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KMID : 0603419990040010111
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Journal of the Korean Society Reconstructive Hand Surgery
1999 Volume.4 No. 1 p.111 ~ p.133
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BIOMECHANICS OF THE WRIST
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Ryu JaI-Young
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Abstract
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To position the hand optimally in space for specific tasks, the wrist must strike a crucial balance between mobility and stability. A ball and socket joint - the basic design for the hip and shoulder joints - provides a large arc of motion but is a poor precursor for the wrist, as its inherent instability is checked mainly by bulky surrounding muscles. The wrist cannot afford such bulk, else its performance would be hindered greatly. Thus, the wrist is designed in another way to maintain both mobility and stability: multi-linked rows. Each link has a small motion but good stability. When assembled, the wrist combines the motions of the multiple links. The links, despite their advantages, do decrease wrist stability somewhat. To compensate, the wrist is designed not only in multi-linked rows, but in columns of these rows as well. An et al. compared the wrist with a Rubik’s cube, with its comparable arrangement of rows and columns. The traditional row theory and the columnar theory, which was first proposed by Navarro then modified by Taleisnik were developed to explain how the columns and rows affect wrist motion and stability. The scaphoid, which connects the proximal and distal rows, makes carpal kinematics and kinetics more complex. Linscheid and Dobyns introduced the slider-crank mechanism of the scaphoid to explain its roles. Lichtman et al. later proposed the ring concept where the proximal and distal rows are connected with radial mobile and ulnar rotatory links. Craigen and Stanley observed that there are two kinds of people: one whose scaphoid stays vertical and translates through radioulnar deviation and the other whose scaphoid flexes with ulnar deviation. Thus, they felt that carpal kinematics covered a spectrum from the row theory to the column theory which is normally distributed. They reported that women were more likely to have column type wrists.
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