The Wrist and Hand-Important Structures Lying in Front of the Wrist-Radial Artery-Tendon of Flexor Carpi Radialis-Tendon of Palmaris Longus (If Present)-Tendons of Flexor Digitorum Superficialis-Tendon of Flexor Carpi Ulnaris-Ulnar Artery-Ulnar Nerve-Important Structures Lying on the Lateral Side of the Wrist-Anatomic Snuffbox-Important Structures Lying on the Back of the Wrist-Lunate-Important Structures Lying in the Palm-Recurrent Branch of the Median Nerve-Superficial Palmar Arterial Arch-Important Structures Lying on the Dorsum of the Hand

The Wrist and Hand

At the wrist, the styloid processes of the radius and ulna can be palpated. The styloid process of the radius lies about 0.75 in. (1.9 cm) distal to that of the ulna.

The dorsal tubercle of the radius is palpable on the posterior surface of the distal end of the radius.

The head of the ulna is most easily felt with the forearm pronated; the head then stands out prominently on the lateral side of the wrist. The rounded head can be distinguished from the more distal pointed styloid process.

The pisiform bone can be felt on the medial side of the anterior aspect of the wrist between the two transverse creases. The hook of the hamate bone can be felt on deep palpation of the hypothenar eminence, a fingerbreadth distal and lateral to the pisiform bone.

The transverse creases seen in front of the wrist are important landmarks. The proximal transverse crease lies at the level of the wrist joint. The distal transverse crease corresponds to the proximal border of the flexor retinaculum.

Important Structures Lying in Front of the Wrist

Radial Artery

The pulsations of the radial artery can easily be felt anterior to the distal third of the radius. Here, it lies just beneath the skin and fascia lateral to the tendon of flexor carpi radialis muscle

Tendon of Flexor Carpi Radialis
The tendon of the flexor carpi radialis lies medial to the pulsating radial artery
.

Tendon of Palmaris Longus (If Present)

The tendon of the palmaris longus lies medial to the tendon of flexor carpi radialis and overlies the median nerve

Tendons of Flexor Digitorum Superficialis

The tendons of the flexor digitorum superficialis are a group of four that lie medial to the tendon of palmaris longus and can be seen moving beneath the skin when the fingers are flexed and extended.

 

Tendon of Flexor Carpi Ulnaris

The tendon of the flexor carpi ulnaris is the most medially placed tendon on the front of the wrist and can be followed distally to its insertion on the pisiform bone. The tendon can be made prominent by asking the patient to clench the fist (the muscle contracts to assist in fixing and stabilizing the wrist joint)
.

Ulnar Artery

The pulsations of the ulnar artery can be felt lateral to the tendon of flexor carpi ulnaris

Ulnar Nerve

The ulnar nerve lies immediately medial to the ulnar artery

Important Structures Lying on the Lateral Side of the Wrist

Anatomic Snuffbox

The “anatomic snuffbox” is an important area. It is a skin depression that lies distal to the styloid process of the radius. It is bounded medially by the tendon of extensor pollicis longus and laterally by the tendons of abductor pollicis longus and extensor pollicis brevis. In its floor can be palpated the styloid process of the radius (proximally) and the base of the first metacarpal bone of the thumb (distally); between these bones beneath the floor lie the scaphoid and the trapezium (felt but not identifiable).

The radial artery can be palpated within the snuffbox as the artery winds around the lateral margin of the wrist to reach the dorsum of the hand. The cephalic vein can also sometimes be recognized crossing the snuffbox as it ascends the forearm.

Important Structures Lying on the Back of the Wrist

Lunate

The lunate lies in the proximal row of carpal bones. It can be palpated just distal to the dorsal tubercle of the radius when the wrist joint is flexed.

Important Structures Lying in the Palm

Recurrent Branch of the Median Nerve

The recurrent branch to the muscles of the thenar eminence curves around the lower border of the flexor retinaculum and lies about one fingerbreadth distal to the tubercle of the scaphoid

Superficial Palmar Arterial Arch

The superficial palmar arterial arch is located in the central part of the palm and lies on a line drawn across the palm at the level of the distal border of the fully extended thumb

Deep Palmar Arterial Arch

The deep palmar arterial arch is also located in the central part of the palm and lies on a line drawn across the palm at the level of the proximal border of the fully extended thumb

Metacarpophalangeal Joints

The metacarpophalangeal joints lie approximately at the level of the distal transverse palmar crease. The interphalangeal joints lie at the level of the middle and distal finger creases.

Important Structures Lying on the Dorsum of the Hand

The tendons of extensor digitorum, the extensor indicis, and the extensor digiti minimi can be seen and felt as they pass distally to the bases of the fingers.

Development of the Upper Limb-Amelia-Congenital Absence of the Radius-Syndactyly-Lobster Hand-Brachydactyly-Floating Thumb-Polydactyly-Local Gigantism

Development of the Upper Limb

The limb buds appear during the sixth week of development as the result of a localized proliferation of somatopleuric mesenchyme. This causes the overlying ectoderm to bulge from the trunk as two pairs of flattened paddles. The arm buds develop before the leg buds and lie at the level of the lower six cervical and upper two thoracic segments. The flattened limb buds have a cephalic preaxial border and a caudal postaxial border. As the limb buds elongate, the anterior rami of the spinal nerves situated opposite the bases of the limb buds start to grow into the limbs.

The mesenchyme situated along the preaxial border becomes associated and innervated with the lower five cervical nerves, whereas the mesenchyme of the postaxial border becomes associated with the 8th cervical and 1st thoracic nerves.

Later, the mesenchymal masses divide into anterior and posterior groups, and the nerve trunks entering the base of each limb also divide into anterior and posterior divisions. The mesenchyme within the limbs differentiates into individual muscles that migrate within each limb. As a consequence of these two factors, the anterior rami of the spinal nerves become arranged in complicated plexuses that are found near the base of each limb so that the brachial plexus is formed.

Amelia

Absence of one or more limbs (amelia) or partial absence (ectromelia) may occur. A defective limb may possess a rudimentary hand at the extremity of the limb or a well-developed hand may spring from the shoulder with absence of the intermediate portion of the limb (phocomelia) .

Congenital Absence of the Radius

Occasionally, the radius is congenitally absent and the growth of the ulna pushes the hand laterally.

Syndactyly

In syndactyly, there is webbing of the fingers. It is usually bilateral and often familial. Plastic repair of the fingers is carried out at the age of 5 years.

Lobster Hand

Lobster hand is a form of syndactyly that is associated with a central cleft dividing the hand into two parts. It is a heredofamilial disorder, for which plastic surgery is indicated where possible.

Brachydactyly

In brachydactyly, there is an absence of one or more phalanges in several fingers. Provided that the thumb is functioning normally, surgery is not indicated .

Floating Thumb

A floating thumb results if the metacarpal bone of the thumb is absent but the phalanges are present. Plastic surgery is indicated where possible to improve the functional capabilities of the hand.

Polydactyly

In polydactyly, one or more extra digits develop. It tends to run in families. The additional digits are removed surgically.

Local Gigantism

Macrodactyly affects one or more digits; these may be of adult size at birth, but the size usually diminishes with age. Surgical removal may be necessary.

Movements of the Thumb-Diseases of the Hand and Preservation of Function-

Movements of the Thumb

Flexion is the movement of the thumb across the palm in such a manner as to maintain the plane of the thumbnail at right angles to the plane of the other fingernails.

The movement takes place between the trapezium and the1st metacarpal bone, at the metacarpophalangeal and interphalangeal joints. The muscles producing the movement are the flexor pollicis longus and brevis and the opponens pollicis.

Extension is the movement of the thumb in a lateral or coronal plane away from the palm in such a manner as to maintain the plane of the thumbnail at right angles to the plane of the other fingernails. The movement takes place between the trapezium and the 1st metacarpal bone, at the metacarpophalangeal and interphalangeal joints. The muscles producing the movement are the extensor pollicis longus and brevis.

Abduction is the movement of the thumb in an anteroposterior plane away from the palm, the plane of the thumbnail being kept at right angles to the plane of the other nails. The movement takes place mainly between the trapezium and the 1st metacarpal bone; a small amount of movement takes place at the metacarpophalangeal joint. The muscles producing the movement are the abductor pollicis longus and brevis.

Adduction is the movement of the thumb in an anteroposterior plane toward the palm, the plane of the thumbnail being kept at right angles to the plane of the other fingernails. The movement takes place between the trapezium and the 1st metacarpal bone.

The muscle producing the movement is the adductor pollicis.

Opposition is the movement of the thumb across the palm in such a manner that the anterior surface of the tip comes into contact with the anterior surface of the tip of any of the other fingers. The movement is accomplished by the medial rotation of the 1st metacarpal bone and the attached phalanges on the trapezium.
The plane of the thumbnail comes to lie parallel with the plane of the nail of the opposed finger. The muscle producing the movement is the opponens pollicis.

 

Diseases of the Hand and Preservation of Function

From the clinical standpoint, the hand is one of the most important organs of the body. Without a normally functioning hand, the patient’s livelihood is often in jeopardy. To students who doubt this statement, I would suggest that they place their right (or left) hand in a pocket for 24 hours. They will be astonished at the number of times they would like to use it if they could.

From the purely mechanical point of view, the hand can be regarded as a pincer-like mechanism between the thumb and fingers, situated at the end of a multijointed lever. The most important part of the hand is the thumb, and it is the physician’s responsibility to preserve the thumb, or as much of it as possible, so that the pincer-like mechanism can be maintained. The pincer- like action of the thumb largely depends on its unique ability to be drawn across the palm and opposed to the other fingers.

This movement alone, although important, is insufficient for the mechanism to work effectively. The opposing skin surfaces must have tactile sensation—and this explains why median nerve palsy is so much more disabling than ulnar nerve palsy.

If the hand requires immobilization for the treatment of disease of any part of the upper limb, it should be immobilized (if possible) in the position of function. This means that if loss of movement occurs at the wrist joint, or at the joints of the hand or fingers, the patient will at least have a hand that is in a position of mechanical advantage, and one that can serve a useful purpose.

Physicians should also remember that when a finger (excluding the thumb) is normally flexed into the palm, it points to the tubercle of the scaphoid; individual fingers requiring immobilization in flexion, on a splint or within a cast, should therefore always be placed in this position.

Always refer to the patient’s fingers by name: thumb, index, middle, ring, and little finger. Numbering the fingers is confusing (is the thumb a finger?) and has led to such disastrous results as amputating the wrong finger.

Wrist Joint (Radiocarpal Joint)-Movements-Important Relations-Wrist Joint Injuries-Falls on the Outstretched Hand-

Wrist Joint (Radiocarpal Joint)

■■ Articulation: Between the distal end of the radius and the articular disc above and the scaphoid, lunate, and triquetral bones below. The proximal articular surface forms an ellipsoid concave surface, which is adapted to the distal ellipsoid convex surface.

■■ Type: Synovial ellipsoid joint

■■ Capsule: The capsule encloses the joint and is attached above to the distal ends of the radius and ulna and below to the proximal row of carpal bones.

■■ Ligaments: Anterior and posterior ligaments strengthen the capsule. The medial ligament is attached to the styloid process of the ulna and to the triquetral bone. The lateral ligament is attached to the styloid process of the radius and to the scaphoid bone.

■■ Synovial membrane: This lines the capsule and is attached to the margins of the articular surfaces. The joint cavity does not communicate with that of the distal radioulnar joint or with the joint cavities of the intercarpal joints.

■■ Nerve supply: Anterior interosseous nerve and the deep branch of the radial nerve

Movements

The following movements are possible: flexion, extension, abduction, adduction, and circumduction. Rotation is not possible because the articular surfaces are ellipsoid shaped.

The lack of rotation is compensated for by the movements of pronation and supination of the forearm.

Flexion is performed by the flexor carpi radialis, the flexor carpi ulnaris, and the palmaris longus. These muscles are assisted by the flexor digitorum superficialis, the flexor digitorum profundus, and the flexor pollicis longus.

Extension is performed by the extensor carpi radialis longus, the extensor carpi radialis brevis, and the extensor carpi ulnaris. These muscles are assisted by the extensor digitorum, the extensor indicis, the extensor digiti minimi, and the extensor pollicis longus.

Abduction is performed by the flexor carpi radialis and the extensor carpi radialis longus and brevis. These muscles are assisted by the abductor pollicis longus and extensor pollicis longus and brevis.

Adduction is performed by the flexor and extensor carpi ulnaris.

Important Relations

■■ Anteriorly: The tendons of the flexor digitorum profundus and superficialis, the flexor pollicis longus, the flexor carpi radialis, the flexor carpi ulnaris, and the median and ulnar nerves

■■ Posteriorly: The tendons of the extensor carpi ulnaris, the extensor digiti minimi, the extensor digitorum, the extensor indicis, the extensor carpi radialis longus and brevis, the extensor pollicis longus and brevis, and the abductor pollicis longus

■■ Medially: The posterior cutaneous branch of the ulnar nerve

■■ Laterally: The radial artery

Wrist Joint Injuries

The wrist joint is essentially a synovial joint between the distal end of the radius and the proximal row of carpal bones. The head of the ulna is separated from the carpal bones by the strong triangular fibrocartilaginous ligament, which separates the wrist joint from the distal radioulnar joint. The joint is stabilized by the strong medial and lateral ligaments.

Because the styloid process of the radius is longer than that of the ulna, abduction of the wrist joint is less extensive than adduction. In flexion–extension movements, the hand can be flexed about 80° but extended to only about 45°. The range of flexion is increased by movement at the midcarpal joint.

A fall on the outstretched hand can strain the anterior ligament of the wrist joint, producing synovial effusion, joint pain, and limitation of movement. These symptoms and signs must not be confused with those produced by a fractured scaphoid or dislocation of the lunate bone, which are similar.

Falls on the Outstretched Hand

In falls on the outstretched hand, forces are transmitted from the scaphoid to the distal end of the radius, from the radius across the interosseous membrane to the ulna, and from the ulna to the humerus; thence, through the glenoid fossa of the scapula to the coracoclavicular ligament and the clavicle; and finally, to the sternum. If the forces are excessive, different parts of the upper limb give way under the strain. The area affected seems to be related to age. In a young child, for example, there may be a posterior displacement of the distal radial epiphysis; in the teenager the clavicle might fracture; in the young adult the scaphoid is commonly fractured; and in the elderly the distal end of the radius is fractured about 1 in. (2.5 cm) proximal to the wrist joint (Colles’ fracture).