polydactyly polydactyly polydactyly or polydactylism (from greek πολύς (polys) 'many', and δάκτυλος (daktylos) 'finger'), also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary fingers and/or toes. polydactyly is the opposite of oligodactyly (fewer fingers or toes). polydactylyother nameshyperdactylya left hand with postaxial polydactylyspecialtymedical geneticsusual onsetduring pregnancydurationlifelong unless surgically removedtreatmentsurgery in some casesdeathsnone context as of 1977, the incidence of congenital deformities in newborns was approximately 2%, and 10% of these deformities involve the upper extremity. in 1961, frantz and o’rahilly proposed, that congenital anomalies of the limb could be classified in seven categories, based on the embryonic failure causing the clinical presentation. these categories are failure of formation of parts, failure of differentiation, duplication, overgrowth, undergrowth, congenital constriction band syndrome, and generalized skeletal abnormalities. in 1976 this was modified by swanson. polydactyly belongs to the category of duplication. as of 2009, research has shown that the majority of congenital anomalies occur during the 4-week embryologic period of rapid limb development. as of 2002, polydactyly has been associated with 39 genetic mutations. signs and symptoms male with unilateral preaxial polydactyly affecting the left thumb. the supernumerary digit had normal sensation but no joint and hence could not move independently. in humans/animals this condition can present itself on one or both hands or feet. the extra digit is usually a small piece of soft tissue that can be removed. occasionally it contains bone without joints; rarely it may be a complete functioning digit. the extra digit is most common on the ulnar (little finger) side of the hand, less common on the radial (thumb) side, and very rarely within the middle three digits. these are respectively known as postaxial (little finger), preaxial (thumb), and central (ring, middle, index fingers) polydactyly. the extra digit is most commonly an abnormal fork in an existing digit, or it may rarely originate at the wrist as a normal digit does. polydactyly can be divided into three major types, which are discussed below, which depend on the location of the additional digit. in 2019 it was found that in cases of polydactyly with a fully functional additional digit, muscles to control the extra digit may be duplicated, resulting in increased motor control that allows the patient to carry out certain tasks with one hand that would normally require two. ulnar or postaxial polydactyly postaxial polydactyly this is the most common situation, in which the extra digit is on the ulnar side of the hand, thus the side of the little finger. this can also be called postaxial polydactyly. it can manifest itself very subtly, for instance only as a nubbin on the ulnar side of the little finger, or very distinctly, as a fully developed 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. mostly one neurovascular bundle can be identified, with no tendons present in the extra digit. in case of a fully developed extra finger, the duplication usually presents itself at the level of the metacarpophalangeal joint. a triplication of the little finger is very rare. ulnar polydactyly occurs ten times more often in african populations. the incidence in caucasians is reported as 1 in 1,339 live births, compared with 1 in 143 live births in africans and african americans. ulnar polydactyly is also often part of a syndrome. in patients with african ancestry ulnar polydactyly mostly occurs isolated, whereas the presentation in caucasians is often associated with a syndrome, though in a retrospective review, only 4 of 37 cases of ulnar polydactyly in caucasians were syndromic. radial or preaxial polydactyly preaxial polydactyly this is a less common situation, in which the affectation is on the side of the hand towards the thumb. radial polydactyly refers to the presence of an extra digit (or extra digits) on the radial side of the hand. it is most frequent in indian populations and it is the second most common congenital hand disorder. the incidence of radial polydactyly is reported as 1 in every 3,000 live births. the clinical features of radial polydactyly will depend upon the extent of duplication. radial polydactyly varies from a barely visible radial skin tag to complete duplication. thumb polydactyly varies from barely visible broadening of the distal phalanx to full duplication of the thumb including the first metacarpal. radial polydactyly is frequently associated with several syndromes. central polydactyly this is a very rare situation, in which the extra digit is on the ring, middle or index finger. of these fingers, the index finger is most often affected, whereas the ring finger is rarely affected. this type of polydactyly can be associated with syndactyly, cleft hand and several syndromes. polysyndactyly presents various degrees of syndactyly affecting fingers three and four. causes preaxial polydactyly: ectopic shh-expression, hemingway mutant, mouse, right forelimb polydactyly is associated with different mutations, either mutations in a gene itself or in a cis-regulatory element responsible for the expression of a specific gene. mutations in hoxa- or hoxd clusters are reported leading to polydactyly. interactions of hoxd13 and gli3 induce synpolydactyly, a combination of extra and consolidated digits. other signal transduction pathways in this context are the wnt signaling pathway or notch. in the specific case of preaxial polydactyly (hemingway mutant), a cis-acting mutation approximately 1mb upstream of shh gene has been implicated. normally shh is expressed in an organiser region, called the zone of polarizing activity (zpa) on the posterior limb side. from there it diffuses anteriorly, laterally to the growth direction of the limb. in the mutant, smaller ectopic expression in a new organiser region is seen on the anterior side of the limb. this ectopic expression causes cell proliferation delivering the raw material for one or more new digits. polydactyly can occur by itself, or more commonly, as one feature of a syndrome of congenital anomalies. when it occurs by itself, it is associated with autosomal dominant mutations in single genes, i.e. it is not a multifactorial trait. but mutation in a variety of genes can give rise to polydactyly. typically the mutated gene is involved in developmental patterning, and a syndrome of congenital anomalies results, of which polydactyly is one feature or two. polydactyly has been linked to the prenatal environment in a 2020 study showing a relationship to maternal pm10 pollution exposure in china. types include: omim type locus 174200 postaxial a1 gli3 at 7p13 602085 postaxial a2 13q21-q32 607324 postaxial a3 19p13.2-p13.1 608562 postaxial a4 7q22 174400 preaxial i ? 174500 preaxial ii shh at 7q36 174600 preaxial iii ? 174700 preaxial iv gli3 at 7p13 syndromes because polydactyly can be part of a syndrome (known genetic defect) or association(genetic defect not known), children with a congenital upper extremity deformity should be examined by a geneticist for other congenital anomalies. this should also be done if a syndrome is suspected, or if more than two or three generations of the family are affected. as of 2009, 97 genetic syndromes have been associated with different kinds of polydactyly. examples of syndromes include diamond-blackfan anemia, and the vacterl association, acrocallosal syndrome, basal cell nevus syndrome, biemond syndrome, ectrodactyly-ectodermal dysplasias-cleft lip/palate syndrome, mirror hand deformity, mohr syndrome, oral-facial-digital syndrome, rubinstein-taybi syndrome, short rib polydactyly. ulnar polydactyly ulnar polydactyly is often bilateral and associated with syndactyly and polydactyly of the feet. this can be a simple or complex polydactyly. ulnar polydactyly occurs as an isolated congenital condition, but can also be part of a syndrome, such as: trisomy 13, greig cephalopolysyndactyly syndrome, meckel syndrome, ellis–van creveld syndrome, mckusick–kaufman syndrome, down syndrome, bardet–biedl syndrome, smith–lemli–opitz syndrome. radial polydactyly type vii of radial polydactyly is associated with several syndromes: holt–oram syndrome, fanconi anemia (aplastic anemia by the age of 6), townes–brocks syndrome, and greig cephalopolysyndactyly (also known to occur with ulnar polydactyly). central polydactyly the syndromes associated with central polydactyly are: bardet–biedl syndrome, meckel syndrome, pallister–hall syndrome, legius syndrome, holt–oram syndrome. central polydactyly can also be associated with syndactyly and cleft hand. diagnosis right-sided duplication of the right little toe in an 8.5 months old male, with two toes (fifth and sixth) apparently forming joints with the fifth metatarsal bone, which is mildly broadened distally. the duplicated toes have almost normal growth. the fifth toe has mild varus angulation, and the sixth toe has substantial valgus angulation. x-ray of type iii central polydactyly (the middle fingers are the same length). classification is performed by using x-ray imaging to see the bone structures. ulnar polydactyly type 1 ulnar polydactyly – an extra digit is attached by skin and nerves. the classification of ulnar polydactyly exists of either two or three types. the two-stage classification, according to temtamy and mckusick, involves type a and b. in type a there is an extra little finger at the metacarpophalangeal joint, or more proximal including the carpometacarpal joint. the little finger can be hypoplastic or fully developed. type b varies from a nubbin to an extra, non-functional little finger part on a pedicle. according to the three-type classification, type i includes nubbins or floating little fingers, type ii includes duplications at the mcpj, and type iii includes duplications of the entire ray. radial polydactyly the wassel classification is the most widely used classification of radial polydactyly, based upon the most proximal level of skeletal duplication. the most common type is wassel 4 (about 50% of such duplications) followed by wassel 2 (20%) and wassel 6 (12%). central polydactyly the classification of central polydactyly is based on the extent of duplication and involves the following three types: type i is a central duplication, not attached to the adjacent finger by osseous or ligamentous attachments; it frequently does not include bones, joints, cartilage, or tendons. type iia is a nonsyndactylous duplication of a digit or part of a digit with normal components, and articulates with a broad or bifid metacarpal or phalanx. type iib is a syndactylous duplication of a digit or part of a digit with normal components, and articulates with a broad or bifid metacarpal or phalanx. type iii is a complete digital duplication, which has a well-formed duplicated metacarpal. treatment ulnar polydactyly ulnar polydactyly usually does not interfere with hand function, but for social reasons it can be treated operatively. left foot with postaxial polydactyly of 5th ray type a ulnar polydactyly the treatment of type a ulnar polydactyly is complex as its goal is to remove the accessory digit while maintaining a stable, functional small finger. when the duplicated proximal phalanx articulates with a common, broad metacarpal head, the ulnar collateral ligament must be considered. in those cases with a common articulation or with a sixth metacarpal the muscle executing the abduction of the little finger (abductor digiti minimi) must be preserved. in patients with a common metacarpal articulation an elliptical incision at the base of the post-axial digit is made. this incision may be extended proximally in order to adequately expose the abductor digiti minimi. the ulnar collateral ligament and the insertions of the abductor digiti minimi are then elevated with a periosteal sleeve. the duplicated extensor and flexor tendons to the ulnar digit are transected and after that the digit is amputated at its articulation with the metacarpal. if the articular surface is wide the metacarpal may be shaved. at last the collateral ligament and abductor digiti minimi are reinserted at the base of the preserved proximal phalanx and a wire is then placed across the reconstructed joint. in patients with a duplicated metacarpal, the accessory digit is amputated in a standard ray fashion with transfer of the abductor digiti minimi to the retained small finger. type b ulnar polydactyly in this situation there is an absence of osseous and ligamentous structures. the surgical technique is analogous to radial polydactyly, in which the level of duplication and anatomical components should guide operative treatment. the pedicled ulnar extra digit can be removed by suture ligation to devise the skin bridge of the newborn child. this might be easier than an excision of the extra digit when the child is 6 to 12 months old. ligation occludes the vascular supply to the duplicated digit, resulting in dry gangrene and subsequent autoamputation. this must be done with consideration of the presence of a neurovascular bundle, even in very small skin bridges.