Surface Anatomy of the Upper Extremity

11. Surface Anatomy of the Upper Extremity

FIG. 1231– Front of right upper extremity.

Skin.—The skin covering the shoulder and arm is smooth and very movable on the underlying structures. In the axilla there are numerous hairs and many sudoriferous and sebaceous glands. Over the medial side and front of the forearm the skin is thin and smooth, and contains few hairs but many sudoriferous glands; over the lateral side and back of the arm and forearm it is thicker, denser, and contains more hairs but fewer sudoriferous glands. In the region of the olecranon it is thick and rough, and is very loosely connected to the underlying tissue so that it falls into transverse wrinkles when the forearm is extended. At the front of the wrist there are three transverse furrows in the skin; they correspond respectively from above downward to the positions of the styloid process of the ulna, the wrist-joint, and the midcarpal joint.

The skin of the palm of the hand differs considerably from that of the forearm. At the wrist it suddenly becomes hard and dense and covered with a thick layer of epidermis; on the thenar eminence these characteristics are less marked than elsewhere. In spite of its hardness and density the skin of the palm is exceedingly sensitive and very vascular, but it is destitute of hairs and sebaceous glands. It is tied down by fibrous bands along the lines of flexion of the digits, exhibiting certain furrows of a permanent character. One of these, starting in front of the wrist at the tuberosity of the navicular bone, curves around the thenar eminence and ends on the radial border of the hand a little above the metacarpophalangeal joint of the index finger. A second line begins at the end of the first and extends obliquely across the palm to reach the ulnar border about the middle of the fifth metacarpal bone. A third line begins at the ulnar border about 2.5 cm. distal to the end of the second and extends across the heads of the fifth, fourth, and third metacarpal bones. The proximal segments of the fingers are joined to one another on the volar aspect by folds of skin constituting the “web” of the fingers; these folds extend across about the level of the centers of the proximal phalanges and their free margins are continuous with the transverse furrows at the roots of the fingers. Since the web is confined to the volar aspect the fingers appear shorter when viewed from in front than from behind.

Over the fingers and thumb the skin again becomes thinner, especially at the flexures of the joints (where it is crossed by transverse furrows) and over the terminal phalanges; it is disposed on numerous ridges in consequence of the arrangement of the papillæ in it. These ridges form, in different individuals, distinctive and permanent patterns which can be used for purposes of identification. The superficial fascia in the palm of the hand is made up of dense fibro-fatty tissue which binds the skin so firmly to the palmar aponeurosis that very little movement is permitted between the two.

On the back of the hand and fingers the subcutaneous tissue is lax, so that the skin is freely movable on the underlying parts. Over the interphalangeal joints the skin is very loose and is thrown into transverse wrinkles when the fingers are extended.

Bones.—The clavicle can be felt throughout its entire length. The enlarged sternal extremity projects above the upper margin of the sternum at the side of the jugular notch, and from this the body of the bone can be traced lateralward immediately under the skin. The medial part is convex forward, but the surface is partially obscured by the attachments of Sternocleidomastoideus and Pectoralis major; the lateral third is concave forward and ends at the acromion of the scapula in a slight enlargement. The clavicle is almost horizontal when the arm is lying by the side, although in muscular subjects it may incline a little upward at its acromial end, which is on a plane posterior to the sternal end.

The only parts of the scapula that are truly subcutaneous are the spine and acromion, but the coracoid process, the vertebral border, the inferior angle, and to a lesser extent the axillary border can also be readily defined. The acromion and spine are easily recognizable throughout their entire extent, forming with the clavicle the arch of the shoulder. The acromion forms the point of the shoulder; it joins the clavicle at an acute angle—the acromial angle—slightly medial to, and behind the tip of the acromion. The spine can be felt as a distinct ridge, marked on the surface as an oblique depression which becomes less distinct and ends in a slight dimple a little lateral to the spinous processes of the vertebræ. Below this point the vertebral border can be traced downward and lateralward to the inferior angle, which can be identified although covered by Latissimus dorsi. From the inferior angle the axillary border can usually be traced upward through its thick muscular covering, forming with its enveloping muscles the posterior fold of the axilla. The coracoid process is situated about 2 cm. below the junction of the intermediate and lateral thirds of the clavicle; it is covered by the anterior border of Deltoideus, and thus lies a little lateral to the infraclavicular fossa or depression which marks the interval between the Pectoralis major and Deltoideus.

The humerus is almost entirely surrounded by muscles, and the only parts which are strictly subcutaneous are small portions of the medial and lateral epicondyles; in addition to these, however, the tubercles and a part of the head of the bone can be felt under the skin and muscles by which they are covered. Of these, the greater tubercle forms the most prominent bony point of the shoulder, extending beyond the acromion; it is best recognized when the arm is lying passive by the side, for if the arm be raised it recedes under the arch of the shoulder. The lesser tubercle, directed forward, is medial to the greater and separated from it by the intertubercular groove, which can be made out by deep pressure. When the arm is abducted the lower part of the head of the humerus can be examined by pressing deeply in the axilla. On either side of the elbow-joint and just above it are the medial and lateral epicondyles. Of these, the former is the more prominent, but the medial supracondylar ridge passing upward from it is much less marked than the lateral, and as a rule is not palpable; occasionally, however, the hook-shaped supracondylar process (page 211) is found on this border. The position of the lateral epicondyle is best seen during semiflexion of the forearm, and is indicated by a depression; from it the strongly marked lateral supracondylar ridge runs upward.

The most prominent part of the ulna, the olecranon, can always be identified at the back of the elbow-joint. When the forearm is flexed the upper quadrilateral surface is palpable, but during extension it recedes into the olecranon fossa. During extension the upper border of the olecranon is slightly above the level of the medial epicondyle and nearer to this than to the lateral; when the forearm is fully flexed the olecranon and the epicondyles form the angles of an equilateral triangle. On the back of the olecranon is a smooth triangular subcutaneous surface, and running down the back of the forearm from the apex of this triangle the prominent dorsal border of the ulna can be felt in its whole length: it has a sinuous outline, and is situated in the middle of the back of the limb above; but below, where it is rounded off, it can be traced to the small subcutaneous surface of the styloid process on the medial side of the wrist. The styloid process forms a prominent tubercle continuous above with the dorsal border and ending below in a blunt apex at the level of the wrist-joint; it is most evident when the hand is in a position midway between supination and pronation. When the forearm is pronated another prominence, the head of the ulna, appears behind and above the styloid process.

Below the lateral epicondyle of the humerus a portion of the head of the radius is palpable; its position is indicated on the surface by a little dimple, which is best seen when the arm is extended. If the finger be placed in this dimple and the semiflexed forearm be alternately pronated and supinated the head of the radius will be felt distinctly, rotating in the radial notch. The upper half of the body of the bone is obscured by muscles; the lower half, though not subcutaneous, can be readily examined, and if traced downward is found to end in a lozenge-shaped convex surface on the lateral side of the base of the styloid process; this is the only subcutaneous part of the bone, and from its lower end the apex of the styloid process bends medialward toward the wrist. About the middle of the dorsal surface of the lower end of the radius is the dorsal radial tubercle, best perceived when the wrist is slightly flexed; it forms the lateral boundary of the oblique groove for the tendon of Extensor pollicis longus.

On the front of the wrist are two subcutaneous eminences, one, on the radial side, the larger and flatter, produced by the tuberosity of the navicular and the ridge on the greater multangular; the other, on the ulnar side, by the pisiform. The tuberosity of the navicular is distal and medial to the styloid process of the radius, and is most clearly visible when the wrist-joint is extended; the ridge on the greater multangular is about 1 cm. distal to it. The pisiform is about 1 cm. distal to the lower end of the ulna and just distal to the level of the styloid process of the radius; it is crossed by the uppermost crease which separates the front of the forearm from the palm of the hand. The rest of the volar surface of the bony carpus is covered by tendons and the transverse carpal ligament, and is entirely concealed, with the exception of the hamulus of the hamate bone, which, however, is difficult to define. On the dorsal surface of the carpus only the triangular bone can be clearly made out.

Distal to the carpus the dorsal surfaces of the metacarpal bones, covered by the Extensor tendons, except the fifth, are visible only in very thin hands; the dorsal surface of the fifth is, however, subcutaneous throughout almost its whole length. Slightly lateral to the middle line of the hand is a prominence, frequently well-marked, but occasionally indistinct, formed by the styloid process of the third metacarpal bone; it is situated about 4 cm. distal to the dorsal radial tubercle. The heads of the metacarpal bones can be plainly seen and felt, rounded in contour and standing out in bold relief under the skin when the fist is clenched; the head of the third is the most prominent. In the palm of the hand the metacarpal bones are covered by muscles, tendons, and aponeuroses, so that only their heads can be distinguished. The base of the metacarpal bone of the thumb, however, is prominent dorsally, distal to the styloid process of the radius; the body of the bone is easily palpable, ending at the head in a flattened prominence, in front of which are the sesamoid bones.

The enlarged ends of the phalanges can be easily felt. When the digits are bent the proximal phalanges form prominences, which in the joints between the first and second phalanges are slightly hollow, but flattened and square-shaped in those between the second and third.

Articulations.—The sternoclavicular joint is subcutaneous, and its position is indicated by the enlarged sternal extremity of the clavicle, lateral to the long cord-like sternal head of Sternocleidomastoideus. If this muscle be relaxed a depression between the end of the clavicle and the sternum can be felt, defining the exact position of the joint.

The position of the acromioclavicular joint can generally be ascertained by determining the slightly enlarged acromial end of the clavicle which projects above the level of the acromion; sometimes this enlargement is so considerable as to form a rounded eminence.

The shoulder-joint is deeply seated and cannot be palpated. If the forearm be slightly flexed a curved crease or fold with its convexity downward is seen in front of the elbow, extending from one epicondyle to the other; the elbow-joint is slightly distal to the center of the fold. The position of the radiohumeral joint can be ascertained by feeling for a slight groove or depression between the head of the radius and the capitulum of the humerus, at the back of the elbow-joint.

The position of the proximal radioulnar joint is marked on the surface at the back of the elbow by the dimple which indicates the position of the head of the radius. The site of the distal radioulnar joint can be defined by feeling for the slight groove at the back of the wrist between the prominent head of the ulna and the lower end of the radius, when the forearm is in a state of almost complete pronation.

Of the three transverse skin furrows on the front of the wrist, the middle corresponds fairly accurately with the wrist-joint, while the most distal indicates the position of the midcarpal articulation.

The metacarpophalangeal and interphalangeal joints are readily available for surface examination; the former are situated just distal to the prominences of the knuckles, the latter are sufficiently indicated by the furrows on the volar, and the wrinkles on the dorsal surfaces.

Muscles (Figs. 1194, 1231, 1232).—The anterior border of the Trapezius presents as a slight ridge running downward and forward from the superior nuchal line of the occipital bone to the junction of the intermediate and lateral thirds of the clavicle. The inferior border of the muscle forms an undulating ridge passing downward and medialward from the root of the spine of the scapula to the spinous process of the twelfth thoracic vertebra.

The lateral border of the Latissimus dorsi (Fig. 1215) may be traced, when the muscle is in action, as a rounded edge starting from the iliac crest and slanting obliquely forward and upward to the axilla, where it takes part with the Teres major in forming the posterior axillary fold.

The Pectoralis major (Fig. 1219) conceals a considerable part of the thoracic wall in front. Its sternal origin presents a border which bounds, and determines the width of the sternal furrow. The upper margin is generally well-marked medially and forms the medial boundary of a triangular depression, the infraclavicular fossa, which separates the Pectoralis major from the Deltoideus; it gradually becomes less marked as it approaches the tendon of insertion and is closely blended with the Deltoideus. The lower border of Pectoralis major forms the rounded anterior axillary fold. Occasionally a gap is visible between the clavicular and sternal parts of the muscle.

When the arm is raised the lowest slip of origin of Pectoralis minor produces a fulness just below the anterior axillary fold and serves to break the sharp outline of the lower border of Pectoralis major.

The origin of the Serratus anterior (Figs. 1215, 1219) causes a very characteristic surface marking. When the arm is abducted the lower five or six serrations form a zigzag line with a general convexity forward; when the arm is by the side the highest visible serration is that attached to the fifth rib.

The Deltoideus with the prominence of the upper end of the humerus produces the rounded contour of the shoulder; it is rounded and fuller in front than behind, where it presents a somewhat flattened form. Above, its anterior border presents a slightly curved eminence which forms the lateral boundary of the infraclavicular fossa; below, it is closely united with the Pectoralis major. Its posterior border is thin, flattened, and scarcely marked above, but is thicker and more prominent below. The insertion of Deltoideus is marked by a depression on the lateral side of the middle of the arm.

Of the scapular muscles the only one which influences surface form is the Teres major; it assists the Latissimus dorsi in forming the thick, rounded, posterior axillary fold.

When the arm is raised the Coracobrachialis reveals itself as a narrow elevation emerging from under cover of the anterior axillary fold and running medial to the body of the humerus.

FIG. 1232– Back of right upper extremity.

On the front and medial aspects of the arm is the prominence of the Biceps brachii, bounded on either side by an intermuscular depression. It determines the contour of the front of the arm and extends from the anterior axillary fold to the bend of the elbow; its upper tendons are concealed by the Pectoralis major and Deltoideus, and its lower tendon sinks into the anticubital fossa. When the muscle is fully contracted it presents a globular form, and the lacertus fibrosus attached to its tendon of insertion becomes prominent as a sharp ridge running downward and medialward.

On either side of the Biceps brachii at the lower part of the arm the Brachialis is discernible. Laterally it forms a narrow eminence extending some distance up the arm; medially it exhibits only a little fulness above the elbow.

On the back of the arm the long head of the Triceps brachii may be seen as a longitudinal eminence, emerging from under cover of Deltoideus and gradually passing into the flattened plane of the tendon of the muscle at the lower part of the back of the arm. When the muscle is in action the medial and lateral heads become prominent.

On the front of the elbow are two muscular elevations, one on either side, separate above but converging below so as to form the medial and lateral boundaries of the anticubital fossa. The medial elevation consists of the Pronator teres and the Flexors, and forms a fusiform mass, pointed above at the medial epicondyle and gradually tapering off below. The Pronator teres is the most lateral of the group, while the Flexor carpi radialis, lying to its medial side, is the most prominent and may be traced downward to its tendon, which is situated nearer to the radial than to the ulnar border of the front of the wrist and medial to the radial artery. The Palmaris longus presents no surface marking above, but below, its tendon stands out when the muscle is in action as a sharp, tense cord in front of the middle of the wrist. The Flexor digitorum sublimis does not directly influence surface form; the position of its four tendons on the front of the lower part of the forearm is indicated by an elongated depression between the tendons of Palmaris longus and Flexor carpi ulnaris. The Flexor carpi ulnaris determines the contour of the medial border of the forearm, and is separated from the Extensor group of muscles by the ulnar furrow produced by the subcutaneous dorsal border of the ulna; its tendon is evident along the ulnar border of the lower part of the forearm, and is most marked when the hand is flexed and adducted.

The elevation forming the lateral side of the anticubital fossa consists of the Brachioradialis, the Extensors and the Supinator; it occupies the lateral and a considerable part of the dorsal surface of the forearm in the region of the elbow, and forms a fusiform mass which is altogether on a higher level than that produced by the medial elevation. Its apex is between the Triceps brachii and Brachialis some distance above the elbow-joint; it acquires its greatest breadth opposite the lateral epicondyle, and below this shades off into a flattened surface. About the middle of the forearm it divides into two diverging longitudinal eminences. The lateral eminence consists of the Brachioradialis and the Extensores carpi radiales longus and brevis, and descends from the lateral supracondylar ridge in the direction of the styloid process of the radius. The medial eminence comprises the Extensor digitorum communis, Extensor digiti quinti proprius, and the Extensor carpi ulnaris; it begins at the lateral epicondyle of the humerus as a tapering mass which is separated above from the Anconæus by a well-marked furrow, and below from the Pronator teres and Flexor group by the ulnar furrow. The medial border of the Brachioradialis starts as a rounded elevation above the lateral epicondyle; lower down the muscle forms a prominent mass on the radial side of the upper part of the forearm; below it tapers to its tendon, which may be traced to the styloid process of the radius. The Anconæus presents as a triangular slightly elevated area, immediately lateral to the subcutaneous surface of the olecranon and differentiated from the Extensor group by an oblique depression; the upper angle of the triangle is at the dimple over the lateral epicondyle.

At the lower part of the back of the forearm in the interval between the two diverging eminences is an oblique elongated swelling; full above but flattened and partially subdivided below; it is caused by the Abductor pollicis longus and the Extensor pollicis brevis. It crosses the dorsal and lateral surfaces of the radius to the radial side of the wrist-joint, whence it is continued on to the dorsal surface of the thumb as a ridge best marked when the thumb is extended.

The tendons of most of the Extensor muscles can be seen and felt on the back of the wrist. Laterally is the oblique ridge produced by the Extensor pollicis longus. The Extensor carpi radialis longus is scarcely palpable, but the Extensor carpi radialis brevis can be identified as a vertical ridge emerging from under the ulnar border of the tendon of the Extensor pollicis longus when the wrist is extended. Medial to this the Extensor tendons of the fingers can be felt, the Extensor digiti quinti proprius being separated from the tendons of the Extensor digitorum communis by a slight furrow.

The muscles of the hand are principally concerned, as regards surface form, in producing the thenar and hypothenar eminences, and cannot be individually distinguished; the thenar eminence, on the radial side, is larger and rounder than the hypothenar, which is a long narrow elevation along the ulnar side of the palm. When the Palmaris brevis is in action it produces a wrinkling of the skin over the hypothenar eminence and a dimple on the ulnar border. On the back of the hand the Interossei dorsales give rise to elongated swellings between the metacarpal bones; the first forms a prominent fusiform bulging when the thumb is adducted, the others are not so marked.

Arteries.—Above the middle of the clavicle the pulsation of the subclavian artery can be detected by pressing downward, backward, and medialward against the first rib. The pulsation of the axillary artery as it crosses the second rib can be felt below the middle of the clavicle just medial to the coracoid process; along the lateral wall of the axilla the course of the artery can be easily followed close to the medial border of Coracobrachialis. The brachial artery can be recognized in practically the whole of its extent, along the medial margin of the Biceps; in the upper two-thirds of the arm it lies medial to the humerus, but in the lower third is more directly on the front of the bone. Over the lower end of the radius, between the styloid process and Flexor carpi radialis, a portion of the radial artery is superficial and is used clinically for observations on the pulse.

Veins.—The superficial veins of the upper extremity are easily rendered visible by compressing the proximal trunks; their arrangement is described on pages 660 to 662.

Nerves.—The uppermost trunks of the brachial plexus are palpable for a short distance above the clavicle as they emerge from under the lateral border of Sternocleidomastoideus; the larger nerves derived from the plexus can be rolled under the finger against the lateral axillary wall but cannot be identified. The ulnar nerve can be detected in the groove behind the medial epicondyle of the humerus.