Analysis of helical axes, pivot and envelope in active wrist circumduction.
OBJECTIVE: To study active wrist circumduction and planar moves, in terms of 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 distance 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 stereophotogrammetric studies of wrist kinematics. However, the distribution of "3D centers of rotation" has never been presented in a non-invasive in vivo study. METHODS: A light 6 degrees of freedom electrogoniometer was built and employed in vivo to measure circumduction, flexion-extension and radioulnar deviation 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 joint but with a non fixed location in the capitate head. The major axis of wrist envelope was not skew. RELEVANCE: The envelope and the precise knowledge of the helical axis pivot and its mean distance to the axes could give precious information on wrist functionality and stability after surgical or conservative treatment.