THE ARM.
130.Clavicle.—The line of the clavicle and the projection of the joint at either end of it can always be felt, even in the fattest persons. Its direction is not perfectly horizontal, but slightly inclined downwards, when the arm hangs quietly by the side. When the body lies flat on the back, the shoulder not only falls back, but rises a little, the weight of the limb being taken off. Hence the modern practice of treating fractures of the clavicle (in the early stage) by the supine position.
On the front surface of the clavicle, not far from its acromial end, there is in many persons of mature age a spine-like projection of bone. So far as I know, it has not been described. A gentleman, himself a surgeon, showed me an instance in his own person. He suspected it was an exostosis.
As a rule the acromio-clavicular joint forms an even plane. But there is sometimes a knob of bone at the acromial end of the clavicle; or it may be only a thickening of the fibro-cartilage, sometimes existing in the joint. In either case this relief might be mistaken for a dislocation, or even for a fracture. A reference to the other shoulder might settle the question.
131.Bony points of the shoulder.—We can distinctly feel the spine of the scapula and the acromion, more especially at the angle where they join behind the shoulder. This angle is the best place from which to measure in taking the comparative length of the arms.
In some shoulders, though very rarely, there is an abnormal symphysis between the spine of the scapula and the acromion. There may indeed be two symphyses and two acromial bones, the acromion having two centres of ossification. These abnormal symphyses might be mistaken for fractures, until we have examined the opposite shoulder, which is sure to present a similar conformation.[9]
Tuberosities.—Projecting beyond the acromion (the arm hanging by the side), we can feel, through the fibres of thedeltoid, the upper part of the humerus. It distinctly moves under the hand when the arm is rotated. It is not the head of the bone which is felt, but the tuberosities, the greater externally, the lesser in front. These tuberosities form the convexity of the shoulder. When the arm is raised, this convexity disappears; there is a slight depression in its place. The head of the bone can be felt by pressing the fingers high up in the axilla.
The absence of this prominence formed by the upper part of the humerus under the deltoid, and the presence of a prominence low in the hollow of the axilla, or in front, below the coracoid process, or behind, on the back of the scapula, bespeak dislocation of the head of the bone.
In examining obscure injuries about the shoulder, it is worth remembering that, in the normal relation of the bones, and in every position, the great tuberosity faces in the direction of the external condyle. The head of the bone faces very much in the direction of the internal condyle.
It is worth remembering also that the upper epiphysis of the humerus includes the tuberosities; and that it does not unite by bone to the shaft, till about the 20th year.
By making deep pressure in front of the shoulder, when the arm is pendent and supine, we can feel the bicipital groove. It looks directly forwards, and runs in a line drawn vertically downwards through the middle of the biceps to its tendon at the elbow. We should be aware of this, lest it be mistaken for a fracture.
132.Coraco-acromial ligament.—Under the anterior fibres of the deltoid, we can distinctly feel the position and extent of the coraco-acromial ligament. A knife, passed vertically through the middle of it, goes at once into the shoulder joint and strikes the bicipital groove with the tendon, a point to be remembered in excision.
In persons of an athletic build the triangular form and beautiful structure of the deltoid become conspicuous when the muscle is in action. The depression on the outer side of the arm, indicating its insertion, is the place selected for issues or setons.
The arm being held up by an assistant, the anterior and posterior borders of the relaxed deltoid admit of being raised so that in amputation at the shoulder the knife can be introduced beneath the muscle to make the flap.
133.Axilla.—The anterior border of the axilla, formed by the pectoralis major, follows the line of the fifth rib. In counting the ribs, or in tapping the chest, it is worth remembering that the highest visible digitation of the serratus magnus is attached to the sixth rib. The angle of the digitation is directed forwards, and corresponds to the upper edge of the rib. The second visible digitation corresponds to the seventh rib; the interval between these digitations, therefore, corresponds to the sixth intercostal space—a convenient place for tapping the chest. (38)
In the normal state no glands can be felt in the axilla.
134.Axillary artery.—When the arm is raised to a right angle with the body, and the head of the humerus thereby depressed, the axillary artery is plainly felt beating, and can be perfectly compressed on the inner side of the coraco-brachialis. This muscle stands out in relief along the humeral side of the axilla, and is the best guide to the artery. A line drawn along its inner border—that is, down the middle of the axilla—corresponds with the course of the artery.
The depth and form of the axilla alter in different positions of the arm. In the arm raised and abducted the axilla becomes nearly flat; hence this position is always adopted in operations.
In opening abscesses in the axilla, the incision should be made midway between the borders, and the point of the knife introduced from above downwards.
135.Brachial artery.—When the arm is extended and supinated, a line drawn from the deepest part of the middle of the axilla down the inner side of the biceps to the middle of the bend of the elbow, corresponds with the course of the brachial artery. The artery can be felt and compressed all the way down; but nowhere so effectually as midway, where it lies on the tendon of the coraco-brachialis close to the inner side of the humerus. The only direction to apply the pressureeffectually is outwards and a little backwards, else the artery will slip off the bone.
The musculo-spiral nerve and superior profunda artery wind round the back of the humerus about its middle, and come to the front of the external condyloid ridge. Thus, for full three inches above the condyles, there is nothing to interfere with operations on the back of the bone, which is here broad and flat.
136.Bend of elbow.—At the bend of the elbow, the tendon of the biceps can be plainly felt, as well as the pulsation of the brachial artery close to its inner side, before dividing into the radial and ulnar.
Cutaneous veins.—The bend of the elbow in young children and in persons with fat and round arms, presents a semicircular fold of which the curve embraces the lower part of the biceps; but in muscular persons we see the distinct boundaries of the triangular space, formed by the pronator teres on the inner side, and the supinator longus on the outer. Here can be traced, standing out in strong relief under the thin white skin, the superficial veins, which, in days gone by, when bloodletting was the fashion, were of such great importance. Their arrangement, although subject to variety, is very much like the branches of the letter M, the middle of the M being at the middle of the elbow. Of these branches the median basilic, which runs over the tendon of the biceps, is the largest and most conspicuous, and is generally selected for venesection; it crosses the course of the brachial artery, nothing intervening but the semilunar aponeurosis from the tendon of the biceps.
137.Landmarks of elbow.—It is of great importance to be familiar with the relative positions of the various bony prominences about the elbow. We can always feel the internal and external condyles. The internal is the more prominent of the two, and a trifle higher.
Olecranon.—We can always feel the olecranon. This is somewhat nearer to the inner than to the outer condyle. Between the olecranon and the internal condyle is a deep depression in which lies the ulnar nerve (vulgarly called the ‘funny bone’).
On the outer side of the olecranon, just below the external condyle, is a pit in the skin, constant even in fat persons (when the elbow is extended). This pit is considered one of the beauties of the elbow in a graceful arm; it is seen in a child as a pretty little dimple. To the surgeon it is most interesting, as in this valley behind the supinator longus and the radial extensors of the wrist he can distinctly feel the head of the radius rolling in pronation and supination of the forearm. It is, therefore, one of the most important landmarks of the elbow, since it enables us to say whether the head of the radius is in its right place, and whether it rotates with the shaft.
Can the tubercle of the radius be felt? Yes, but only on the back of the forearm in extreme pronation. Its projection is then distinctly perceptible just below the head of the bone.
Relations of olecranon and condyles.—To examine the relative positions of the olecranon and condyles in the different motions of the elbow joint, place the thumb on one condyle, the tip of the middle finger on the other, and the tip of the forefinger on the olecranon. In extension, the highest point of the olecranon is never above the line of the condyles; indeed, it is just in this line. With the elbow at right angles the point of the olecranon is vertically below the line of the condyles. In extreme flexion the point of the olecranon lies in front of the line of the condyles.
All these relative positions would be altered in a dislocation of the ulna, but not (necessarily) in a fracture of the lower end of the humerus.
Sometimes, though rarely, we meet with a hook-like projection of bone above the internal condyle. It is called a ‘supra-condyloid’ process; it can be felt through the skin, with its concavity downwards, and is a rudiment of the bony canal which, in many mammalia, transmits the median nerve and ulnar artery. A third origin of the pronator teres is always attached to it; this origin covers the brachial artery.[10]
Bursæ.—The subcutaneous bursa over the olecranon, if distended, would be as large as a walnut. A second bursa sometimes exists a little lower down upon the ulna. Thereis also a small subcutaneous bursa over each of the condyles.
The vertical extent of the elbow joint is limited, above by a line drawn from one condyle to the other; below, by a line corresponding to the lowest part of the head of the radius.
138.Interosseous arteries.—About one inch below the head of the radius, the ulnar artery gives off the common interosseous; and this divides, about half an inch lower, into the anterior and posterior interosseous. Thus, in amputating the forearm, say two inches below the head of the radius, four arteries at least would require ligature.
By flexion of the elbow to the utmost, the circulation through the brachial artery can be arrested; but the position is painful, and can be tolerated only for a short time.
Lymphatic gland.—There is a small lymphatic gland just above the inner condyle, in front of the intermuscular septum. It is the first to take alarm in poisoned wounds of the hand.