The term “congenital hand abnormality” refers to a malformation of the hand that develops while a fetus is in utero. The American Society for Surgery of the Hand has approved classification of these abnormalities into seven categories. The first, problems in development of the parts, indicates the premature cessation of a body part’s development. This may include underdevelopment of the hand or finger bones on either the thumb or little finger side of the hand.
Other malformations include fusion of the fingers, also known as syndactyly, which is caused by cells (tissue and/or bone) failing to differentiate in utero. Contractures of the hand, which is another instance of a failure of the hand to separate, is a condition that, due to problems with muscle or skin, causes one or more digits to curl into the palm, unable to extend.
Additional common abnormalities include duplication of digits, underdevelopment of one or more fingers, and the abnormally large growth of a digit. Ring constriction, when a band of tissue grows around a digit or arm, may also lead to deformities and can be associated with other structural issues such as clubfoot or cleft palate. The cause of ring constriction remains unknown.