Missing or Incompletely Formed Limbs
Limbs can be missing, deformed, or incompletely developed at birth.
A child with one limb abnormality is more likely to have another related abnormality.
Limbs may form abnormally. For example, bones in the hand and forearm may be missing because of a genetic defect (see Chromosome Abnormalities). Normal development of a limb can also become disrupted in the womb. In amniotic band syndrome, limbs develop abnormally when they are constricted by thin strands of tissue from the amniotic sac (the sac that holds the amniotic fluid surrounding the developing fetus in the womb). Abnormalities of the limbs can also be caused by a teratogen, which is a harmful substance that the mother was exposed to while pregnant and that causes birth defects. The drug thalidomide, which was taken by some pregnant women in the late 1950s and early 1960s for morning sickness, caused a variety of limb defects—usually short, deformed, and underdeveloped limbs with limited function. At the time, doctors did not know that thalidomide was a teratogen, so a number of babies were born with missing or incompletely formed limbs. Doctors cannot always determine what causes abnormally formed limbs.
Abnormalities of the arms and legs may occur in a horizontal fashion (for example, if the arm is shorter than normal) or in a lengthwise fashion (for example, the arm is abnormal on the thumb side—from the elbow to the thumb—but normal on the little finger side).
Children with underdeveloped forearm bones may have heart and blood abnormalities.
Children often become very adept at using a malformed limb. An artificial limb (prosthesis) can often be fitted (usually when the child is able to sit independently) to make the limb easier to use.