Analysis of helical axes, pivot and envelope in active wrist circumduction

Objective. To study active wrist circumduction and planar moves, in terms o f anatomical angles and envelope and of finite helical axes and mean pivot point. Design. We measured the position of the "mean pivot point" and its mean dis tance to the axes as anatomical angles in an in vivo full range movement. Background. The mean pivot point has been used in in vitro and roentgen ste reophotogrammetric studies of wrist kinematics. However, the distribution o f "3D centers of rotation" has never been presented in a non-invasive in vi vo study. Methods. A light 6 degrees of freedom electrogoniometer was built and emplo yed in vivo to measure circumduction, flexion-extension and radioulnar devi ation on both wrists of twenty one volunteers. Results. Results were in general agreement with previously published ranges of wrist planar motion. The circumduction envelope proved to be a relevant representation of active wrist motion. The "mean pivot point" displayed a relative dispersion in localization of this point. Conclusion. The pivot results suggest that the wrist acts as a universal jo int but with a non fixed location in the capitate head. The major axis of w rist envelope was not skew.