The mechanism of the carpal joint.

The morphologic features of the carpal bones and their contacts play a highly significant role in the mechanism of the wrist joint. Displacements of the proximal carpal bones in both flexion and deviation of the hand take place in longitudinal articulation chains that are linked one to another. This concept is supported by the following observations: differences in curvature between the facets of the proximal carpals at the radiocarpal level suggest that simultaneous movements occur at the midcarpal level; the position of the proximal carpal bones is determined by their position with respect to both the distal carpal bones and the radius; displacements of the proximal carpal bones to the distal carpals result in swerving motions in the transverse plane in addition to dorsopalmar rotation (as a result, the volar rotated position of a proximal carpal in the volar flexed hand will differ from its position in the radial deviated hand and the positions of the proximal carpals in the dorsiflexed hand will differ from these in the ulnar deviated hand); and the three articulation chains, radial, central, and ulnar, cannot function on their own, since the linkage in the longitudinal direction is associated to a transverse linkage by the mutual joint contacts between the chains and by ligamentous interconnections.