Polydactyly
Polydactyly, also known as polydactylia or hyperdactyly, is a congenital condition characterized by the presence of one or more extra digits on the hands and/or feet. This condition arises from errors during fetal development and can manifest in different forms, including preaxial duplication (extra digit on the thumb or big toe side), central duplication (extra digit in the middle), and postaxial duplication (extra digit on the little finger or toe side). While polydactyly can occur as an isolated trait, it is often associated with various genetic disorders, such as Carpenter syndrome and Ellis-van Creveld syndrome, which may also involve additional health complications.
The incidence of polydactyly is approximately 1 in 1,000 births for hands and 1 to 2 in 1,000 for feet, with varying prevalence across different ethnic groups. Diagnosis typically involves a comprehensive medical history, imaging studies, and physical examination to assess the extent of the condition. While the only symptom is the physical presence of the extra digits, additional symptoms may indicate other genetic issues.
Treatment usually involves surgical intervention, especially if the extra digit affects function or aesthetics, with procedures often performed around the age of one for optimal outcomes. Although there is no known prevention for spontaneous cases, genetic counseling can assist families with a history of polydactyly. Overall, the prognosis for isolated polydactyly is generally very positive following surgical correction.
Polydactyly
ALSO KNOWN AS: Polydactylia; polydactylism; hyperdactyly; extra digits; supernumerary digits
DEFINITION Polydactyly is a relatively common congenital deformity that occurs due to errors during fetal development and results in the presence of one or more extra digits on the hand and/or foot. It occurs as follows: preaxial duplication—thumb side of hand/hallux (big toe) side of foot; central duplication—middle digit area of hand/foot; postaxial duplication—little digit side of hand/foot.
Risk Factors
Polydactyly can occur spontaneously (familial polydactyly) or in conjunction with a number of genetic disorders. Asphyxiating thoracic dystrophy (Jeune syndrome) is a bone growth disorder. Carpenter syndrome is an acrocephalopolysyndactyly (ACPS) disorder that affects bone growth. Ellis-van Creveld syndrome (chondroectodermal dysplasia) is a bone growth disorder involving growth hormone deficiency; the highest incidence rate of this syndrome occurs in Old Order Amish from Lancaster County, Pennsylvania. Laurence-Moon-Biedl syndrome is a mitochondrial myopathic disorder characterized by intellectual disability and possibly short stature.
Rubinstein-Taybi syndrome is a rare disorder characterized by intellectual disability and short stature. Smith-Lemli-Opitz syndrome is a disorder characterized by microcephaly (small head circumference), hypotonia (weak muscle tonus), and possible organ malformations; the highest incidence of this syndrome occurs in Caucasians of central European ancestry. Trisomy 13 (Patau syndrome) is a usually fatal disorder characterized by multiple structural and developmental abnormalities.
Familial may occur independent of any other symptoms or disease. The highest incidence of sixth digit inheritance occurs in African Americans. In those rare instances where polydactylism causality cannot be definitively attributed to genetic abnormality, it is hypothesized that womb abnormality or exposure to toxins may be contributing factors.
Etiology and Genetics
Although it can occur independent of genetic factors, polydactyly is most commonly a heritable, autosomal dominant trait involving a single gene that is capable of causing several variations in expression. Therefore, inheritance is not gender linked and does not require that both parents have the trait. It most likely occurs as the result of duplication of a single embryologic bud.
Incidence rate for polydactyly of the hand is approximately 1 per 1,000 births. It is the most common hand anomaly and occurs most frequently as preaxial (thumb) polydactyly in those of Asian ancestry who have the trait and as postaxial (little finger) polydactyly in those of African ancestry who have the trait. It does not usually occur bilaterally.
Incidence rate for polydactyly of the foot is approximately 1 to 2 per 1,000 births. In approximately 50 percent of all cases, it occurs bilaterally although not necessarily symmetrically. In approximately 33 percent of all cases, it occurs in conjunction with polydactyly of the hand.
Incidence of fused extra digits indicates the concomitant occurrence of polydactyly and syndactyly (fusion of digits) and is termed polysyndactyly.
Symptoms
The only symptom of polydactyly is the presence of one or more extra digits. The presence of other symptoms may indicate the possibility of a concomitant genetic disorder.
Screening and Diagnosis
Screening consists of obtaining a comprehensive medical history and performing chromosome studies. Diagnosis is possibly via fetal sonogram and is immediately apparent at birth. Radiographic evaluation may be necessary to determine the extent of possible skeletal involvement and to confirm that there is no underlying deformity. Other tests that may be used to confirm the diagnosis are tests and metabolic studies.
Treatment and Therapy
Treatment most often involves surgery, the extent of which is dependent upon the degree of bone, ligament, and tendon involvement. In order to reduce the risk of anesthesia yet allow for the maximum potential for remodeling, surgical excision usually occurs when a baby is approximately one year old.
Standard practice for correction of a “floppy digit,” one attached only by soft tissue, is application of suture ligature while the baby is in the hospital nursery. This practice is not recommended, however, if the extra digit has metacarpal/metatarsal duplication and/or residual cartilage, due to the risk of future deformity.
Extensive surgical intervention may require subsequent stabilization of the joint area via short-term casting and maximization of function via physical therapy. Additional surgery may be required during childhood to prevent or correct growth deformity.
Prevention and Outcomes
There is no known means of prevention for spontaneously occurring polydactyly. Possible prevention of polydactyly that occurs in conjunction with genetic disorders would require genetic screening and counseling of prospective parents. The prognosis for isolated polydactyly is extremely favorable with surgical excision.
Bibliography
Al Amin, A.S.M., and Kevin R. Carter. "Polydactyly." StatPearls, 8 Aug. 2022, www.ncbi.nlm.nih.gov/books/NBK562295/. Accessed 4 Nov. 2022.
Barnhill, Raymond L., and A. Neil Crowson. Textbook of Dermatopathology. 3rd ed. New York: McGraw, 2010. Print.
Holmes, Lewis B. Common Malformations. New York: Oxford UP, 2012. Print.
Hosalkar H. S., Spiegel D. A., and Davidson R. S. “Toe Deformities.” Nelson Textbook of Pediatrics. 19th ed. Ed. R. M. Kliegman, et al. Philadelphia: Saunders, 2011. Print.
Kumar, Praveen, and Barbara K. Burton. Congenital Malformations Evidence-Based Evaluation and Management. New York: McGraw, 2011. Digital file.
Kyriazis, Zisis, et al. "Polydactyly: Clinical and Molecular Manifestations." World Journal of Orthopedics, vol. 14, no. 1, 18 Jan. 2023, pp. 13-22, doi.org/10.5312%2Fwjo.v14.i1.13. Accessed 4 Sept. 2024.
Malik, S. "Polydactyly: Phenotypes, Genetics and Classification." Clinical Genetics 85.3 (n.d.): 203–12. Biological Abstracts. Web. 7 Aug. 2014.
McGlamry, Dalton, et al. McGlamry’s Comprehensive Textbook of Foot and Ankle Surgery. 3rd ed. Philadelphia: Lippincott, 2001. Print.
Tickle, C. “Embryology.” The Growing Hand: Diagnosis and Management of the Upper Extremity in Children. Ed. A. Gupta, S. P. J. Kay, and L. R. Scheker. London: Mosby, 2000. Print.