Surface anatomy of Free Upper limb .
The bones of the upper limb, their main parts and surface projections, articulations, and movements at the joints are described here. Make use of the dried bones to identify the parts and bony landmarks. The surface anatomy of the upper limb should be appreciated on your own upper limb.
The arm region .
The humerus is almost entirely covered by the muscles of the arm, so that its outlines can only be felt indistinctly. In the distal part, it expands transversely, and its lateral and medial margins (supracondylar ridges) become readily palpable. The lateral and medial margins end inferiorly in the lateral and medial epicondyles. The medial epicondyle is more prominent than the lateral epicondyle.
In the anatomical position, the epicondyles are in the positions suggested by their names, and the hemispherical head of the humerus faces medially. When the palms of the hands face medially (the arm is semi-pronated), the lateral epicondyle is more anterior, and the head of the humerus is directed posteromedially . The upper half of the humerus is covered on its anterior, lateral and posterior surfaces by the deltoid muscle. Inferiorly, the apex of that muscle is attached to the lateral side of the middle of the humerus—the deltoid tuberosity.
The upper part of the bone consists of the head. This is separated by a shallow groove—the anatomical neck from the greater (lateral) and lesser (anterior) tubercles. Both the head and tubercles are continuous inferiorly with the body or shaft of the bone through the narrow surgical neck. The greater tubercle is the most lateral bony part of the shoulder. The lower half of the bone is covered anteriorly by the biceps and brachialis muscles, and posteriorly by the triceps muscle.
The anterior surfaces of the epicondyles and supracondylar ridges give rise to the forearm muscles. At the midpoint of the anterior surface of the bend of the elbow, find the tendon of the biceps. Medial to this, feel the pulsations of the brachial artery, and trace it superiorly on the medial side of the arm. The median nerve may be palpable, posteromedial to the artery. The distal end of the humerus articulates with the radius and ulna. There are four named bony prominences at this end. The medial and lateral epicondyles have been described. Immediately lateral to the medial epicondyle is the trochlea.
The trochlea has a pulley-shaped articular surface for articulation with the ulna. The capitulum lies lateral to the trochlea and has a rounded articular surface for the head of the radius. Three bony fossae (depressions) are seen at the lower end of the humerus, immediately above the articular surfaces. On the anterior surface, the coronoid fossa lies medially, superior to the trochlea, and the radial fossa is lateral, superior to the capitulum. On the posterior aspect, the single olecranon fossa lies superior to the trochlea.
The forearm region .
The two bones of the forearm are the radius (lateral) and the ulna (medial) . Proximally, the trochlear notch of the ulna articulates with the trochlea of the humerus . The ulnar trochlear notch has two processes—the coronoid process inferiorly and the olecranon process superiorly. The olecranon and coronoid fossa of the humerus are occupied by the olecranon process in full extension of the elbow and the coronoid process in full flexion.
The proximal part of the ulna (the olecranon) is readily palpable. On its posterior surface is a triangular subcutaneous area which is continuous distally with the posterior margin (border) of the ulna. The entire length of this posterior margin is palpable. The ulna ends distally in the styloid process which projects from the posteromedial aspect of the cylindrical, slightly expanded head of the bone. This palpable margin not only allows the entire length of the ulna to be examined for fractures but also forms the line of separation between the anteromedial flexor group of muscles of the forearm (supplied by the median and ulnar nerves) and the posterolateral extensor group (supplied by the radial nerve) .
The proximal end or head of the radius is a short cylinder. Its concave proximal surface articulates with the capitulum of the humerus, and its circumference articulates with the radial notch of the ulna and the annular ligament. The annular ligament is loop-shaped and attached to the margins of the radial notch on the ulna. It narrows inferiorly to fit the superior part of the neck of the radius . This narrowing prevents the head from being pulled out of the ligament when the arm is pulled upon.
Palpate the head of the radius just distal to the lateral epicondyle of the humerus, and feel it rotating within the annular ligament when you pronate and supinate your forearm. The radial tuberosity lies on the medial aspect of the radius, distal to the neck. It has the tendon of the biceps brachii attached to its posterior part. Beyond this point, the radius is markedly convex laterally, and only its distal part is readily palpable through the muscles which cover it.
The wrist region .
At the lower end, the radius expands into a cuboidal mass. The lateral surface of this mass extends distally to form the blunt styloid process. When the thumb is fully extended, i.e. moved laterally, a surface depression—‘the anatomical snuffbox’—appears on the lateral side of the back of the wrist between the tendons passing to the thumb . The styloid process of the radius lies in the proximal part of the depression and is covered by tendons of the short extensor and long abductor muscles of the thumb.
The bones at the lateral ends of the proximal and distal rows of the carpal bones (scaphoid and trapezium) and the base of the metacarpal of the thumb can be felt in the ‘snuffbox’, distal to the styloid process. Light pressure applied over the trapezium reveals the pulsations of the radial artery. The ‘radial pulse’ is more easily felt where the artery crosses the anterior surface of the distal end of the radius (medial to the styloid process). Feel your radial and ulnar styloid processes simultaneously.
Note that the radial styloid projects further distally than the ulnar styloid—a situation which is altered when the radius is fractured. If the tendon forming the posterior boundary of the ‘snuffbox’ (extensor pollicis longus) is followed proximally, it curves round the medial surface of the dorsal tubercle of the radius which is readily palpable. The distal end of the radius articulates medially with the ulna (ulnar notch) and distally with the lateral two carpal bones—the scaphoid and lunate of the proximal row.
This forms the only direct articulation of the carpal bones with the bones of the forearm. Forces transmitted from the hand to the forearm pass through the scaphoid and lunate to the radius—a feature which accounts for the fracture of the scaphoid or radius (but not the ulna) from falling on the outstretched hand. The dorsal surfaces of both rows of carpal bones can be felt through the tendons which cover them, though the individual bones cannot be defined. On the palmar surface of the wrist, only the pisiform bone (medially) and the tubercle of the scaphoid (laterally) can be felt at the level of the distal transverse skin crease (junction of the forearm and wrist) when the wrist is fully extended.
If the wrist is passively flexed, the pisiform may be gripped between the finger and thumb and moved on the triquetrum bone with which it articulates and the tendon of the flexor carpi ulnaris can be felt passing to its proximal surface. The hook of the hamate can be felt deeply through the proximal parts of the muscles forming the ball of the little finger (hypothenar eminence) and the tubercle of the trapezium can be felt deeply through the proximal parts of the muscles forming the ball of the thumb (thenar eminence).
These four palpable bony points lying at the ends of the two rows of the carpal bones—tubercle of the scaphoid, pisiform, tubercle of the trapezium and hook of the hamate—give attachment to the flexor retinaculum. The flexor retinaculum is the deep fascia which connects these bones, maintains the palmar concavity of the carpal bones, and completes the fibro-osseous tunnel through which the flexor tendons and the median nerve pass from the forearm into the hand.
The palm region .
The skin of the central region of the palm is firmly bound to the thickened underlying deep fascia (palmar aponeurosis). The palmar aponeurosis is continuous distally with the deep fascia of the fingers and proximally with the flexor retinaculum and the tendon of the palmaris longus. If present, this tendon enters the palm, superficial to the retinaculum and is the most superficial tendon immediately proximal to the wrist.
Contraction of the palmaris longus and extension of the fingers tighten the palmar aponeurosis and stabilize the palmar skin to maintain a firm grip. The distal skin crease of the palm lies just proximal to the metacarpophalangeal joints, while that at the roots of the fingers lies approximately 3 cm distal to them . The middle skin crease of each finger lies at the level of the proximal interphalangeal joint, and the distal skin crease lies proximal to the distal interphalangeal joint.
The metacarpals (hand bones) are readily palpated on their dorsal surfaces. When a fist is formed, the knuckles are the distal ends of the heads of the metacarpal bones, uncovered by the movement of the proximal phalanges on to the palmar surfaces of these heads. The heads of the proximal and middle phalanges of the fingers are similarly exposed.
The digits region .
The thumb has two phalanges; the other fingers have three. The thumb lies at right angles to the fingers, with its nail facing laterally and not posteriorly. Thus, flexion moves the tip of the thumb medially across the palm, while extension moves it laterally. Abduction swings the tip of the thumb anteriorly; adduction moves it to the index finger. The first carpometacarpal joint between the metacarpal of the thumb and the trapezium, allows for greater freedom of movement, when compared with the carpometacarpal joints of the fingers.
To test this, grip the head of each metacarpal in turn, with the thumb and index finger of your other hand on the palmar and dorsal surfaces, and attempt to move it. The metacarpal of the middle finger scarcely moves, while those of the index, ring, and little finger, in that order, have an increasing, but small, range of flexion and extension and slight rotation only in the little finger. None can be abducted or adducted. Next flex your thumb at the metacarpophalangeal joint, and attempt to rotate its metacarpal using the phalanges as a lever.
Only a small amount of movement is possible, compared with the free flexion/extension and abduction/adduction at the carpometacarpal joint of the thumb. Flexion of the metacarpophalangeal joint of the thumb is less than 90 degrees. It is 90 degrees in the index and middle fingers and exceeds this in the ring and little fingers. There is some degree of rotation in the ring and little fingers. Check the bones, and note that there is nothing in their contours to prevent rotation. Rotation is limited by ligaments. Also there is very little abduction or adduction at the metacarpophalangeal joint in the thumb, though it is relatively free in the fingers.
The interphalangeal joint of the thumb flexes to approximately 90 degrees. The proximal interphalangeal joints of the fingers flex to more than 90 degrees, and the distal interphalangeal joints slightly less than 90 degrees. The fingers separate on extension and come together in flexion. This is the result of the curve in which the heads of the metacarpals lie and a slight obliquity of the interphalangeal joints. Note also that the tips of all four fingers meet the palm at the same time, despite the differences in their lengths.
Check your interphalangeal joints for rotation. This is minimal because of the shape of the articular surfaces of the phalanges. Cup the palm of your hand by spreading the fingers as though to grasp a large ball. The hollow between the proximal parts of the thenar and hypothenar eminences marks the position of the flexor retinaculum. The tightening of the skin on the medial side of the hypothenar eminence is produced by the contraction of the palmaris brevis which heaps up the hypothenar skin to form a pad for grasping.
Note too that the thumb is slightly flexed at the carpometacarpal joint and rotated medially, so that its palmar surface faces that of the little finger (opposition), which is also rotated laterally. The other three fingers are not parallel to each other but, on flexion, converge to meet the tip of the thumb.
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