Syndactyly is the fusion of soft tissue and bone of the finger. This article details the aetiology, diagnosis, and treatment of syndactyly.
A failure of differentiation fuses soft tissue ± bone of the finger
This can be classified as incomplete or complex, simple or complex.
A clinical diagnosis. Bony involvement is confirmed on the X-Ray.
Before the age of 2. Earlier if length discrepancy or border digits.
Definition of Syndactyly
Syndactyly is a failure of differentiation that results in the fusion of interdigital soft tissue and bones. It is classified as simple or complex, complete or incomplete.
Classification of Syndactyly
Syndactyly is classified as complete or incomplete, simple or complex. This is related to the extent of fusion and structures involved.
Syndactyly is classified by the extent of the fusion (entire finger or partial) and the structures (bone or soft tissue) involved.
- Simple: no synostosis (soft tissue only)
- Incomplete: fusion does not involve distal phalanx or overlying soft tissue.
- Complete: fusion involves the distal phalanx and/or overlying soft tissue.
- Complex: soft tissue with adjacent phalangeal fusion or accessory bones/
- Complicated: accessory digits or phalanges, additional cleft hand
- Acrosyndactyly: shortened digits fused distally with proximal fenestration.
This classification is illustrated in the diagram below.
Diagnosis of Syndactyly
Syndactyly is a clinical diagnosis that can occur in isolation or with an association syndrome. A plain X-ray will confirm synostosis.
Syndactyly is a clinical diagnosis. It most commonly occurs in the middle-ring fingers and can be associated with other structural abnormalities.
It typically occurs in caucasian males with family history and can be bilateral in ~50% of cases.
The important pathological features of syndactyly include:
- Bone: degrees of synostosis, joints usually preserved unless symphalangism.
- Ligaments: Cleland's and Grayson's ligaments thickened and coalesced.
- Tendons: duplicated or shared flexor and extensor tendons, sheaths
- Neurovascular: duplicate or shared vessels and nerves
- Skin: short of skin
Syndactyly can be associated with other structural and craniofacial conditions. This includes:
- Poland Syndrome: chest wall abnormalities and symbrachydactyly
- Apert Syndrome: craniosynostosis and complex syndactyly
- Carpenter syndrome
- Constriction ring syndrome (distal digital fusion, proximal digit fenestrations)
- Familial syndactyly is associated with syndactyly of the second and third toes
Management of Syndactyly
Syndactyly is generally treated in the first 24 months. This is influenced by the finger(s), webspace, and length discrepancies
Patient care should be individualised. In the immediate setting, patient education and family counselling are essential. This should all be managed by a multi-disciplinary team.
Timing of surgery
Syndactyly release should be performed by school-age and ideally before age 2. The exact timing is influenced by the type of finger and webspace involvement.
- Earlier surgery if border digits are involved or a length discrepancy (<6 months)
- Later surgery if "similar" digits are involved (e.g. ring-long, long-index) as a larger hand enables a technically more straightforward operation with more predictable results
Principles of Surgery Techniques
Surgery aims to separate digits, create minimal scarring and respect the web space. This is performed through a combination of flaps and grafts adhering to the following principles:
- Age: do all releases before school age
- Length: release digits with length discrepancy first.
- Location: release border digits first (ring-little, thumb-index).
- Multiple digits: staged release to avoid vascular issues.
- Bilateral: simultaneously if < 18 months (less active) or staged if older.
- Incisions: dorsal and volar interdigitating zigzag 60° flaps to the midline whilst preserving the paratenon
- Flaps: dorsal and volar random-pattern proximal flaps for webspace.
- Graft: FTSG from wrist crease for colour, consistency, no hair, less contracture.
- Nailfold: "stilleto flap" is a hyponychial interdigitating flap described by Buck-Gramcko or Hentz's "pulp plasty" with a composite graft.
- Sutures: use absorbable sutures
- Defatting: reduce tension and graft requirements, increase vascular injury
For the commissure flap,
- Dorsal: begins at the level of the metacarpal heads and ends two-thirds of the length of the proximal phalanx.
- Volar: a rectangular flap is fashioned to resurface the proximal area of a digit adjacent to the commissure. The proximal transverse incision represents the level of commissure reconstruction, and the distal transverse edge equals the length of the dorsal commissure flap.
- Subsequently, interdigitating zigzag dorsal and palmar flaps are constructed distal to the dorsal commissure and palmar rectangular flap (Fig 7). The dorsal zigzag incision begins at one distal corner of the commissure flap, whereas the palmar starts at the opposite corner of the rectangular flap.
The web space can be a challenging anatomical area in syndactyly. Here are some general principles:
- Reconstruct with dorsal fasciocutaneous flaps
- Location defined by the level of the bifurcating neurovascular bundles
- It can be deepened with multiple z-plasty
- If all the web spaces are involved, the release of the first and third web spaces first
In the thumb-index webspace:
- Mild: four-flap Z-plasty to access to adductor & first dorsal interosseous muscles (may require a partial release for adequate web-space breadth)
- Complete: modified dorsal rotation advancement flap by Abdel Ghani
Complications of syndactyly release can be intra-operative or post-operative and relate to the surgery or the anaesthetic.
- Peri-operative: nerve, tendon, artery or vein injury; haematoma
- Wound: infection, dehiscence
- Scarring: hypertrophy, contracture, web creep (commissure pulled distally)
- Bone: joint instability due to insufficient collateral ligaments
- Nail: nail deformities
Venous complications are more common and often related to too tight a closure.