Syndactyly

1. Syndactyly is, with polydactyly, one of the two most common congenital hand differences; it is more common in males and is bilateral in about half of affected children.

True

Syndactyly and polydactyly are the two most frequent congenital differences of the hand, with population estimates of roughly 2–10 per 10,000 live births, the textbook figure being about 1 in 2,000–3,000. Males are affected about twice as often as females, half of cases are bilateral, and syndactyly may be isolated or part of more than 300 syndromes. In isolated cases the third web (middle–ring) is involved most often, followed by the fourth; the first web is the least common and is usually syndromic.

• Dao KD, Shin AY, Billings A, Oberg KC, Wood VE. Surgical treatment of congenital syndactyly of the hand. J Am Acad Orthop Surg. 2004;12(1):39-48. PMID 14753796
• Tonkin MA. Failure of differentiation part I: Syndactyly. Hand Clin. 2009;25(2):171-93. PMID 19380059

2. Complex syndactyly is defined as fusion that extends to the fingertip and involves the nail folds.

False

Two independent axes describe a syndactyly. Simple versus complex refers to the tissue joined: simple when only skin and soft tissue are involved, complex when there is a bony or cartilaginous connection, most often between the distal phalanges. Complete versus incomplete refers to extent: complete when the fusion includes the nail folds, incomplete when the web is merely distal to its normal position. Complicated syndactyly denotes additional tissue abnormalities such as interposed abnormal bones or a syndromic hand, so 'simple complete' and 'complex incomplete' both exist.

• Tonkin MA. Failure of differentiation part I: Syndactyly. Hand Clin. 2009;25(2):171-93. PMID 19380059

3. Border webs (thumb–index and ring–little) are released earlier than central webs, which are usually released at around 12–18 months, because the unequal lengths of the joined digits risk angular deformity with growth.

True

Digits of markedly different length tether each other as they grow, so the thumb–index and ring–little webs, and complex unions, are released early, often before six months, to prevent flexion and rotational deformity of the longer digit. Simple central webs can wait until 12–18 months, when the structures are larger and the higher scar-contracture rate of very early surgery is avoided. In syndromic hands such as Apert syndrome release begins by about six months and is completed by around three years, the first web taking priority.

• Dao KD, Shin AY, Billings A, Oberg KC, Wood VE. Surgical treatment of congenital syndactyly of the hand. J Am Acad Orthop Surg. 2004;12(1):39-48. PMID 14753796
• Swarup I, Zhang Y, Do H, Daluiski A. Epidemiology of syndactyly in New York State. World J Orthop. 2019;10(11):387-393. PMID 31840019

4. In syndactyly the common digital artery frequently bifurcates more distally than normal, which limits how far proximally the new commissure can be set, and each separated digit must retain at least one proper digital artery.

True

Angiographic and magnetic resonance studies show a distal bifurcation of the common digital artery in roughly 60–77% of syndactylised hands, together with hypoplastic proper digital arteries in a minority and, occasionally, a single shared neurovascular bundle. The proximal limit of the dissection is the arterial bifurcation, so the surgeon may have to ligate one branch or accept a more distal web, and the digital nerve may need intraneural splitting. Because the central digit of a three- or four-finger syndactyly may depend on anomalous vessels, both sides of one digit are not routinely released at the same sitting; single-stage separation is feasible only when at least one proper digital artery to each finger is verifiably preserved.

• Inoue G. [An angiographic study of congenital hand anomalies (author's transl)]. Nihon Seikeigeka Gakkai Zasshi. 1981;55(2):183-97. PMID 6268720
• Tian X, Xiao J, Li T, Chen W, Lin Q, Chim H. Single-Stage Separation of 3- and 4-Finger Incomplete Simple Syndactyly With Contiguous Gull Wing Flaps: A Technique to Minimize or Avoid Skin Grafting. J Hand Surg Am. 2017;42(4):257-264. PMID 28372639

5. Web creep after syndactyly release is rare, affecting under 1% of webs, and follow-up beyond wound healing is unnecessary.

False

Web creep, the distal migration of the reconstructed commissure with growth, affects roughly 8–20% of webs in contemporary series and is the commonest reason for revision. In a series of 514 webs followed for a mean of six years, 12.8% underwent revision, most often web-space deepening for creep. Revisions occurred a median of 1.7 years after primary reconstruction; first-web involvement, complete syndactyly and complications after the primary operation predicted revision, whereas age at surgery did not. Split-thickness grafts and skin grafting in simple syndactyly are associated with more creep and hypertrophic scarring, and children are reviewed to skeletal maturity because creep appears late.

• Belardo ZE, Graham EM, Pehnke M, Chang B, Mendenhall SD, Mori S, et al.. Revision Surgery Following Primary Reconstruction for Hand Syndactyly. J Hand Surg Am. 2024;49(12):1228-1238. PMID 39365243
• Graham EM, Belardo ZE, Tipps JA, Chang B, Shah AS, Mendenhall SD. Predictors of early and late complications after syndactyly release: a retrospective review of 684 cases. J Hand Surg Eur Vol. 2026;51(9):1158-1165. PMID 41845958