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.]
Fig. 140. - Excision Of The Lateral Cartilage. (After Moller And Frick.) A, The Thinned Horny 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 passed 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 passed 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 the posterior 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 assistant 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.
Fig. 141. - Excision Of The Lateral Cartilage. (After Bayer.) The Horny 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 circumference 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 scraped 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 scraped, 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 circumference of the incision.