Definition. - A fistulous wound of the foot in which the lower and blind end of the fistula is situated below the level of the coronary margin of the wall.
Causes. - These, again, will be practically the same as those mentioned in the cause of cutaneous quittor - namely, bruises, punctures, wounds - in fact, any injury upon the coronet severe enough to cause death of tissue and a suppurating wound. We may thus expect sub-horny quittor to follow upon treads, overreach, accidental injuries with the stable-fork, and kicks from other animals.
Sub-horny quittor may also arise without original injury at all to the coronet. Either from a violent blow upon the hoof, or from the animal himself kicking violently against a wall, death of a portion of the sensitive structures takes place within the hoof, suppuration ensues, and the formation of quittor commences. With the escape of the pus at the coronet the quittor is fully formed.
Any other diseased condition of the foot in which suppuration is present may in like manner terminate in quittor. In complicated sand-crack, suppurating corn, or in ordinary pricked foot quittor may be a sequel. In these conditions the pus formation either goes unnoticed or is neglected, and after seriously invading the sensitive structures within the hoof, breaks out at the coronet. Again, too, as with the simpler form of quittor, and as with coronitis, we may always regard as a predisposing cause the action of excessive cold in promoting septic infection of the wound when occurring at the coronet.
Symptoms and Diagnosis. - Where the fistulous wound has had its starting-point in an injury to the coronet diagnosis is, of course, easy. The history of the case explains it. Nothing in this instance remains but to probe the opening, and ascertain its direction, depth, and extent.
An animal with the wound thus open at the coronet, and freely discharging its contents, may, if no serious complications exist, walk tolerably sound. It is only when put to the trot that symptoms of lameness are apparent.
It may so happen, however, that we first see the case when the symptoms are wholly those arising from a painful suppuration within the horny box. This occurs when the original injury has taken place at a more dependent position than the coronet. Either from violent blows upon the hoof, puncture from below, from corn or from sand-crack, or any other causes we have enumerated, suppuration is occurring deeply within the hoof, with as yet no opening upon the coronet.
Even when an opening has already occurred on the coronet, the same condition of sub-horny suppuration may be met with in cases when the opening of the fistula has by some means or other become occluded. Granulation tissue, for instance, may have temporarily closed the mouth of the fistula. The pus, instead of continuing its discharge thereat, is made to burrow in other directions.
In either of these cases pain is excessive, the animal walks on three legs, the foot is painful to percussion, and grave constitutional disturbance is noticeable. The presence of pus is immediately suspected, and, in the absence of any indication of an opening having existed at the coronet, searched for at the sole. It may or may not be found. If found it is given exit, and the case ends as one of ordinary pricked foot, of suppurating corn, or some other condition equally simple when compared with quittor. In those cases where the pus is not discovered at the sole, one adopts the expectant treatment of poulticing. This, if pus is present, is followed by a painful swelling of the coronet. At one point there forms a hot and tender enlargement, with the hairs on it standing straight up from the skin, which latter is seen below red and inflamed in appearance.
Later, the abscess - for abscess it is - discharges its contents, the opening is explored, and we find that in extent it is not confined to the coronary region, but that it is deep enough to constitute a true sub-horny quittor.
This discharge of the abscess contents may take place at a well-defined spot on the coronet, or it may ooze out at the junction of the wall with the skin. In appearance the discharged pus varies. When the softer structures only are attacked it is thick, and yellow or white in colour; when bone is involved it is ichorous; and when attacking the horn itself black or gray. It may or may not be extremely foetid, and often it is mingled with blood.
When evidence of a previous opening upon the coronet is plain, then it is not considered wise to attempt a paring of the sole. Instead, poulticing is at once resorted to, to induce the discharge of the pus through its original channel. Once this has occurred a fistulous wound remains, which is open for treatment upon one or other of the lines we shall afterwards indicate.
Complications - (a) Necrosis of the Lateral Cartilage. - This is the so-called 'cartilaginous quittor' of other writers. In all probability it is the condition generally understood when the word 'quittor' is used by one practitioner to the other. Its tendency to keep the disease existing in a chronic form renders it of grave importance, and for that reason we give it first mention among the complications.
It may occur as a sequel either of cutaneous or of sub-horny quittor, and may result either from actual wounding and infection of the cartilage, or from an attack on it of septic matter originating elsewhere.
Unless there has been discovered a fistula, which on probing is seen to lead direct to the position in which we know the cartilage to be, we know of no precise means by which the existence of this condition may be diagnosed. When free from other complications, the horse with his foot in this state may travel fairly sound. This is so when the necrosis is situate in the posterior half of the cartilage, in which case the irritation set up by the disease is confined to the comparatively non-sensitive tissues of the cartilage itself and the fibrous mass of the plantar cushion. When attacking the anterior half of the cartilage, the close contiguity of the joint renders the disease of a more serious nature. It is then that we have acute pain, and with it extreme lameness, for in this position it is more than likely that we have involved either the synovial membrane of the articulation or the tops of the sensitive laminae. It will be remembered that here the synovial membrane protrudes as a small sac between the antero- and postero-lateral ligaments of the joint. More or less easily then it is bound to come into intimate contact with the septic matter attending the necrosis of the cartilage, and so share in the inflammatory processes, afterwards communicating them to the interior of the articulation.