Syndactyly
Failure of Digital Separation
Syndactyly Classification
Critical Must-Knows
- Simple: Skin only connection between digits.
- Complex: Bone, joint, or nail involvement.
- Complete: Web extends to fingertip.
- Incomplete: Partial webbing (proximal only).
- Border Digits (thumb-index, ring-small): Operate earlier (6-12 months) due to length inequality causing angular deformity.
Examiner's Pearls
- "3rd web space most commonly affected
- "Border digits need EARLIER surgery (6-12mo)
- "NEVER release both sides of digit at once
- "Full-thickness skin graft (usually groin)
- "Web creep is most common complication
Clinical Imaging
Imaging Gallery
Border Digit Syndactyly - Earlier Surgery
Border digit syndactyly (thumb-index, ring-small) requires EARLIER surgery at 6-12 months.
- Reason: Length inequality between adjacent digits
- The shorter digit tethers and angulates toward the longer one
- Delayed surgery causes permanent angular deformity
- First web space (thumb-index) is functionally critical
Simple Syndactyly
Skin Only Connection
- Soft tissue bridge
- No bony involvement
- Separate nail folds
- Straightforward surgery
Complex Syndactyly
Bone/Joint Involvement
- Shared bony elements
- Abnormal joints
- May share nails
- Osteotomy required
Complicated
Complex + Accessory
- Complex features PLUS
- Accessory phalanges
- Multiple deformities
- Syndromic association
Simple vs Complex Syndactyly
| Feature | Simple | Complex |
|---|---|---|
| Skin/soft tissue only | Bone, joint, nail involved | |
| Normal bony anatomy | Shared/abnormal bones | |
| Straightforward separation | Osteotomy, nail reconstruction | |
| Excellent function | Good but may need revision |
BORDER Digit Early Surgery
Memory Hook:BORDER digits need early surgery (6-12mo) to prevent angular deformity from length inequality
Overview and Epidemiology
Syndactyly is failure of digital separation during embryological development, representing the most common congenital hand anomaly.
Epidemiology
- Incidence: 1 in 2,000 live births
- Most Common Location: 3rd web space (long-ring fingers)
- Bilaterality: 50% are bilateral
- Male:Female: 2:1 male predominance
- Inheritance: Can be sporadic or autosomal dominant
Embryology
- Digital rays form at 4-5 weeks gestation
- Interdigital separation (apoptosis) occurs at 7-8 weeks
- Syndactyly results from failure of programmed cell death
- Sonic Hedgehog and WNT signalling pathways involved
Associated Syndromes
Syndromes with Syndactyly
| Syndrome | Syndactyly Pattern | Other Key Features |
|---|---|---|
| Complex, complete - 'mitten hand' | Craniosynostosis, midface hypoplasia | |
| Simple, often symbrachydactyly | Absent pec major, chest wall anomaly | |
| Variable syndactyly | Craniosynostosis, polydactyly | |
| Hands and feet | Craniosynostosis, broad thumbs/toes |
Pathophysiology
Embryological Development
Digital separation occurs through programmed cell death (apoptosis) of interdigital tissue between weeks 6-8 of gestation. Syndactyly results from failure of this normal apoptotic process.
Normal Digital Development:
- Week 4-5: Limb buds appear as paddle-shaped structures
- Week 6: Digital rays become visible within hand plate
- Week 6-8: Interdigital mesenchyme undergoes apoptosis
- Week 8: Digits fully separated with distinct web spaces
Molecular Mechanisms:
- Sonic Hedgehog (SHH) signaling: Regulates anterior-posterior patterning
- WNT signaling pathway: Controls apoptosis of interdigital tissue
- Bone Morphogenetic Proteins (BMPs): Trigger interdigital cell death
- FGFR mutations: Associated with syndromic syndactyly (Apert)
Pathophysiology by Type
Simple Syndactyly:
- Failure of soft tissue apoptosis only
- Skin and subcutaneous tissue remain connected
- Normal skeletal development
- Often familial with autosomal dominant inheritance
Complex Syndactyly:
- Abnormal skeletal patterning in addition to soft tissue
- May involve delta phalanges, shared joints
- Associated with FGFR2 mutations in syndromic cases
- More severe embryological disruption
Genetic Factors:
- Isolated syndactyly: Often autosomal dominant with variable penetrance
- Syndromic syndactyly: FGFR2 (Apert), TWIST1 (Saethre-Chotzen)
- Environmental factors rarely implicated
Third Web Space Predilection
The 3rd web space (long-ring) is most commonly affected because these digital rays separate latest in embryological development (week 7-8), providing longer window for developmental disruption.
SCCC Classification
Memory Hook:SCCC: Simple/Complex describes tissue involvement, Complete/Incomplete describes extent
Classification
By Tissue Involvement
Simple Syndactyly
- Only soft tissue (skin, subcutaneous) connection
- No bony involvement
- Separate nail folds
- X-ray shows normal skeletal anatomy
- Most common type (70-80%)
Complex Syndactyly
- Bony connection between digits
- Shared joints or abnormal skeletal elements
- May have shared or abnormal nails
- X-ray shows bone fusion, delta phalanges
- Requires osteotomy during surgery
Complicated Syndactyly
- Complex features PLUS accessory phalanges
- Multiple abnormalities
- Often associated with syndromes
- Most challenging surgical reconstruction
3rd Web Space Most Common
The 3rd web space (between long and ring fingers) is most commonly affected in syndactyly. This relates to embryological timing - the 3rd and 4th digital rays separate last. The 1st web space (thumb-index) is least commonly affected as it separates earliest.
Clinical Assessment
History
- Family history: Autosomal dominant inheritance in some forms
- Pregnancy history: Teratogen exposure, maternal diabetes
- Syndromic features: Head shape, chest wall, other anomalies
- Functional concerns: Grip, fine motor development
Physical Examination
Inspect the Web
- Extent: Complete vs incomplete
- Which web spaces affected
- Skin quality/scars
- Associated anomalies
Assess the Digits
- Length discrepancy
- Angular deformity
- Rotation
- Nail appearance (shared?)
Function
- Active movement
- Independent flexion/extension
- Grip patterns
- Opposition (if thumb involved)
Key Examination Points
- Complete vs Incomplete: Does web reach fingertip?
- Simple vs Complex: Palpate for bony connection
- Nail Assessment: Shared nail suggests complex type
- Border Digit Involvement: Assess for angular deformity
- Other Hand Anomalies: Polydactyly, camptodactyly
- Syndromic Features: Head, chest, feet
Investigations
Imaging
- X-ray: Essential for surgical planning
- Assess bony anatomy
- Identify shared/fused bones
- Evaluate joint anatomy
- Detect accessory phalanges
When to Consider Further Investigation
- Genetic Testing: If syndromic features (Apert, Poland)
- Cardiac Echo: Associated cardiac anomalies in syndromes
- CT/MRI: Rarely needed, complex cases only
X-ray Findings by Type
| Type | X-ray Appearance |
|---|---|
| Simple | Normal bony anatomy |
| Complex | Shared phalanges, delta phalanx |
| Complicated | Accessory bones, abnormal joints |
Never Release Both Sides of Same Digit
CRITICAL: When releasing syndactyly in multiple adjacent web spaces, NEVER release both sides of a digit at the same time. This compromises blood supply and can cause digital necrosis. Stage surgery 3-6 months apart.
GRAFT for Web Reconstruction
Memory Hook:GRAFT: Groin donor, Rectangular dorsal flap, Acute zigzag angles, Full-thickness graft, Tension-free closure
Management
Surgical Timing
Border Digits (Thumb-Index, Ring-Small)
- 6-12 months - Earlier surgery
- Reason: Length inequality causes angular deformity
- Shorter digit tethered by longer, bends toward it
- Early release prevents permanent deformity
- First web space critical for thumb function
Central Digits (Index-Long, Long-Ring)
- 12-18 months - Standard timing
- Digits similar length, less deformity risk
- Larger digits easier to operate
- Before fine motor development critical period
Multiple Web Spaces
- Stage surgery - 3-6 months apart
- Never release both sides of same digit at once
- Vascular compromise risk if both sides released
Complex/Syndromic
- May require earlier intervention
- Often staged multiple procedures
- Coordinate with craniofacial team (Apert)
Apert Syndrome - Special Considerations
Apert syndrome has complex, complete syndactyly often described as "mitten hand" or "spade hand". Surgery is challenging due to shared bony structures and multiple digits involved. Requires staged procedures, often 4-5 operations. Coordinate with craniofacial team for concurrent craniosynostosis management.
CREEP - Web Creep Prevention
Memory Hook:CREEP prevention: Correct flap, Rectangular commissure, Enough graft, Easy tension, Protect with spacer
Complications
Early Complications
- Vascular compromise: From releasing both sides of digit
- Flap necrosis: Tension, poor design
- Graft failure: Infection, haematoma, poor bed
- Infection: Standard surgical risk
Late Complications
Web Creep
Most Common (10-20%)
- Distal migration of commissure
- Develops over months-years
- Due to inadequate flap/graft
- May need revision surgery
Scar Contracture
- Linear scars contract
- Zigzag design prevents this
- May need Z-plasty revision
- Hand therapy important
Angular Deformity
- From delayed surgery in border digits
- May need corrective osteotomy
- Prevention: early surgery
Revision Surgery Indications
- Significant web creep
- Scar contracture limiting function
- Angular deformity
- Nail deformity
- Growth-related changes
Evidence Base
- Classic text on congenital hand surgery
- Syndactyly classification system
- Surgical principles and techniques
- Foundation for modern approach
- Web creep incidence 10-20%
- More common with full-thickness webs
- Adequate flap design reduces risk
- May present years after surgery
- Long-term outcomes of syndactyly release
- Good functional outcomes in most
- Complex type has higher revision rate
- Border digit early surgery prevents deformity
- Comprehensive review of syndactyly management
- Timing recommendations validated
- Flap design principles
- Complication prevention strategies
- Graftless syndactyly release techniques
- May be possible for incomplete simple
- Standard approach still needs FTSG
- Complete syndactyly requires graft
Viva Scenarios
Practice these scenarios to excel in your viva examination
Border Digit Syndactyly
"6-month-old infant presents with complete simple syndactyly between thumb and index finger. What is your management?"
Diagnosis: Complete simple syndactyly of the first web space (thumb-index) - border digit syndactyly.
Critical Point: This is border digit syndactyly requiring earlier surgery at 6-12 months (not the standard 12-18 months).
Reason for Early Surgery:
- Length inequality between thumb and index finger
- Shorter digit (thumb) tethered by longer (index)
- Delayed surgery causes angular deformity toward index
- First web space critical for thumb opposition and grip
Surgical Technique:
- Zigzag interdigitating incisions (prevents linear scar)
- Dorsal rectangular flap for first web commissure
- Careful dissection preserving digital NV bundles
- Full-thickness skin graft (groin donor) for coverage
- Wide first web space essential for function
Postoperative: Bulky dressing, splint 3-4 weeks, hand therapy, monitor for web creep.
Multiple Web Syndactyly
"10-month-old with complete simple syndactyly involving 2nd, 3rd, and 4th web spaces bilaterally. Parents want all corrected. How do you approach this?"
Diagnosis: Multiple web space syndactyly - complete simple involving 2nd, 3rd, 4th webs bilaterally.
Critical Safety Rule: NEVER release both sides of the same digit at once - this compromises blood supply and risks digital necrosis.
Staged Surgical Plan:
- Stage 1 (12 months): Release 2nd and 4th web spaces on one hand
- Stage 2 (15-18 months): Release 3rd web space same hand + start other hand
- Stage 3-4: Complete remaining webs on other hand
Rationale:
- Long finger has 2 adjacent webs - cannot release both at once
- 2nd and 4th webs can be done together (different digits)
- 3-6 months between stages for healing
Counselling:
- Multiple surgeries required (4+ stages)
- Process takes 1-2 years to complete
- Each surgery requires FTSG
- Risk of web creep, may need revision
Complex Syndactyly - Apert
"Infant with Apert syndrome presents with complex complete syndactyly of all digits ('mitten hand'). Parents ask about treatment options and prognosis. How do you counsel them?"
Diagnosis: Apert syndrome with complex complete syndactyly - "mitten hand" or "spade hand" deformity.
Apert Syndrome Overview:
- Autosomal dominant (usually new mutation)
- FGFR2 gene mutation
- Craniosynostosis (skull), midface hypoplasia
- Symmetric complex syndactyly hands and feet
Hand Features:
- All digits fused - complex complete syndactyly
- Shared bones (delta phalanges)
- Often thumb-index web involvement
- "Mitten" appearance - digits in single mass
Treatment Plan:
- Multiple staged surgeries - typically 4-5 procedures
- First priority: First web space (thumb-index) for function
- Timing: Start 6-12 months for border digits
- Coordination: With craniofacial team for skull/face surgery
Prognosis Counselling:
- Functional improvement expected but hands never normal
- Multiple surgeries over years
- Cognitive development usually normal
- Life expectancy normal
- Support groups and genetic counselling available
Australian Context
Syndactyly occurs at similar incidence in Australia (1:2000 births) as internationally. Early referral to paediatric hand surgery units at tertiary children's hospitals is recommended, with most cases managed at major centres in capital cities. For syndromic cases such as Apert syndrome, multidisciplinary management through craniofacial teams is essential.
Geographic access to specialist services can be challenging for remote and Indigenous communities, with telehealth consultations increasingly utilized for initial assessment and follow-up. However, surgical management still requires travel to tertiary centres. Families should be counselled on optimal surgical timing to prevent delayed presentation from affecting outcomes, particularly for border digit syndactyly where early intervention (6-12 months) is critical to prevent angular deformity.
Surgical management follows international best practice with zigzag incisions and full-thickness skin grafting. Groin crease remains the preferred donor site for skin grafts due to good colour match and concealed scar. Staged procedures for multiple web spaces are typically performed through the public health system with appropriate spacing (3-6 months) between surgeries. Some centres are exploring synthetic alternatives (such as Integra) for complex cases, though traditional FTSG remains the gold standard.
SYNDACTYLY
High-Yield Exam Summary
CLASSIFICATION
- •Simple: Skin only connection
- •Complex: Bone/joint/nail involved
- •Complete: Web to fingertip
- •Incomplete: Partial proximal web
- •3rd web space most common
TIMING
- •BORDER (thumb-index, ring-small): 6-12 months
- •CENTRAL (index-long, long-ring): 12-18 months
- •NEVER release both sides of digit at once
- •Stage multiple webs 3-6 months apart
SURGICAL TECHNIQUE
- •Zigzag interdigitating incisions
- •Dorsal rectangular flap for commissure
- •Full-thickness skin graft (groin)
- •Complex: osteotomy + nail reconstruction
COMPLICATIONS
- •WEB CREEP: Most common (10-20%)
- •Scar contracture
- •Vascular compromise (both sides released)
- •Angular deformity (delayed border surgery)
- •Nail deformity (complex type)
ASSOCIATED SYNDROMES
- •APERT: Mitten hand + craniosynostosis
- •POLAND: Symbrachydactyly + absent pec major
- •CARPENTER: Craniosynostosis + polydactyly
- •PFEIFFER: Broad thumbs/toes + craniosynostosis