Background: Polydactyly is the second most common congenital hand difference. A higher incidence, particularly postaxial polydactyly, amongst African Americans is widely documented. Understanding ethnic variations in the incidence and presentation of polydactyly is important for patient counseling and understanding the genetic basis of polydactyly. This study is a comprehensive systematic review collating the reported incidence of polydactyly around the world.
Methods: MEDLINE searched from inception until August 2022 using keywords “prevalence” [OR] “incidence” [AND] “polydactyly”. English language epidemiological and population studies were included; case series and case reports were excluded. Data on population demographics and incidence of preaxial and postaxial polydactyly were collected.
Results: Fifty studies were included, reporting outcomes for fourty-seven countries. The highest incidence rates were reported in Africa (21 - 239 per 10,000 live births). The lowest incidence rates were reported in Southeast Asia (1 - 6 per 10,000 live births). The remaining countries (European, South Asian, East Asian, North and South American) reported similar incidence rates (2 - 41 per 10,000 live births). There were no studies out of Oceania or the Pacific Islands. Only eight (16%) studies reported separate preaxial and postaxial polydactyly incidences. Of these papers, the vast majority of countries reported greater incidences of postaxial polydactyly with the highest postaxial to preaxial polydactyly ratio observed amongst African ethnicities (170:1). Only one paper out of Japan reported a preaxial polydactyly predominance. Nineteen (38%) studies reported sex specific figures, with fourteen (28%) reporting a male predominance.
Conclusions: There are clear regional variations in polydactyly incidence, with the greatest burden amongst the African population. Researchers should continue to report the incidence of congenital anomalies to better understand the trends of polydactyly within different populations. The incidence of polydactyly in Oceania and the Pacific Islands is yet to be characterised and is an area of future research.