Geometric Morphometric Analysis of the Human Hand Morphology Based on X-ray Imaging

Abstract

Currently, in humans, the ratio of the index and ring fingers (2D:4D ratio) determines the morphological type of the hand: type 1 or radial (2D>4D), type 2 or neutral (2D=4D), type 3 or ulnar (2D<4D). However, the above differences do not allow for morphological verification of the hand shape as a whole.The aim of the study was to inspect the hand shapes depending on its morphology based on radiographical images with geometric morphometric methods.Material and methods. Geometric morphometry included an analysis of the right hand shape described by 20 landmarks located on digital radiographic images (anteriorposterior projection) in 50 males and 50 females. Each hand was classified according to whether the index finger was longer, equal to, or shorter than the ring finger by visual assessment.Results. The study revealed differences between the hand shapes in the transverse direction, namely, the hands of the ulnar type (U) were wider, while the hands of the radial type (R) were narrower. The hands of neutral shape, unlike the other two types, were more oval in shape. In average, the hand shape depended on the morphological type. The most pronounced shape transformations were due to the geometry of the metacarpal bones in the transverse direction, and due to the geometry of the II, IV and V fingers in the longitudinal direction. Intergroup differences in width were revealed between the group of hands of radial (R)-neutral (N) types and ulnar (U) type, and in length between the group of hands of radial (R)-ulnar (U) types and neutral (N) type. The allometry of the hand shape was minimal.Conclusion. The results of the study demonstrate the potentials of geometric morphometry for analysis of the human hand shapes and their variability depending on the morphological type.