Polydactyly of the Foot

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 predominance (Male greater than Female).
• Laterality: 50% bilateral.
• Association: While foot polydactyly can be isolated, hand polydactyly is more often syndromic. Always check the hands!

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.

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:

1. 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.
2. Function: Tickle the foot. Which toe flexes/extends better? Keep the functional one.
3. Palpation: Feel the metatarsal head. Is it wide?
4. Neurovascular: Ensure the digit to be kept has good perfusion.

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.

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.

• 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).

• 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.

Global epidemiology

• Polydactyly is one of the most common congenital limb anomalies worldwide. Type B postaxial polydactyly is the single commonest form.
• Birth prevalence varies strikingly by ancestry. In US surveillance, postaxial polydactyly was roughly 26 times more frequent in infants of African ancestry than White infants (0.91 vs 0.035 per 100); Texas registry data show a prevalence ratio of about 4.4 for non-Hispanic Black versus non-Hispanic White births. Hand involvement is more common than foot involvement.
• Around 95 percent of postaxial type B cases are isolated and autosomal dominant; foot polydactyly is bilateral in about half of cases.

Guidance across societies (no formal single guideline exists) There is no dedicated international guideline for foot polydactyly; practice is governed by classification-led principles and society/textbook consensus rather than randomised evidence.

Registry note: unlike arthroplasty, congenital toe deformities are not captured in implant registries (NJR/AJRR/AOANJRR). Population-level data come from birth-defect surveillance programmes (e.g. EUROCAT in Europe, US National Birth Defects Prevention Network, Texas Birth Defects Registry).

High- vs limited-resource practice variation

• Well-resourced settings: elective day-case surgery near walking age, formal excision over ligation, microsurgical/reconstructive options (on-top plasty, lengthening) for hypoplastic rays, and genetics input for syndromic disease.
• Limited-resource settings: later presentation is common; bedside suture ligation of type B digits in the newborn period persists for access/cost reasons despite the higher nubbin/neuroma rate; complex pre-axial and central reconstruction may be referred to tertiary centres.

Cultural sensitivity: in some communities an extra digit is regarded as auspicious; families may decline or delay surgery. Counsel on function, shoe-wear, and cosmesis without coercion.

• Ligation vs formal excision for type B digits. The dominant evidence (Chopan systematic review: 23.5 vs 3 percent complications) favours excision, yet Ganju's patient-reported data suggest ligation is acceptable in selected cases with similar long-term pain — the trade-off is a higher rate of residual bumps and raised scars. There is no randomised trial.
• Optimal timing. "Before walking age (9-12 months)" is convention, not evidence-based dogma; some advocate early newborn excision of simple type B digits, others delay complex reconstructions until structures are larger. Anaesthetic safety, surgeon preference and complexity all weigh in.
• Which classification to use. Pre-axial duplication is variably described by Venn-Watson, Blauth-Olason and Watanabe; medial duplication now has the Rotterdam system. None is universal, and inter-observer reliability is only moderate, complicating cross-study comparison.
• Bilhaut-Cloquet's place. Effective for two equal hypoplastic digits but near-universally produces a nail ridge and stiffness; many surgeons now prefer ablation-plus-reconstruction or on-top plasty, reserving Bilhaut-Cloquet for narrow indications.
• Role of advanced imaging. Plain films underestimate the cartilaginous infant skeleton; the added value of routine ultrasound/MRI versus operative assessment is unsettled.

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 anterior expression of SHH (often via ZRS regulatory mutations) causes Pre-axial Polydactyly and, in the extreme, mirror foot.
• GLI3: A key downstream effector, normally processed into a repressor anteriorly to oppose SHH. GLI3 haploinsufficiency causes both pre- and post-axial polydactyly and underlies Greig cephalopolysyndactyly and Pallister-Hall syndrome — i.e. GLI3 is not exclusively a "post-axial" gene.

According to PubMed, Quinn et al (Hum Mol Genet 2012) showed that loss of Zic3 rescues the polydactylous phenotype of Gli3-haploinsufficient mice by normalising the Gli3-repressor/activator ratio and abolishing ectopic anterior Shh — confirming GLI3 dosage as the pivotal regulator of digit number (DOI).