The growth and development of the limbs are controlled by specific genes. At the tip of each limb bud is a collection of ectodermal cells called the apical ectodermal ridge (AER) that regulates limb growth in the proximodistal axis. The zone of polarizing activity (ZPA) is located at the posterior margin of the limb bud and controls the anteroposterior pattern of limb development through sonic hedgehog genes.

By the 48th day, the shape of the hand is well defined, and the skeleton is cartilaginous except for the distal phalanges, which have not yet chondrified. No further differentiation occurs after about the 50th day, and by 12 weeks the ossification centers are present in all the long bones. Later changes are essentially related only to increase in size and to the relative position and proportion of the parts.

Most limb malformations develop during the embryonic phase (approximately the 3rd to 7th weeks). During this period, teratogenic factors inhibit the rate of orderly differentiation of the part that is changing most rapidly and whose cellular components are highly sensitive at that moment. The type of deformity is determined by the stage in limb development at which the insult occurs and the location of the destructive process. The severity of the deformity reflects the degree of destruction within the limb mesenchyme.

The exact cause of limb malformations or deficiencies is rarely known. There are a few malformations associated with known genetic diseases; however, most abnormalities arise spontaneously without any identifiable genetic, environmental, or traumatic causes. The incidence of recurrence of a particular limb malformation in subsequent children is only slightly higher than that of the general population. Furthermore, although many medications and drugs are known teratogens, thalidomide is the only medication that has been widely linked to limb abnormalities.

CLASSIFICATION OF CONGENITAL LIMB DEFECTS

In the past, Greek and Latin names were used to describe common limb deficits, resulting in much semantic confusion. Despite their confusing nature, some of these terms are still commonly used to describe specific deformities. A workable classification to identify, categorize, and readily retrieve the specific diagnosis of congenital malformations had long been needed, and, in 1961, Frantz and O’Rahilly published the first attempt at such a practical classification. The method of grouping cases according to the parts that have been primarily affected by certain embryologic failures was first proposed by Swanson in 1964. Committees of the American Society for Surgery of the Hand and the International Federation of Societies for Surgery of the Hand further developed this classification, which was published in 1968 by Swanson, Barsky, and Entin. This classification, used in this discussion, has been accepted by both societies, as well as by the International Society of Prosthetics and Orthotics.