Polydactaly

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Here is a thorough overview of polydactyly drawn from multiple authoritative sources.

Polydactyly

Polydactyly is the presence of supernumerary (extra) digits on the hands or feet - more than five fingers or toes. It is one of the most common congenital limb anomalies, with an overall incidence of approximately 1-2 per 1,000 live births. The extra digit is often incompletely formed and lacks normal muscular development.

Fig. 16.14 - The Developing Human: Clinically Oriented Embryology. Polydactyly of the hands (A) and feet (B).

Classification by Location

Polydactyly is classified based on which side of the limb is affected:

Type	Location	Also Known As
Preaxial	Radial side of hand / tibial side of foot	Thumb or hallux duplication
Postaxial	Ulnar side of hand / fibular side of foot	Small finger / 5th toe duplication
Central	Index, middle, or ring fingers	Rare; often hidden by syndactyly

1. Postaxial Polydactyly (Most Common Overall)

Duplication of the small finger (hand) or lateral toe (foot).

Most common in people of African descent: ~1 in 143 live births (vs. 1 in 1,339 in Caucasians)
Autosomal dominant inheritance with variable expression
In the Black population: usually isolated, not syndromic
In Caucasians: more frequently associated with syndromes and chromosomal abnormalities - warrants a more thorough genetic workup

Temtamy and McKusick Classification:

Type A - Fully developed, well-formed extra digit; rare; equal incidence across races; may be associated with syndromes (Cornelia de Lange, Chondroectodermal dysplasia, Schinzel syndrome)
Type B - Rudimentary nubbin attached pedunculated at the proximal phalanx level; much more common in people of African descent (10x); autosomal dominant

Further subclassification (Pritsch et al.):

Type 1: Soft tissue duplication only
Type 2: Partial duplication including bone
Type 3: Complete ray duplication

- Campbell's Operative Orthopaedics 15th Ed 2026, p. 4662

2. Preaxial Polydactyly (Thumb / Hallux Duplication)

Incidence: ~1 in 3,000 live births
Usually unilateral and sporadic (not syndromic), except for Wassel Type VII
Thumb duplication is not a true extra digit but a splitting of a single digit with variable development in each part

Wassel Classification of Thumb Polydactyly

Type	Description	Frequency
I	Bifid distal phalanx	2%
II	Duplicated distal phalanx	15%
III	Bifid proximal phalanx	6%
IV	Duplicated proximal phalanx	43% (most common)
V	Bifid metacarpal	10%
VI	Duplicated metacarpal	4%
VII	Triphalangia	20%

Type VII is associated with: Holt-Oram syndrome, Fanconi anemia, Blackfan-Diamond anemia, imperforate anus, cleft palate, and tibial defects.

Type IV thumb duplication showing duplicated proximal and distal phalanges

Fig. 7.82 - Miller's Review of Orthopaedics 9th Ed. Type IV duplication.

- Miller's Review of Orthopaedics 9th Edition, p. 2070

3. Central Polydactyly

Rare - involves index, middle, or ring finger duplication
Ranges from incomplete to fully formed extra digits
Commonly associated with syndactyly, cleft hand, and other syndromes
- Mulholland and Greenfield's Surgery 7e, p. 6046

Associated Syndromes / Genetics

Polydactyly (especially postaxial) is a key feature of the ciliopathies - defects in ciliary proteins produce wide-ranging effects including postaxial polydactyly, retinal degeneration, renal/hepatic cysts, and situs inversus:

Syndrome	Type of Polydactyly	Inheritance
Bardet-Biedl syndrome	Postaxial	AR (ciliopathy)
Short-rib polydactyly syndromes	Postaxial	AR (ciliopathy)
Smith-Lemli-Opitz	Postaxial (~50% of cases)	AR
Gorlin syndrome	Postaxial (occasional)	AD
Rubinstein-Taybi syndrome	Postaxial (occasional)	AD
Simpson-Golabi-Behmel	Postaxial	X-linked
Greig cephalopolysyndactyly	Preaxial/mesoaxial	AD (GLI3 variants)
Pallister-Hall syndrome	Mesoaxial/postaxial	AD (GLI3)
Pfeiffer syndrome	Broad thumbs/halluces	AD (FGFR1/2)
Holt-Oram syndrome	Preaxial (thumb)	AD

- Emery's Elements of Medical Genetics and Genomics

Treatment

Postaxial - Type A

Surgical excision in the operating room under tourniquet at ~1 year of age due to the complexity of the duplication
Ulnar digit is removed; soft tissue from ablated digit augments the retained finger

Postaxial - Type B

Suture ligation / vascular clip in the nursery: fast, no anesthesia needed, cost-effective - BUT 42% revision rate (neuromas, residual polydactyly)
Surgical excision: preferred - only ~3% complication rate vs. 23.5% for ligation (systematic review data); higher overall patient satisfaction; no revisions needed
Some centers now perform simple excisions in an office setting under local anesthesia

Preaxial (Thumb)

Best possible thumb is reconstructed from available anatomic structures (not simple amputation)
If duplicated thumbs are equal in size: preserve the ulnar thumb to maintain the ulnar collateral ligament (UCL) for pinch
Soft tissue from the ablated thumb is used to augment the retained one
Complications: nail deformity, IP joint angulation
Bilhaut-Cloquet procedure (or modified): used for Wassel types II-III (combines both halves)

Foot Polydactyly

Preoperative X-rays mandatory before any non-trivial excision
Extra metatarsal elements must also be removed
Soft-tissue webspace reconstruction required when central digits are removed
Optimal age: 6-18 months
Kirschner wire fixation may be used for 4-6 weeks in preaxial cases after capsule repair

- Campbell's Operative Orthopaedics 15th Ed 2026

Embryological Basis

Polydactyly results from abnormal signaling in the zone of polarizing activity (ZPA) during limb development. It is inherited most often as an autosomal dominant trait with variable expression. The extra digit usually lacks complete muscular development, explaining the importance of selecting the better-developed digit for retention during surgery.

- The Developing Human: Clinically Oriented Embryology, p. 1004

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