Non-invasive detection of carpal mechanics in wrist flexion under load

An apparatus capable of following hand motion while exerting an opposing force in the flexion-extension plane of motion was designed, built and tested. The apparatus consisted of a forearm support and a custom fitted handle which could move unconstrained in the plane of motion. The subject's forearm was fixed while the subject grasped the handle and moved it though the flexion range of motion while the apparatus recorded the motion of the handle with an accuracy of 0.35 mm. and 0.63$\sp\circ$. The apparatus software then calculated the trajectory of the hand, the location of the centre of rotation and magnitude of the radius of curvature (ROC) using an angular step size of 8$\sp\circ$. The magnitude of ROC oscillations was shown to depend on the magnitude of the load at the wrist. This change in the ROC of the hand may be interpreted as the first noninvasive detection and quantification of carpal bone rearrangement expected from the complex anatomy of the wrist. The repeatability of the ROC oscillations may indicate that wrist flexion consists of a fixed sequence of carpal bone configurations which manifest as a cyclical change in the proportion of sliding/rotating tendencies of the hand as the flexion motion progresses. (Abstract shortened by UMI.)