Lameness of the Horse Part 7

The parts more frequently affected are the supra- and infrascapularis (antea- and posteaspinatus) muscles. But in some cases the triceps group is involved; however, this occurs in unusual and chronic affections. No doubt, these chronic cases are due to suspended innervation and are not to be cla.s.sed with the ordinary case of atrophy of the abductor muscles of the humerus (supra- and infraspinatus) as in the usual case of "sweeny."

Occurrence.--Shoulder atrophy such as the general pract.i.tioner commonly meets with, is an affection, more often seen in young animals and it seems to be due to injuries of various kinds which contuse the muscles of the shoulder. Ill-fitting collars and pulling in a manner that there occurs side draft with unusual strain on the muscles of one side of the neck and shoulder, seem to be the more frequent causes of this trouble. Blows such as are occasioned by kicks and falls frequently result in atrophy of shoulder muscles.

Course.--In some cases a rapidly progressive atrophy characterizes the case and lameness and atrophy appear at about the same time. The affection in such instances does not recover spontaneously but const.i.tutes a condition which requires prompt and rational treatment so that function may be fully restored to the parts involved.

Occasionally one may observe cases where there is but slight atrophy; where the disease progresses slowly and atrophy is not extensive or marked. In vigorous young animals that are left to run at pasture when so mildly affected, spontaneous recovery occurs.

Symptomatology.--Lameness is the first manifestation of shoulder atrophy, and in many cases where lameness is slight, the veterinarian may fail to discover the exact nature of the trouble if he is not very proficient as a diagnostician of lameness or if he is careless in taking into consideration obtainable history, age of the subject, etc. Because of the fact that the average layman believes that practically every case of fore-leg lameness wherein it is not obvious that the cause is elsewhere, is due to a shoulder affection of some kind, we may be too hasty in giving the client a.s.surance that no "sweeny" exists. In some of these cases where a diagnosis of "shoulder lameness" has been made and the client has been a.s.sured that no sweeny exists, the patient is returned in about a week and there is then marked atrophy of one or both of the spinatus muscles.

A mixed type of lameness characterizes this affection, and in the average case there exists little evidence of local pain. The salient points in recognizing the condition are a consideration of history if obtainable; age of the subject; finding slight local soreness, by carefully manipulating the muscles which are usually involved; noting the character of the lameness if any is present; and where atrophy is evident, of course, the true condition is obvious.

Treatment.--Subcutaneous injections of equal parts of refined oil of turpentine and alcohol, with a suitable hypodermic syringe, is a practical and ordinarily effective treatment. From five to fifteen cubic centimeters (the quant.i.ty varies with the size of the animal), of this mixture is injected into the atrophied parts at different points, taking care to introduce only about one to two cubic centimeters at each point of injection. The syringe should be sterile and, needless to say, the site of injections must be surgically clean.

Other agents, such as tincture of iodin, solutions of silver nitrate, saline solutions and various more or less irritating preparations have been employed; but in the use of these preparations one may either fail to stimulate sufficient inflammation to cause regeneration to take place, or infection is apt to occur. Where suppuration results, surgical evacuation of pus must be promptly effected else large suppurating cavities form.

The employment of setons const.i.tutes a dependable method of treatment of shoulder atrophy, but because of the attendant suppurative process which inevitably results, this method is not popular with modern surgeons and is a last resort procedure.

After-care.--Regular exercise such as the horse usually takes when at pasture, is very helpful in treating atrophy, and in some cases it has been found that no reasonable amount of irritation would stimulate muscular regeneration; but by later allowing patients to exercise at will, recovery took place in a satisfactory manner. No special attention is ordinarily necessary.

Paralysis of the Suprascapular Nerve.

Anatomy.--The suprascapular (anterior scapular) nerve, a small branch of the brachial plexus, is given off from the anterior portion of this plexus. The nerve rounds the anterior border of the neck of the scapula, pa.s.sing upward and backward under the supraspinatus (antea-spinatus) muscle and terminating in the infraspinatus (postea-spinatus) muscle.

Etiology and Occurrence.--As the result of direct injury to this nerve by contusion such as may be received in runaway accidents, collar bruises, especially collar bruises in young horses that are not accustomed to pulling and that walk in a manner to cause side draft, injury to the nerve occurs, and partial or complete paralysis supervenes. Some writers state that it may be produced by confining an animal in rec.u.mbency, with the casting harness. The common cause of paralysis or paresis of this nerve in cases such as one observes in country practice, is bruises from the collar in colts that are put to heavy farm work or where ill fitting collars are used.

Symptomatology.--With partial or complete suspension of function of the suprascapular nerve there results enervation of the supraspinatus and infraspinatus muscles. Since these muscles act as external lateral ligaments of the scapulohumeral joint, when they are incapacitated, there naturally follows more or less abduction of the shoulder when weight is borne.

In extreme cases, as soon as the ailing animal is caused to support weight with the affected member, the joint is suddenly thrown outward in a manner that the average layman at once concludes that there must be scapulohumeral luxation, and the veterinarian receives a call to see a case wherein the "shoulder is out of place." There exists, however, no luxation in such cases.

If serious injury is done the nerve so that it undergoes degenerative changes, there will result atrophy of the muscles that derive their nerve supply from the suprascapular nerve.

[Ill.u.s.tration: Fig. 7--Paralysis of the suprascapular nerve of the left shoulder]

Treatment.--During the first few days following injuries which result in this form of paralysis, it is well to keep the subject inactive, and if much inflammation of the injured structures contiguous to the nerve exists, the application of cold packs is beneficial. Later, as soon as acute inflammation has subsided, vesication of a liberal area around the anteroexternal part of the scapulohumeral joint and over the course of the suprascapular nerve, will stimulate recovery in favorable cases. As a rule, in mild cases, the subject is in a condition to return to work in two or three weeks.

Radial Paralysis.

Described under the t.i.tles of "Radial Paralysis" and "Brachial Paralysis," there is to be found in veterinary literature a discussion of conditions which vary in character from the almost insignificant form of paresis to the incurably affected conditions wherein the whole shoulder is completely paralyzed.

When one considers the anatomy of the brachial nerve plexus and the distribution of its various branches, the location of this plexus and its proximity to the first rib, and the inevitable injury it must suffer in fracture of this bone, together with the inaccessibility of the plexus, it is not strange that a correct diagnosis of the various affections of the brachial plexus and the radial nerve is often impossible until several days or weeks have pa.s.sed. And, in some instances, diagnosis is not established until an autopsy has been performed. Here, too, we fail to find cause for paralysis in some rare instances.

Anatomy.--The radial nerve is a large branch of the brachial plexus and is chiefly derived from the first thoracic root of the plexus and is here situated posterior to the deep brachial artery. It is directed downward and backward under the subscapularis and teres major muscles, rounding the posterior part of the humerus, and pa.s.sing to the anterior and distal end of the humerus, it finally terminates in the anterior carpal region. The radial nerve supplies branches to the three heads of the triceps brachii, to the common and lateral extensors of the digit and also to the skin covering the forearm.

Etiology and Occurrence.--Nothing definite is known about the cause of some forms of radial paralysis. However, radial paralysis is encountered following injury to the nerve occasioned by its being stretched, as in cases where the triceps brachii is unduly extended in restraining subjects by means of a casting harness. Berns[10] states that in confining horses on an old operating table where it was necessary to draw the affected foot forward twenty-four to thirty-six inches in advance of its fellow, which was secured in a natural vertical position, radial paralysis of a mild form was of frequent occurrence.

Country pract.i.tioners, in restraining colts by casting with harness or ropes, occasionally observe a form of paresis wherein the radial nerve suffers sufficient injury that there is caused a temporary loss of function of the triceps brachii. Such cases recover within three or four days and are not a true paralysis, but nevertheless const.i.tute conditions wherein normal nerve function is temporarily suspended.

[Ill.u.s.tration: Fig. 8--Radial paralysis.]

Symptoms.--Immediately subsequent to injuries which involve the radial nerve, there is manifested more or less impairment of function.

Remembering the structures supplied by the radial nerve and its branches, one can readily understand that there should occur as Cadiot[11] has stated:

In complete paralysis, the joints of the affected limb with the exception of the shoulder are usually flexed when the horse is resting. In consequence of loss of power in the triceps and anterior brachial muscles, the arm is extended and straightened on the shoulder, the scapulohumeral angle is open, and the elbow depressed. The forearm is flexed on the arm by the contraction of the coracoradialis (biceps brachii), while the metacarpus and phalanges are bent by the action of the posterior antibrachial muscles. The knee is carried in advance, level with, or in front of, a vertical line dropped from the point of the shoulder. The hoof is usually rested on the toe, but when advanced beyond the above mentioned vertical line, it may be placed flat on the ground, the joints then being less markedly bent. When the limb as a whole is flexed, it may be brought into normal position by thrusting back the knee with sufficient force to counteract the action of the flexor muscles.

[Ill.u.s.tration: Fig. 9--Merillat's method of fixing carpus in radial paralysis. Courtesy, Alex. Eger.]

When made to walk, the animal being unable to exert muscular action with the paralyzed structures, limply carries the member as a whole, and there is shortening of the anterior portion of the stride. There being loss of function of the triceps brachii, it is impossible for the subject to straighten the leg in the normal position for supporting weight; therefore, any attempt to bear weight results in further flexion of the affected member and the animal will fall if the body is not suddenly caught up with the sound leg.

Differential Diagnosis.--In making examination of these cases, one can exclude fracture by absence of crepitation and usually, also, swelling is absent in radial paralysis. In a typical case of radial paralysis, the affected leg can sustain its normal share of weight if placed in position, that is, if the carpal joint is extended in such manner that the leg is positioned as in its normal weight-bearing att.i.tude. In brachial paralysis, whether due to fracture of the first rib or to other serious injury, it is impossible for the subject to support weight with the affected member even when it is pa.s.sively placed in position.

No difficulty is ordinarily experienced in differentiating radial paralysis from muscular injuries to the triceps; yet, in some cases of "dropped elbow," it is necessary to observe the progress of the case for ten days or two weeks before one can positively establish a diagnosis.

Quoting Merillat[12]: "When, after four weeks, there is no amelioration of the paralysis, the muscles have atrophied, and the patient has become emaciated from pain and discomfort, the diagnosis of brachial paralysis with fracture of the first rib may then be announced."

Prognosis.--When no complete paralysis of the brachial plexus or no fracture of the first rib exists, the majority of cases recover completely in from ten days to six weeks. Some writers claim that recoveries occur in ninety per cent of cases when conditions are favorable.

Treatment.--When incomplete radial paralysis exists, little needs be done except to allow the subject moderate exercise and to provide for its comfort. Local applications, stimulative in character, are beneficial, and the internal administration of strychnin is indicated.

In the cases where weight is not supported without the affected leg being pa.s.sively placed in position, it is necessary to provide for the subject's comfort in several ways.

Mechanical appliances such as braces of some kind in order to keep the affected leg in a position of carpal extension, const.i.tute the essential part of treatment. The leg is supported in such a manner that flexion of the carpus is impossible. Due regard is given to prevent chafing or pressure necrosis by contact of the skin with the braces--this may be done by bandaging with cotton. The supportive appliance is kept in position for ten days or two weeks. At the end of this time the brace may be removed and the subject given a chance to walk, and improvement, if any exists, will be evident. When there is manifested an amelioration of the condition, moderate daily exercise and ma.s.sage of the affected parts are helpful.

Should the subject be seriously inconvenienced by the application of a brace or other supportive appliances, it is necessary to employ slings.

Further, if weight is supported entirely by the unaffected member, laminitis may supervene if a sling is not used.

Thrombosis of the Brachial Artery.

Thrombosis of the brachial artery or of its princ.i.p.al branches is of very rare occurrence in horses.

Etiology.--Partial or complete obstruction of arteries (brachial or others) occurs as the result of direct injury to the vessel wall from compression and tension of muscles and resultant arteritis; lodging of emboli; and parasitic invasion of vessel walls causing internal arteritis.

Symptomatology.--If sufficient collateral circulation exists to supply the parts with blood, no inconvenience is manifested while the subject is at rest. Where the lumen of the affected vessel is not completely occluded, there may be no manifestation of lameness when the ailing animal is moderately exercised. Consequently, the degree of lameness depends upon the extent of the obstruction to circulation; and, likewise, the course and prognosis depend upon the character and extent of such obstruction.

In severe cases, lameness is markedly increased by causing the animal to travel at a fast pace for only a short distance. There are evinced symptoms of pain, muscular tremors and sudation, but the affected member remains dry and there is a marked difference of temperature between the normal areas and the cool anemic parts. When the subject is allowed to rest, circulation is not taxed, and there is a return to the original and apparently normal condition, only to recur again with exertion. This condition characterizes thrombosis.

Treatment.--In these cases, little if any good directly results from any sort of treatment in the way of medication. Absolute rest is thought to be helpful. Pota.s.sium iodid, alkaline agents such as ammonium carbonate and pota.s.sium carbonate, have been administered. Circulatory stimulants also have been given, but it is doubtful if any good has come from medication.

Fracture of Humerus.

The shaft of the humerus, protected as it is by heavy muscles, is not frequently fractured; and fractures of its less protected parts, as for example, the head, are complicated in such manner that resultant arthritis soon const.i.tutes the more serious condition.

As a result of falls on frozen ground, kicks or any other form of heavy contusion, the humerus is occasionally broken. It is rarely fractured otherwise. Because of the force of contusions usually required to effect humeral fracture, the manner in which the bone is broken, with respect to direction, is variable. Often oblique fractures exist and occasionally there occurs multiple fracture. In addition to the ordinarily serious nature of the fracture itself, there is always much injury done the adjoining structures.

Symptomatology.--Mixed lameness and manifestation of severe pain characterize this affection. Considerable swelling which increases, in some cases for a week or more, is to be observed. Crepitation is readily detected, if pain and swelling is not too great to prevent pa.s.sive movement of the member. Where intense pain is not manifested, because of manipulation, one may abduct the extremity and thereby occasion distinct crepitation; but when it is possible to recognize crepitation by holding the hand in contact with the olecranon while the animal is made to walk, this method is to be preferred, if the subject can move without serious difficulty. The pathognomonic symptom here is recognition of crepitation, but this may be very difficult to recognize in fracture of condyles, and in such instances, a careful examination is necessary.

Gentle manipulation in a manner that pain is not aggravated will tend to inspire confidence on the part of the subject and relaxation of muscles will enable the operator to detect crepitation.