Ulnar Polydactyly: Family History, Phenotypes, Associated Anomalies, and Surgical Treatment in a Prospective 7-Year Registry Study

Purpose Ulnar polydactyly (UP) is a common congenital upper limb anomaly, yet prospective data on inheritance patterns, phenotypic distribution, associated anomalies, and treatment outcomes remain limited. Methods We conducted a registry-based observational study of consecutive children with UP enrolled in a prospectively maintained congenital upper limb anomaly registry at a tertiary referral center between 2018 and 2025. Data included family history, pregnancy characteristics, Congenital Upper Limb Differences database classification of phenotypes (A1–A6 and B), laterality, associated anomalies and genetically verified syndromes, and interventions. We analyzed the strength of associations between hand presentation and associated anomalies using multivariable logistic regression. Results We included 98 patients with 160 affected hands. Fifty-four percent had a non-Nordic family background, substantially exceeding the proportion of individuals with a non-Nordic background in the general population. Forty-two percent reported a positive family history of UP. Type B UP predominated (85%). Associated lower limb anomalies occurred in 24% of patients. Phenotypes A and bilateral affection showed strong associations with lower limb anomalies and genetic syndromes and/or anomalies besides the limbs. Our unit performed all surgeries without any complications, yet we reoperated many patients after inadequate ligation of type B UP in the maternity wards. Conclusions Ulnar polydactyly comprises phenotypic subgroups with differing risks of associated anomalies, supporting a phenotype-based approach to clinical assessment. We recommend genetic evaluation for all patients with phenotype A and for those with bilateral type B with associated lower limb anomalies. In contrast, unilateral and bilateral type B without lower limb involvement or associated anomalies on routine clinical examination do not require further evaluation. Type of study/level of evidence Clinical II.