Polydactyly
Extra Digit Formation
Polydactyly Types
Critical Must-Knows
- Preaxial: Thumb duplication - use Wassel classification (I-VII).
- Postaxial: Small finger - Type A (well-formed) vs Type B (rudimentary).
- Wassel IV: Most common thumb type - duplicated proximal phalanx.
- Bilhaut-Cloquet: Combine two equally hypoplastic thumbs into one (Wassel I/II).
- Retain the more functional digit: Usually the ulnar thumb.
Examiner's Pearls
- "Wassel IV = Most common thumb duplication
- "Postaxial more common in African descent
- "Type B postaxial can ligate in nursery
- "Bilhaut-Cloquet for equal hypoplastic thumbs
- "Reconstruct collateral ligaments - critical
Clinical Imaging
Imaging Gallery
Wassel Classification - KNOW THIS
Wassel classification for thumb duplication (Roman numerals I-VII):
- Based on level of bifurcation from DISTAL to PROXIMAL
- Odd numbers = bifid (shared element)
- Even numbers = duplicated (separate elements)
- Wassel IV (duplicated proximal phalanx) is MOST COMMON
- Wassel VII is triphalangeal thumb component
At a Glance
Polydactyly is congenital duplication of digits, classified as preaxial (thumb/radial), postaxial (small finger/ulnar), or central. Preaxial is more common in Caucasians; postaxial is common in African descent (1:300). For thumb duplication, the Wassel classification (I-VII) is essential: odd numbers indicate bifid elements, even numbers indicate duplicated elements. Wassel IV (duplicated proximal phalanx) is most common. Surgery at 12-18 months: retain the more functional digit (usually ulnar thumb) and reconstruct collateral ligaments. Postaxial Type B (rudimentary) can be ligated in nursery; Type A requires formal excision.
Polydactyly Quick Decision Guide
| Type | Features | Surgery Timing | Key Surgical Point |
|---|---|---|---|
| Duplicated proximal phalanx | 12-18 months | Reconstruct collateral ligaments | |
| Well-formed digit with bone | 12-18 months | Formal surgical excision | |
| Rudimentary/pedunculated | Nursery ligation OR 6-12mo formal | Neuroma risk with ligation | |
| Two equally hypoplastic thumbs | 12-18 months | Bilhaut-Cloquet procedure |
WASSEL Classification Memory
Memory Hook:WASSEL: Wassel IV most common, Articulation level determines type, Shared (odd) vs Separate (even), Excise hypoplastic, reconstruct Ligaments
ODD vs EVEN Wassel Types
Memory Hook:ODD = bIfId (shared element), EVEN = sEparatE (duplicated)
THUMB Selection for Retention
Memory Hook:THUMB: The ulnar thumb is usually retained - Thenar bulk, Heavier, Ulnar, Motion, Better FPL
Overview and Epidemiology
Polydactyly is the congenital duplication of digits, one of the most common congenital hand anomalies.
Epidemiology
- Overall Incidence: 1-2 per 1,000 live births
- Preaxial (Thumb): More common in Caucasians and Asians
- Postaxial (Small Finger): 10x more common in African descent (1:300)
- Central: Rare (1:100,000)
Genetics and Inheritance
- Postaxial: Often autosomal dominant with variable penetrance
- Preaxial: Usually sporadic, can be autosomal dominant
- Associated Syndromes: Holt-Oram, Ellis-van Creveld, trisomy 13
Embryology
- Develops during limb bud formation (4-8 weeks gestation)
- Sonic Hedgehog (SHH) signalling pathway involved
- Zone of Polarising Activity (ZPA) regulates digit formation
- Duplication from abnormal signalling in limb bud
Anatomy and Biomechanics
Thumb Anatomy
- Unique Features: Thumb has 2 phalanges (vs 3 in fingers)
- Triphalangeal Thumb: Wassel VII has 3 phalanges - abnormal
- FPL Insertion: Critical for thumb function - inserts on distal phalanx
- Thenar Muscles: APB, FPB, OP provide thumb opposition
Key Anatomical Considerations in Thumb Duplication
- Metacarpal: May be single (Wassel I-V) or duplicated (Wassel VI)
- Growth Plates: Preserve physis during surgery to maintain growth
- Collateral Ligaments: Essential for joint stability - MUST reconstruct
- Neurovascular Bundle: Each thumb has its own digital nerves/arteries
Biomechanics of the Thumb
- Opposition: Unique to thumb - enables pinch grip
- Stability: UCL and RCL provide MCP joint stability
- Angular Deformity: Occurs if asymmetric ligament support
- Growth: Unequal growth can cause progressive deformity
Postaxial Anatomy
- Small Finger UCL: Critical for power grip
- Hypothenar Muscles: ADM, FDM, ODM provide small finger function
- Type A: Has articulation with 5th metacarpal
- Type B: Minimal bone - mainly skin bridge
Classification Systems
Wassel Classification (I-VII)
Principle: Higher number = more proximal duplication
Wassel Classification - Thumb Duplication
| Type | Level of Bifurcation | Frequency |
|---|---|---|
| Bifid distal phalanx (shared) | Rare (2%) | |
| Duplicated distal phalanx | 15% | |
| Bifid proximal phalanx (shared) | Rare (6%) | |
| Duplicated proximal phalanx | MOST COMMON (43%) | |
| Bifid metacarpal (shared) | Uncommon (10%) | |
| Duplicated metacarpal | Rare (4%) | |
| Triphalangeal thumb component | Rare (20%) |
Remember:
- Odd numbers = Bifid (shared element)
- Even numbers = Duplicated (separate elements)
- Wassel IV is the EXAM answer for most common type
The Wassel classification provides a systematic approach to describing thumb duplication patterns.
Wassel IV - Most Common
Wassel IV represents duplicated proximal phalanx - meaning two complete proximal phalanges articulating with a single metacarpal. This occurs in 43% of thumb duplications. The ulnar thumb is usually more functional (better FPL insertion) and is retained, while the radial thumb (often more hypoplastic) is excised.
Clinical Assessment
History
- Family history: Especially for postaxial (autosomal dominant)
- Pregnancy history: Maternal diabetes, teratogens
- Syndromic features: Cardiac, renal anomalies
- Functional concerns: Parents' goals, cosmetic concerns
Physical Examination
Inspection
- Location: Preaxial, postaxial, central
- Size: Well-formed vs rudimentary
- Skin bridge width (Type B)
- Associated syndactyly
Function
- Active movement of each thumb
- Thenar muscle bulk
- Stability assessment
- Grip pattern
Associated Features
- Cardiac murmur (Holt-Oram)
- Syndactyly (central)
- Other limb anomalies
- Facial dysmorphism
Key Examination Points for Thumb Duplication
- Which thumb is dominant? (usually ulnar)
- FPL insertion: Which thumb has better flexor function?
- Thenar muscles: Which side has better bulk?
- Stability: MCP and IP joint stability
- Size comparison: Often radial thumb is hypoplastic
Investigations
Imaging
- X-ray: Essential for surgical planning
- Level of bifurcation/duplication
- Bony anatomy of each digit
- Joint articulation
- Metacarpal morphology
When to Consider Further Investigation
- Cardiac echo: Holt-Oram syndrome (radial anomalies + ASD/VSD)
- Renal ultrasound: Associated GU anomalies
- Genetic testing: If syndromic features
Associated Syndromes
Syndromes with Polydactyly
| Syndrome | Polydactyly Type | Key Features |
|---|---|---|
| Preaxial | Radial dysplasia, ASD/VSD | |
| Postaxial | Short stature, cardiac defects | |
| Postaxial | Multiple malformations, poor prognosis | |
| Postaxial | Obesity, retinitis pigmentosa, renal |
Management Algorithm
Management Decision Tree
Step 1: Identify Type
- Preaxial (thumb) → Wassel classification
- Postaxial (small finger) → Type A vs Type B
- Central → Complex reconstruction planning
Step 2: Timing Decision
- Preaxial: 12-18 months (optimal)
- Postaxial Type A: 12-18 months
- Postaxial Type B: Nursery ligation vs 6-12 months formal excision
Step 3: Surgical Planning
- Assess which digit to retain (preaxial)
- Plan incision design
- Anticipate need for ligament/tendon reconstruction
- Consider Bilhaut-Cloquet if both thumbs equally hypoplastic
The management approach is individualized based on type and functional considerations.
Surgical Technique
Thumb Duplication Surgery
Surgical Technique:
- Racquet incision around hypoplastic thumb
- Identify and preserve neurovascular bundle to retained thumb
- Detach collateral ligament from hypoplastic thumb
- Detach FPL/EPL if inserting on hypoplastic thumb
- Excise hypoplastic thumb with its metacarpal portion if needed
- Reconstruct collateral ligament to retained thumb
- Transfer/balance tendons
- Correct any angular deformity
Special Cases:
- Bilhaut-Cloquet: Combine two equally hypoplastic thumbs
- Used for Wassel I/II with equal thumbs
- Create one thumb from nail, bone, and soft tissue of both
The key to successful surgery is meticulous soft tissue reconstruction.
Critical Surgical Pearls
Must reconstruct collateral ligaments - failure to do so results in an unstable thumb. Always check joint stability intraoperatively after reconstruction. Consider osteotomy if angular deformity persists after ligament reconstruction.
EXCISE - Surgical Principles
Memory Hook:EXCISE: Evaluate dominance, X-ray, Collateral ligament repair, Intrinsic transfer, Stability check, Epiphysis preservation
Complications
Early Complications
- Wound infection: 1-2% incidence
- Flap necrosis: Avoid excessive tension
- Nerve injury: Digital nerve at risk
- Vascular compromise: Ensure perfusion intraoperatively
Late Complications
Joint Instability
Most Common Complication
- Inadequate ligament reconstruction
- Angular deformity progression
- Requires revision surgery
- Prevention: meticulous technique
Angular Deformity
Progressive Malalignment
- Growth-related
- Asymmetric growth plate injury
- May need corrective osteotomy
- Monitor during growth
Nail Deformity
Cosmetic Issue
- Bilhaut-Cloquet: central ridge
- Small/hypoplastic nail
- May need nail bed reconstruction
- Usually cosmetic only
Revision Surgery Requirements
- 15-20% may need secondary procedures
- Collateral ligament reconstruction most common
- Corrective osteotomy for angular deformity
- Tendon rebalancing
- Web space deepening
Postoperative Care and Rehabilitation
Immediate Postoperative (0-2 weeks)
- Splinting: Thumb spica or volar splint
- Wound care: Keep clean and dry
- Elevation: Reduce swelling
- Pain management: Paracetamol typically sufficient
Early Phase (2-6 weeks)
- Suture removal: 2 weeks postoperatively
- Splint weaning: Gradual reduction
- Gentle ROM: Passive then active
- Monitor for: Infection, stiffness
Late Phase (6 weeks to 6 months)
- Full ROM exercises: Encourage normal use
- Strengthening: Age-appropriate activities
- Monitor growth: Assess for angular deformity
- Occupational therapy: If functional concerns
Long-term Follow-up
- Monitor through growth: Annual assessments until skeletal maturity
- Assess stability: Check ligament integrity
- Functional assessment: Pinch, grip strength
- Consider revision: If progressive deformity or instability
Outcomes and Prognosis
Expected Outcomes
Thumb Duplication:
- Good functional outcomes in most cases
- Some residual instability common
- May have slightly smaller thumb than normal side
- May need secondary procedures (15-20%)
Postaxial Polydactyly:
- Excellent outcomes with proper technique
- Type B ligation: Risk of neuroma, bump
- Type A excision: Low complication rate
Prognostic Factors
Factors Affecting Outcome
| Factor | Good Prognosis | Poor Prognosis |
|---|---|---|
| Simple duplication | Complex with bone involvement | |
| Ligament reconstruction done | Ligaments not reconstructed | |
| 12-18 months | Delayed beyond 24 months | |
| Pediatric hand specialist | General surgeon |
Patient Satisfaction
- High satisfaction rates overall
- Cosmetic concerns more common than functional
- Realistic expectations important
- Secondary procedures may be needed
Evidence Base
- Original classification for thumb duplication
- Types I-VII based on level of bifurcation
- Type IV identified as most common
- Foundation for surgical planning
- Modified Wassel classification proposed
- Better describes soft tissue anatomy
- Guides surgical reconstruction
- Emphasizes collateral ligament reconstruction
- Long-term outcomes of thumb duplication surgery
- Good function in majority
- Secondary surgery in 15-20%
- Instability most common issue
- Bilhaut-Cloquet procedure outcomes
- High rate of IP joint stiffness
- Nail ridge deformity common
- Reserve for specific indications
- Postaxial polydactyly Type B outcomes
- Ligation vs surgical excision compared
- Neuroma and bump more common with ligation
- Many recommend formal excision
Viva Scenarios
Practice these scenarios to excel in your viva examination
Wassel IV Thumb Duplication
"10-month-old child presents with bilateral thumb duplication. X-rays show Wassel IV bilaterally. Parents ask about treatment. What is your management?"
Postaxial Polydactyly - Type Selection
"Newborn of African descent has bilateral pedunculated extra digits on ulnar side of hands. Midwife asks about suture ligation in nursery. What is your advice?"
Bilhaut-Cloquet Indication
"6-month-old with Wassel I thumb duplication - two equally small thumbs with bifid distal phalanx. Neither appears adequate alone. What are your options?"
MCQ Practice Points
Most Common Wassel Type
Q: A 1-year-old child presents with bilateral thumb duplication. What is the most common Wassel classification type?
A: Wassel Type IV (duplicated proximal phalanx) - occurs in 43% of thumb duplications. Remember: even numbers = duplicated (separate elements), odd numbers = bifid (shared elements). Wassel IV has two complete proximal phalanges articulating with a single metacarpal.
Postaxial Polydactyly Epidemiology
Q: What is the incidence of postaxial polydactyly in people of African descent, and what is the inheritance pattern?
A: 1 in 300 in African descent (compared to 1 in 3,000 in Caucasians). Inheritance is typically autosomal dominant with variable penetrance. It is 10 times more common than in other populations.
Surgical Timing for Polydactyly
Q: What is the optimal timing for surgical correction of preaxial (thumb) polydactyly and why?
A: 12-18 months is optimal. This timing allows adequate size for surgical manipulation, is performed before functional hand patterns are established, and occurs before the child's memory of surgery. Operating too early (less than 6 months) makes surgery technically difficult due to small structures.
Critical Surgical Step
Q: What is the most critical step in thumb duplication surgery that, if omitted, leads to the most common complication?
A: Reconstruction of the collateral ligaments. Failure to reconstruct the radial or ulnar collateral ligament from the excised thumb to the retained thumb results in joint instability - the most common complication requiring revision surgery.
Bilhaut-Cloquet Indication
Q: What is the indication for the Bilhaut-Cloquet procedure, and what is the main disadvantage?
A: Indicated for Wassel Type I or II with two equally hypoplastic thumbs where neither is adequate alone. The main disadvantage is IP joint stiffness because the procedure crosses the physis. Also expect a central nail ridge deformity and wide thumb appearance.
Postaxial Type B Controversy
Q: A newborn has a rudimentary pedunculated extra digit (Type B postaxial polydactyly). What are the two management options and their respective risks?
A: (1) Suture ligation in nursery (traditional): Risks include incomplete removal, neuroma formation, and unsightly bump/scar. (2) Formal surgical excision at 6-12 months (preferred by many): Allows complete removal under vision with proper nerve division and better cosmetic result. Many hand surgeons now prefer formal excision despite the need for general anaesthetic.
Associated Syndromes
Q: A child with preaxial polydactyly is found to have an atrial septal defect. What syndrome should you consider, and what other features would you look for?
A: Holt-Oram syndrome - characterized by radial ray anomalies (including preaxial polydactyly) with cardiac defects (ASD/VSD). Other features include radial dysplasia, hypoplastic or absent thumb, and other upper limb anomalies. Cardiac echo is essential in all patients with radial-sided upper limb anomalies.
Which Thumb to Retain
Q: In Wassel IV thumb duplication, which thumb is typically retained and why?
A: The ulnar thumb is usually retained because it typically has: (1) Better FPL insertion and function, (2) Greater thenar muscle bulk, (3) Larger size, (4) Better active movement. The radial thumb is often more hypoplastic. However, always assess each case individually based on function.
Secondary Surgery Rate
Q: What percentage of patients require secondary surgery after thumb duplication correction, and what are the common reasons?
A: 15-20% require secondary procedures. Common reasons include: (1) Joint instability from inadequate ligament reconstruction, (2) Angular deformity from growth, (3) Tendon imbalance, (4) Web space narrowing. Parents should be counselled about this possibility preoperatively.
Odd vs Even Wassel Numbers
Q: How do you remember the difference between odd and even Wassel classification numbers?
A: ODD = bIfId (shared element) - Types I, III, V have a bifid bone where digits share a single element. EVEN = sEparatE (duplicated) - Types II, IV, VI have completely duplicated separate elements. Wassel IV (even) = duplicated PP, Wassel III (odd) = bifid PP.
Australian Context
Polydactyly management in Australia follows international best practice guidelines with paediatric hand surgery services available in major metropolitan centres. Early referral to specialist paediatric hand surgeons is recommended for optimal surgical timing and outcomes. In Australia, the incidence of polydactyly mirrors global patterns, with postaxial types showing similar ethnic variation. Indigenous Australian populations do not show significantly different rates compared to non-Indigenous populations.
Multidisciplinary assessment is available through public hospital paediatric hand clinics, with genetic counselling services accessible for familial cases or syndromic presentations. Telehealth consultations are increasingly utilized for regional and remote families to facilitate specialist access without requiring extensive travel for initial assessments.
Surgery is typically performed at 12-18 months in both public and private systems, though public hospital waiting lists may occasionally delay procedures. Most procedures are performed as day surgery cases. Occupational therapy services for hand therapy and functional assessment are available through both public paediatric hospitals and private providers.
POLYDACTYLY
High-Yield Exam Summary
WASSEL CLASSIFICATION
- •I-VII: Distal to proximal bifurcation
- •IV = MOST COMMON (43%) - duplicated PP
- •ODD (I, III, V) = BIFID (shared)
- •EVEN (II, IV, VI) = DUPLICATED (separate)
- •VII = Triphalangeal thumb
POSTAXIAL TYPES
- •Type A: Well-formed with articulation
- •Type B: Rudimentary/pedunculated
- •1:300 in African descent
- •Autosomal dominant inheritance
- •Type B ligation controversial
THUMB SURGERY PRINCIPLES
- •Timing: 12-18 months
- •Retain more functional (usually ulnar)
- •RECONSTRUCT COLLATERAL LIGAMENTS
- •Transfer intrinsics from excised thumb
- •Correct angular deformity
BILHAUT-CLOQUET
- •For Wassel I/II equal thumbs
- •Combines both thumbs into one
- •Expect IP stiffness
- •Nail ridge deformity
- •Reserve for specific cases
ASSOCIATED SYNDROMES
- •Holt-Oram: Preaxial + ASD/VSD
- •Ellis-van Creveld: Postaxial + cardiac
- •Trisomy 13: Postaxial + poor prognosis
- •Bardet-Biedl: Postaxial + obesity + retinal
COMPLICATIONS
- •Joint instability (most common)
- •Angular deformity
- •15-20% need secondary surgery
- •Type B ligation: neuroma risk
- •Bilhaut: IP stiffness expected