SECTION III.

LAMENESS IN THE FORE LEG.

For supporting weight, whether the subject is at rest or in motion, the bony column of the leg, together with attached ligaments, tendons and muscles, is wonderfully well adapted by nature for the function which they perform. The several bones which go to make up the supportive portion of the leg, are so joined at their points of articulation, that a minimum degree of strain is put upon each attachment.

The upper third of the scapula, with its cartilage of prolongation, is sufficiently broad and flattened that it fits snugly against the thorax without necessity for a complicated method of attachment—the clavicle being absent, attachment is muscular.

Undue extension, (by extension is meant such movement as will cause the long axis of two articulating bones to assume a position which approaches or forms a straight line—opposite to flexion), of the scapulohumeral joint is impossible while weight is borne, because of the normally flexed position of the humerus on the scapula; whereas flexion, beyond desirable limits, is inhibited by the biceps brachii (flexor brachii or coracoradialis) muscle.

The distal end of the humerus, however, articulating with the radius and ulna in a fashion that no support is lent by any sort of contact with the body, is a ginglymus (hinge) joint and lateral motion, because of the long transverse diameter of its articular portions, is easily prevented by the medial and lateral ligaments (internal and external ligaments). Flexion of this, the humeroradioulnar joint (elbow), is restrained by the triceps brachii and extension is checked by the biceps brachii (flexor brachii).

The carpal joint (erroneously called the knee joint), is composed of the several carpal bones which interarticulate and, when taken as a group, serve as a means of attachment and articulation for the radius and metacarpal bones.

The transverse diameter of this joint is long, thus giving it contacting surfaces that are sufficiently extensive to minimize the strain upon the mesial and lateral ligaments (internal and external lateral common ligaments). Motion is that of flexion and extension; slight rotation is possible when the position is that of flexion. While supporting weight the carpus is fixed in position by a slight dorsal flexion, but undue dorsal flexion is prevented by the flexor muscles and tendons and volar-carpal or annular ligament, together with the superior check ligament.

The distal end of the second phalanx (os corona) has but slight lateral motion and this is manifested principally when it is in a state of volar flexion. Undue dorsal flexion is prevented by the deep flexor tendon (perforans) and volar flexion is inhibited by the extensor of the digit (extensor pedis). Thus it is seen, that when the leg is a weight-bearing member, weight is supported by the bony framework whose constituent parts are joined together by ligaments and tendons and each one of the several bones articulates in such manner that the joint is locked. The articular parts of bones rest upon or against an inhibitory apparatus, and are slightly flexed, as in the carpus, or considerably flexed such as in the fetlock joint when weight is being supported. In the first instance, for example, the flexors of the carpus and the superior check ligament assisted by the flexors of the phalanges constitute the inhibitory apparatus.

As propelling members the front legs bear weight and are advanced alternately when the horse is walking or trotting—in cantering this is not so. When the normal subject travels in a straight line, at a walk or a trot, the length of the stride is the same with the right and left members. The stride of the right foot then, for example, is equally divided by the imprint of the left foot, in the normal horse, when traveling at a walk and in a straight line.

This enigmatical term is frequently employed by the diagnostician when he is baffled in the matter of definitely locating the cause of lameness; when he has by exclusion and otherwise arrived at a decision that lameness is "high up." Shoulder lameness may be caused by any one or several of a number of conditions, e.g., fractures of the scapula or humerus; arthritis of the shoulder or elbow joint; luxation of the shoulder or elbow joint (rarely); injuries of muscles and tendons of the region due to strains, contusions or penetrant wounds; paralysis of the brachial plexus or of the prescapular nerve; involvement of lymph glands; arterial thrombosis; metastatic infections; rheumatic disturbances; and as the result of inflammation, infectious or non-infectious occasioned by collar bruises. In some instances such inflammation is due to the manner of treatment of collar injuries. Therefore, when one considers the numerous and dissimilar possible causes of shoulder lameness, it behooves the practitioner to become proficient in diagnostic principles.

Fractures that extend to the articular surface are very serious, and complete recovery in such instances is practically impossible. The cartilage of prolongation of the scapula is sometimes seriously involved in certain cases of fistulous withers, and in some instances it has been separated from its attachment to the rhomboidea muscles, and lameness has resulted. In such instances, the upper portion of the scapula is disjoined from all attachment, and with every movement the animal makes, the scapula is moved back and forth. Complete recovery in such cases does not occur.

Symptomatology.—Fractures of the scapular spine are ordinarily readily recognized because there is usually visible displacement of the broken part. Crepitation is also detected without difficulty.

In fractures of the body of the scapula where an examination may be made before much swelling has taken place, and in subjects that are not heavily muscled, one should have no difficulty in recognizing the crepitation.

Fractures of the neck of the scapula are recognized by crepitation, by passively moving the leg, but it is necessary to exclude fractures of the humerus when one depends upon the finding of crepitation by this means. However, unless undue swelling exists, the exact location of the crepitation is recognized without serious difficulty.

Treatment.—The treatment of compound fractures of the scapular spine consists in the removal of the broken piece of bone by way of a cutaneous incision so situated that good drainage of the wound will follow.

Simple fractures of the body of the scapula are best treated by placing the subject in a sling, if the animal is halter broken, and enforcing absolute quiet for a period of from three to six weeks. Splints or similar appliances are not of practical value in scapular fractures.

Anatomy.—The scapulohumeral joint is an enarthrodial (ball and socket) joint wherein the ball or humeral articulating head greatly exceeds in size the socket or glenoid cavity of the scapula. The capsular ligament surrounding this joint is very large and admits of free and extensive movement of the articulation. There exist no lateral or common ligaments jointing the scapula and humerus as in other joints, but instead the tendinous portions of muscles perform this function. The principal ones which are attached to the scapula and humerus that act as ligaments are the supraspinatus (antea-spinatus), infraspinatus (postea-spinatus) biceps-brachii (flexor brachii) and subscapularis muscles.

Etiology and Occurrence.—Inflammation of the scapulohumeral articulation results from injuries of various kinds, including punctures which perforate the joint capsule, bruises from collars, metastatic infections and involvement as a result of direct extension of infectious conditions situated near the joint.

Classification.—Acute arthritis may be septic or aseptic, and there seems to be a remarkable tendency for recovery in cases of septic arthritis involving this joint in the horse.

Chronic arthritis with destruction of articular surfaces and ankylosis, is seldom observed. It is only in cases of severe injury, where the articular portions of the bones are damaged at the time of infliction of the injury, and where the articulation remains exposed for weeks at a time, together with immobility of the parts because of attending pain, that permanent ankylosis results.

Scapulohumeral arthritis may result then from infections, local or metastatic; from injuries, such as contusions of various kinds; from wounds, which break the surface structure or perforate the joint capsule; or from luxations.

Infectious arthritis of the scapulohumeral joint the result of local causes other than produced by septic wounds, seldom causes serious inconvenience to the subject. Where such occurs, however, there is manifested mixed lameness and complete extension of the extremity is impossible. Local swelling is present and manifestations of pain are evident upon palpation of the affected area.

Treatment.—During the first stage of the infection, local applications, hot or cold, are indicated. A hot poultice of bran or other suitable material contained within a muslin sack, may be supported by means of cords or tapes which are passed over the withers and tied around the opposite fore leg. Such an appliance may be held in position more securely by attaching it to the affected member. Following the acute stage of such an infection, any local counter-irritating application or even a vesicant is in order.

Where abatement of the infectious process does not take place, and suppuration of the structures in the vicinity of the joint occurs, it is necessary to provide drainage for pus. In some cases of strangles, for instance, large pus cavities are formed and drainage is imperative. However, metastatic inflammation of this joint is seldom observed except in cases of strangles. The animal should be kept perfectly quiet until recovery has taken place.

Injuries to the scapulohumeral joint may be the result of kicks, runaway accidents or bruises from the collar, and there may result, because of such injuries, reactionary inflammation which will vary in intensity from the mildest synovitis to the most severe arthritis, causing more or less lameness.

Treatment.—The general plan of treatment in this form of arthritis is the same as has been outlined under the head of infectious arthritis, with the exception that there is seldom occasion to provide for drainage of pus.

Wounds which cause a break of the skin and fascia overlying the scapulohumeral joint are usually of little consequence, unless the blow is of sufficient force to directly injure the articulation, and in such cases, the treatment of the injury along general surgical principles, such as cleansing the area, providing drainage for wound secretion, and the administration of suitable dressing materials such as antiseptic dusting powder, is all that is required for the wound. The symptoms manifested by the subject in such cases are the same as have been discussed heretofore and merit no special consideration.

Prognosis.—Unless very serious injury be done the articular portions of the scapula or the humerus, resulting in the destruction of the capsular ligament, prognosis is entirely favorable.

Open Joint.—Where the capsular ligament is perforated and the condition becomes one of open joint, then a special wound treatment becomes necessary. The surface of the skin is first freed from all hair and filth in the vicinity of the wound. The wound proper is cleared of all foreign material either by clipping with the scissors, curetting or mopping with cotton or gauze pledgets. The whole exposed wound surface as well as the interior of the joint cavity, if much exposed, is moistened with tincture of iodin. Subsequent treatment consists in a local application of a desiccant dusting powder, which should be applied five or six times daily. The composition of the powder should be such as to permit of its liberal use, thereby affording mechanical protection to the wound as well as exerting a desiccative effect. Equal parts of boric acid and exsiccated alum serve very well in such cases.

Animals suffering from open joints of this kind should be confined in a standing position, preferably in slings, and kept so confined for three or four weeks. Since they usually bear weight upon the affected member, there is no danger of laminitis resulting.

Chronic inflammation of the bicipital bursa is occasionally met with wherein both members are affected. Because of the nature of the structures involved, when inflamed, chronic inflammation is a more frequent termination than is complete recovery. Bilateral affections are seen in horses that are driven for years, regularly at a fast pace on paved streets. In such cases, the gait is stilted, that is, there is incomplete advancement of both members and, of course, the period of weight bearing is correspondingly shortened; hence the short strides.

In chronic cases, little if any evidence of inflammation is to be detected by digital manipulation of the parts. If flinching occurs, one is often unable to interpret the manifestation as to whether it is due to inflammation or not.

There is no marked "warming out" in this condition, and animals are nearly as lame after having been driven a considerable distance as when started, although the lameness is not as a rule very great.

Anatomy.—The triceps brachii is the principal structure which fills the space between the posterior border of the scapula and the humerus. The several heads originate for the most part on the border of the scapula, the deltoid tuberosity of the humerus and the shaft of the humerus. Insertion of this large muscular mass is effected by means of several tendons to the olecranon. A synovial bursa is situated underneath the tendinous attachment of the posterior portion of the triceps brachii—the long head or caput magnum.

The function of the triceps as a whole is to flex the shoulder joint and extend the forearm. The triceps brachii is the chief antagonist of the biceps brachii.

Symptomatology.—As the triceps brachii is not particularly taxed during weight bearing in the subject at rest, there may be no unnatural position assumed during inflammation of the triceps. More or less swelling and supersensitiveness is always present, however, and great care and discrimination must be exercised in digital manipulation of the triceps region because many animals are normally sensitive to palpation of these parts. It is sometimes difficult to correctly interpret the true state of conditions because of this peculiarity.

There is always swinging-leg-lameness, which is accentuated when the subject is urged to trot. Where symptoms are pronounced, it is unnecessary to cause the subject to move at a faster pace than at a walk to recognize the condition. The forward stride is shortened and in extremley painful conditions, no attempt is made to extend the leg. It is simply carried en une piéce—flexion of the shoulder and elbow joints is carefully avoided.

Treatment.—During the early stage of inflammation, hot or cold applications are beneficial. Long continued use of moist heat—fomentations—allays pain and stimulates resolution. Keeping in contact with the painfully swollen parts a suitable bag filled with bran, which can be moistened at intervals with warm water, constitutes a practical and easy means of treatment. By employing this method, one is more likely to succeed in having his patient properly cared for, in that less work is entailed than if hot fomentations are prescribed.

After the acute and painful stage has subsided, a stimulating liniment is of benefit. The subject should be kept within a comfortable and roomy box stall for a sufficient length of time to favor prompt resolution. Wild and nervous subjects, if not so confined, will probably overexert the affected parts if allowed the freedom of a paddock or pasture.

No satisfactory consideration of the pathogeny of this condition is recorded, but practitioners have long distinguished between muscular atrophies which are apparently caused without doing serious injury to nerves and muscular atrophy which seems to be due to nerve affection. In the first instance, recovery when proper attention is given, is prompt; whereas, in the latter, regeneration of the wasted tissues requires months in spite of the best sort of treatment.

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 classed 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 practitioner 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 constitutes 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 assurance that no "sweeny" exists. In some of these cases where a diagnosis of "shoulder lameness" has been made and the client has been assured 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.

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 constitutes 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.

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, passing upward and backward under the supraspinatus (antea-spinatus) muscle and terminating in the infraspinatus (postea-spinatus) muscle.

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.

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.

Described under the titles 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 passed. 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 passing 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.