LAMENESS ARISING FROM PARALYSIS OF PERIPHERAL NERVES Suprascapular Paralysis — Shoulder Slip. - Causes. Paralysis of the suprascapular nerve is seen more often in country districts than in large towns, particularly amongst young horses used in ploughing. This has led many veter many surgeons to regard the condition as due to strain either of the nerve or of the muscles themselves through stretching of these tissues as the animal slips in and out of the furrow or constantly walks on uneven ground. In country practice it is indeed but rarely that one meets with the condition except in young plough horses, and it is evident that whether the theory as regards slipping is correct or otherwise the act of ploughing is in some way responsible. Possibly bruising of the nerve may result from collar pressure induced by walking on an irre gular surface.
Another commonly accepted theory is that paralysis results from stretching of the supra scapular nerve by forcible backward movement of the limb, possibly at a time when no weight is being placed upon the foot. Such an acci dent may occur when a horse, suddenly startled, jumps forward against the manger, or when a runaway horse collides with some low or pro jecting object. Cavalry horses are said to be commonly affected through galloping into another animal. Forcibly drawing back the fore limb and maintaining it in that condition for some length of time, as may happen when the limb is, fixed for operation on a quittor, may cause undue stretching of the nerve.
Rheumatism is regarded by some observers as a frequent cause, whilst haamoglobinuria with muscular lesions in the region of the shoulder may produce paralysis of the suprascapular nerve, just as crural paralysis may result from the same condition affecting the hind limb.
Possibly neuritis may be of more frequent occurrence in the horse than is generally imagined and may account for many of the peripheral paralyses which are otherwise almost incapable of explanation.
Symptoms. The two muscles supplied by the suprascapular nerve are the supraspinatus and the infraspinatus. The former is an extensor of the shoulder, whilst the latter is an abductor. The tendons of these muscles take the place of external ligaments to the joint.
Relaxation as a result of paralysis results in lack of support at the outside of the shoulder joint, and accordingly when the foot is brought to the ground and at the moment when the greatest weight is placed upon it the point of the shoulder jerks outwards. During movement there is abduction of the limb, but whilst the animal is at rest there is a tendency to adduc tion owing to lack of function of the infra spinatus. The foot of the affected limb ap proaches more nearly to the middle line of the body than does its fellow, and this can be more readily seen when the two fore limbs are viewed from the front of the horse. Owing to loss of power in the supraspinatus there is difficulty in advancing the limb, the toe is dragged some what, and is usually brought forward with a circular, swinging motion.
The acute symptoms may subside very quickly and are immediately followed by rapidly advancing atrophy of the supraspinatus and infraspinatus. The spine of the scapula then appears very prominent, whilst a flat or de pressed surface exists on either side. The deltoid muscle does not share in this atrophy as it derives its nerve supply from the circum flex. In some cases, in spite of the loss of function in wasted muscles, the horse may show no marked peculiarity of action, but in the majority of cases conspicuous abduction of the limb and rolling of the shoulder-joint (supporting leg lameness) persists until such time as the muscles have regained their former power of contraction.
Prognosis. According to the degree of injury to the nerve and the extent of the resulting atrophy, recovery may occur in from six weeks to eighteen months. In some cases, however, restoration of function remains incomplete. Cases of the rheumatic type—that is to say, paralysis attributable to exposure to cold or occurring in subjects with a predisposition to develop rheumatism—usually make a speedy recovery. The same may be said of"shoulder slip"in young cart-horses which have received prompt attention when the symptoms have first manifested themselves.
Horses which have sustained violent blows on the shoulder or have become involved in collisions or accidents attended by excessive stretching of the nerve are less likely to recover.
Treatment. During the acute stage, hot fomentation of the outer surface of the shoulder, followed by friction with stimulating liniments, tends to relieve the inflammatory swelling in cases arising from collision or injury and asso ciated with bruising.
In the early stages rest is essential, but as soon as commencing atrophy appears exercise is beneficial. In mild cases the horse may be worked in a breast strap in place of a collar on level ground, but must not be used for ploughing or working on soft, broken ground.
Repeated blistering with a run at grass is the best treatment is most cases.
Subcutaneous injection of oil of turpentine along the course of the affected muscles has been recommended by many practitioners, as has also veratrine. One and a half grains are shaken up with seventy-five minims of water and injected subcutaneously. Pain and swell ing result in both cases, and upon the dispersal of the latter after some days it is stated that visible improvement is usually evident. Intra muscular injections of turpentine are not to be recommended, as they frequently cause abscess formation and sloughing. Strychnine injections into the muscular tissue may be employed, sometimes with advantage, but due attention must be paid to asepsis.
Internally iron, arsenic, and strychnine may be of some assistance, given daily in bolus form.
Paralysis of the Nerve. Radial Paralysis. - -The musculo-spiral nerve is at its origin the thickest nerve of the brachial plexus. It derives its fibres from the seventh and eighth cervical and from portions of the first two dorsal nerves. In common with the other nerves of the brachial plexus it emerges from between the upper and lower divisions of the scalenus muscle in fairly close proximity to the first rib. The dorsal roots of the plexus turn FIG. 166. Radial paralysis.
round the anterior border of the rib and leave on it a smooth impression near its upper end.
The musculo-spiral nerve supplies the three heads of the triceps, the anconeus, scapulo ulnaris, flexor metacarpi externus, and all the extensors of the metacarpus.
Causes. The condition now termed radial paralysis has been recognized by veterinary surgeons for a large number of years, but was formerly attributed to strain of the muscles involved. Probably in many cases this dia gnosis was a correct one, and it is quite possible to confuse the two conditions even in the light of present-day knowledge. That true cases of paralysis of the musculo-spiral do exist is certain, as has been demonstrated by autopsies which have revealed a hyperaemic condition of the nerve produced either by local pressure or by some form of neuritis.
Of late years radial paralysis has become associated in the minds of most veterinary surgeons with fracture of the first rib, and although post-mortem examination of a number of cases has revealed the fact that the two conditions. may exist together, it has also shown that the identical symptoms may exist without any visible rib injury.
It is curious to note that the musculo-spiral nerve derives the majority of its fibres from the cervical roots of the brachial plexus, which do not come into contact with the first rib. Further, other nerves which are composed par tially of branches from the first and second dorsal nerves, as the nerve to the latissimus dorsi, do not appear to be affected, and we have never observed paralysis of this muscle as a result of fracture of the first rib, nor is there any evidence that other veterinary surgeons have done so. It is as yet unexplained why the musculo-spiral nerve should be the only one to become involved in fracture of the first rib, especially as the amount of swelling and infil tration of the tissues might be expected to involve other nerve-trunks also.
Rogers was probably the first in this country to show that radial paralysis was often caused by this particular fracture, whilst Hunting regarded all cases of"dropped elbow"as due to first-rib fracture.
Probably many cases originate in the muscle tissue, and the changes observed in the nerve may be only secondary. The same remark may also be, in some instances, applied to other paralyses, possibly to suprascapular paralysis.
Symptoms. In complete paralysis the animal stands with the shoulder and elbow extended and the knee and phalanges flexed. The toe of the foot is the only portion which rests on the ground. The triceps being relaxed allows of full extension of the elbow, so that the point of the elbow appears to be dropped. The appearance presented to the untrained eye suggests that the affected limb is much longer than the sound one.
When an attempt is made to move the horse, he first advances both hind legs with the object of relieving his weight from the fore limbs. He next attempts to advance the lame leg but is unable to carry it forward beyond half of the ordinary stride, where it comes to rest, the toe on the ground and the knee and fetlock flexed. Without assistance the horse, if now urged on again, will either fall or by quickly advancing the sound fore limb he may regain his balance. If, however, the foot be brought forward by the hand until the sole rests upon the ground, and if pressure be brought to bear upon the forearm just above the knee, the animal will complete his stride and will continue to advance just as long as the limb is extended for him and supported.
In partial paralysis the caput medium and extensors of the forearm are not affected. The animal can then advance the limb and place weight upon it, but at the moment of doing so the shoulder is suddenly jerked forwards as opposed to suprascapular paralysis, in which the point of the shoulder rolls outwards.
Prognosis. The majority of cases of radial paralysis recover, though occasionally lameness may persist for as long as twelve months. The average duration is probably about three months. Partial paralysis may disappear in one or two weeks.
Treatment. - Blistering the affected muscles, hand - rubbing with liniments, or injection of turpentine, strychnine, or veratrine, may all be tried, but the sheet-anchor of treatment should be exercise in a flat field whenever weather con ditions permit, or a large barn in winter, and above all, patience on the part of both owner and veterinary attendant.
Paralysis of the Brachial Plexus.This con dition results from local pressure, produced by collision with heavy bodies, injury occurring from casting or from lying for some length of time in certain positions, as with the fore and hind legs tied together for operation, sub scapular haemorrhage, extensive wounds of the axilla or front of the breast, abscess formation, exostoses occurring on the first few ribs, bullet or shell wounds, etc.
Symptoms. Complete paralysis of all the muscles of the limbs may exist, or the condition may be confined to certain nerves, whilst others retain their function to a greater or less degree.
When the musculo-spiral nerve is uninjured, the horse can usually support his weight upon the limb whilst in the standing position.
Treatment. As in radial paralysis.
Gluteal Paralysis.This form of lameness is very uncommon. It is characterized by marked wasting of the gluteal muscles. The affected limb is usually adducted and at each step the foot is advanced farther than its fellow and set down with a peculiar tapping movement. The hock and phalangeal joints are usually flexed during movement of the limb.
Paralysis of the Sciatic Nerve.Causes. - Bi lateral paralysis is usually of cerebral or spinal origin.
Unilateral paralysis, whilst not common, is occasionally met with in horses and dogs. In both animals falls are usually responsible, though in some cases a neuroma has been discovered on the course of the. nerve.
The muscles supplied by the great sciatic are the semi membranosus, quadratus femoris, biceps femoris, and semitendinosus (in part), obturator internus, pyriformis, and gemelli. The first two muscles are extensors of the hip, the hiceps femoris is an extensor of the stifle, whilst the semitendinosus is a flexor of the same joint. The quadratus femoris, obturator internus, pyriformis, and gemelli are all outward rotators of the hip. The action of the rectus and vasti muscles is unimpaired.
The sciatic is also the parent trunk of the external popliteal, which divides into the musculo-cutaneous and anterior tibial nerves. The former, after giving off a branch to the peroneus, supplies the skin covering the outer surface of the metatarsus. The anterior tibial supplies the extensors of the digit and the flexor metatarsi.
Symptoms. Paralysis of the sciatic nerve is accompanied by loss of function of the muscles of the quarter, but without impairment of that of the rectus and vasti. There is therefore in ability to carry out voluntary movement of the limb, which hangs loosely. When urged on, the pull of the rectus and vasti is unopposed by the semitendinosus, and so the lower part of the limb is jerked upwards and forwards. The gastrocnemius tendon is relaxed, the fetlock and pastern are flexed, and the front of the foot rests upon the ground. As in radial paralysis, the animal is able to place weight upon the foot when the limb is placed in position with the phalanges extended.
Prognosis depends upon the cause of injury.
Treatment consists of rest in slings whilst para lysis is complete, and repeated blistering. Sub sequently exercise helps to restore the action of the affected muscles.
Paralysis of the External Popliteal Nerve. Causes. Usually injury to the thigh from falls, accidental or bullet wounds. It has been known to follow strangles. In cattle particularly it may occur as the result of difficult parturition.
In the standing position there may be no evidence that anything is wrong with the animal, though in cases of complete paralysis the hock may be extended and the fetlock flexed with the front of the foot resting on the ground. When caused to walk the flexor muscles are un opposed and so the limb is jerked backwards with the hock extended and the fetlock flexed. It is then brought partly forward, chiefly by means of the extensors of the stifle, and comes to rest with the front of the foot touching the ground. If the foot be placed in position, the animal can usually place weight on the limb.
Prognosis. In cases where the cause is known to be bruising, recovery may be hoped for, though sometimes several months may elapse before marked improvement appears. Cases occurring in cattle after parturition more commonly affect the left leg, and the animal frequently dies from prolonged decubitus. In those animals that remain standing severe injury may occur to the front of the fetlock and coronet through bruising.
Treatment. In order to cause the animal to place weight upon the foot a plaster bandage should be applied around the fetlock. Horses may also be shod with a long toe-prong well curved in front. In one case successfully treated a strong indiarubber band was attached from the foot to a rope, a loop at the end of which was tied around the neck. This took the place of the useless extensor muscles, and served to oppose the flexor muscles and helped the limb forward.
Blistering along the course of the affected muscles, and exercise, may be supplemented by local injections of strychnine.
Paralysis of the Internal Popliteal Nerve. Symptoms. The muscles at the back of the thigh are affected, and so marked flexion of the hock exists. Owing to the fact that the forans muscle is provided with a long inexten sible tendon, flexion of the hock is accompanied by corresponding flexion of the digits. The hock is fixed by the gastrocnemius, and the animal is therefore capable of placing weight upon the limb.
On movement the limb is flexed and the foot is carried high and brought to ground with a peculiar jerking motion.
Atrophy of the muscles at the back of the thigh usually follows.
Treatment. Exercise and repeated blistering may be tried, but the condition appears to be very intractable, judging from the results of reported cases.
Obturator Paralysis.Causes. majority of cases occur as the result of undue traction upon a mal-presentation. Melanotic tumours upon the course of the nerve and pelvic frac tures are other causes.
Symptoms. Marked abduction of the limb and dragging of the foot with a circular sweeping movement. Atrophy of the adductors follows.
Prognosis. In cattle after calving recovery usually occurs in from three to six weeks, pro vided that fracture of the pelvis does not exist.
Treatment. Rest is essential, particularly as there must in most cases be suspicion of pelvic injury. Apart from this, treatment is of little value.
Crural Paralysis.Causes . Hmmoglobinuria is responsible for many cases showing typical symptoms of crural paralysis, but it is difficult to decide whether the condition is actually paralysis or a myositis. Absence of sensation on the inner surface of the thigh is indicative of true paralysis.
Symptoms. At rest the affected quarter appears lower than the other, and the limb is flexed. Upon movement this becomes more marked; the whole of the hinder part of the body sinks at every step, owing to flexion of the stifle, hock, and fetlock. The rectus and vasti muscles rapidly atrophy, and when weight is placed on the limb they stand out as thick, tightly stretched cords.
The horse learns in time to fix the stifle-joint and so walks better.
Course. Paralysis following haernoglobinuria usually requires from five to six months to restore normal action and to regain the usual size and condition of the muscles. Laminitis in the other hind foot often causes trouble.
Treatment. Shoeing with heels is helpful, but should not be continued too long. The other hind foot should have the shoe removed, or may be shod with a thick leather with plenty of stopping beneath it. A level field with bare keep, necessitating plenty of exercise, helps to maintain the nutrition of the muscles, as also will blistering at intervals of a few weeks. In jections of turpentine, strychnine, or veratrine may be tried; sometimes they are beneficial. Internally, strychnine, iron, and arsenic are useful.
R. H. S.