[Torsion of the metacarpals II to V. Functional and clinical significance].

Torsion of the metacarpals II to V was measured in 50 pairs of human hand skeletons. The in-situ position of the metacarpals was reconstructed and the influence of the torsion of the morphological radioulnar head axes analysed. It is shown that during flexion of the metacarpophalangeal joint these morphological radioulnar axes serve as functional axes. Because of the specific position of the radioulnar axes through the metacarpal heads, the hand can be divided into three functional units: the thumb; the index and middle fingers; the fourth and fifth fingers. Within such a functional unit, lines perpendicular to the aforementioned radioulnar axes converge. In contrast to earlier investigations, these lines do not intersect at one common point. There are two separate intersections: one for the metacarpals II and III and another for the metacarpals IV and V. The torsion of right and left metacarpals shows significant differences. The lines perpendicular to the radioulnar metacarpal head axes in left hands generally show a more radial deviation, whereas in right hands they run more parallel to the metacarpals' longitudinal axes. This investigation shows that the precision grip of the right hand and the power grip of the left is supported by the morphology of the metacarpal bones. Finally, the clinical significance of our results is pointed out.