Radiologically Assessed Sex-Specific Left-Hand Digit Ratio (2D:4D) in Caucasian Children and Adolescents from South Germany

The relative length of the 2nd (index) and 4th (ring) finger, i.e., digit ratio (or 2D:4D) is known to be different in males and females. Few radiologically assessed data on 2D:4D for children and adolescents are available. The aim of this study was to create a local database (MuC-2020) for the radiologically assessed sex-specific left-hand 2D:4D, and to compare this data to historical cohorts from three radiographic atlases of skeletal development of the hand and wrist. Therefore, left-hand X-ray images of 169 female and 199 male children and adolescents (age: 8-18 years) who presented at our endocrine unit in 2019 and 2020 mostly for reasons of predicting final height were analyzed. The 2D:4D ratio was calculated and compared with ratios determined from X-ray images of patients > 8 years of the atlases Greulich and Pyle (G&P, data from USA, 1936-1942), Gilsanz and Ratib (G&R, data from USA, 1980-2000), and Thiemann and Nitz (T&N, data from German Democratic Republic, 1977). Female individuals showed a higher 2D:4D ratio with a mean of 0.936 compared to males (0.919, p < 0.001). When comparing to historical data, the MuC-2020 2D:4D ratio significantly differed (females, G&P, p = 0.029; males, G&P p < 0.001, G&R, p = 0.018), with an overall increasing 2D:4D trend over time. The results of this analysis underpin the binarity of sex-specific left-hand 2D:4D in children and adolescents, and show differences to previously published cohorts suggesting an increasing 2D:4D ratio trend over the last decades. The underlying reasons are unknown, but environmental factors may be a reason (e.g., endocrine disrupting substances).