Kinematic considerations of the wrist.

Mechanically the wrist is the most complex joint in the body, providing a large range of motion in the flexion-extension and radial-ulnar deviation planes. By virtue of the constraints at the radiocarpal level, strong torque may be delivered to the grasping hand for work in the grasping mode through the rotational axis of the forearm. The intrinsic forces acting on the wrist are well distributed around the perimeter, while the extrinsic forces for the fingers are centralized to affect wrist position minimally. The stability of the wrist in which the proximal carpal row presents an inherently unstable intercalated segment is provided by a complex osseoligamentous arrangement. The scaphoid performs a unique function as a mechanical link between the carpal rows, interacting with two arcs of oblique ligamentous support for the radiocarpal area. This allows synchronous angulation of the proximal and distal carpal rows and, by virtue of conjunct angulation, adaptive geometric change to encourage radial-ulnar deviation. The distal radioulnar joint functions both as the support of the carpus on the ulnar aspect of the joint and as a primary pivot for forearm rotation through a unique anatomic arrangement.