Load dependence in carpal kinematics during wrist flexion in vivo

Objective. The hypothesis tested was that generation of torque at the wrist affects joint kinematics. Design. An in vivo study of normal wrist kinematics during plantar flexion motion against a constant load was undertaken, using a custom-designed instrumented apparatus to track the motion of the hand during the task. Background. Despite clinical observations of a relationship between motion-loading and pain in wrists affected by rheumatoid arthritis, there is little published literature on the in vivo kinematics of the normal human wrist under load. Methods. Ten volunteers with no wrist pathology were tested while generating torques of zero, 1.1 and 2.2 N m in a planar, unidirectional flexion motion. Hand kinematics were computed using the Planar Rigid Body Method algorithm and an 8 ° angular step size. The finite radius of motion and the range and standard deviation of the residuals to a fitted second-order curve were used as indices of changes in the kinematics. Results. The magnitude of both the range and standard deviation of the residuals were found to increase significantly with torque at the 95% confidence level. Conclusions. The wrist does not behave like a smooth mechanism when generating torque. Load affects carpal kinematics.