Diseases of the Horse's Foot
by
Harry Caulton Reeks
Part 2 out of 8
giving the _inter_-tubular substance. We have thus produced hollow tubes,
united together by cells, all arising from the rete Malpighii of the
coronary corium. Section of the lower part of the horn tubes shows them to
contain a cellular debris.
Thus, in all, in the horn of the wall we find a tubular, an intertubular,
and intratubular substance. In fact, hairs matted together by intertubular
material, and only differing from ordinary hairs in their development in
that they arise, not from papillae sunk in the corium, but from papillae
projecting from its surface.
Although this disposes of the wall proper, there still confronts us the
question of the development of the horny laminae. To accurately determine
this point it is absolutely essential to examine, histologically, the feet
from embryos.
In the foot of any young ungulate in the early stages of intra-uterine
life horizontal sections will show a covering of epidermis of varying
thickness.[A] This may be only two or three cells thick, or may consist of
several layers. Lowermost we find the cells of the rete Malpighii. As some
criterion of the activity with which these are acting, it may be noted that
with the ordinary stains their nuclei take the dye intensely. The cells of
this layer rest upon a basement membrane separating the epidermis from the
corium. At this stage _the corium has a perfectly plane surface_.
[Footnote A: Equine foetus, seventy-seven days old.]
[Illustration: FIG. 26.--SECTION OF FOOT OF EQUINE FOETUS, SEVENTY-SEVEN
DAYS OLD. The rete Malpighii rests on a plane corium; the rent in the
section is along the line of the cells of the rete (Mettam).]
[Illustration: FIG. 27.--SECTION FROM FOOT OF SHEEP EMBRYO. It shows a
pronounced epithelial ingrowth into the corium (Mettam).]
The next stage will demonstrate the first step in the formation of the
sensitive laminae.[A] The plain surface of the corium has now become broken
up, and what is noticed is that the broken-up appearance is due to the
epithelial cells irrupting and advancing _en echelon_ into its connective
tissue. Each point of the ingrowing lines of the _echelon_ has usually
one cell further advanced into the corium than its neighbours, and may be
termed the _apical cell_. The fine basement membrane separating epithelium
from corium is still clearly evident. This epidermal irruption of the
corium takes place at definite points right round the foot. It is extremely
probable, however, that it commences first at the toe and spreads
laterally.
[Footnote A: Sheep embryo, exact age unknown.]
As yet, these cellular ingrowths (which are destined to be the _horny_
laminae, and cut up the corium into _sensitive_ laminae) are free from
irregularities or secondary laminae. Before these are to be observed other
changes in connection with the ingrowths are to be noticed.
[Illustration: FIG. 28.--SECTION FROM CALF EMBRYO. The epithelial ingrowths
hang down from the epidermis into the corium like the teeth of a comb
(Mettam).]
The first is merely that of elongation of the epithelial processes into the
connective tissue, until the rete Malpighii gives one the impression that
it has hanging to its underneath surface and into the corium a number of
thorn-like processes. These extend all round the front of the foot, and
even in great part behind. Accompanying this elongation of the processes
is a condensation of the epithelial cells immediately above the rete
Malpighii, with a partial or total loss of their nuclei. This is the first
appearance of true horn, and its commencement is almost coincident with the
first stages of ossification of the os pedis.
[Illustration: FIG. 29.--SECTION OF AN EPITHELIAL INGROWTH FROM AN EQUINE
FOETUS. It shows commencing secondary laminar ridges. In the centre are
epithelial cells which are undergoing change into horny elements to form
the horn core, or 'horny laminae' (Mettam).]
With the appearance of horn comes difficulty of sectioning. The last
specimen that Professor Mettam was able to satisfactorily cut upon the
microtome was from a foetus between three and four months old. In this the
secondary laminar ridges were clearly indicated, and the active layer of
the rete Malpighii could be traced without a break from one ingrowing
epithelial process to the next, and around this, following all the
irregularities of its outline, and covering the branches of the nascent
laminae. The laminae mostly show this branching as if a number of different
growing points had arisen, each to take on a function similar to the
epithelial process as it at first appeared.
In the centre of the processes a few nuclei may be observed, but they are
scarce, and stain only faintly; they have arisen from the cells of the rete
Malpighii which have grown into the corium. In fact, the active cells are
passing their daughters into the middle of the process, and these pass
through similar stages as those derived from the ensheathing epidermis. In
other words, the daughter cells of the constituents of the rete Malpighii
which have grown into the corium pass through a degeneration precisely
similar to that undergone by cells shed at desquamation, or those which
eventually give rise by their agglutination to a hair.
This is the real origin of the horny laminae, and the thickness of these is
increased merely by an increase in the area covered by the cells of the
rete Malpighii--i.e., by the development of secondary laminar ridges. If
a section from a foal at term be examined, the processes will be found far
advanced into the corium, and, occupying the axis of each process, will
be seen a horny plate, continuous with the horn of the wall. No line of
demarcation can be observed between the horn so formed and the intertubular
material of the wall. They merge into and blend with each other, with no
indication of their different origins. The cells that have invaded the
corium have thus _not lost their horn-forming function_. There has merely
been an increase in the area for horn-producing cells. The horny processes
are continuous with the hoof proper at the point where the epithelial
ingrowth first commenced to invade the corium, and fuses here with the
horn derived from the cells of the rete Malpighii which have _not_ grown
inwards, and which are found between the processes in the intact foot. From
this it is clear that some considerable portion of the horn of the wall is
derived from the cells of the rete Malpighii covering the corium of the
foot. It becomes even more clear when we remember the prompt appearance of
horn in cases where a portion, or the whole, of the wall has been removed
by operation or by accident (see reported cases in Chapter VII.).
The activity of the cells of the rete Malpighii of the corium covering the
remainder of the foot will be quite as necessary as the activity of the
cells of the coronary papillae which form the horn tubes themselves. 'For,'
in Professor Mettam's own words, 'I am inclined to believe that much of the
"white line" which is found uniting the wall of the hoof to the sole has
been derived from the horn formed from the rete of the foot corium. This
origin will explain the absence of pigment from this thin uniting "line,"
as it does from the horn lining the interior of the wall. The cells of the
rete are free of colouring matter.'
[Illustration: FIG. 30.--SECTION THROUGH HOOF AND SOFT TISSUES OF A FOAL AT
TERM. The horn of the wall is shown, and the horn-core ('horny laminae') of
the epithelial ingrowth. The latter has advanced far into the corium, and
is now provided with abundant secondary laminar ridges (Mettam).]
From the matter here given us it is easy to understand how, in a macerated
foot, the appearance is given of interlocking of the sensitive and horny
laminae. We see that the horny laminae are ingrowths of the rete Malpighii,
ploughing into and excavating the corium into the shape of leaves--the
sensitive laminae. Putrefactive changes simply break into two separate
portions what originally was one whole, by destroying the cells along its
weakest part. This part is the line of soft protoplasmic cells of the rete
Malpighii. Thus the more resistant parts (the horn on the one hand, and the
corium covering the foot on the other) are easily torn asunder.
As a result of the evidence we have quoted, we are able to answer our
original question in the affirmative. Seeing that the horny and the
sensitive laminae are both portions of the same thing--namely, a modified
skin, in which the epidermis is represented by the horny laminae, and the
corium by the sensitive--it is clear to see that the cells covering the
inspreading horny laminae are dependent for their growth and reproduction
upon the cells with which they are in immediate contact--namely, those
of the sensitive laminae--and that therefore the sensitive laminae are
responsible for the growth of the horny.
B. CHEMICAL PROPERTIES AND HISTOLOGY OF HORN.
Horn is a solid, tenacious, fibrous material, and its density in the hoof
varies in different situations. It is softened by alkalies, such as caustic
potash or soda and ammonia, the parts first attacked being the commissures,
then the frog, and afterwards the sole and wall. Strong acids, such as
sulphuric acid and nitric acid, also dissolve it.
The chemical composition of the hoof shows it to be a modification of
albumin, its analysis yielding water, a large percentage of animal matter,
and materials soluble and insoluble in water. The proportions of these, as
existing in the various parts of the hoof, have been given by Professor
Clement as follows:
Wall. Sole. Frog.
Water 16.12 36.0 42.0
Fatty matter 0.95 0.25 0.50
Matters soluble in water 1.04 1.50 1.50
Insoluble salts 0.26 0.25 0.22
Animal matter 81.63 62.0 55.78
Horn appears to be identical with epidermis, hair, wool, feathers, and
whalebone, in yielding 'keratin,' a substance intermediate between albumin
and gelatine, and containing from 60 to 80 per cent. of sulphur.
That horn is combustible everyone who has watched the fitting of a hot shoe
knows. That it is a bad conductor of heat, the absence of bad after-effects
on the foot testifies.
[Illustration: FIG. 31.--PERPENDICULAR SECTION OF HORN OF WALL.]
In a previous page we have described the manner of growth of the horn
tubules, and noted the direction they took in the wall; also, we have
noticed the existence between them of an intertubular horn or cement.
Those who wish to give this subject further study will find an excellent
series of articles by Fleming in the _Veterinarian_ for 1871. We
shall content ourselves here with introducing one or two diagrams and
photo-micrographs, and dealing with the histology very briefly.
Under the microscope the longitudinal striation of the wall is found to be
due to the direction taken by the horn tubules.
Fig. 31 is a magnified perpendicular section of the wall. In it the
parallel dark striae are the horn tubules in longitudinal section. The
lighter striae represent the intertubular material.
Fig. 32 gives us the wall in horizontal section. To the left of this
picture we find the horn tubules cut across, and standing out as so many
concentrically ringed circles. In the centre of the figure are seen the
horny laminae, with their laminellae, and the sensitive laminae. The right
portion of the figure pictures the corium.
[Illustration: FIG. 32.--HORIZONTAL SECTION OF HORN OF WALL.]
Fig. 33 is, again, a horizontal section, cut this time at the junction of
the wall with the sole. To the left are seen, again, the horn tubules of
the wall, and to the centre the horny laminae. In this position, however,
the structures interdigitating with the horny laminae are not sensitive, but
are themselves horny. As the diagram shows, they contain regularly arranged
horn tubules cut across obliquely. It is this horn which forms the 'white
line.' To the extreme right of the figure are seen the horn tubules of the
sole.
There remains now but to notice the arrangement of the horn tubules in the
frog. The peculiar, indiarubber-like toughness of this organ is well known.
Histological examination gives a reason for this.
[Illustration: FIG. 33.--HORIZONTAL SECTION OF HORN THROUGH THE JUNCTION OF
THE WALL WITH THE SOLE. _a_, Horn tubule of the wall; _b_, horn tubule of
the sole; _c, d_, horny laminae.]
[Illustration: FIG. 34.--SECTION OF FROG THROUGH CORIUM AND HORN. The long
finger-like projections of corium into epidermis are sections of the long
papillae from which the horn-tubes of the sole grow. In the stainable
portion of the epidermis are to be clearly seen light and dark streaks
pointing out the alternate strata-like arrangement of cells mentioned in
the text (Mettam).]
The horn tubules of the frog are sinuous in their course. This is accounted
for by the fact that in the horn of the frog there is a large amount of
intertubular material, this having the effect of frequently turning the
horn tubules from the straight. In addition to this, the intertubular
material has a peculiar arrangement of the cells composing it. These
are laid down in alternating striae (1) of cells with their long axes
longitudinal, and (2) of cells with their long axes horizontal. This is
seen in Fig. 34, between the long papillae of the corium, where the lines of
longitudinally arranged cells in horizontal section stand out darker than
the adjoining strata in which their arrangement is horizontal. The tortuous
direction of the horn tubules, and the almost interlocking nature of the
alternating strata of the intertubular material, together combine to give
the frog its characteristic toughness and resiliency.
C. EXPANSION AND CONTRACTION OF THE HOOF.
Among other questions productive of heated argument come those relating to
expansion of the horse's hoof. In the past many observers have strenuously
insisted on the fact that expansion and contraction regularly occur during
progression. Opposed to them have been others equally firm in the belief
that neither took place. Quite within recent times this question also
has been settled once and for all by the experiments of A. Lungwitz, of
Dresden. His conclusions were published in an article entitled 'Changes in
Form of the Hoof under the Action of the Body-weight.'[A]
[Footnote A: _Journal of Comparative Pathology and Therapeutics_, vol.
iv., p. 191. The whole of the matter in this article, from which we have
borrowed Figs. 35 and 36, is too long for reproduction here. It forms,
however, most instructive reading, and its careful perusal will well repay
everyone interested in this most important question (H.C.R.).]
In connection with this it is interesting to note how, all unconsciously,
two separate observers were simultaneously arriving by almost identical
means at an equally satisfactory answer to the question. Prior to the
publication of Lungwitz's article on the subject, Colonel F. Smith, A.V.D.,
had arrived at similar conclusions by working on the same methods.
[Illustration: Fig. 35. I. Electric Bell with Dry Element. a, Under
part, with box, for the dry element; 6, roller for winding up the
conducting-wires; c, dry element, with screw-clamp for attachment of the
conducting-wires; c', conducting-wire leading to the screw-clamp, with
contact-spring in c', Fig. 2, or to the wall in Fig. 3; d, upper part, with
bell; d', conducting-wire to the shoe d' in Figs. 2 and 3; e, strap for
slinging the apparatus around the body of the assistant or rider; f,
connecting-wire between bell and dry element.]
[Illustration: Fig. 35. II. Hoof Shod with Shoe provided with Toe-piece and
Calkins; Wall of the Hoof covered with Tinfoil. a, Heel angle, with b, the
contact-screws; c, screw-clamp, with contact-spring (isolated from
the shoe); c' conducting-wire from the same; d, screw-clamp, with
conducting-wire (d') screwed into the edge of the shoe; e, nails isolated
by cutting a small window in the tinfoil.]
[Illustration: Fig. 35. III. Hoof Shod with Plain Shoe; Horny Wall covered
with Tinfoil. a, Toe and heel angle, with b, the contact-screws; c,
conducting-wire passing from the tinfoil on the wall; d, conducting-wire
passing from the shoe; c', d', ends of the conducting-wires, which must be
imagined connected with the ends c', d', passing from the apparatus.]
It is unnecessary for our purpose here to minutely describe the exact
_modus operandi_ of these two experimenters. Briefly, the method of inquiry
adopted in each case was the 'push and contact principle' of the ordinary
electric bell, and the close attention which was paid to detail will be
sufficiently gathered from Figs. 35 and 36.
[Illustration: Fig. 36. I. LEFT FORE-FOOT SHOD AND MOUNTED TO RECOGNISE THE
SINKING OF THE SOLE. _a_, Iron plate covering the inner half of the horny
sole; _b_, openings in the same, with screw-holes for the reception of the
contact-screw _c_ (the part of the sole under the plate is covered with
tinfoil, which at _d_ passes out under the outer branch of the shoe, and
becomes connected with the tinfoil of the wall; in order to give the
freshly applied tinfoil a better hold, copying-tacks are at _e_ passed
through it into the horn, and one is similarly used to protect the tinfoil
at the place where the contact-screw touches the latter); _f_, holes
with screw thread for the fastening of the angle required to measure the
movement of the wall, and also for the fastening of the conducting-wire,
_g; h_, conducting-wire passing from the tinfoil; _i_, isolated nails.]
[Illustration: Fig. 36. II. BAR-SHOE WITH OPENINGS. _a_, Near the inner
margin and in the longitudinal bar; _b_, for the reception of the
contact-screw _c; d_, openings for fastening the angle and the
conducting-wires.]
After numerous experiments with the depicted contact-screws, moved to the
various positions indicated in the drawings, the following conclusions were
arrived at:
1. BEHAVIOUR OF THE CORONARY EDGE.--During uniform weighting of all four
hoofs the coronary edge shows a tendency to contraction in the anterior and
lateral regions of the hoof, and a tendency to expansion posteriorly. With
heavy weighting of the hoof, which is shown by a backward inclination of
the fetlock, contraction in the anterior and lateral regions is slight, but
the expansion behind, in the region of the heels, is distinct, commencing
gradually in front, becoming stronger, and diminishing again posteriorly.
The coronary edge of the heels becomes slightly bulged outwards. The bulbs
of the heels swell up and incline a little backwards and downwards.
When the fetlock is raised the expansion of the coronary edge of the heels
disappears from behind forwards, passing forwards like a fluid wave. In
the lateral and anterior regions of the coronary edge the contraction
disappears; and when the weight is thrown off the foot it passes into a
gentle expansion of the coronary edge of the toe. During the opposite
movement of the fetlock, that of sinking backwards, this change of form is
executed in the converse manner.
In short, the coronary edge resembles a closed elastic ring, which yields
to pressure, even the most gentle, of the body-weight, in such a way that a
bulging out of any one part is manifested by an inward movement of another
part.
In Fig. 37, _b_, the dotted line represents the changes of form in
comparatively well-formed and sound hoofs at the moment of strongest
over-extension[A] of the fetlock-joint.
[Footnote A: The term 'over-extension,' as employed by Lungwitz, is
intended to indicate that position assumed by the fetlock-joint when the
opposite foot is raised from the ground.]
2. BEHAVIOUR OF THE SOLAR EDGE.--Under the action of the body-weight this
is somewhat different from that of the coronary edge. Anteriorly, and at
the sides, as far as the wall forms an acute angle with the ground,
the tendency to expansion exists, but the change of form first becomes
measurable in the region where the lateral cartilages begin. Quite
posteriorly the expansion again diminishes.
Fig. 37, _a_, by the dotted line represents the expansion at the moment of
over-extension of the fetlock-joint. This expansion is itself rather less
than at the coronary edge, and it shows itself distinctly _only when the
weighted hoof is exposed to a counter-pressure on the sole and frog_, no
matter whether the counter-pressure is produced naturally or artificially.
Thus anything tending to the removal of the pressure from below, such as
a decayed condition of the frog or excessive paring in the forge, will
diminish the extent of expansion of the solar edge.
Contraction of the solar edge of the heels occurs at the moment of greatest
over-extension of the fetlock-joint--that is, in a foot with pressure
from below absent. On the face of it, this appears impossible. Lungwitz,
however, has perfectly demonstrated it; and, when dealing with the
functions of the lateral cartilages in a later paragraph, we shall show
reason for why it is but a simple and natural result of the foot dynamics.
3. BEHAVIOUR OF THE SOLE.--The horny sole becomes flattened under the
action of the body-weight. This is most distinct at the solar branches, and
gradually shades off anteriorly and towards the circumference. As might be
supposed, width of hoof and thickness of the solar horn exert an influence
on the extent of this movement. The sinking of the horny sole is most
marked in flat hoofs.
D. THE FUNCTIONS OF THE LATERAL CARTILAGES.[A]
[Footnote A: Extracted from a paper by J.A. Gilruth, M.R.C.V.S., in the
_Veterinary Record_, vol. v., p. 358.]
We have just referred to contraction of the heels as taking the place of a
normal expansion in those cases where ground frog-pressure was absent. We
shall readily understand this when we bear in mind the anatomy of the
parts concerned, especially that of the plantar cushion. This wedge-shaped
structure we have already described as occupying the irregular space
between the two lateral cartilages, the extremity of the perforans tendon,
and the horny frog.
Now, when weight or pressure is exerted from above on to this organ, and
the _frog is in contact with the ground below_, it is clear from the
position the cushion occupies that, whatever change of form pressure from
above will cause it to take, it must certainly be limited in various
directions.
[Illustration: FIG. 37. _a_, The dotted lines in this diagram represent the
expansion of the solar edge of the hoof at the moment of over-extension of
the fetlock-joint; _b_, the dotted line represents the change in form of
the coronary edge under similar circumstances.]
Because of the shape of the cushion its change of form cannot be forwards
(simultaneous pressure from above and below on to this wedge with its apex
forwards must tend to give it a backward change of form). Because of the
pastern being horizontal, and aiding in the downward pressure, its
change of form cannot be upwards. And because of the ground it cannot be
downwards. It follows, therefore, that the movement must be backwards and
outwards, being especially directed outwards because of its shape and the
median lacuna in its posterior half--this latter, the lacuna, accommodating
as it does the frog-stay, preventing the tendency to backward movement
becoming excessive, and directing the change of form to the sides. Where
the greatest pressure is transmitted, then, is to the inner aspects of the
flexible lateral cartilages. The coronary cushion being continuous with the
plantar, the backward and outward movements of the latter will tend to pull
upon and tighten the former, especially _in front_. This will account for
the contraction noted by Lungwitz in the _anterior half_ of the coronary
edge of the hoof.
Remove the body-weight, and naturally the elastic nature of the lateral
cartilages and the coronary and plantar cushions, with, in a less degree,
that of the hoof, cause things to assume their normal position.
Repeat the weighting of the hoof, in this second case _without
frog-pressure_, and we shall see at once that we have done away with one of
the greatest factors in determining the outward and backward movements of
the plantar cushion--namely, the pressure from below on its wedge-shaped
mass. The movement of the plantar cushion will now be _downwards_ as well
as backwards; and, seeing that it is attached to the inner aspect of each
lateral cartilage, we shall expect these latter, by the downward movement
of the plantar cushion, to be drawn _inwards_. This Lungwitz has shown to
occur.
The chief function of the lateral cartilages, therefore, is to _receive
the concussion engendered by locomotion_, which concussion is directed
backwards and outwards by the pad-like plantar cushion.
In addition to this, the lateral cartilages, together with the plantar and
coronary cushions, _play the part of a valve to the whole of the veins of
the foot_.
It is in this way: We have only to refer to the chapter on anatomy to see
that the whole of the foot is covered with a tissue of extreme vascularity.
Thus we find papillae--the over the coronary cushion; enlarged and modified
papillae sensitive laminae--covering the anterior face of the os pedis; and
numberless papillae again covering the sole. There can be no doubt that the
quantity of fluid brought by the bloodvessels of these papillae to the foot
acts largely as a means of hydraulic protection to the soft structures.[A]
In like manner as that delicate organ, the brain, is best protected by
being floated upon the cerebro-spinal fluid and bloodvessels (which fluids
transmit waves of concussion or pressure _through_ the organ without injury
to the delicate cells forming it), so, in like manner, does the extreme
vascularity of the foot protect the cells of its softer structures from the
effects of pressure and concussion.
[Footnote A: The _Veterinary Record_, vol. iii., p. 518.]
That this law of hydraulics may operate in the horse's foot to the best
advantage, the veins must be provided with valves, and valves of no
mean strength. These we know to be absent. It is here that the lateral
cartilages and the elastic substances of the coronary and plantar cushions
step in to supply the deficiency.
At the time when weight is placed upon the foot (with, of course, a
tendency to drive the blood upwards in the limb), and, therefore, the time
when a valvular apparatus is needed to retain the fluid in the foot, we
find the wanting conditions supplied by the pressure outwards of the
plantar cushion compressing the large plexuses of veins on each side of the
lateral cartilages, to which plexuses, it will be remembered, the bulk
of the venous blood from the foot was directed. A more perfect valvular
apparatus, automatic and powerful, it would be difficult to imagine.
E. GROWTH OF THE HOOF.
We will conclude this chapter with a few brief remarks on the growth of
the hoof. That the rate of growth is slow is a well-known fact to every
veterinarian, and it will serve for all practical purposes when we state
that, roughly, the growth of the wall is about 1/4 inch per month. This
rate is regular all round the coronet, from which it follows that the time
taken for horn to grow from the coronary edge to the inferior margin
will vary according as the toe, the quarters, or the heels are under
consideration.
As might naturally be expected, the rate of growth will depend on various
influences. Any stimulus to the secreting structures of the coronet, such
as a blister, the application of the hot iron, or any other irritant,
results in an increased growth. Growth is favoured by moisture and by
the animal going unshod, as witness the effects of turning out to grass.
Exercise, a state of good health, stimulating diets--in fact, anything
tending to an increased circulation of healthy blood--all lead to increased
production of horn. With the effects of bodily disease and of ill-formed
legs and feet on the wear of the hoof, and the growth of horn, we shall be
concerned in a future chapter.
CHAPTER IV
METHOD OF EXAMINING THE FOOT
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 deg. or 50 deg. 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:
Cocaine hydrochlorate 2-1/2 grains.
Morphia 1-1/2 "
Aqua destil 1-1/2 drams.
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.
CHAPTER V
GENERAL REMARKS ON OPERATIONS ON THE FOOT
A. METHODS OF RESTRAINT.
Many of the simple operations on the foot, such as the probing of a sinus,
the paring out of corns, or the searching of pricks, may most suitably be
performed with the animal's leg held by the operator as a smith holds it
for shoeing. According to the temperament of the animal, even the operation
for the removal of a portion of the sole, or the injection of sinuses with
caustics, may be carried out with the animal simply twitched.
When the operation is still a simple one, casting inconvenient or
impossible, and the animal restive, the twitch must be supplemented by some
other method. The most simple and one of the most effective is the blind,
cap, or bluff (Fig. 38). With it the most vicious animal or the most
nervous is in many instances either cowed into submission or soothed into
quietness.
At the same time, more forcible means than the operator's own strength
must be taken to hold the animal's foot from the ground. If the foot is a
fore-foot, and the point desired to be operated on is to the outside, the
pastern should be firmly lashed to the forearm by means of a thin, short
cord, or a leather strap and buckle. Much may then be done in the way of
paring and probing that would otherwise be impossible.
[Illustration: Fig. 38--The BLIND.]
[Illustration: Fig. 39--THE SIDE-LINE.]
If the foot is a hind one, one of the many methods of using what is
termed by Liautard, in his 'Manual of Operative Veterinary Surgery,' the
plate-longe, must be adopted. This, in its most useful form, is a length of
closely-woven cotton webbing, from about 2 to 2-1/2 inches wide, and from 5
to 6 yards long, provided with a small loop formed on one of its ends, and
perhaps better known to English readers as a 'side-line.' If webbing be not
available, a length of soft cotton rope, or a rope plaited and sold for the
purpose, as Fig. 39, will serve equally well. One of the most convenient
methods of using the side-line for securing the hind-foot is depicted in
Figs. 40 and 41.
[Illustration: FIG. 40.--THE SIDE-LINE ADJUSTED PREPARATORY TO SECURING THE
NEAR HIND-FOOT.]
[Illustration: FIG. 41.--THE NEAR HIND-FOOT SECURED WITH THE SIDE-LINE.]
Here the side-line has formed upon it a loop sufficiently large to form a
collar. This is placed round the animal's neck, the free end of the line
run round the pastern of the desired foot, and the foot drawn forward, as
in Fig. 40.
The loose end of the line is then twisted once or twice round the tight
portion, and finally given to an assistant to hold (see Fig. 41). The foot
is thus held from the ground, and violent kicking movements prevented.
Where the operation is a major one, restraint of a distinctly more forcible
nature becomes imperative. Many of the more serious operations can most
advantageously be performed with the patient secured in some form or other
of stock or trevis, and the foot suitably fixed. It is not the good fortune
of every veterinary surgeon, however, to be the lucky possessor of one of
these useful aids to successful operating. Perforce, he must fall back on
casting with the hobbles (Fig. 42).
[Illustration: FIG. 42.--CASTING HOBBLES.]
With the use of these we will assume our readers to be conversant, and will
imagine the animal to be already cast. It remains, then, but to detail the
most suitable means for firmly fixing the foot to be operated on.
Here the side-line is again brought into use. Care should previously have
been taken when casting to throw the animal so that the portion of the foot
to be operated on, whether inside or outside, falls uppermost, and that the
buckle of the hobble on that particular foot is placed so that it also is
within easy reach when the animal is down.
In the case we are illustrating the point of operation was the outside of
the near hind coronet. We will, therefore, describe the mode of fixing the
near hind-foot upon the cannon of the near fore-limb.
[Illustration: FIG. 43.--PHOTOGRAPH ILLUSTRATING METHOD OF ADJUSTING THE
SIDE-LINE PREPARATORY TO FIXING THE HIND-LEG UPON THE FORE.]
The side-line is first adjusted as follows: It is fixed upon the cannon of
the near hind-leg (A) by means of its small loop. From there it is passed
under the forearm of the same limb, over the forearm, under the rope
running from A to B; from there over and under the thigh, to be finally
brought in front of the thigh, and below the portion of rope running from
arm to thigh. The loose end of the side-line is then given to an assistant
standing behind the animal's back, the buckle of the hobble restraining the
foot unloosed, and strong but steady traction brought to bear from behind
upon the line. The operator should now stand in front of the fore-limbs,
and, by placing a hand on the rope passing round the arm, prevent the line
from slipping below the knee.
By this means the hind-limb is pulled forward until the foot projects
beyond the cannon of the front-limb. When that position is reached, the
operator grasps the hock firmly with one hand, and, directing the side-line
to be slackened, gently slides downward the coils of rope round the arm
and thigh until they encircle the cannons of both limbs. The cannon of the
hind-limb is firmly lashed to the cannon of the fore, and the foot firmly
and securely fixed in the best position for operating (see Fig. 44).
[Illustration: FIG. 44.--PHOTOGRAPH SHOWING THE NEAR HIND-FOOT SECURED UPON
THE CANNON OF THE NEAR FORE-LIMB.]
Similarly, with the horse still on his off side, the off hind-limb may be
fixed to the near fore, and the near fore and the off fore to the near
hind.
With the animal on his near side, we may fix the near hind and the off hind
to the off fore, and the off fore and near fore to the near hind.
The points to be remembered in fixing the limbs thus are: (1) The side-line
should always commence upon the cannon of the limb to be operated on; (2)
it should next pass under and over (or over and under, it is immaterial
which) first the arm and then the thigh, or the thigh and the arm, as the
case may be; (3) in every case, whether rounding the thigh and the arm from
above or below, the piece of rope completing the round should always finish
below that portion preceding it, so that traction upon it from behind the
animal's back should tend to keep all portions of it from slipping below
the knee and the hock.
With the uppermost fore-limb secured to the hind-limb in the manner we have
described, we have the underneath fore-limb suitably exposed for both the
higher and lower operations of neurectomy. The position for this operation
will be made better still if the lowermost limb (the one to be operated on)
is removed from the hobbles and drawn forward by an assistant by means of a
piece of rope fastened to the pastern.
Taking what we have described as a general guide, other modifications of
thus securing the foot will suggest themselves to the operator to meet the
special requirements of the case with which he is dealing.
Regarding the administration of chloroform, no description of the method
is needed here, as it will be found fully detailed in most good works on
general surgery. Where great immobility is needed, it is one of the most
valuable means of restraint we have. Apart from that, its use in any
serious operation is always to be advocated, if only on the score of humane
consideration for the dumb animal helpless under our hands.
B. INSTRUMENTS REQUIRED.
In addition to those required for operations on the softer structures--such
as scalpels, forceps, artery forceps, directors, scissors, etc.--the
surgery of the foot demands instruments specially adapted for dealing with
the horn.
A great deal will depend upon the operator as to whether these are few or
many. The average man of resource will deem a smith's rasp and one or two
strong drawing-knives amply sufficient, and on no account should they be
omitted from the list of those ready to hand.
[Illustration: FIG. 45.--THE ORDINARY DRAWING-KNIFE.]
The ordinary smith's drawing-knife (Fig. 45) is well known to almost
everyone, and is well suited for much of the rougher part of the work.
The careful following up of pricks, however, and some of the more special
operations demanding removal of portions of the lateral cartilages call for
instruments of a more delicate character and peculiar construction. These
are to be found in the so-called sage-knife, and the modern (French)
pattern of drawing-knife.
[Illustration: FIG. 46. _a, b_, Modern forms of drawing-knife; _c, d, e_,
sage-knives.]
The modern drawing-knife differs from the smith's instrument in being
attached to a straight, instead of a curved, handle, and in usually being
sharp on both edges instead of only on one. These are made in various sizes
(Fig. 46, _a, b_), and the blades flat, curved on the flat, or curved at an
angle with the edges of the haft.
The sage-knife, as its name indicates, is a knife with a lanceolate-shaped
blade. These also may be obtained in varying forms and sizes (Fig. 46, _c,
d, e_). Fig. 46, _c_, is a single-edged, right-handed sage-knife. Fig.
46, _d_, is a left-handed instrument of the same type. The double-edged
sage-knife is represented in Fig. 46, _e_.
[Illustration: FIG. 47.--SYMES'S ABSCESS-KNIFE.]
It may be mentioned too, in passing, that the ordinary Symes's
abscess-knife (Fig. 47) is a most useful instrument when performing the
operation of partial excision of the lateral cartilages, its peculiar shape
lending itself admirably to the niceties of the operation.
One or two good-shaped firing-irons will also be found useful. They will
lighten the labour of tediously excavating grooves with the knife,
where that procedure is necessary; and, used in certain positions to be
afterwards described, will afford just that necessary degree of stimulus to
the horn-secreting structures of the foot, which the use of the knife alone
will not.
The man in country practice will also be well advised in carrying to every
foot case a compact outfit, such as that carried by the smith. This will
consist of hammer and pincers, drawing-knife and buffer. Much valuable time
is then often saved which would otherwise be wasted in driving round for
the nearest smith.
There are other special operations requiring the use of specially-devised
instruments for their successful carrying out. These we shall mention when
we come to a consideration of the operations in which they are necessary.
C. THE APPLICATION OF DRESSINGS.
One of the most common methods of applying a dressing to the foot is
poulticing. Usually resorted to on account of its warmth-retaining
properties, the poultice may also be medicated. In fact, a poultice,
strongly impregnated with perchloride of mercury or other powerful
antiseptic, is a useful dressing in a case of a punctured foot, or a
wise preliminary to an operation involving the wounding of the deeper
structures. The poultice may consist of any material that serves to retain
heat for the longest time. Meal of any kind that contains a fair percentage
of oil is suitable. Crushed linseed, linseed and bran, or linseed-cake dust
are among the best.
To prepare it, all that is necessary is to partly fill a bucket with the
material and pour upon it boiling water. The hot mass is emptied into a
suitable bag, at the bottom of which it is wise to first place a thin layer
of straw, in order to prevent the bag wearing through, and then secured
round the foot. This is generally done by means of a piece of stout cord,
or by straps and buckles fastened round the pastern and above the fetlock.
An improved method of fastening has been devised by Lieutenant-Colonel
Nunn:
'A thin rope or stout piece of cord about 5 feet long is doubled in two,
and a knot tied at the double end so as to form a loop about 5 or 6 inches
long, this length depending on the size of the foot (as at A, Fig. 48). The
poultice or other dressing is applied to the foot, and the cloth wrapped
round in the ordinary way, the loop of the cord being placed at the back of
the pastern (as in A, Fig. 49); the ends of the cord are passed round, one
on the inside and the other on the outside, towards the front (as in B,
Fig. 49). These ends are then twined together down as far as the toe (see C
in Fig. 49). The foot is now lifted up, and the ends of the cord (CC, Fig.
49), are passed through the loop A (as at D, Fig. 49), and then drawn
tight. The ends of the cord are now separated, and carried up to the
coronet (as at EE, Fig. 49), one on the outside, the other on the inside of
the foot. They are then again twisted round each other once or twice (as at
F, Fig. 50), and are passed round the pastern once or twice on each side.
They are now passed under the cord (E, Fig. 49), and then reversed, so
as to tighten up E, and are finally tied round the pastern in the usual
manner. The arrangement of the cords on the sole is shown in Fig. 51, which
is a view from the posterior part.
[Illustration: FIGS. 48, 49, 50, 51.--ILLUSTRATING LIEUTENANT-COLONEL
NUNN'S METHOD OF APPLYING A POULTICE TO THE FOOT.]
'The advantages of this method of fastening have been found to be: (1) It
does not chafe the skin; (2) if properly applied it has never been known
to come undone; (3) it is the only way we know that a poultice can be
satisfactorily applied to a mule's hind-foot; (4) horses can be exercised
when the poultice is on the foot, which is almost impossible with the
ordinary leather boot; (5) the sacking or canvas does not cut through so
quickly.'
[Illustration: FIGS. 52, 53.--TWO FORMS OF POULTICE-BOOT.]
A further method of applying the poultice is by using one of the
poultice-boots made for that purpose (see Figs. 52 and 53).
These have an objection. They are apt to be allowed to get extremely dirty,
and so, by carrying infective matter from the foot of one animal to that of
another, undo the good that the warmth of the poultice is bringing about.
The advantage of the ordinary sacking or canvas is that it may be cast
aside after the application of each poultice. Where the boot is kept clean,
however, it will save a great deal of time and trouble to the attendant.
While on the subject of poulticing, it is well to remark that in many cases
it may be more advantageous to supply the necessary warmth and moisture to
the foot by keeping it immersed in a narrow tub of water maintained at the
required temperature. By this means the warmth is carried further up the
limb (sometimes an important point), and the water can more conveniently be
medicated with whatever is required than can the poultice. In fact, it is
the author's general practice, where the attendants can be induced to take
the necessary pains, to always advise this latter method.
[Illustration: FIG. 54.--SWAB FOR APPLYING MOISTURE TO THE FOOT.]
Where a dressing is relied upon by some practitioners on account of the
warmth it gives, others, even in identical cases, will depend upon the
effects of cold. This may be applied by means of what are called 'swabs.'
In their simplest form swabs may consist only of hay-bands or several
layers of thick bandage bound round the foot and coronet, and kept cool by
having water constantly poured upon them. In many cases the form of swab
depicted in Fig. 54 will be found more convenient.
When only one foot is required to be dressed, and a water-supply is
available, by far the preferable method is to attach one end of a length
of rubber tubing to the water-tap, and fasten the other just above the
coronet, allowing the water to trickle slowly over the foot. In cases where
a forced water-supply is unobtainable, and the case warrants the extra
trouble, much may be done with a medium-sized cask of water placed
somewhere over the animal, and the rubber tubing connected with that.
Where the dressing is desired to be kept applied to the sole and frog only,
there is no method more satisfactory than the shoe with plates.
[Illustration: FIG. 55.--THE SHOE WITH PLATES. _A_, The plates in position;
_B_, the plates separated from the shoe.]
[Illustration: FIG. 56.--THE QUITTOR SYRINGE.]
The plates are of metal, preferably of thin sheet iron or zinc, and are
slipped between the upper surface of the shoe and the foot after the manner
shown in Fig. 55. The plates themselves are shaped as depicted in Fig.
55, _a, b, c, a_ and _b_ curved to meet the outlines of the shoe, and _c_
shaped so as to wedge tightly over the posterior ends of the side plates,
and between them and the shoe. A distinct advantage of the plate method of
dressing is that a certain amount of pressure may be maintained on the sole
and frog, a very important consideration in connection with some of the
diseases with which we shall later deal.
When dealing with sinuous wounds of the foot, another favourite mode of
applying dressings is by means of the syringe, and no better instrument for
all cases can be found than that known as a quittor syringe (Fig. 56).
A further mode of applying dressing, and one frequently practised
in connection with the foot, is known as 'plugging.' This is almost
sufficiently indicated by its name. It consists in rolling portions of
the dressing into little cylinders, wrapped round with thin paper, and
introduced into a sinus or other position where considered necessary.
D. PLANTAR NEURECTOMY.
As a last resort in the treatment of many diseases of the foot the
operation of neurectomy is often advised. It will be wise, therefore, to
insert a description of the operation here.
_Derivation of the Word_.--For many years the operation was known simply as
'nerving' or 'unnerving,' and it was not until 1823, at the suggestion
of Dr. George Pearson, that Percival introduced the word _neurotomy_
to signify the operation with which we are now about to deal. The word
neurotomy, however, used strictly, means the act or practice of dissection
of nerves, and, when applied to the operation as practised to-day,
describes only a step in the procedure.
As the operation really consists in cutting down upon, and afterwards
excising a portion of the nerve, the modern appellation of
_neurectomy_--from the Greek _neuron_, a nerve; and _tome_, a cutting,
signifying the cutting out of a nerve or the portion of a nerve--is far
more suitable.
According as the nerve operated on is the plantar or the median, the
operation is known as plantar or median neurectomy.
_History of the Operation_.--It is to two English veterinarians that we
owe the introduction of the operation to the veterinary world. In 1819
Professor Sewell announced himself as the originator of neurotomy. This
claim was disputed by Moorcraft, who appears to have successfully
shown himself to be the real person entitled to that honour, he having
satisfactorily performed the operation on numerous animals for fully
eighteen years prior to Professor Sewell's announcement. It appears that
Moorcraft left this country for India in 1808, having practised the
operation in more or less obscurity for some six or seven years previous
to that. After his departure neurectomy, as introduced by him, either died
away in repute, or was not made by him sufficiently public to become a
matter of general knowledge. To Professor Sewell, therefore, although not
the actual originator of the operation, belongs the honour of making it
public to the veterinary profession.
In 1824, five years after Sewell's introduction, we find it practised on
the Continent by Girard. We gather, however, from the writings of Percival
and Liautard, that both in this country and on the Continent the operation
was for several years largely in the stage of experiment. Unsuitable
subjects were operated on; the work afterwards given to the animal
improperly adjusted to his altered condition; and the bad after-results of
the operation almost ignored by some, and greatly exaggerated by others.
In fact, some long time elapsed before veterinary surgeons allotted to the
operation that measure of credit which the results following it warranted.
_The Object of the Operation_ is to render the foot insensitive to pain,
and to give to an otherwise incurably lame animal a further period of
usefulness. After the operation, as time goes on, this object may become
defeated by the reunion of the divided ends of the nerve. In that case,
neurectomy must necessarily be performed again.
_The Operation_.--Two forms of neurectomy are recognised--the high
operation and the low. The low operation deals with the posterior digital
branch of the plantar nerve, and the high operation with the plantar
itself.
It is the latter operation with which we shall deal first. In our opinion
it is that most likely to be followed by satisfactory results. The area
supplied by the posterior digital is mainly the posterior portion of the
digit. Thus, unless the cause of the lameness is diagnosed with certainty
to be situated somewhere in the posterior region of the foot, section of
the posterior digital alone will not give total insensibility to pain.
Added to that, we may remember this: Below the point at which the digitals
branch off from the plantar there is always more likelihood of the part
we are attempting to render insensible being supplied by another and
adventitious branch, or a branch that, as regards its direction, is
abnormally distributed. As a last consideration, we may say that the higher
operation is the easier to perform.
Percival, in his works on lameness, has some very sage remarks to make by
way of a preliminary, and we cannot do better than quote them here. He
says:
'To command success in neurectomy three considerations demand attention:
'1. The subject must be fit and proper; in particular, the disease for
which neurectomy is performed should be suitable in kind, seat, stage, etc.
'2. The operation must be skilfully and effectually performed.
'3. The use that is made of the patient afterwards should not exceed what
his altered condition appears to have fitted him for.
'The veterinarian who is guided by considerations such as those will find
that he has restored to work horses who would otherwise have been utterly
useless. A plain and safe argument wherewith to meet the objections to
neurectomy is simply to ask the question what the animal is worth, or to
what useful purpose he can be put, that happens to be the subject of such
an operation.
'If the horse can be shown to be still serviceable and valuable, then he is
not a legitimate subject for the operation. The rule of procedure I have
laid down is to operate on no other but the _incurably lame horse_; and
whenever this has been attended to, not only has success been the more
brilliant, but indemnification from blame or reproach has been assured.'
_Preparation of the Subject_.--But little in the way of medicinal
preparation is necessary. When the animal is a gross, heavy feeder, and
carries a more than ordinary amount of cupboard, all that is needed is to
withhold his usual allowance of food for some time prior to the operation,
simply to avoid risk of rupture when casting. If considered advisable, a
dose of physic may also be administered.
To the seat of operation, however, careful attention should be given. On
the day previous to the operation the hair should be closely removed with
the clipping machines, and the skin thoroughly cleansed with warm water
and soap. After this, a bandage soaked in a 4 per cent, watery solution
of carbolic acid should be wrapped lightly round the limb, and allowed to
remain in position until the animal is cast and ready for the operation the
following morning. On removing the bandage prior to operating, the part
should again be bathed with a cold 5 per cent. solution of carbolic acid
and swabbed dry. Attention to these details will serve to leave the wound
in that favourable condition in which it heals nicely, and with the minimum
amount of trouble.
_Preliminary Steps_.--By some practitioners the operation is performed with
the animal standing, local anaesthesia having been first obtained by the use
of cocaine, or an ethyl chloride spray. There is no gainsaying the fact,
however, that the operation of neurectomy is a painful one, and that, with
most operators, success will be more fully guaranteed with the animal cast
and the limb held in a suitable position by an assistant.
The animal is thrown by the hobbles upon the side of the leg which is to be
operated on. The cannon of the upper fore-limb is then fixed to the cannon
of the upper hind, as described under the section of this chapter devoted
to the methods of restraint, and the lower limb freed from the hobbles and
drawn forward by an assistant by means of a stout piece of cord round the
pastern.
An alternative method of holding the limb is to bind both fore-legs
together above the knee by means of the side-line run round a few times in
the form of the figure 8, and then fastened off. As in the former method,
the lower foot is then removed from the hobble, and again held forward by
an assistant. By either method the inside of the limb is operated on first.
[Illustration: FIG. 57.--THE ESMARCH RUBBER BANDAGE AND TOURNIQUET.]
Although it is not absolutely necessary, it is an advantage, especially to
the inexperienced operator, to apply before operating an Esmarch's bandage
and tourniquet (Fig. 57). This expels the greater part of the blood from
the limb, and renders the operation comparatively bloodless.
[Illustration: FIG. 58.--RUBBER TOURNIQUET WITH WOODEN BLOCK.]
The Esmarch bandage is composed of solid rubber, and with it the limb is
bandaged tightly from below upwards. On reaching the knee the tourniquet is
stretched round the limb, fastened by means of its buckle and strap, and
the bandage removed. Those who feel they can dispense with the bandage use
the tourniquet alone. For this purpose the form depicted in Fig. 58, and
the one in general use at the Royal Veterinary College, is more suitable,
on account of its wooden block, which may be placed so as to press on the
main artery of supply.
[Illustration: Fig. 59. NEURECTOMY BISTOURY.]
_Instruments Required_.--These should be at hand in an earthenware or
enamelled iron tray containing just sufficient of a 5 per cent. solution
of carbolic acid to keep them covered. Those that are necessary will be a
sharp scalpel, or, if preferred, one of the many forms of bistoury devised
for the purpose (see Fig. 59), a pair of artery forceps, a needle ready
threaded with silk or gut, one of the patterns of neurectomy needle (see
Fig. 60), and a pair of blunt-pointed scissors curved on the flat. It is
also an advantage, when once the incision through the skin is made, to
employ one of the forms of elastic, self-adjusting tenacula (see Fig. 61)
for keeping the edges of the wound apart while searching for the nerve.
[Illustration: FIG. 60. NEURECTOMY NEEDLE.]
_Incision through the Skin_.--We remember that the plantar nerve of the
inner side is in close relation with the internal metacarpal artery, and
that both, in company with the internal metacarpal vein, run down the limb
in close proximity with the inner border of the flexor tendons. Also, we
remember that the external plantar nerve has no attendant artery, although,
like its fellow, it is to be found in close touch with the edge of the
flexor tendons.
Bearing these landmarks in mind, we feel for the nerve in the hollow
just above the fetlock-joint by noting the pulsations of the artery, and
determining the edge of the flexor tendons. This done, a clean incision is
made with the bistoury or the scalpel in the direction of the vessels. The
incision should be made firmly and decisively, so that the skin may be
cleanly penetrated with one clear cut. If judiciously made, little else in
the shape of dissection will be needed.
[Illustration: FIG. 61.--DOUBLE TENACULUM.]
It is now that the double tenaculum (Fig. 61) is applied. One clip is fixed
to the anterior edge of the wound, and the other carried beneath the limb
and made to grasp the posterior edge. If found desirable to keep the
edges of the wound apart, and no tenaculum to hand, the same end may be
accomplished by means of a needle and silk. In like manner as is the
tenaculum, the silk is attached to one edge of the wound, carried under the
limb, and firmly secured to the other.
Having made the incision, the wound should be wiped free from blood by
means of a pledget of cotton-wool previously soaked in a carbolic acid
solution and squeezed dry. At the bottom of the wound will now be seen
the glistening white sheath, containing the vein, artery, and nerve. This
should be picked up with the forceps, and a further incision made with the
bistoury. Care should be exercised in making this second incision, or the
artery may accidentally be opened. If an ordinary scalpel is used, the
lower end of the sheath should be picked up and the point of the scalpel
inserted through it. With the cutting edge of the scalpel turned towards
the opening of the wound, the sheath is then slit from below upwards. The
second incision satisfactorily made, the wound is again wiped dry, and the
nerve seen as a piece of white, curled string in the posterior portion of
the wound.
At this stage it is advisable to accurately ascertain whether what we have
taken to be the nerve actually is it. This is done by taking it up with the
forceps and giving it a sharp tweeze. A sudden struggle on the part of the
patient will then leave no doubt in the operator's mind that it is the
nerve he has interfered with.
_Section of the Nerve_.--The neurectomy needle (Fig. 60) is now taken, and,
excluding the other structures, passed under the nerve. A piece of stout
silk or ordinary string is then threaded through the eye of the needle, the
needle withdrawn, and the silk left in position under the nerve. The silk
is now tied in a loop, and the nerve by this means gently lifted from its
bed. With the curved scissors or the scalpel it is severed as high up as is
possible. The lower end of the severed nerve is then grasped firmly with
the forceps, pulled downwards as far as possible, and then cut off. At
least an inch of the nerve should be excised.
The animal is then turned over, and the opposite side of the limb operated
on in the same manner.
The tourniquet is now removed, and the wound is examined for bleeding
vessels. If the haemorrhage is only slight, the wound should be merely
dabbed gently with the antiseptic wool until it has stayed. A larger vessel
may be taken up with the artery forceps and ligatured, or the haemorrhage
stopped by torsion. On no account, unless it it done to stay haemorrhage
that is otherwise uncontrollable, should the wound be sutured with blood in
it. With the wound once dry and clean, it is well to insert three or four
silk sutures, but care must be taken not to draw them too tightly. This
done, the patient may be allowed to get up. _After-treatment_.--This is
simple. Over each wound is placed a pledget of antiseptic cotton-wool or
tow, and the whole lightly covered with a bandage soaked in an antiseptic
solution. For the first night the animal should be tied up short to the
rack, and the following morning the bandages removed. A little boracic
acid or iodoform, or a mixture of the two combined with starch (starch and
boracic acid equal parts, iodoform 1 drachm to each ounce) should now be
dusted over the wounds, the antiseptic pledgets renewed, and the bandage
readjusted over all.
At the end of three or four days the bandages may be dispensed with. All
that is necessary now is an occasional dusting with an antiseptic powder,
and, as far as possible, the restriction of movement. At the end of a week
the sutures may be removed, and the animal turned into a loose box or out
to pasture.
E. MEDIAN NEURECTOMY.
As a palliative for lameness when confined to the foot, one would imagine
that the plantar operation would be all sufficient. There are operators,
however, who state that the results following section of the median nerve
have been such as to cause them to entirely abandon the lower operation in
its favour. If only for that reason a brief mention of the operation must
be made here.
The operation was first performed in this country in October, 1895, the
subject being one of the out-patients at the Royal Veterinary College Free
Clinique.
For five or six years following this date Professor Hobday performed the
operation some several hundred times, and was certainly instrumental in
bringing the operation into prominence. Though so recently introduced here,
it appears to have been practised for several years on the Continent,
originating in Germany as early as 1867. In that country a first public
account of it was published in 1885 by Professor Peters of Berlin, while in
France it was introduced by Pellerin in 1892. In this operation a portion
of the median nerve is excised on the inside of the elbow-joint just below
the internal condyle of the humerus. Here the nerve runs behind the artery,
then crosses it, and descends in a slightly forward direction behind the
ridge formed by the radius.
The position of the limb most suitable for the operation is exactly that we
have described as most convenient for the plantar excision. The animal is
cast, preferably anaesthetized, and the limb removed from the hobbles, and
held as far forward as is possible by an assistant with the side-line.
Professor Hobday's description of the operation is as follows:
'A bold incision is made through the skin and aponcurotic portion of
the pectoralis transversus and panniculus muscles, about 1 to 3 inches
(depending on the size of the horse) below the internal condyle of the
humerus, and immediately behind the ridge formed by the radius. This
latter, and the nerve which can be felt passing over the elbow-joint, form
the chief landmarks. The haemorrhage which ensues is principally venous, and
is easily controlled by the artery forceps. In some cases I have found it
of advantage to put on a tourniquet below the seat of operation, but this
is not always advisable, as it distends the radial artery. We now have
exposed to view the glistening white fascia of the arm, which must be
incised cautiously for about an inch. This will reveal the median nerve
itself situated upon the red fibres of the flexor metacarpi internus
muscle. If not fortunate enough to have cut immediately over the nerve, it
can be readily felt with the finger between the belly of the flexor muscle
and the radius.'[A]
[Footnote A: _Journal of Comparative Pathology and Therapeutics_, vol. ix.,
p. 181.]
The nerve exposed, the remainder of the operation is exactly as that
described in removing the portion of the nerve in the plantar operation.
The wound is sutured and suitably dressed, and a fair amount of exercise
afterwards allowed the patient.
F. LENGTH OF REST AFTER NEURECTOMY.
This is placed by the majority of surgeons at about three weeks to a
month. Within that period no excessive exertion should be undergone by
the patient. A certain amount of quiet exercise, however, is beneficial,
facilitating the healing of the wounds, and accustoming the animal to the
altered condition of his limb.
G. SEQUELAE OF NEURECTOMY.
These we shall relate collectively, making no distinction between those
following excision of the plantar nerve and those succeeding section of the
median. It must be remembered by the surgeon, however, that the unfortunate
sequelae we are now about to describe are likely to be far more grave when
following section of the larger nerve.
_Liability of Pricked Foot going undetected_.--On account of the warning
they convey to the surgeon, first place among the sequelae of neurectomy
must be given to accidents following loss of sensation. Take, for example,
punctured foot. In any case, in the sense of being unforeseen, it is
accidental. In the neurectomized foot it becomes doubly accidental, in that
not only is it unforeseen, but that it is for some time indiscoverable.
With the foot deprived of sensation, a nail may be picked up, or a prick
sustained at the forge, and no intimation given to the attendant until pus
has underrun the horn, and broken out at the coronet. What follows, then,
is that the hoof as a whole, or the greater part of it, sloughs off.
No neurectomy should be undertaken unless this contingency has been allowed
for. The owner should be advised of it by the surgeon, who should at the
same time enjoin on his client the absolute necessity of giving to the
neurectomized foot daily and careful attention.
_Loss of Tone in the Non-sensitive Area_.--In addition to the mischief
resulting from a wound going undetected, it must be remembered that the
loss of tone resulting from the operation gives to every wound (however
slight), in the region supplied by the removed nerve, a sluggish and
troublesome character. Difficult to deal with as wounds about the foot
ordinarily are, they are rendered more so by a previous neurectomy.
_Gelatinous Degeneration_. This is a condition liable to occur in cases
where the operation has been too long deferred, and when considerable
structural alteration has already taken place in the shape of diseased bone
or tendon, more especially in navicular disease. It consists in a peculiar
softening of the structures of the limb, accompanied with enlargement,
due to swelling of the connective tissues, the enlargement and softening
generally making itself first apparent by a soft, pulpy swelling in the
hollow of the heel.
From this onwards the enlargement increases, and lameness becomes
excessive, the animal going more and more on his heels, until, finally, no
portion of the solar surface of the foot comes to the ground at all.
The case is hopeless, and destruction should be advised.
_Reported Case_.--'The patient, a brown carriage gelding, was brought to
the Royal Veterinary College infirmary in a cart on December 31, the only
previous history obtainable being that it had suddenly fallen lame a month
before.
'The symptoms presented were excessive lameness of the near fore-limb. On
being trotted, the toe was elevated each time the foot reached the ground,
progression being entirely on the heels. Separation of the hoof for about 2
inches at the hinder part of the coronet; oedematous swelling from foot to
knee, extending during the next three days to the elbow. Great tenderness
between the knee and the fetlock; below this no sensation whatever, as a
pin was inserted in several places round the coronet without causing any
symptoms of pain. On further examination, two unnerving scars were found.
No treatment was adopted, and the horse was destroyed on January 6.
'On dissecting the leg, the following appearances presented themselves:
'The limb was very much enlarged, due to thickening of the connective
tissue, the skin being removed only with difficulty. The tendons were soft
and much thickened. A rupture of the skin at the coronet, just where the
skin meets the wall of the foot. Large extravasations of blood at the back
of the tendons, situated in the lower half. _External_ nerve trunk had
become reunited, at the point of junction there being a hard lump about
the size of a walnut. _Internal_ nerve trunk also had become reunited, and
presented a thickened portion at the point of junction, but not so large as
that of the outer side, and situated in the lower half of the tendon, about
2 inches higher than that on the external nerve. This nerve trunk was
atrophied below the thickening, and had undergone gelatinous degeneration.
Judging from the scars on the skin, this side had evidently been unnerved a
week or ten days previously to that on the outer side. The band stretching
across the back of the perforatus, between the external and internal
nerves, appeared on the inside to have become firmly fixed into the tendon.
'On removing the hoof, under the sole there appeared a large quantity of
very foetid pus; the laminae were very much inflamed in patches. There
was an enormous thickening of connective tissues in the heel. On cutting
longitudinally through the perforatus tendon, there was exposed a large
blood-coloured mass, of a gelatinous appearance, situated on the perforatus
tendon, the latter being very much thickened, and growing to the navicular
bone. The underneath surface of the superior suspensory ligament was much
thickened, and firmly adherent to the bone; at the posterior surface of
the metacarpus there was a quantity of gelatinous substance. The anterior
ligament of the fetlock-joint was thickened; the navicular bone was entire,
but showed lesions of navicular disease, being ulcerated. Section through
the bone did not reveal anything further. It may be here remarked that the
ulcerations were on either side of the central ridge, and not at all on the
ridge itself.
'Microscopic examination of the tissue joining the two ends of the nerve
together revealed a few nerve fibres; the general appearance was that
of granulation tissue, containing capillary vessels, which were fairly
plentiful, and comparatively large in size.'[A]
[Footnote A: _Veterinary Record_, vol. iv., p. 386 (Hobday)]
_Chronic Oedema of the Leg_.--In some cases there is a distinct swelling
of the leg some time after the operation. This exposes the limb to the
infliction of sores from striking with the opposite foot, with, of course,
the difficulty in healing we have just described.
_Persistent Pruritus_.--This annoying sequel occurs in the neurectomized
limb, with or without gelatinous degeneration, and appears to be without a
remedy. The itching in some cases is so intense as to lead the animal to
constantly gnaw at the top of the foot. As one observer has remarked, the
animal may begin literally biting pieces out of his limb. The result of the
irritation and gnawing is fatal. Great sloughing of the parts takes place,
and the animal has eventually to be slaughtered.
_Fracture of the Bones_.--The sudden loss of sensation in a foot may cause
the animal to use violently the limb he has for months past been carefully
nursing. It may be that the lameness for which the operation has been
performed has been due to disease existing in the navicular bone, and
extending, perhaps, to the os pedis. By the disease the bone has already
been made brittle, its substance and ligamentous attachments perchance
weakened and broken up by a slow-spreading caries, and rarefaction of the
remaining bone substance rendered almost certain. In this instance, the
free use of the foot, and the application to the diseased structures of an
unwonted pressure immediately after the operation results in fracture. With
the rupture of the structures we get the elevated toe and soft swelling in
the heel, as described in gelatinous degeneration. Treatment, of course, is
out of the question.
_Neuroma_.--A further sequel is the appearance at the seat of the operation
of what is termed an 'amputational neuroma.' This is a tumour-like
growth occurring on the end of the divided nerve. It is composed of
connective-tissue elements permeated by nerve fibres which have grown out
from the axis-cylinders of the nerve stump. It may vary in size from a pea
to a hazel-nut, and is frequently the cause of much pain. This must be cut
down upon and cleanly removed, taking away at the same time as much of the
nerve as is possible.
_Reunion of the Divided Nerve_.--We may say at once that 'reunion' in the
popular sense of the word does not take place. At a varying period after
section, however, we do get a return of sensation. This is brought about in
the following manner: The axis-cylinder of the nerve, still in connection
with the spinal cord, swells somewhat, and hypertrophies. The cells of this
hypertrophied portion show a great tendency to proliferate and produce
new nerve structure. This growing point splits, and gives rise to several
fibrils, which are new axis-cylinders. These commence to grow towards the
periphery, and, in so doing, grow through the cicatricial tissue that has
formed at the seat of the operation.
After passing through the cicatricial tissue (the amount of which tissue,
of course, controls the length of time that insensibility remains), the
growing axis-cylinders reach the degenerated portions of the nerve below
the point of section. It is along the track of the old nerve that the new
growths from the stump reproduce themselves.
The fact of the new growths having to pass through the fibrous tissue of
the cicatrix before they can gain the course of the old nerve, along which
latter their progress of growth is comparatively easy, affords ample
illustration that as large a portion as is possible of the nerve should be
removed when operating, in order to convey insensibility for the longest
time. After reunion, of course, nothing remains but to repeat the
operation.
_The Existence of an Adventitious Nerve-supply_.--While not exactly a
sequel of the operation, the fact that it is not discovered until after the
operation has been performed warrants us in mentioning it here. It is
not an uncommon thing in the lower operation to find that sensation and
symptoms of lameness still persist after section of the nerve. In many
cases this has been traced to the existence of an abnormal nerve branch.
In the higher operation this is not so likely to be met with. That it may
occur, however, is shown by the following interesting case related by
Harold Sessions, F.R.C.V.S.:[A]
[Footnote A: _Journal of Comparative Pathology and Therapeutics_, vol.
xii., p. 343.]
'In June of 1898 I saw a hunter suffering from navicular disease. After
carefully examining the leg, I advised the owner to have the operation of
neurectomy performed upon him. This he decided to do, and the horse was
sent to me about the beginning of July.
[Illustration: FIG. 62.--DISSECTED EXTERNAL METACARPAL NERVE AND BRANCHES.
_a_, Metacarpal; _b_, anterior plantar; _c_, extra branch (probably from
the internal metacarpal), conveying sensation after division of the
external metacarpal.]
'The operation was performed in the ordinary way, without any difficulty
whatever. The wounds healed nicely, but the horse still continued to go
lame. Careful examination showed that there was still sensation on the
outside of the foot. Thinking that possibly there might be two external
metacarpal nerves, the horse was again cast, the operation being performed
slightly lower down. Only the main branch of the external metacarpal nerve
could be found. A piece of this was taken out, and the horse let up. On
examination, sensation was still found in the posterior part of the outside
of the foot. It was very evident that there was some abnormal distribution
of the nerve, as sensation was still being conveyed to that part of the
foot.
'As the horse was absolutely useless, and would have to be shot unless this
piece of nerve could be found, he was again thrown, and after he had been
anaesthetized I determined to follow the course of the nerve down, until I
found where the accessory branch came from. This I found a little below the
fetlock, about 1/2 inch below the point where the anterior plantar nerve is
given off from the metacarpal nerve. It was about 1/2 inch below the spot
where the anterior plantar nerve passes between the artery and vein of the
foot, and it was somewhat difficult to get at it.
'Fig. 62 shows the exact size and distribution of the nerves. After the
separation of the accessory branch, sensation was taken from the foot, and
the horse went perfectly sound.'
_Stumbling_.--In addition to the sequelae we have mentioned, it is urged
against the operation of neurectomy that one of the first effects of
depriving the foot of the sense of touch is a tendency on the part of
the animal to stumble. From the cases we have seen we cannot regard
this objection as a serious one. Nevertheless, as veterinarians, with a
knowledge of the physiology of the structures with which we are dealing,
we must treat the objection with respect, for, after all, we are bound to
allow that stumbling, and a bad form of it, would be but a natural sequence
of the operation we have just performed. The real fact remains, however,
that cases of stumbling, even immediately after the operation, are
rare; and that even when they do occur, the animal seems easily able to
accommodate himself to the altered condition, and as readily uses the
comparatively inert mass at the end of his limb as he did previously the
intact foot.
H. ADVANTAGES OF THE OPERATION.
From the prominence we have given to the unfortunate sequelae of the
operation it might possibly be inferred that, while not giving it our
absolute condemnation, we regard neurectomy with a certain amount of
distrust. That we may contradict any such false impression, we state here
that in many cases the operation is the only measure which will offer
relief from pain, and restore to work an otherwise useless animal. In
support of that we will now quote the recognised advantages of the
operation.
That in many cases, when all other methods--surgical and medicinal--have
failed, there is an immediate and total freedom from pain and lameness no
one will deny. This, if it restores to active work an animal that would
otherwise have had to have been cast aside, is ample justification for
giving the operation, in spite of its many unfortunate terminations, a real
place among the more highly favoured remedial measures to our hand.
'For _Contracted Hoofs_, viewing them in the light of idiopathic disease,
or as being the immediate cause of the existing lameness in the uninflamed
condition of the foot, and when consequential changes of its organism have
taken place which bid defiance to therapeutic measures, _neurotomy_ is a
_warrantable resource_' (Percival).
'For _Ringbone_ neurotomy has been practised with perfect success, after
blistering and firing had both failed, notwithstanding the work the animal
had to perform afterwards was of the most trying nature' (_ibid_.).
For _Navicular Disease_, when that malady is diagnosed, the earlier
neurectomy is performed the better. The greater work given to the diseased
bursa and bone, and the return of the contracted heels to the normal,
brought about by the greater freedom with which the foot is used, are
claimed by many to effect a cure.
Writing of navicular disease, and mentioning his belief in the possibility
of the diseased bone effecting its own repair after the operation, Harold
Leeney, M.R.C.V.S., says:
'The expansion of the heel, and rapid development of the frog (in this and
many other cases) immediately after the operation, has not, I venture to
think, attracted so much attention as it deserves, and may have something
to do with those cases which appear to be actually _cured_, not merely made
to go sound by absence of pain.'[A]
[Footnote A: _Veterinary Record_, vol. xi., p. 297.]
Speaking of the median operation before a meeting of the Central Veterinary
Medical Society, Professor Hobday says:[A]
[Footnote A: _Veterinary Record_, vol. xiii., p. 427.]
'For old-standing lamenesses, when due to splints, exostoses, chronically
sprained, thickened, and painful perforans and perforatus tendons, or cases
of that kind which cause pain by pressing on the adjacent nerve structures,
after all other known methods have failed, median neurectomy is the
operation which will be most likely to give the animal a new lease of life
and usefulness.'
'Of the _Humanity and Utility of Neurectomy_ there can be no question
whatever, and provided the cases are well selected, and the operation
is efficiently performed, the advantages to be derived from it are most
striking as well as enduring. But the disadvantages attending the loss of
sensation in the foot have been brought forward on many occasions as
an argument against neurectomy, and no one can deny that the foot with
sensation is better than one without that faculty. But in a long experience
of the operation I have never found these disadvantages outweigh the great
advantages which have immediately followed it.'[A]
[Footnote A: _Veterinary Journal_, vol. ix., p. 178 (Fleming).]
Beyond these, the direct advantages of neurectomy, are other and more
indirect advantages which claim attention.
The most astonishing among them is the fact noted by many writers of repute
that exostoses (ringbones, side-bones, splints, etc.) rapidly diminish in
size. This is vouched for by such well-known authorities as Zundel and
Nocard.
Percival, too, mentions at some length the effect of the removal of pain on
the oestral and generative functions, quoting a case of a brood cart-mare
by reason of bony deposits being stayed from breeding for some years. Two
months after the operation she went to work, and moved sound, her altered
condition leading her to breed several healthy foals.
I. THE USE OF THE HORSE THAT HAS UNDERGONE NEURECTOMY.
No operation is of any considerable value to the veterinary surgeon unless
he is able to show that after it he has left his patient workable. The
alleviation of pain alone, commendable as it is from a humanitarian
standpoint, is of no interest to the average owner of horse-flesh, unless
with it he sees his animal capable of justifying his existence by the
amount of labour performed.
Criticised in this way, is the operation of neurectomy justifiable? Upon
that point the opinions of many practitioners, even at the present day,
differ. We have already partly answered the objections likely to be raised
on this score by stating that the work afterwards allotted the animal
should be fixed to suit his altered condition. It may be taken as a general
rule that in all cases where the animal's usefulness depends upon his
delicacy of touch, as, for example, animals used solely for hacking or
hunting, his future usefulness in that special sphere of work will be done
away with.
Percival himself, always a strong advocate for the operation, fully
recognises this. 'Does the neurotomized horse maintain the same step
as before?' he asks. 'To this important question,' he replies, 'I
unhesitatingly answer no; he does not. There can be no doubt but that the
horse _feels_ the ground upon which he is treading, and that he regulates
his action in consonance with such feeling, so as to render his step the
least jarring and fatiguing to himself, and therefore the easiest and
pleasantest to his rider.... Such impressions'--those of touch--'being
in the neurotomized subject, so far as regards the feeling of the foot,
altogether wanting, a bold, fearless projection of the limb in action will
be the consequence, followed by a putting down of the hoof flat upon the
ground, as though it were a block, creating a sensation alike unpleasant
both to horse and rider.'
Emphatic as Percival is upon this point, there are, nevertheless, others
who maintain with equal stoutness that the unnerved animal is positively as
safe, if not safer, than the animal who has not been so treated.
'That the tactile sense in the horse's foot is useful, it would be idle to
deny; but that it is absolutely essential, even to safe progression, no one
who has paid attention to the results of plantar neurectomy will maintain.
On several occasions for years I have hunted, hacked, and driven horses
which have been deprived of sensation in their fore-feet, and never had an
accident with them. Their action has not been impaired by the operation; on
the contrary, it has been vastly improved compared with what it had been
previous to it. And my opinion has not been single in this respect, as many
competent horsemen can give like evidence after long and severe trials of
neurotomized horses. The opponents of neurotomy were, probably, not aware
that there is in progression a _muscular_ as well as a _tactile sense_.'
This latter contention is supported by numerous cases, reported at the time
when the operation of neurectomy was at the heyday of its popularity. Two I
select from writings of a later period:
_Recorded Cases_.--1. 'Two of the finest among the many fine horses in the
Second Life Guards were so lame from navicular disease, when I joined the
regiment, that they were unsafe and unsightly to ride, and were therefore
entered on the list to be cast off and sold. One was so crippled that it
could scarcely be moved out of its stable. Peeling sorry at having to get
rid of such good horses, and anxious to give another blow to the mistaken
theory that unnerved animals were unsafe, I obtained the consent of my
commanding officer, who patronizes practical conclusions, to perform
neurotomy. This was carried out on both horses about eighteen months ago.
Within a fortnight they were at their duty, absolutely free from lameness,
and with first-rate action, and one of them, from being troublesome and
unsteady in the ranks--probably from the pain in its feet--had become quite
steady and tractable. Instead of being lame, blundering, and unsafe, both
were sound, free in movement, and secure, and, the pain being abolished,
they looked improved in condition.
'During the month of July the regiment attended the summer drills at
Aldershot, and five days every week for a month these horses carried a
weight of about 22 stones each over the roughest and most dangerous ground,
nearly always at a fast pace, and for four, five, or six hours each day;
and yet they never fell or blundered, and the troopers who rode them had
unbounded confidence in their sure-footedness. They returned to Windsor, at
the end of the month's severe test, as sound in their paces as when they
left, and certainly now offer no indication whatever that they are less
safe to ride than any other horse in the regiment. The effects of the
relief from pain are also most marked, not only in the altered gait out of
doors, but also in the stable.'[A]
[Footnote A: _Veterinary Journal, vol_. ix., p. 178 (George Fleming,
F.B.C.V.S.).]
2. 'Some years ago I operated upon a valuable hunter, the property of a
gentleman in Kildare, the animal having shown unmistakable symptoms
of navicular disease for some months previously, and which had been
unsuccessfully combated by the milder forms of treatment for the disease
without any benefit. Although the horse went sound, the owner feared to
ride him, and sent him to be sold in Dublin, where he was disposed of for a
small price, and I then lost sight of him. The following Punchestown
Races, to my surprise, amongst a group of horses walking round the paddock
previous to saddling for an important race, I recognised my old patient,
bandaged, clothed, and trained, ready to take his part in the cross-country
contest, and surrounded by a host of admirers willing to back him at any
price.
'Having satisfied myself that it was no other than the same animal, my
first impulse was at once to find out the jockey who was to ride him, and
warn him of his danger by telling him his mount was devoid of feeling
in both fore-feet; but the saddling-bell had already rung, and in a few
moments more the jockey emerged from the weighing-room and the next view of
the horse was his tearing up the course in the preliminary, and "pulling
double." I was sorry for the jockey if he felt as I did at that moment, for
if he did I fear he and his horse would have parted company at the first
fence, as I was certain there would be a smash before the end of the long
and difficult three miles of the Kildare Hunt Cup course. It was not until
I saw him again in the front rank passing the stand, in the first round,
that I breathed freely, and even then I felt very guilty, and, had he come
to grief badly, I don't think I should ever have operated on another horse
except in such a way as would have left unmistakable traces after it.
'"The old horse wins!" screamed a thousand voices as the competitors safely
cleared the last bank (now taken away for a gorse fence) the last time
round, and from that moment the operation went up in my estimation a
hundredfold, and I almost lost all interest in the finish (and it was a
close one, with my patient a good third), resolving I would operate for the
future on every animal, young and old, which showed symptoms of navicular
disease.
'Neither owner nor jockey knew the horse had been operated on, and he was
soon after, on the strength of his performance, sold for a good price to
come to England. It is idle to think that all cases are as successful as
this was, as experience soon told me; but I consider that, in careful
hands, the advantages well outweigh the disadvantages of the operation, and
I have selected this instance merely as a practical example.'[A]
[Footnote A: _Veterinary Journal_, vol. iii., p. 254 (W. Pallin,
M.B.C.V.S.).]
It is solely with the object of ventilating both sides of the question
that we quote the last two cases. In our opinion, the colours in which
the results of the operation are there painted are far too rosy. The
practitioner who has before him the task of satisfying a client as to what
will or what will not be the results of an operation he has suggested will
do well to weigh each side of the argument carefully, and endeavour in his
explanation to strike the happy mean.
We hold, further, that the animal who has previously been accustomed to
fast work, and to work entailing a large call upon the sense of touch when
passing over rough and uneven ground, will be far more likely, in his
neurectomized condition, to give satisfaction to his owner if put to a
slower and a more suitable means of earning his living.
CHAPTER VI
FAULTY CONFORMATION
Under this heading we shall deal with such formations of the feet as depart
sufficiently from the normal to render them serious. Faulty conformation
may be either congenital or acquired, and acquired gradually as the result
of slowly operating causes, or suddenly as the sequel to previous acute
disease. Whether congenital or acquired, serious in its nature or
comparatively of no account, the veterinary surgeon will often find that
the matter of conformation is one which will have a direct bearing on many
of his 'foot' cases, and, furthermore, that it is one upon which he will
often be called to give advice.
A. WEAK HEELS.
_Definition_.--That condition of the wall in which, owing to the softness
of the horn and the oblique direction of the horn fibres, the heels are
unable properly to bear the body-weight, and, as a consequence, curve in
beneath the sole. We give the condition first mention, not because of its
greater importance, but for the reason that it is frequently the forerunner
of the condition to be next described--namely, contracted feet.
_Symptoms_.--The extreme point of the heel is not affected unless the foot
has been greatly neglected, and the condition allowed to develop. Where,
however, the foot has been uncared for, curving in of the wall takes place
to an alarming degree, and the heels curl underneath the foot to such an
extent as to grow over the sole and the bars. By the pressure they exert on
the sole corns result, and the animal is lamed.
_Causes_.--In the main this defect is hereditary. It is seen commonly in
connection with flat-foot, and where the horn of the wall is thin and
shelly.
_Treatment_.--In the case of weak or 'turned in' heels no suitable bearing
is offered for the shoe in the posterior half of the foot. Any attempt to
induce the heels to bear weight is immediately followed by their bending
in. It follows from this that the best shoe to be used here is one in which
the bearing is confined to the anterior half of the wall, the heels being
relieved by being sufficiently pared. As might be expected, this bearing on
the anterior half only of the foot is insufficient; pressure must be given
the frog. This latter end is best gained by a bar shoe (Fig. 68). With it
the anterior portions of the wall, the whole of the bars, and the whole
of the frog may be in contact, and the heels only so pared as to take no
bearing at all. A few such shoeings sees the defect remedied. In every
instance paring of the sole should be discouraged, as it serves but to
increase the deformity.
B. CONTRACTED FOOT.
_(a)_ GENERAL CONTRACTION--CONTRACTED HEELS.
_Definition_. By the term contracted foot, otherwise known as hoof-bound,
is indicated a condition in which the foot, more especially the posterior
half of it, is, or becomes, narrower from side to side than is normal.
It must be borne in mind, however, that certain breeds of horses have
normally a foot which nearer approaches the oval than the circular in form,
and that a narrow foot is not necessarily a contracted foot.
The contraction may be bilateral when affecting both heels of the same foot
and extending to the quarters, or unilateral when the inside or outside
heel only is affected.
In some cases contraction is confined to one foot, while in others it may
be noticed equally bad in both. It is a matter of common knowledge that
contraction is usually seen in the fore-feet, while the hind seldom or
never suffer from it, a fact which, to our minds, seems difficult of
adequate explanation. Zundel explains this by stating that contraction is
principally _observed_ in the fore-feet, by reason of the fact that when
lameness arises from it alteration in action will more readily be detected
in front than behind. Percival, on the other hand, suggests that the
greater expansive powers of the hind-foot, by reason of the impetus of its
action, is able to overcome any influence operating towards contraction. It
may be, however, that given a cause for contraction, such as the removal of
the frog's counter-pressure with the ground by faulty shoeing or excessive
paring, the fore-feet, by reason of their being called upon to bear the
greater part of the body-weight, are the first to suffer.
Flat feet with weak heels are those most frequently affected, and, as we
have already intimated, the condition may exist with or without other
disease of the foot.
Depending upon its degree, contracted foot may vary from a simple
abnormality, non-inflammatory and painless, to a condition in which it
becomes a veritable disease, giving rise to a bad form of lameness, and
bringing about a withered and sometimes discharging and cankerous affection
of the frog.
_Symptoms_.--In its early stages contraction is difficult of detection, and
where both feet are affected may for some time go unsuspected. With only
one foot undergoing change, the early stages may the more readily be
marked, for in this case comparison with the other and sound foot will at
once reveal the alteration in shape. If lameness in the suspected foot is
present, then any lingering doubt will be quickly dispelled.
When far advanced, contraction offers signs that cannot well be missed. The
converging of the heels narrows the V-shaped indentation in the sole for
the reception of the frog. As a consequence of this, the frog itself
becomes atrophied by reason of the _continual_ pressure exerted upon it by
the ingrowing horn of the wall and the bars. The median and lateral lacunae
of this organ, from being fairly broad and open channels, become pressed
into mere crack-like openings (see the commencing of this condition in Fig.
80, and a badly wasted frog in Fig. 74A). As the case goes on, the lateral
branches of the frog entirely disappear, and all that is left of the organ
is a remnant of its body or cushion, now wedged in tightly between the
bars. Following upon the disappearance of the frog, we find that the bars
are in contact, or, in some cases, actually overlapping each other at their
posterior extremities.
At this stage, perhaps, the whole condition has become aggravated by a foul
discharge from the place originally occupied by the frog, and the foot,
especially in the region of the heels, has become hot and tender--really a
form of local and subacute laminitis.
The long-continued inflammation, although only of a low type, renders the
horn of the hoof hard and dry, and only with difficulty will the ordinary
foot instruments cut it. This in its turn leads to cracks and fissures in
various places, but more especially in the bars and what is left of the
frog. Often, too, cracks will appear in the horn of the quarters, and a
troublesome and incurable form of sand-crack results.
An animal with contraction advanced as far as this, especially if confined
to one foot, goes unmistakably lame. With both feet affected, he ordinarily
starts out from the stable in a manner that is commonly called 'groggy.' In
other words, the gait is uncertain, and feeling; and stumbling is frequent.
Anyone who has had the misfortune to drive an animal with feet in this
condition knows full well that every little irregularity in the road at
once makes itself felt to the feet, and that the animal, as time goes on,
learns to carefully avoid any suspicious-looking group of stones he may
see. To drive an animal like this is to keep one's self continually on
tenter-hooks, for, sooner or later, the inevitable happens, and the animal
comes down.
Up to now we have described the changes of form in the hoof as seen when
the contracted foot is viewed from the solar surface. With those changes as
evident as we have depicted them, there will be no difficulty in detecting
the alterations in the form of the wall.
In addition to a narrowing from side to side there will be noticed an
abnormal straightness of the quarters, with a turning in, more or less
sudden, of the heels. This effect is given in these cases by the smith
maintaining the shoe of a length and width that should normally fit a foot
of that particular animal's size and substance. This is probably done with
the idea of deceiving anyone examining the solar surface. Viewed from this
position, the width of the shoe at the heels gives the impression that it
is attached to a foot of normal breadth. This deception is heightened if
at the same time has been practised the process of 'opening up the heels.'
That expression indicates that the bars have been removed, and the lateral
lacunae of the frog made to continue the concavity of the sole. The arch of
the latter is thus made to appear of much greater extent than it really is,
and the heels, by reason of their being abruptly cut off when removing the
bars, also convey the false impression of being wide apart.
The practitioner unversed in the tricks of the forge will best guard
against this by viewing the foot, while on the ground, from behind. From
that position he will be able to detect the lowness of the quarters, and
the projecting portion of the shoe, that the hoof, by reason of its sudden
bending inwards, does not touch.
The 'feeling' manner of the gait before alluded to, together with the
disinclination to put the foot firmly and squarely forward, will sometimes
lead the examiner to over-look the contraction, and diagnose his case as
one of shoulder lameness. In many cases, too, such consequent conditions
as 'thrushy frogs' and 'suppurating corns' are often treated with utter
disregard of the contraction that has really brought them about. But above
all, the disease most likely to be confounded with simple contraction is
navicular disease. More than probable it is that many cases of so-called
'navicular' have in reality been nothing more than contraction brought
about by one or other of the causes we shall afterwards enumerate--cases
where a due attention to the prime cause of the mischief would, in all
likelihood, have remedied the lameness.
_Changes in the Internal Structures_.--It follows as a matter of course
that the changes we have described in the form of the hoof itself carry
with them alterations in the bones and sensitive structures beneath it. The
tissues, as a whole, become atrophied. The os pedis becomes deformed, loses
its circular shape, and gradually becomes more or less oval in contour.
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