Comparison of glenohumeral motion using different rotation sequences.

Glenohumeral motion presents challenges for its accurate description across all available ranges of motion using conventional Euler/Cardan angle sequences without singularity. A comparison of the description of glenohumeral motion was made using the ISB recommended YX'Y″ sequence to the XZ'Y″ sequence. A direct in-vivo method was used for the analysis of dynamic concentric glenohumeral joint motion in the scapular plane. An electromagnetic tracking system collected data from ten healthy individuals while raising their arm. There were differences in the description of angular position data between the two different sequences. The YX'Y″ sequence described the humerus to be in a more anteriorly rotated and externally rotated position compared to XZ'Y″ sequence, especially, at lower elevation angles. The description of motion between increments using XZ'Y″ sequence displacement decomposition was comparable to helical angles in magnitude and direction for the study of arm elevation in the scapular plane. The description of the direction or path of motion of the plane of elevation using YX'Y″ angle decomposition would be contrary to that obtained using helical angles. We recommend that this alternate sequence (XZ'Y″) should be considered for describing glenohumeral motion.