Association between digit ratio (2D:4D) and palmaris longus muscle agenesis according to gender: a radiological study

Abstract

Objectives: The palmaris longus (PLM) muscle is a superficial forearm muscle that may be congenitally absent, with prevalence varying among populations. This study aimed to investigate the association between PLM agenesis, sex, and the digit ratio (2D:4D) using radiological imaging methods. Methods: Wrist magnetic resonance imaging (MRI) examinations of 264 individuals (115 males and 149 females) performed at Bolu Abant İzzet Baysal University, Faculty of Medicine, Department of Radiology between 2020 and 2024 were evaluated retrospectively to assess the presence or absence of the PLM. The 2D:4D digit ratio was assessed using hand radiographs. Descriptive statistics were calculated. An independent samples t-test and Pearson’s chi-square test were applied, with the significance level set at p≤0.05. Results: PLM was present in 83.7% and absent in 16.3% of cases. PLM was absent in 13.9% of males and 18.1% of females, with no statistically significant sex difference (p=0.359). Right and left sided absence rates were 17.4% and 15.0%, respectively, showing no significant side-related difference (p=0.605). PLM was absent in 16.1% of individuals with a 2D>4D ratio and in 16.5% of those with a 4D>2D ratio (p=0.928). No significant association was found between PLM presence and the 2D:4D ratio. Conclusion: PLM agenesis is a relatively uncommon anatomical finding. The absence rate observed in this study and the lack of significant differences between sexes or sides are consistent with previous imaging-based studies. No significant association was identified between PLM presence or absence and the 2D:4D digit ratio.

Keywords

• digit ratio (2D:4D)
• magnetic resonance imaging
• palmaris longus absence
• radiography
• sex

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