Supernumerary Digit

Earn CME/CE in your profession:

Continuing Education Activity

Polydactyly or supernumerary digit is a common malformation. It involves mostly the upper limbs. Classifications have been established to ease its management. This activity reviews the evaluation and treatment of supernumerary digits and highlights the role of the interprofessional team in the care of patients with this condition.


  • Describe the etiology of supernumerary digits.
  • Review the appropriate evaluation of supernumerary digits.
  • Outline the management options for supernumerary digits.
  • Summarize the importance of improving care coordination amongst the interprofessional team to enhance the care of patients with supernumerary digits.


Supernumerary digit, or polydactyly, is an autosomal dominant congenital defect of the upper and/or lower extremity that is typically discovered immediately after birth.[1] Polydactyly is characterized by a person having fingers or toes numbering greater than 5. It is the most common congenital hand anomaly.[2] Parey, who lived in the 16th century, initially described polydactyly as “superfluous fingers” when describing persons with greater than five fingers.[3] In addition to Parey’s historical description, artwork in the southwest “Four Corners” region of the United States depicts persons with hands and feet with six digits. It is believed this artwork comes from an early population living in the area around 600 to 1280 AD.[4] 

Polydactyly is categorized based upon its location. Preaxial polydactyly involves the radial or great toe side of the extremity, whereas postaxial polydactyly involves the ulnar or 5th toe side of the extremity. Central or meso axial polydactyly involves the 2-4 digits.[1]


Polydactyly is primarily thought to be a failure in digit control during development.[5] Typical limb development occurs between 4-8 weeks of gestational age. Multiple signal centers exist that guide limb and digit development. The most prominently involved signaling molecule with polydactyly is Sonic Hedgehog (SHH), working from the zone of polarizing activity (ZPA). The ZPA is responsible for anterior-posterior (radial-ulnar) axis development.[6]

SHH is vital to digit number and type development.[5] In normal hand development, limb length is determined by fibroblast growth factor signals from the apical ectodermal ridge. The development of digits occurs in a radial-ulnar axis and is regulated by members of the bone morphogenetic proteins (BMP) family and SHH.[7] SHH is in higher concentrations ulnarly than radially, which aids in digit differentiation.[8] Mutations in the LMBR1 gene have also been implicated in the development of polydactyly due to upregulated SHH expression in the developing limb.[9] 

Glioma-associated oncogene homolog 3 (Gli3) is an SHH antagonist, which has been shown in a group of people with Greig cephalopolysyndactyly to have a missense mutation in Gli3. This missense mutation can lead to an upregulation of SHH, which can contribute to polydactyly due to disrupted definition of the radial-ulnar axis.[6][10]


Polydactyly is estimated to occur in 1.6 to 10.7 in 1,000 live births. Males are twice as often affected as females.[1] Polydactyly of the fingers has an incidence of 1 in 300 in Blacks and 1 in 3000 in Whites.[11] Preaxial polydactyly is more common in Whites, whereas postaxial polydactyly is more common in Blacks. Preaxial polydactyly is also more common in American Indian and Asian populations.[11][12] Postaxial polydactyly has a prevalence of 1 to 2 per 1000 live births.[1] Preaxial polydactyly is less common, with an incidence reported between 0.08 to 1.4 per 1000 to 1 per 3,000 live births.[11][12]


During limb development in an embryo, the typical pattern of digit development is controlled by the interactions of multiple signaling molecules. When one or more of these signaling molecules has upregulation or downregulation, supernumerary digits can occur on one or both hands and/or feet. This up or down-regulation typically occurs due to genetic errors in a number of possible chromosomal regions. Most commonly, polydactyly of the hand occurs, involving the ulnar side of the hand more than the radial side.[1]

History and Physical

As a congenital disorder, polydactyly may be commonly seen in familial patterns, so it is important to obtain a good family history. Patients presenting with polydactyly will have an extra finger and/or toe, and this is most often discovered in the immediate post-natal period of life for a neonate.

Physical exam findings include the observation of a supernumerary digit. Imaging, including radiographs, is useful for possible surgical planning and to further classify the specific pattern of polydactyly.

The Wassel classification is used for preaxial (radial) polydactyly of the hand. There are seven classes of polydactyly in this system. Type I involves a bifid distal phalanx. In type II the distal phalanx is duplicated. Type 3 is characterized by bifid proximal phalanges. The most common is type IV, with duplicated proximal phalanx. With type V, a bifid metacarpal exists. Duplicated metacarpals are the finding in type VI. Type VII consists of triphalangia.[13] (Figure 1)

Postaxial polydactyly is duplications of the small finger (ulnar border) of the hand or along the lateral border of the foot. The Stelling and Turek classification is used to describe postaxial polydactyly of the hand. This classification is divided into 3 types. Type 1 involves soft tissue duplication. Type 2 has bony duplication, while type 3 includes a full ray, including the metacarpal.[14] (Figure 1)

Central polydactyly is a duplication of the index, long, or ring fingers, or toes 2,3, or 4. It accounts for a much smaller proportion of polydactyly.[14] The ring finger is more commonly affected.[11] Type 1 central polydactyly is a duplication with no adjacent finger attachments. Type 2 share a joint, or bifid metacarpal or phalanx with an adjacent finger. Type 3 central polydactyly has a fully formed independent digit, including the metacarpal.[14] Central polydactyly is often an autosomal dominant inherited disorder and is commonly seen with syndactyly or polydactyly of the feet.[11]

When describing polydactyly of the foot, the main classification used is the Venn-Watson, which has 6 subdivisions based upon metatarsal anatomy. Class 1 involves distal duplication with a normal metatarsal. Class 2 has a block metatarsal, whereas class 3 has a Y shaped metatarsal and class 4 a T shaped metatarsal. Class 5 exhibits a normal metatarsal shaft with a widened head, and class 6 involves complete duplication, including the metatarsal.[15]


Polydactyly can be detected on anatomic ultrasounds done prenatally. However, it is typically diagnosed at birth. To properly treat polydactyly, the provider must fully understand the exact type of polydactyly involved. This must include a thorough understanding of the musculoskeletal components involved. Part of the evaluation must include radiographs and physical examination to assess stability, motor function, and cosmesis.[15][16] 

Practitioners must also consider and evaluate if polydactyly is presenting as part of a syndrome. Syndromes that are reported with a higher incidence include Holt-Oram syndrome and Fanconi anemia.[12]

Treatment / Management

Treatment aims to improve hand function and cosmesis.[12] Once a diagnosis is made, surgical management can be undertaken when needed. The decision of surgical treatment versus non-operative management is primarily guided by the anticipated function of the supernumerary digit. Often if the digit has fully developed skeletal components and is anticipated not to interfere with hand function, nonoperative management is considered. Multiple surgical techniques exist to manage polydactyly of the hand. General principles that must be adhered to include preservation of viable skin flaps, preservation of ligamentous structures to maintain a stable finger, and surgical planning to maintain a strong pinch grip.[16]

Some authors recommend that preaxial polydactyly be surgically managed in patients between 7 and 12 months old.[17] A common consensus is an intervention for preaxial polydactyly at least by close to 12 months of age to optimize functional outcomes. Operative interventions can include digit ablation, the Bilhaut-Cloquet procedure, or an on-top plasty.[12] Surgical ablation is the most common choice. Typically with this procedure, the goal is to preserve the more dominant thumb, ablate the smaller, more hypoplastic thumb, and reconstruct the collateral ligaments as necessary.[12] The goal is to create a stable and functional thumb and minimize the need for future repeat procedures. Simple suture ligation has numerous potential complications, which are discussed below and are not favored for the management of preaxial polydactyly.[16] 

The Bilhaut-Cloquet procedure involves zig-zag incisions on the volar and dorsal surfaces of the bifid thumb portions. Then a resection of the central portions of the two thumbs via osteotomy is performed. The remaining osseous structures are encircled with K wires allowing the healing of the bone and soft tissues. This technique allows the creation of a typically more normal-sized and functional thumb. The On-top plasty is reserved for triphalangeal thumbs. In this procedure, the most functional distal thumb portion is transferred to the most suitable metacarpal of the thumbs available.[12]

Postaxial polydactyly is usually managed with surgical excision or suture ligation when no bony structures exist. If bony structures are present, surgical management with similar goals to preaxial polydactyly is important. The creation of a structurally sound and functional digit is key to good outcomes. Typically the more ulnar and less developed digit is removed. When partial duplication exists, it is important to transfer tendinous and ligamentous structures to the remaining digit for good function.[12]

Central polydactyly is often treated between 6-12 months of age. Again, the focus is on aesthetics and function. Surgical options most often used include excision or ligation of the more rudimentary digits. One guiding principle advocated by small studies of surgical outcomes for central polydactyly is to create an opposable thumb and 3 functional digits over creating a 5 fingered hand.[18][19]

Treatment of polydactyly of the foot again focuses on function and cosmetic outcome. Guiding principles for surgical treatment include recreating a normal foot contour, maintaining physeal alignment, and keeping proper soft tissue tension around the joints of the toes.[15]

Differential Diagnosis

Typically the diagnosis of polydactyly is readily apparent when the extra digit includes bony and soft tissue features. However, when a more rudimentary digit exists with possibly only soft tissue, a differential must include acquired digital fibrokeratoma.[20]


Polydactyly has aesthetic and functional implications. The primary concerns with polydactyly center around its impact upon fine motor development and function. With appropriate and well-timed intervention, the vast majority of cases of polydactyly have good functional outcomes, and the overall prognosis is favorable.


Surgical treatment of polydactyly has multiple potential complications. When suture ligation is used, a painful neuroma often ensues.[16] Suture ligation has also been linked to cyst formation.[14] Other reported complications related to the treatment of polydactyly include painful scarring, infection, joint instability, residual deformity, angulated growth, growth arrest, joint stiffness, and nail bed deformities.[14][16] One study cites a 19% revision rate for preaxial polydactyly, typically for pain or instability.[21]

Deterrence and Patient Education

It is important to have early conversations with the parents of a patient with polydactyly. As early intervention can lead to more optimal outcomes, parents should be educated about the etiology, outcomes, and potential complications of polydactyly and its management. Parents need to understand that while surgical complications are generally uncommon, painful scarring, growth disturbances, and neuroma formation can occur.[14][16]

Enhancing Healthcare Team Outcomes

The clinical workup, management, and follow-up of patients with supernumerary digits require an interprofessional team approach. Typically the diagnosis is made early in life by a primary clinician. Prompt referral to an orthopedic specialist can allow for early intervention when necessary. If surgical intervention is pursued, one of many specialists may be involved, including orthopedic surgeons, plastic surgeons, and anesthesiologists. All medical professionals involved should be aware that polydactyly may present as part of a syndrome, and referral to a genetic specialist may be necessary. In addition, other team members can include occupational therapists and physical therapists for strengthening and development of motor skills. As in all areas of interprofessional management, communication between team members is important to optimize outcomes for patients.

(Click Image to Enlarge)
Figure 1: Preaxial and postaxial polydactyly classifications
Figure 1: Preaxial and postaxial polydactyly classifications
Contributed by Franco L. De Cicco, MD
Article Details

Article Author

Curtis J. Barnes

Article Editor:

Franco L. De Cicco


7/10/2022 3:26:11 PM

PubMed Link:

Supernumerary Digit



Umair M,Ahmad F,Bilal M,Ahmad W,Alfadhel M, Clinical Genetics of Polydactyly: An Updated Review. Frontiers in genetics. 2018;     [PubMed PMID: 30459804]


Farrugia MC,Calleja-Agius J, Polydactyly: A Review. Neonatal network : NN. 2016;     [PubMed PMID: 27194607]


Malik S, Syndactyly: phenotypes, genetics and current classification. European journal of human genetics : EJHG. 2012 Aug;     [PubMed PMID: 22333904]


Hirthler MA,Hutchison RL, Polydactyly in the Southwest: art or anatomy-a photo essay. Hand (New York, N.Y.). 2012 Dec;     [PubMed PMID: 24294174]


Malik S, Polydactyly: phenotypes, genetics and classification. Clinical genetics. 2014 Mar;     [PubMed PMID: 24020795]


Oberg KC,Feenstra JM,Manske PR,Tonkin MA, Developmental biology and classification of congenital anomalies of the hand and upper extremity. The Journal of hand surgery. 2010 Dec;     [PubMed PMID: 21134615]


Daluiski A,Yi SE,Lyons KM, The molecular control of upper extremity development: implications for congenital hand anomalies. The Journal of hand surgery. 2001 Jan;     [PubMed PMID: 11172363]


Al-Qattan MM,Yang Y,Kozin SH, Embryology of the upper limb. The Journal of hand surgery. 2009 Sep;     [PubMed PMID: 19700076]


Farooq M,Troelsen JT,Boyd M,Eiberg H,Hansen L,Hussain MS,Rehman Su,Azhar A,Ali A,Bakhtiar SM,Tommerup N,Baig SM,Kjaer KW, Preaxial polydactyly/triphalangeal thumb is associated with changed transcription factor-binding affinity in a family with a novel point mutation in the long-range cis-regulatory element ZRS. European journal of human genetics : EJHG. 2010 Jun;     [PubMed PMID: 20068592]


Debeer P,Peeters H,Driess S,De Smet L,Freese K,Matthijs G,Bornholdt D,Devriendt K,Grzeschik KH,Fryns JP,Kalff-Suske M, Variable phenotype in Greig cephalopolysyndactyly syndrome: clinical and radiological findings in 4 independent families and 3 sporadic cases with identified GLI3 mutations. American journal of medical genetics. Part A. 2003 Jul 1;     [PubMed PMID: 12794692]


Gallant GG,Bora FW Jr, Congenital Deformities of the Upper Extremity. The Journal of the American Academy of Orthopaedic Surgeons. 1996 May;     [PubMed PMID: 10795051]


Guo B,Lee SK,Paksima N, Polydactyly: a review. Bulletin of the Hospital for Joint Disease (2013). 2013;     [PubMed PMID: 24032579]


Manske MC,Kennedy CD,Huang JI, Classifications in Brief: The Wassel Classification for Radial Polydactyly. Clinical orthopaedics and related research. 2017 Jun;     [PubMed PMID: 27613532]


Comer GC,Potter M,Ladd AL, Polydactyly of the Hand. The Journal of the American Academy of Orthopaedic Surgeons. 2018 Feb 1;     [PubMed PMID: 29309292]


Turra S,Gigante C,Bisinella G, Polydactyly of the foot. Journal of pediatric orthopedics. Part B. 2007 May;     [PubMed PMID: 17414786]


Little KJ,Cornwall R, Congenital Anomalies of the Hand--Principles of Management. The Orthopedic clinics of North America. 2016 Jan;     [PubMed PMID: 26614930]


Cabrera González M,Pérez López LM,Martínez Soto G,Gutiérrez de la Iglesia D, Prognostic value of age and Wassel classification in the reconstruction of thumb duplication. Journal of children's orthopaedics. 2013 Dec;     [PubMed PMID: 24432120]


Wood VE, Treatment of central polydactyly. Clinical orthopaedics and related research. 1971 Jan;     [PubMed PMID: 4322173]


Tada K,Kurisaki E,Yonenobu K,Tsuyuguchi Y,Kawai H, Central polydactyly--a review of 12 cases and their surgical treatment. The Journal of hand surgery. 1982 Sep;     [PubMed PMID: 7130654]


Shih S,Khachemoune A, Acquired digital fibrokeratoma: review of its clinical and dermoscopic features and differential diagnosis. International journal of dermatology. 2019 Feb;     [PubMed PMID: 29777543]


Stutz C,Mills J,Wheeler L,Ezaki M,Oishi S, Long-term outcomes following radial polydactyly reconstruction. The Journal of hand surgery. 2014 Aug;     [PubMed PMID: 24996673]