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.