Abstract
BACKGROUND: Ulnar polydactyly, a common congenital hand anomaly, exhibits significant phenotypic variability. Existing classification systems have limitations, particularly in categorizing rare variants. This study introduces a new classification system for ulnar polydactyly that addresses these limitations. METHODS: We retrospectively reviewed the medical records of 35 patients with ulnar polydactyly treated at our institution between 2010 and 2022. Data collected included patient demographics, clinical presentation, radiographic findings, family history, associated anomalies, and surgical procedures. Based on detailed morphological and radiographic assessments, we developed a novel classification system comprising five main types (0-4) and associated subtypes. RESULTS: The 35 patients (23 males, 12 females) had a mean age of 3.2 years. Thirty patients had bilateral involvement, with 16 exhibiting symmetry. In total, 65 hands were affected, and one hand was excluded because the patient underwent surgery in another hospital. Type 0 was the most common (38 cases), followed by Type 4 (19 cases), Type 3 (4 cases), and Type 1 (3 cases). Our classification system effectively categorized all cases, including rare variants such as Type 1b (duplicated distal phalanx) and Type 4d (duplication originating from the deformed fourth metacarpal), which are not adequately addressed by previous classifications. CONCLUSIONS: Existing classification systems for ulnar polydactyly omit two key variants: Type 1b (duplicated distal phalanx) and Type 4d (duplication from the deformed fourth metacarpal). Our system specifically incorporates these types, providing a more comprehensive framework to guide diagnosis and improve surgical planning for these rare conditions. TRIAL REGISTRATION: Retrospectively registered.