Polydactyly or supernumerary digit refers to the presence of means extra digits in the hand or foot. It is also called hyperdactyly.
It is the most common congenital digital anomaly of the hand and foot. It may appear in isolation or in association with other birth defects and syndromes.
The sporadic polydactyly is often autosomal dominant, while polydactyly associated with syndromes [syndromic polydactyly] is often autosomal recessive.
Despite being a common malformation, the true incidence of polydactyly is not fully known.
The condition is less common in the foot than in hand.
Hand involvement is more common in Asians whereas is foot involvement is more common in African Americans.
The condition is bilateral in most cases and has slight male preponderance.
Causes, Pathophysiology, and Associations
There are many specific mutations linked to polydactyly. But a clear mechanism is yet to be involved.
HOXD13 gene are associated with synpolydactyly, a term that denotes the presence of poly as well as syndactyly. Per se polydactyly may be associated with syndactyly.
Similarly, GLI3 mutations are have been reported in nonsyndromic postaxial polydactyly.
Other genes are ZNF141, MIPOL1, IQCE, PITX1, and GLI1.
There is very little association between hand and foot polydactyly. They occur independently.
When these occur together, it is generally a crossed polydactyly. In this there is preaxial involvement of the hand and postaxial involvement of the foot occurs or vice versa [See below for preaxial and postaxial]
Often, the supernumerary digits are not associated with congenital anomalies, except in recognizable syndromes.
The following syndromes are associated
- Trisomy 13
- Meckel syndrome
- Down syndrome [strong association with duplication of the first digit.]
- Acrocallosal syndrome [Agenesis of corpus callosum]
- Bardet-Biedl syndrome
- Biemond syndrome
- Ellis van Creveld syndrome
- Ulnar dimelia
- VATER
Types of Polydactyly
Broadly speaking, there are three types of polydactyly
- Postaxial
- Ulnar side of hand or Fibular lateral side of foot
- Involves little finger or toe
- Central
- Involve 2nd, 3rd or 4th digit
- Preaxial
- Also called radial in upper limb or tibial in lower limb
- Involves thumb or great toe
We would further discuss polydactyly of hand and foot in different sections.
Diagnostic Work-up of Supernumerary Digit
Prenatal Ultrasound
Finger buds can be seen in the fetus by 13 weeks of pregnancy by transvaginal ultrasound. If supernumerary digits are seen, a detailed evaluation of the heart, nervous system, limbs, and kidneys should be done to look for syndromic association.
Follow-up ultrasounds between 17 and 34 weeks can be done.
X-rays
X-rays are useful in knowing whether the extra digit contains bony elements or not. The degree of deviation of the digit and the metacarpal/metatarsal size may be helpful in surgical planning.
Treatment Approach to Polydactyly
Here we discuss the general approach to polydactyly treatment. Individual treatments of hand and foot are discussed in their respective section.
The treatment of supernumerary digits should be done early in life. After 3 years of age self-awareness of the disease and peer inquiry adds to the stress.
The surgical treatment depends on the complexity of the condition and region of the deformity.
Concerns of the hand are different from that of the foot. The foot has its own problem of ill-fitting footwear in addition to cosmesis through the cosmesis of greater concern in the hand.
Bleeding, ligamentous laxity, contracture, or neuromas [generally after suture ligation] are common complications after surgery.
Complications in the perioperative timeframe include those secondary to bleeding and anesthesia.
Polydactyly of Hand
Preaxial or Radial [Thumb Duplication]
Preaxial polydactyly is the presence of extra thumbs are common.
The incidence is 1 per 1,000 to 10,000 live births.
Most of the cases are sporadic. Type VII [see below] is known to be associated with the following syndromes-
- Holt-Oram syndrome
- Fanconi’s anemia
- Blackfan-Diamond anemia
- Imperforate anus
- Cleft palate
- Tibial defects
Thumb polydactyly is usually sporadic but could be familial when associated with triphalangeal thumb. The thumb would vary from rudimentary and hnaging fromskin tag to complete duplication of thumb.
There are seven types of duplicated thumbs.
Type I – The distal phalanx is bifid
Type II– The distal phalanx is duplicated
Type III – The proximal phalanx is bifid but the distal phalanx is duplicated
Type IV – Both the proximal and distal phalanges of the thumb are duplicated [Most common type]
Type V – The metacarpal of the thumb is bifid, the proximal and distal phalanges are duplicated
Type VI – The thumb metacarpal and both proximal and distal phalanges are duplicated (4 percent) and
Type VII – The thumb is triphalangeal
In thumb duplication, each thumb may be supplied by a different artery.
Often, one of the thumbs is dominant while the other is underdeveloped.
Treatment
The treatment is sought because of cosmetic concerns mainly. In northern India, people consider the duplicated thumb to be lucky and often persuade their children to keep them and adapt to them.
Treatment aims at
- Resect smaller thumb
- Provide functional thumb
There are various procedures described. the various surgical options are
- Type 1 combination procedure (Bilhaut-Cloquet)
- In type I, II, or III
- Involves removal of central tissue and combining both digits into
- Complications are late deformity, stiffness, angular and size deformity, growth arrest, and nail deformities
- type 2 combination procedure
- For type III and IV
- Preservation of skeleton and nail of one component
- Augmentation with soft tissue from other digit
- Ablation of lesser digit often radial
- Type 3 Combination Procedure
- For types type V, VI, and VII
- Segmental distal transfer from one to other (on-top plasty)
Central
This type is commonly associated with syndactyly.
Duplication of the index, long, and ring fingers is referred to as axial or central polydactyly. Often the extra digit of a long or ring finger is concealed in a web between adjoining normal digits.
The tendons, nerves, and vessels of the supernumerary digits are usually abnormal, as are the epiphyses of the extra digit.
The epiphysis of the extra digit usually does not lie in the normal line of growth. As a result, its phalanges diverge from the longitudinal axis into ulnar or radial deviation and distort adjacent digits.
Duplication of the index finger is very rare, representing about 3.5 percent of all cases.
The usual treatment is osteotomy and ligament reconstruction with the removal of extra tissue.
Postaxial or Ulnar Polydactyly
It is the most common type of polydactyly where the extra digit is on the ulnar side of the hand [side of the little finger].
Most commonly, the extra finger is rudimentary, consisting of an end phalanx with a nail, and connected to the hand with a small skin pedicle.
Postaxial type is more common in African Americans. It is an autosomal dominant inheritance.
The common associations are chondroectodermal dysplasia or Ellis-van Creveld syndrome.
There are two types of postaxial polydactylies
- Type A – well-formed digit
- Type B – rudimentary skin tag
Type B can be tied in the nursery to make it fall or amputated later.
In other types, the radial digit is preserved and reconstructed if required.
Polydactyly of Foot
This refers to extra toes. The condition occurs 1 in 500 births.
The postaxial (lateral side of the foot) polydactyly is the most common. It occurs in 80% of the cases. Preaxial is the next most common.
Foot supernumerary digits are more common in African-Americans and usually transmitted as autosomal dominant
The condition may cause problems like poor shoe fitting and angular deformity of the toes.
The patient can be seen in infancy or later when the shoe fit is an issue.
Classification of Foot Polydactyly
Venn-Watson Classification
It is based on the anatomic configuration of the metatarsal and the duplicated bony parts.
- Postaxial
- ‘Y’ metatarsal
- ‘T’ metatarsal
- Wide metatarsal head
- Complete duplication
- Central*
- Duplication of the second, third or fourth toe
- Preaxial
- Short block first metatarsal
- wide metatarsal head
*Not part of original classification
The Postaxial is lateral side of the foot and preaxial is the medial side of the foot [great toe]
Treatment
In the case of postaxial [little toe involvement] or central polydactyly, the treatment is may not be required unless alignment is severely affected.
Surgery is done to enhance cosmesis for cosmetic reasons and for improving shoe fit. The extra toe in preaxial polydactyly can be ablated by one year or before. reconstruction of the other abnormalities, as needed, should be done.
References
- Chen X, Yuan L, Xu H, Hu P, Yang Y, Guo Y, et al. Novel GLI3 Mutations in Chinese Patients with Non-syndromic Post-axial Polydactyly. Curr Mol Med. 2019. 19(3):228.
- Cohen MS. Thumb duplication. Hand Clin. 1998 Feb. 14(1):17-27.
- Malik S, Grzeschik KH. Synpolydactyly: clinical and molecular advances. Clin Genet. 2008 Feb. 73(2):113-20.
- Zimmer EZ, Bronshtein M. Fetal polydactyly diagnosis during early pregnancy: clinical applications. Am J Obstet Gynecol. 2000 Sep. 183(3):755-8.
- suggestions for surgical management. Br J Plast Surg. 2001 Jan. 54(1):34-8.
- Katz K, Linder N. Postaxial type B polydactyly treated by excision in the neonatal nursery. J Pediatr Orthop. 2011 Jun. 31 (4):448-9.
- Belthur MV, Linton JL, Barnes DA. The spectrum of preaxial polydactyly of the foot. J Pediatr Orthop. 2011 Jun. 31 (4):435-47.
