Coupling between wrist flexion–extension and radial–ulnar deviation

Abstract

Background. Conventional wrist joint goniometry evaluates range of motion in isolated directions. The coupling between wrist flexion–extension and radial–ulnar deviation was investigated. Methods. Ten healthy young male subjects performed wrist flexion–extension, radial–ulnar deviation, and circumduction motions. Flexion–extension and radial–ulnar deviation angles were computed from the coordinates of surface markers attached to the forearm and hand. A motion analysis system recorded marker motion. Findings. During radial–ulnar deviation, the amount of accompanying flexion–extension movement was linearly related to the amount of radial–ulnar deviation. The secondary (flexion–extension) range of motion (48.3°) was about 75% of the primary (radial–ulnar deviation) range of motion (55.1°). During the flexion–extension task, the coupling was less linear. The motion range in radial–ulnar deviation (21.2°) was about 20% of the primary (flexion–extension) range of motion (108.3°). The radial–ulnar deviation and flexion–extension motions combined extension with radial deviation, and flexion with ulnar deviation. The convex hull of the flexion–extension and radial–ulnar deviation angles during circumduction was “egg-shaped” and asymmetric with respect to the anatomically defined flexion–extension and radial–ulnar deviation axes. Wrist position in one direction strongly influenced the range of motion in the other. Maximum range of motion in flexion–extension occurred with the wrist near the neutral radial–ulnar deviation position, and vice versa. Wrist deviation from neutral position in one direction diminished wrist range of motion in the other. Interpretation. Wrist movements in flexion–extension and radial–ulnar deviation are coupled. Maximal wrist range of motion is near the neutral position. To account for the naturally coupled wrist motion in work station design and rehabilitation, the wrist should be placed at a neutral position.