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.
No comments:
Post a Comment