into an open wound. The parts are then washed in a perchloride of mercury solution, covered with a mixture of powdered iodoform and boracic acid, over which a pledget of carbolized tow is placed, and then a bandage over the whole. This dressing should be left on three or four days, after which the injury should be treated as an ordinary wound. In conclusion, the author says: 'I can safely recommend this line of treatment to any pract.i.tioner having an obstinate case under treatment.'

_Removal of the Wall and Excision of the Necrotic Tissue_.--This we may term the radical operation for sub-h.o.r.n.y quittor, for it is often productive of a successful issue when all other means have failed. No matter in what position the sinus is, whether at the extreme anterior portion of the coronet, or whether in the region of the heels, it is to be thoroughly opened up. To do this, the fistula is carefully explored with the probe and a knowledge of its exact dimensions arrived at. This is carefully noted, and the horn of the wall for some little distance around it then rasped down quite thin. Immediately over the sinus, and for a short distance on either side of it, the horn is stripped away to the sensitive structures. The cavity of the fistula is then opened up with a scalpel, and every particle of diseased tissue removed with this instrument and a pair of forceps. After-dressing consists simply in the application of suitable antiseptics.

_When the Complication of Necrosed Tendon or Ligament exists_.--We may take it as an axiom that wherever this exists, whether it is in the extensor pedis, in the lateral ligaments of the joint, or in portions of the flexors, all diseased structures should, where possible, be removed. This is done either with a scalpel or with a curette.

When septic matter has gained the sheath of the perforans, and the formation of pus therein is indicated by inflammatory swellings in the hollow of the heel, it is sometimes advisable to lay the sheath open for 1 to 2 inches along the course of the tendons. This, if a fistula is present, may be best done with a blunt-pointed bistoury, or with a cannulated director and a scalpel. With the pus thus given exit, and an antiseptic dressing regularly applied, the case sometimes ends in rapid resolution.

More often than not, however, it is found that the pus has been liberated too late, and that it has gravitated in the sheath to the extent of affecting the plantar aponeurosis. Or it may be, of course, that it was in the plantar aponeurosis the disease commenced. Whichever may have been the case, we have in the hollow of the heel one or more fistulous openings, or an opening we have made ourselves, leading down to a necrosed portion of the terminal expansion of the perforans.

In such cases we ourselves have derived benefit from a regular flushing of the sinuses with a 1 in 2,000 solution of perchloride of mercury, introduced by means of a gla.s.s syringe, followed later by flushing in the same manner with a 1 in 40 solution of carbolic acid, the hollow of the heel meanwhile being kept clean with an antiseptic pad and bandage, or by liberal applications of an antiseptic powder.

The septic materials are in this way destroyed, and the wound heals without further complication. We must admit, however, that the cure of the lesion is generally at the expense of slight lameness, due, in all probability, to inflammatory tissue adhesions between the flexor perforans and the perforatus, and to a partial destruction of the synovial membrane of the sheath.

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.

_First Method_.--This is the oldest method of the three, and consists in making (1) a horizontal incision through the sensitive laminae along the lower border of the cartilage, and (2) a vertical incision through the skin of the coronet, the coronary cushion, and a portion of the sensitive laminae (see Fig. 139).

The flaps (Fig. 139, _a, a_) are now held back by tenaculae, and the whole of the cartilage, or only the necrosed portion, carefully excised by means of right- and left-handed sage-knives. Fistulous openings in either of the flaps _a, a_ must now be carefully curetted and dressed, and the flaps allowed to fall into position. They are then sutured with carbolized gut, and the wound finally dressed as to be described later (p. 357).

[Ill.u.s.tration: FIG. 139.--EXCISION OF THE LATERAL CARTILAGE (OLD METHOD).

The wall covering the lateral cartilage first thinned and stripped off; the two flaps (_a, a_) of skin and the coronary cushion made by the vertical incision turned back. _a_, The operation flaps; _b_, the exposed cartilage; _c_, the sensitive laminae; _d_, the coronary cushion.]

_Second Method (after Holler and Frick_[A]).--These operators deem it wise to leave untouched the skin of the coronet and the coronary cushion. They therefore make their first incision along the lower border of the coronary cushion (see Fig. 140), afterwards exposing the lower half of the cartilage by removing a half-moon-shaped portion of the thinned horn and underlying sensitive laminae (see Fig. 140, _b_).

[Footnote A: Two cases of quittor successfully treated by this method are reported by R. Paine, M.R.C.V.S., in the _Journal of Comparative Pathology and Therapeutics_, vol. xv., p. 81.]

[Ill.u.s.tration: FIG. 140.--EXCISION OF THE LATERAL CARTILAGE. (AFTER MOLLER AND FRICK.) _a_, The thinned h.o.r.n.y wall covering the coronary cushion; _b_, the lateral cartilage exposed by stripping off the thinned wall; _c_, the sensitive laminae.]

This done, the external face of the cartilage is separated from the skin of the coronet. To do this a double sage-knife is run flatwise between the coronary cushion and the cartilage, with the convex surface of the blade towards the skin. The knife is then pa.s.sed backwards and forwards until the necessary separation is accomplished. During these movements of the knife a finger of the unoccupied hand should follow the knife, and guard the coronary cushion against injury.

Following this, the inner surface of the cartilage must be also separated from the structures lying beneath it. To this end a sage-knife (right- or left-handed, according as to whether the anterior or posterior portion of the cartilage is to be first removed) is again pa.s.sed into the incision.

With the cutting-edge of the knife forward, it is gradually reached round and under the hindermost end of the cartilage, and theposterior half of the cartilage separated from underlying structures, and at the same time excised by one clean cut forwards. Using the second sage-knife in a similar manner, the cutting-edge this time backwards, it is reached in front of the cartilage, whose anterior half is then excised by a careful cut backwards.

Any small portions of cartilage remaining after this are sought for with the finger, and carefully removed by means of a scalpel and a tenaculum.

The fistulous opening or openings in the skin of the coronet should now be thoroughly curetted, and the whole of the wound dressed as to be described later.

In removing the anterior half of the cartilage it is highly important to remember the close contiguity to it of the synovial membrane of the pedal articulation. This projects as a small sac between the antero- and postero-lateral ligaments of the joint. Risks of injury to it may be diminished by having the foot secured with a line, and pulled forward by an a.s.sistant while the cut is being made.

_Third Method (after Bayer)_.--This operator recommends that, after stripping a half-moon-shaped piece of horn from the seat of operation, instead of raising the skin of the coronet and the attached coronary cushion in two flaps (as Fig. 139, a, a), that the cartilage be exposed by raising up one flap only (Fig. 141, a), consisting of a portion of the sensitive laminae, the coronary cushion, and the skin and underlying structures of the coronet.

With the horse cast and the preliminary steps over, the thinned horn of the quarter is incised in a semicircular fashion, and the half-moon-shaped piece thus separated from its surroundings stripped off. At about 1/4 inch from the incision in the horn, a second incision of similar shape is made through the sensitive structures, which incision is also carried up into the skin and structures of the coronet. This incision severs, from bottom to the top, (1) the sensitive laminae covering a portion of the pedal bone and a portion of the lateral cartilage, (2) the coronary cushion, and (3) the skin of the coronet and such structures as lie between it and the cartilage.

[Ill.u.s.tration: FIG. 141.--EXCISION OF THE LATERAL CARTILAGE. (AFTER BAYER.) The h.o.r.n.y wall is stripped off over the seat of operation. _a_, Semicircular flap of sensitive laminae, coronary cushion, and skin; _b_, the lateral cartilage; _c_, the sensitive laminae; _d_, the coronary cushion.]

That this incision of the sensitive structures should be kept at 1/4 inch from the one in the horn has a reason. It is that when this flap is again placed into position (as later it will have to be) we have round its circ.u.mference a rim of soft structures into which to place the sutures. And in this connection it is well to advise the operator that the thinness of the keratogenous membrane (the laminal portion of it) should warn him that the portion of it to be turned up--namely, that forming the tip of the flap--should be _sc.r.a.ped_ away quite close to the os pedis. Unless this is done, there will not be a sufficient thickness left to afterwards bring into position and suture.

The half-moon-shaped piece of tissue incised is now carefully dissected away from the external face of the cartilage, until it may be turned up as a flap (see Fig. 141, _a_), and held from off the cartilage by a tenaculum.

The exposed cartilage is now carefully removed by the aid of a sage-knife and a stout pair of forceps, the same precaution of holding the foot well forward being again taken in order to avoid wounding of the articular capsule.

At this stage in the operation considerable care is required. The operator must remember that close beneath him, and more particularly in front, is the pedal articulation. It is better, therefore, to excise the cartilage piecemeal, and to do it carefully, than to attempt, at the risk of injury to the joint, to make the operation 'showy.'

During removal of the cartilage, the terminal branches of the digital arteries are wounded, as also are the veins of the coronary plexus. Should either of these stand out with extra prominence from the others, it should be picked up with a pair of forceps, and ligatured with either carbolized gut or silk.

Attention should then be given to the flap of skin and coronary cushion.

Wherever a sinus has existed in it, it is to be carefully sc.r.a.ped, and all dead portions of tissue removed. This done, the flap is allowed to fall into position, and is there carefully sutured, not only at the skin of the coronet, but along the whole circ.u.mference of the incision.

_Dressing of the Wound and After-Treatment_.--The whole secret of the success of this operation is in afterwards maintaining a strict asepsis of the wound. Unless there is reasonable room for belief that this may be done, the operation had far better not be advised, for if the wound is afterwards suffered to get into a suppurating and dirty condition, the last stage of the case may be worse than the first Synovitis and arthritis, with certain anchylosis of the joint, and a probable loss of our patient, is almost bound to follow.

We cannot, therefore, too strongly insist upon the advice that the whole of the preliminary antisepticising of the foot that we have described, and the after maintaining of asepsis that we are now about to relate, _must_ be methodically and thoroughly carried out. It is of even _more_ importance than little details in the operation itself.

In the first and second methods of operating, directly the actual operation is over, the surface of the wound and both surfaces of the skin-flaps should first be thoroughly douched with a 1 in 1,000 solution of perchloride of mercury. Bayer prefers a 1 in 5 solution of iodoform in ether.

Next, either iodoform or chinosol in the powder should be dusted over the whole surface, including again both inner and outer faces of the reverted skin-flaps. This done the flaps are allowed to fall into position and sutured there with carbolized silk or gut.

Another liberal application of an antiseptic dressing follows this.

Iodoform, iodoform and boracic acid, or chinosol, is freely dusted over the wound and for some distance around it. Bayer, however, again prefers a dressing of the wound, and especially the moistening of the line of sutures with the 1 in 5 solution of iodoform in ether.

Over the wound is then placed a protective layer of gauze, impregnated either with boric acid, with a mercuric salt, or with iodoform.