Syndactyly

Syndactyly is the congenital fusion (webbing) of adjacent fingers or toes, occurring when the normal programmed cell death (apoptosis) that separates the digital rays in the embryo fails between weeks 6 and 8 of fetal development. It differs from polydactyly (extra digits); syndactyly involves existing digits failing to separate. Simple syndactyly involves only soft tissue and skin connection; complex syndactyly involves bony fusion of phalanges; and complicated syndactyly involves shared nail plates, neurovascular structures, or absent bones. The most commonly affected web space is between the long (middle) and ring fingers (50%), followed by the ring-little finger web.

Surgical timing depends on which fingers are involved. For border digit syndactyly (thumb-index or ring-little finger), early release before 6 months is recommended — because digits of different lengths grow at different rates, and continued fusion creates deforming rotational forces on the shorter digit. For central digit syndactyly (long-ring), correction between 12 and 18 months is standard. In complete syndactyly involving multiple web spaces, procedures are staged (one web space per operative session, at least 3 months apart) to protect the blood supply — as each finger receives neurovascular input from its lateral aspects, which are surgically opened during separation.

Web space reconstruction requires a zigzag incision pattern (Bauer or similar) on the dorsal and palmar aspects of the fused digits to create interlocking skin flaps — this irregular design breaks the straight-line scar that would otherwise contract and deepen the web space over time. After flap rearrangement, the remaining raw triangular areas (where skin is inherently insufficient — as nature provides less skin between fused digits than is needed to cover two separate ones) are covered with full-thickness skin grafts (FTSG) harvested from the groin crease, inner arm, or volar wrist. Grafts must not be placed on the flexor surface of finger joints, as linear contracture would impede flexion.

Web space creep (proximal migration of the interdigital web over time) is the most common long-term complication of syndactyly release, occurring in 5 to 30% of patients as scar contracture gradually pulls the web margin proximally — narrowing the web and reducing the depth of the reconstructed space. Prevention strategies include: careful dorsal flap design that creates a wide commissure with the correct depth (55% of the proximal phalanx length), use of full-thickness rather than split-thickness grafts in the commissure, long-term post-operative splinting and scar management, and revision surgery in cases of significant functional or aesthetic compromise.

Post-operative care is critical to outcome. Immediately after surgery, the hand is immobilized in a padded cast for 3 to 4 weeks with fingers in a fully extended position to prevent flexion contracture while grafts take. After cast removal, a custom thermoplastic web-spacer splint is worn between the separated digits for 3 to 6 months (initially full-time, then at night). Hand therapy begins with scar massage, silicone gel sheeting, range-of-motion exercises, and play-based sensory re-education. Compliance with splinting is the single most important factor in preventing web creep and achieving lasting functional separation.