Limbs may form abnormally. For example, bones in the hand and forearm may be missing because of a genetic defect (see Chromosome Abnormalities), or sometimes part or all of a hand or foot may be missing. 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 an infection or 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).
A child who has one birth defect of the limbs is more likely to have another abnormality.
Before birth, doctors are sometimes able to diagnose these defects during an ultrasound.
After birth, doctors typically take x-rays and may do other imaging tests to determine which bones are affected. When defects seem to run in the child's family or if doctors suspect the child has a genetic syndrome, they also examine the child for other physical abnormalities and take a sample of blood to do genetic testing.
Children often become very adept at using a malformed or artificial limb.
An artificial limb (prosthesis) can often be fitted (usually when the child is able to sit independently) to make the malformed limb easier to use or to replace a limb that is missing or mostly missing. Children use a prosthesis most successfully when it is fitted early and becomes an integral part of their body and body image during the developmental years. During infancy, prostheses should be as simple and durable as possible. For example, a baby can be fitted with a hook rather than a bioelectric arm.
Most children who are born with a birth defect of the limbs lead normal lives.