Effects of Wrist Orthoses on Wrist Dynamics

Wrist orthoses are commonly used to cope with the myriad of disorders associated with the hand and wrist. These orthoses can be complex or simple, physician-prescribed or self-administered, custom-made or off-the-shelf, but one thing they all have in common is the desired goal to alter wrist motion in order to allow healing and facilitate proper wrist function. Although wrist orthoses have been in use for a very long time, there is little to no quantitative research into how they affect the dynamics of the wrist joint. Because the dynamics of the wrist-orthosis system are unknown, it is impossible to predict and/or precisely control the ensuing behavior of the wrist joint. Thus, despite their popularity, wrist orthoses have remained unsophisticated devices, indiscriminately altering the dynamics of the wrist joint in an attempt to assist its recovery from injury or disease. The purpose of this study is to take the first step toward understanding wrist joint-orthosis dynamics by characterizing how wrist orthoses alter the stiffness of the wrist joint. Using a forearm and wrist rehabilitation robot, we are currently conducting an experiment to measure the stiffness profile of twelve commonly purchased commercial wrist orthoses. Our preliminary findings have shown that wrist orthoses significantly increase the magnitude of wrist joint stiffness, but do not significantly alter the inherent anisotropy of natural wrist stiffness. The results of this experiment will allow for the design of future wrist orthoses targeted to impart specific stiffness characteristics to the wrist joint.