Webbed fingers.

W ebbing of the digits, or syndactyly, is not caused by the fingers sticking together in the womb; rather, it is caused by failure, during the sixth to eighth weeks of intrauterine life, of the usual longitudinal interdigital necrosis that normally separates the fingers. This " webbing " is the most common abnormality of the newborn hand. It happens either as an isolated anomaly or as part of a syndrome. When it occurs alone it is always inherited as an autosomal-dominant disorder. Five types of syndactyly are generally recognized: • Type 1: Zygodactyly. This is the most common form of syn-dactyly, occurring between the long and ring fingers. • Type 2: Synpolydactyly. This also involves the long and ring fingers but includes a duplication of the ring finger between the fingers. • Type 3: Ring-small syndactyly. This is usually bilateral, and occasionally the distal phalanges are fused. There may be only a rudimentary middle phalanx in the small finger. • Type 4: Haas-type syndactyly. In this rare type, described by Haas in the American Journal of Surgery in 1940, there is a complete syndactyly of all digits. Occasionally a sixth metacarpal and phalanges may be included in the cup-shaped hand. • Type 5. In this rare type, both the long and ring fingers and second and third toes are syndactylized. The fourth and fifth metacarpals and metatarsals may be fused. Genetic counseling may be difficult, since the dominant genes show reduced penetrance and variable expressivities. Each future child carries a 50% chance of having the anomaly, but occurrence is rarely consistent from one generation to the next. A child's hand may well be different than a parent's hand, or neither parent may have a syndactyly. It does appear that paternal genes have a stronger influence than their maternal counterparts (Figure 1). Syndactyly also occurs as part of many syndromes. In one group it predominates and is basic to identification of the syndrome ; in a second, larger group it is a feature, but other medical problems are more characteristic of the syndrome. These problems are discussed in the second half of this paper. INCIDENCE In my personal series of over 3000 patients with congenital hand anomalies are more than 500 cases of true or isolated syndactyly. Nearly 40% of these patients were known to have a family history of the disorder. Syndactyly is thought to occur about once in every …