Webbed fingers, medically termed Syndactyly, is a congenital difference where two or more adjacent digits are fused together. This condition is one of the most common congenital hand malformations, occurring in approximately one in every 2,000 to 3,000 live births. It can range in severity from a thin webbing of skin to a complete fusion of bone, and it may affect fingers, toes, or both. This physical difference originates during the earliest stages of fetal development and requires surgical intervention for correction.
The Developmental Process That Fails
The formation of distinct fingers and toes occurs during the sixth to eighth week of gestation. Initially, the developing hand is shaped like a paddle, with the future digits connected by a layer of tissue. The separation of these digits is achieved through a precise biological process known as apoptosis, or programmed cell death.
Apoptosis is the body’s mechanism for eliminating unnecessary cells, dissolving the interdigital tissue to form individual fingers. Syndactyly occurs when this process fails to fully or partially execute within the developing limb bud. The tissue between the digits is not resorbed, leaving the fingers conjoined at birth.
Genetic and Syndromic Origins
Syndactyly is caused by genetic factors, which can be inherited or occur spontaneously. In many cases, it is an isolated finding, known as non-syndromic or familial Syndactyly, and often follows an autosomal dominant inheritance pattern. This means only one copy of the altered gene from one parent is needed for the condition to be passed on, though severity can vary widely.
Between 10 and 40 percent of isolated Syndactyly cases have a family history, suggesting a strong genetic component. The condition is also frequently a feature of broader, more complex genetic disorders, known as syndromic Syndactyly.
For instance, Apert syndrome is characterized by craniosynostosis (premature fusion of skull bones) and severe, complex Syndactyly of the hands and feet. Another associated condition is Poland syndrome, which involves underdevelopment or absence of the chest muscle on one side, often accompanied by Syndactyly on the hand. Syndactyly is a feature in over 28 different syndromes, highlighting that the underlying issue is often a disruption in the signaling pathways that control early limb development.
Different Types of Webbing
Syndactyly is classified based on the type of tissue involved and the extent of the fusion. The two primary classifications are Simple versus Complex, and Complete versus Incomplete. Simple Syndactyly involves only the fusion of soft tissues, such as skin and fibrous tissue, between the adjacent digits.
Complex Syndactyly is present when there is a fusion of the underlying bone, cartilage, or nails of the conjoined fingers. Complete Syndactyly is where the webbing extends all the way from the base of the fingers to the fingertips, including the nail folds. Incomplete Syndactyly describes a fusion that only extends part of the way up the digits. The most common presentation is a simple, incomplete fusion between the long and ring fingers.
Identifying and Correcting Syndactyly
Syndactyly is most commonly identified immediately after birth during a physical examination, though it can sometimes be detected prenatally with ultrasound. Post-natal diagnosis requires a physical assessment and imaging, such as X-rays, to accurately classify the condition. X-rays determine if the fusion involves only soft tissue or underlying bony fusion, which affects the surgical plan. Identifying any associated anomalies or features of a genetic syndrome also influences the overall treatment approach.
Surgical separation is the standard treatment for Syndactyly, aimed at optimizing hand function and preventing deformity. The timing of surgery is carefully considered, with simple Syndactyly often corrected between 12 and 18 months of age. Complex cases, especially those involving digits of unequal length like the ring and small fingers, are often addressed earlier, sometimes as early as six months, to prevent the longer digit from bending the shorter one.
The surgical technique involves meticulous separation of the conjoined digits while preserving the delicate neurovascular bundles. Surgeons use a zigzag incision pattern along the length of the web to divide the digits, preventing the formation of a straight scar line that could contract and restrict future growth. Because separating the digits creates a larger surface area, the resulting open areas require coverage with full-thickness skin grafts. These grafts are usually taken from the groin or wrist area and are necessary to ensure a tension-free closure and a functional result.