Polydactyly of the Foot
More Than Just an Extra Toe
Anatomical Classification
Critical Must-Knows
- Post-axial (Lateral) is common and often isolated.
- Pre-axial (Medial) is rare and associated with Hallux Varus recurrence.
- Central is rare and often syndromic.
- Syndromes: Ellis-van Creveld (Post-axial), Polydactyly-Syndactyly syndromes.
- Surgery: Ideally before walking age (9-12 months) for shoe fit.
Examiner's Pearls
- "Look for hands (often present in hands too)
- "Check for syndactyly (webbing)
- "Assess function (does the extra toe move?)
- "Palpate the metatarsal head (is it wide or duplicated?)
The Pre-Axial Trap
Don't treat Pre-axial Polydactyly lightly.
- Duplication of the Hallux (Pre-axial) is fraught with complications.
- The medial collateral ligament is often anomalous or absent.
- Ablating the medial duplicate without securing the ligament or correcting the alignment almost ALWAYS leads to Hallux Varus.
- The remaining toe drifts medially, making shoe wear impossible.
Pre-axial vs Post-axial Polydactyly
| Feature | Post-axial (Lateral) | Pre-axial (Medial) |
|---|---|---|
| Common (80%) | Rare (15%) | |
| Autosomal Dominant (African) | Sporadic / Syndromic | |
| Simple (often skin tag) | Complex (Shared joints) | |
| Residual bump | Hallux Varus |
Surgical Goals
Memory Hook:Act FAST.
Syndromes to Consider
Memory Hook:TEMP (Temperature check for syndromes).
Classification (Temtamy and McKusick)
Memory Hook:PPC hierarchy.
Overview/Epidemiology
Polydactyly refers to the presence of supernumerary digits. It is the most common congenital foot deformity.
- Epidemiology: 1.7 per 1000 live births.
- Race: Significantly higher in African American populations (10-15x higher), where it is often purely Autosomal Dominant and Post-axial.
- Gender: Male > Female.
- Laterality: 50% bilateral.
- Association: While foot polydactyly can be isolated, hand polydactyly is more often syndromic. Always check the hands!
Pathophysiology and Mechanisms
The Duplication Pattern:
- Skin Tag: Only soft tissue attachment (Type B post-axial).
- Partial: Duplication of phalanx only, sharing a metatarsal head.
- Complete: Complete duplication of the entire ray (phalanx + metatarsal). This essentially creates a "6th ray" and widens the foot significantly.
Associated Anomalies:
- Syndactyly: The extra digit is often webbed to the adjacent digit (Polysyndactyly).
- Bracket Epiphysis: Can be present in the duplicated parts, causing curvature.
- Tarsal Coalition: Rare but can occur in complex pre-axial cases.
Classification Systems
Anatomical Classification
Pre-axial: Medial side (Tibial). Involves the Hallux.
- Associated with tibial hemimelia, Carpenter syndrome.
- High risk of Hallux Varus outcome.
Central: 2nd, 3rd, or 4th rays.
- Rare. Usually syndactyly prevents separation.
- Often involves a "T-shaped" metatarsal.
Post-axial: Lateral side (Fibular). Involves the 5th toe.
- Type A: Well-formed digit. Articulates with metatarsal or phalanx.
- Type B: Rudimentary skin tag. Pedunculated.
Clinical Assessment
History:
- Family Hx: Anyone else in the family? (Suggests AD inheritance).
- Pregnancy: Any complications?
- Syndrome Review: Heart defects? Kidney issues? (Ellis-van Creveld, Patau).
Physical Exam:
- Count: Count the toes. Identifying which one is the "extra" one can be hard. Usually, the outer/marginal one is the extra one, but sometimes the inner one functions better.
- Function: Tickle the foot. Which toe flexes/extends better? Keep the functional one.
- Palpation: Feel the metatarsal head. Is it wide?
- Neurovascular: Ensure the digit to be kept has good perfusion.
Investigations
Plain Radiographs (AP and Oblique):
- Mandatory for surgical planning.
- Determine Level: Is the duplication at the PIP, MTP, or TMT joint?
- Determine Connection: Is it a bifid head? A bracket epiphysis? A completely separate ray?
- Ossification: Remember that in infants, much of the bone is cartilaginous and won't show. The X-ray underestimates the deformity.
Genetic Testing:
- Indicated if Central Polydactyly, Bilateral Pre-axial, or other dysmorphic features are present.
Management Algorithm
1. Observation / Suture Ligation
- Observation: Rarely indicated unless the extra digit is not causing shoe conflict (e.g., small central nubbin).
- Suture Ligation: Historically used for Type B Post-axial (skin tags) in the nursery.
- Current view: Discouraged. Can leave a painful neuroma or residual "nubbin" of cartilage. Surgical excision is cleaner.
Surgical Techniques
Post-Axial Ablation (Type A)
- Incision: Racket-shaped or elliptical incision around the base of the extra digit.
- Dissection: Trace the tendons. Often the abductor digiti minimi inserts on the extra toe. This must be transferred to the remaining 5th toe.
- Capsulotomy: Open the joint.
- Resection: Remove the extra phalanx. If the metatarsal head is bifid, shave down the prominent condyle (The "Block Test" - make sure it's not too wide for shoes).
- Reconstruction: Repair the Lateral Collateral Ligament using the periosteum sleeve from the amputated toe.
- Closure: Z-plasty if needed to prevent scar contracture.
This ensures a cosmetically acceptable narrowing of the foot.
Deep Dive: Surgical Pearls
1. The "Nubbin" Problem If you or a paediatrician ties off a Type B skin tag in the nursery, often a small "nubbin" of cartilage or nerve remains. This becomes painful in shoes later.
- Recommendation: Formal excision under local anaesthetic (if older) or GA (around 6-12 months) is superior. You can dissect out the nerve and ensure the bone is flush.
2. The Shared Epiphysis In Type A post-axial digits, the extra toe joint might share a common epiphysis with the normal toe.
- Risk: If you simply disarticulate, you leave an exposed, wide joint surface.
- Technique: You may need to perform an intra-articular osteotomy to narrow the metatarsal head, preserving the collateral ligament origin.
3. Pre-axial Hallux Varus The classic complication of removing the medial hallux.
- Cause: You have removed the medial buttress and the insertion of the Abductor Hallucis.
- Solution: You MUST reattach the Abductor Hallucis to the base of the remaining proximal phalanx. Often, a K-wire is needed to hold the toe in neutral / slight valgus for 4-6 weeks while this heals.
Complications
| Complication | Rate | Prevention/Management |
|---|---|---|
| Residual Deformity | Common | Angulation of remaining toe. Osteotomy correction. |
| Hallux Varus | High (Pre-axial) | Proper tendon transfer/capsule repair. |
| Nail Dystrophy | Common | Especially with Bilhaut-Cloquet procedure. |
| Widened Foot | Common | Failure to narrow the metatarsal head. |
| Neuroma | Rare | Bury the nerve endings deep. |
Postoperative Care
- Cast: Below-knee cast or soft bandage depending on stability. K-wires are protected for 4-6 weeks.
- Walking: If walking age, casts are essential to protect the reconstruction/wire.
- Shoe Wear: Resume normal shoes once swelling subsides (6-8 weeks).
- Follow-up: Essential to watch for growth deviation (physeal arrest/tether).
Outcomes/Prognosis
- Cosmesis: Generally excellent for post-axial ablation.
- Function: Normal gait is expected.
- Nail: Nail appearance is the most common complaint after Bilhaut-Cloquet.
- Retained Ray: Sometimes parents notice "the foot is still wide" if the metatarsal wasn't narrowed.
Evidence Base
- Large review of polydactyly
- Post-axial type B most common
- Complication rate 7% (mostly minor)
- Review of Bilhaut-Cloquet
- Nail deformity in 90% of cases
- Functional outcome good, cosmetic outcome mixed
- Suture ligation vs Surgical Excision for Type B
- Ligation had 23% complication rate (residual nubbin, infection)
- Excision had 0% complication rate
- Hallux Varus after Pre-axial ablation
- Incidence 15%
- Risk factors: medial duplication, failure to repair collateral ligament
- Central Polydactyly management
- Often requires ray resection
- Good functional results despite complexity
Viva Scenarios
Practice these scenarios to excel in your viva examination
The Newborn Consult
"Neonate with Type B post-axial polydactyly (skin tag). Paediatrician asks if they can just tie it off with a suture."
I would advise **against** suture ligation. Evidence shows a high rate of complications including residual painful nubbins (neuroma/cartilage) and infection. It is cleaner and safer to perform a formal excision under local anaesthetic (if very small) or a brief GA at 6-12 months. This allows me to identify and cut the neurovascular bundle cleanly and ensure no cartilaginous prominence remains.
The Pre-axial Problem
"1-year-old with duplicated Hallux. Medial toe is smaller. Lateral toe is normal. Plan?"
This is Pre-axial polydactyly. The goal is to preserve the best digit, which is the lateral one here. I would plan for ablation of the medial digit. However, this is NOT a simple amputation. I must identify the Abductor Hallucis tendon (which inserts on the medial toe) and transfer/reattach it to the lateral toe to prevent **Hallux Varus**. I would also repair the medial collateral ligament and likely use a K-wire for 6 weeks.
Syndromic Association
"Child with bilateral post-axial polydactyly, short stature, and a heart murmur. Diagnosis?"
This clinical picture (specifically Post-axial polydactyly + Heart defects + Short limb dwarfism) is highly suggestive of **Ellis-van Creveld Syndrome** (Chondroectodermal dysplasia). Other possibilities include Jeune syndrome or Trisomy 13 (Patau), though Patau is usually lethal/severe. I would refer for Genetic counselling and Cardiology review (ASD/VSD common). Orthopaedic management is standard (ablation) but risks of anaesthesia are higher.
MCQ Practice Points
Epidemiology MCQ
Q: Which population has the highest incidence of Polydactyly? A: African Ancestry (Post-axial, Autosomal Dominant).
Surgical Technique MCQ
Q: What is the most common complication of simple ablation of a medial (pre-axial) supernumerary digit? A: Hallux Varus (due to loss of medial stabilizers).
Syndrome MCQ
Q: Ellis-van Creveld syndrome is associated with which type of polydactyly? A: Post-axial (Lateral).
Anatomy MCQ
Q: In central polydactyly, what is the most appropriate surgical management? A: Ray Resection (Filleting) helps narrow the foot and remove the duplicated ray.
Procedure MCQ
Q: What is the Bilhaut-Cloquet procedure? A: Sharing procedure combining halves of two hypoplastic digits to form one normal digit.
Australian Context
- Referral: Common referral to paediatric clinics.
- Cultural: In some cultures, extra digits are seen as "lucky" or "special". Sensitivity is required if parents decline surgery.
POLYDACTYLY FOOT
High-Yield Exam Summary
CLASSIFICATION
- •Pre-axial (Medial)
- •Post-axial (Lateral - Common)
- •Central (Rare)
- •Type A / Type B
SYNDROMES
- •Ellis-van Creveld
- •Trisomy 13 (Patau)
- •Carpenter Syndrome
- •Greig Cephalopolysyndactyly
KEY RISKS
- •Nubbin formation (Ligation)
- •Hallux Varus (Pre-axial)
- •Nail Dystrophy (Bilhaut-Cloquet)
- •Dehiscence
MANAGEMENT
- •Observation
- •Suture Ligation (Avoid)
- •Formal Ablation
- •Ray Resection
Deep Dive: The Genetics of Polydactyly
SHH Pathway The Sonic Hedgehog (SHH) gene is the master regulator of limb anterior-posterior patterning.
- Zone of Polarizing Activity (ZPA): Located on the posterior margin of the limb bud. It secretes SHH.
- Gradient: High concentrations of SHH on the posterior side specify "Little Finger/Toe". Low concentrations on the anterior side specify "Thumb/Hallux".
- Mutation: Ectopic expression of SHH on the anterior margin causes Pre-axial Polydactyly (Mirror hand/foot).
- GLI3: A downstream repressor. Mutations in GLI3 (e.g., Grieg syndrome) lead to Post-axial Polydactyly.