OUTLINE OF THE ANATOMY OF THE SHOULDER,

The shoulder is pressed backward, from the median plane of the body, braced from within, and permitted to move within a limited arc, by the clavicle.

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One of the shoulder joints-the acromioclavicular articulation-is very superficially located, being immediately under the integument. It is remarkable, because of its exclusive ligamentous composition, and its great resistance, to the application of violence. On the integrity of this joint, the equilibrium of shoulder action depends. It is a true arthrodia. In motion of the shoulder girdle, the scapula moves upon the outer end of the clavicle. Morris puts it, "the entire scapula moves in the arc of a circle, whose center is the sterno-clavicular point, and whose radius is the clavicle" (Morris Human Anatomy, the Articulations, p. 232). Through this joint, the scapula moves on the thoracic walls, backward and forward, and without it, the constantly forward obliquity of the articular surface of the glenoid cavity, would be impossible. By its means, the shoulder can be forcibly advanced forward, on the thorax, and the combined action of the muscles of the scapula and thorax, can be brought into play, in the application of force. Around the end of the clavicle, the shoulder moves to and fro, as a hinge, on the horizontal axis of a joint.

If the acromio-clavicular junction is signalized, by the absence of muscles, the scapulo humeral depends almost alone on them, for support and retention. The former is the passive articulation of the shoulder, and the latter the active, the one serving as the true joint, to connect the shoulder to the trunk, maintaining a steady unremitting functional action; the other, only called into play periodically, to fulfill special demands. If the scapula be suspended from the end of the clavicle, from a point devoid of any special bone support, except from underneath, the humeral head is quite equally devoid, of any direct osseous collateral support, within its investing capsule. Its chief supports are but accessory, or extra articular, as not more than one-fourth of the head of the humerus, is in contact, at one time, with the narrow, nearly flat surface of glenoid cavity. The head of this bone, then rests rather against an articular surface, than is enclosed by one. It is held up against the scapula, by

muscular action, partly assisted by the long head of the biceps, immoderate forward, or upward movement, being restrained by the coracoid and acromion processes.

The capsular ligament of the scapulo-humeral joint, equal to more than twice the capacity of humeral head, is sometimes continuous with long fibers of the biceps, and by a diverticulum, with the large subacromial bursa. It may be well to note that although this ligamentous support of this joint is unimportant, with the exception of the deltoid, all the muscles inserted into, or near the tuberosities of the humerus, end in broad tendinous expansions, those coming from the dorsum of the scapula, having a dense resisting fasciæ, before they converge at the point of insertion. The shelving arch of the acromion process, affords the greatest protection, to the head of the humerus, which, indirectly, through the medium of the deltoid muscle, is intimately united with it. In sudden muscular strain, or the relaxation consequent on paralysis, the head of the humerus is prone to slide out of its cavity. After certain dislocations, following violent strains or twists, such extensive laceration of muscle, or possible detachment of tendinous fibres follows, that the reduced humeral head persistently falls away from its scapular receptacle.

The head and the greater tuberosity of the humerus contribute an important part of the shoulder. In fact, the whole architecture of this region is primarily formed, and ultimately intended to act on, support and protect this disc of bone, with the shaft and forearm below.

The articular surface of the head, and epiphyseal junction of the humerus are within the capsule, and are so well protected, as to be entirely beyond surface examination, except through the axilla, when the arm is at right angles with the body laterally, or, is forcibly raised to a plane, in the same line of axis with the body.

The great muscular leverage of the upper end of the humerus, has its principal insertion, in the apophyses or the tuberosities, which are primarily possessed of independent centers. This group of muscles serves a dual function, of imparting motion to parts beyond the joint, besides, in a large measure, acting as ligamentous stays.

The whole osseo-muscular structure of the

shoulder is a study of great interest, if we regard it from its mechanical standpoint, alone. Here we have the entire structure of support and motion of the arm and forearm, slung loosely on the walls of the thorax, without any apparent definite fixed center of support, with nothing of greater strength, than the costal bows and inflated pulmonary tissue, underneath to oppose violence, and yet, in the event of danger, or, when necessity demands it, the elastic lung is suddenly expanded, and the pendant scapular wings become fixed, as though set in steel braces. The pneumatic chamber, by some provision of the economy, not easily explained by physics, is suddenly transformed into a pedestal or base, which may receive a tremendous force of impact, through the humerus, with comparative impunity.

When the muscles are in a relaxed state, and are taken, as it were, by surprise, as in many falls, blows, etc., force applied over the latteral aspect of the shoulder, is transmitted through, the clavicle, but, when great force is applied obliquely, from before or behind, or, when notice of its approach is possible, quick muscular adjustment serves to transmit it directly to the chest walls, as well as, to the clavicle.

THE BLOOD VESSELS AND NERVES.

The nerve and blood trunks, on their course to the upper-extremity, are forced to make their way, through a narrow, movable gap, at the point, where they dip under the distal curve of the clavicle, and pass down over the first rib, to reach the armpit, where they are very superficial, and yet, well protected from their sheltered position under the arm.

Except for a few recurrent branches in the axillary space, the parts immediately above the scapulo humeral articulation, derive their arterial supply, from the thyroid axis of the subclavian.

In the axilla, the great blood trunks lie in a loose bed of myxomatous tissue, imbedded in which, are numerous lymph ganglia, arranged in two layers. Besides performing the functions appertaining to these bodies, they no doubt, serve to modify pressure on the vessels, in the event of concussion, or compression from mechanical causes.

NERVES.

The close proximity of the brachial plexus of nerves with the humeral head-being

separated only, by the tendon of the subscapularis and capsule of the joint-would seem to expose it, to serious damage, in the event of dislocation, or any sudden strain on the humerus. But the inherent property of nerve tissue, to resist injury, with their free, unfettered position, enables this leash of cords to generally escape serious damage. The peripheral nerves of the shoulder, which come down from the upper conical roots, being more exposed, are most frequently affected, by an injury.

It is only in fractures, occupying the upper division of the surgical neck of the humerus, that the deep branches of the brachial plexus, as, the circumflex, muscul and spiral are severely lacerated, or contused.

CHARACTER OF LESIONS MOST COMMONLY BORNE BY THE SHOULDER, AND STRUCTURES IMMEDIATELY CONTIGUOUS

WITH IT.

By some singular provision of the economy, the osteo-arthritic elements of the shoulder, are by far, less susceptible to pathological changes, subsequent to, or simultaneous with, constitutional diseases, than those in other situations. The same may be said of the neurovascular structures. Thus, tubercular synovitis or osteo-arthritis, at the humero-scapular joint, is a rare condition. Why this should be so, in an articulation, the center of such activity, and so near the center of circulation, while the more distant hip and knee are implicated, is not easy of explanation. We will observe, also, that, when rheumatic inflammation falls, with its greatest force on the joints, those of the shoulder more often escape, than the hip, knee or ankle. It is certainly unusual to find the shoulder locked in permanent anchylosis, by an organized plastic exudation of rheumatism, into the tendo-vaginal spaces, or, between the articular surfaces.

When one finds an acute monarticular, paninflammation of a rheumatoid character, at the shoulder, fixing the ends of the bones, and rendering all motion difficult or painful, in an adult previously healthy, we have good reason to suspect, the metastalic transference of gonorrhoeal infection.

In quite a few, after a moderate injury at the shoulder, we may find a marked element of hysteria, with the most intense hyperæsthesia,

two at the clavicular-acromial joint, the two latter, having been treated as "sprains."

Modern surgery has opened the way, to the successful reduction of those cases, otherwise rebellious to manipulation, by free dissection. But, infection almost invariably follows arthrotomies, and, in any event, so many tendinous structures must be divided, and adhesions of the vessels and nerve cords are so common, that after the large wound has cicatrized, the functional result may be no better, if they are as good, as a pseudarthrosis.

Fractures through the omoplate or shoulder blade, whether they involve the spine of the scapula or not, result from direct violence, and usually do well, when there are no internal complications, as anything more, than a slight displacement is not possible.

In the lower extremity, in those railroad accidents, which cause a crunching off of the limb, the conformation of the external surface of the hip, often causes a sliding away of the joint, so that a disorganization, through the shaft above the trochanters is never seen, except, when the pelvis itself has been implicated. Through a somewhat similar arrangement of the shoulder, the claviculo-scapular slope, force is deflected away from the body, and the point of mutilation, is below the insertion of the latissimus-dorsi muscle. Thus, the humero-scapular articulation is spared destruction, though generally, the object which crushes through the limb, destroys so much of the integument above, that, in order to provide a covering for the stump, the remaining root of the humerus must be sacrificed.

MORBID ANATOMY.

Having, in a very brief and superficial manner, considered some of the grosser anatomical structures of the shoulder, their relations and functions, it now remains, to deal with some of the lesions of tissues, resulting in this situation, from the application of violent force.

A correct understanding of this division of the subject, at once elucidates diagnostic difficulties, and suggests a rational treatment. But, to deal with it, in detail, or on any systematic plan, would be to enter on a large undertaking, far beyond the scope of this contribution; therefore, nothing more, than a rudimentary and fragmentary presentation of the subject, embracing in a measure, only the principal features of shoulder lesions, which strike

me, as of the greatest practical interest, will be considered, without dwelling on details with that fullness and minutiæ, which properly belong, to special works on the subject.

SPRAINS, ENTASIS, ETC.

In the most common varieties of severe shoulder injuries, the articular structures, the main blood trunks and large nerve cords, passing through the armpit, escape serious damage. The structures which suffer most serious harm are the peripheral nerves; these are overstretched or contused. The circumflex or musculo-spiral nerves, in super-rotation, or violent extension of the arm, are unduly strained, resulting in hyperæsthesia, and diminution in power in the muscles, supplied by them. In violent blows over the deltoid, the shoulder movement for a time, may be as effectively crippled, as by a fracture or dislocation. It is so well known, that, if caution be not exercised in examinations, a possible dislocation may be overlooked, it being hastily assumed, that only a sprain exists. In aggravated cases of this description, traumatic inflammation follows, in all the soft parts overlapping the head of the humerus. The shoulder becomes fixed, swollen and painful. At the tip of the acromion, the firm attachment of the deep fascia, securely holds the skin in close contact with the bone, but, beyond this point, as this becomes more loosely applied over the deltoid, cellular inflammation produces so much swelling, as to obor obliterate many well-recognized anatomical landmarks. Under these circumstances, without a test examination, a conclusion may be hastily made, that a complete luxation or a fracture exists. Many of these shoulder injuries of this class, may pursue a very tedious course, when the contusive force has been so great, as to lacerate muscular tissue, and induce consecutive myotrophic changes, atrophy, contraction or adhesions between the overlying and intervening fasciæ and muscle sheaths; a low grade of bursitis synovitis, with or without effusion, arthritis or peri-arthritis. The tendency of those parts, after trauma to pathological changes, is greatly accentuated by various constitutional conditions and hygienic surroundings. With those of a syphilitic taint, a tubercular diathesis, or a tendency to rheumatism, a severe wrench of the shoulder, may give rise to such organic changes, as require a long time in recovering

scure

from, if not lead to a permanent impairment, in the strength or function of the articulation. In those of a nemotic habit, with hysterical tendencies, in the female sex, psychical impressions profoundly influence the course of cure, in the traumatic artherosis. In malarious districts paludal influence should not be overlooked, as a complicating factor, as local repair is quite impossible, while this lethal element operates in the system.

DISLOCATIONS.

Treves claims, that in cases of full dislodgment, or dislocation, the capsule is always torn, the head of the humerus passing out through it, producing the so-called "buttonhole" rupture. No opportunity has yet permitted me to verify this, on the subject. In only one case of humero-scapula dislocation, coming under my care, did death soon follow injury. In this, the young man had simultaneously suffered an extensive rent in the liver, followed by mortal internal hemorrhage. But, in spite of appeal to the coroner and relatives, an autopsy was denied.

The tension of the muscles with atmospheric pressure, so firmly retains the humeral head in position, that it is probable it is only when these are off guard, and the parts are relaxed, luxation is possible. My own impression is, that in the greater number, the capsule is not torn but stretched, while in aggravated cases, not only the synovial investment is lacerated in its long axis, but even torn through, or disconnected, with its attachment around the epiphyseal line or anatomical neck. It is highly probable, too, that the insertion of the scapular muscles may give, or the long head of the biceps be torn off, from its root, in the fibro-cartilaginous margin of the glenoid cavity. Therefore, generally speaking, it may be stated, that in one variety, by far the most common in young, growing subjects, the head of the bone leaves its socket, through relaxation or extreme tension, on the capsule and muscles. In this type, reduction is usually simple, and restoration of function, prompt and complete.

In the second, the extent of disorganization has been considerable. Not only has there. been extensive rupture of the capsular ligament, tendon and muscle, but the whole nerve structure of the joint has sustained violent shock. This class is often unsatisfactory to treat, and may force the attending surgeon into

a defensive litigation. Conditions resulting from the innate character of the primary lesion, may be charged against him, on the score of incompetence or neglect. Relocation or reduction in this class, may be attended with great difficulties, and while attempting it, further damage may be inflicted on contiguous structures, as great or greater, than those borne by the primary trauma. And, what is equally unfortunate, in quite a few, the tendency of the head of the bone, to fall out of the glenoid cavity, after reduction, is very great; not, for a few days only, but sometimes this predisposition to relapse, may remain for weeks. When, however, this does not occur, yet such pathologic changes may occur, as tend to diminish shoulder power, or reduce power of action.

Dislocations at the acromio-clavicular joint, at the movable part of the shoulder, though not so common as those just considered, are nevertheless more common than is generally supposed. This joint, lying immediately under the integument, when the head of the clavicle is dislodged, it can be generally easily detected on inspection; or, by manipulation. But, if this lesion is simple of recognition, it is not so, with treatment, for, in all cases of complete luxation, the capsule and synovial membrane are disorganized beyond repair; the coracoid and coroco acromion ligaments are sundered, and permanent reduction, with restitution of integrity, seldom occurs. It is through this joint, it will be remembered, that uniform relations are preserved, with the movement of the scapulahumeral joint, forward and backward, over the latteral arc of the thorax. And, through it, to the "leg" of the shoulder-the clavicle, transmits in a certain degree, the impact of force, from the shoulder to the sternum.

This dislocation is often overlooked. We will find, on close inspection, not a few of those "lame shoulders" following sprains, are really dislocations of this type. The arm preserves its strength, but through laxity at the joint and a swaying motion, the patient is conscious of a sense of insecurity, at this point of the shoulder.

FRACTURES OR FRACTURE-DISLOCATIONS AT THE SHOULDER JOINT.

The bones which constitute the framework of the shoulder are often fractured, after the application of direct or indirect force; more often the latter. Sometimes dislocation is