Quantification of Shoulder Joint Passive Rotation Range of Motion in Vivo
Jia-rea Chang Chien
Passive rotation range of motion (ROM) is an important factor in shoulder joint behavior. Previous work has shown shoulder joint rotation ROMs to be significantly dependent on arm position. However, the studies were either in vitro cadaver studies, or basically qualitative in vivo investigation on one plane of elevation. No research has investigated the quantitative relationships of internal and external rotations of the shoulder joint at multiple positions in normal subjects in vivo. Therefore, this study investigated quantitatively using an electromagnetic motion tracking system in vivo passive rotation ROM at a known rotational moment in multiple angles of arm elevation and planes of elevation. In 10 normal subjects, dominant arm was tested for humerus ROM for every 30 degree of elevation in various elevation planes under 4 N•m of moment. Internal rotation angle was found to decrease with arm elevation in most planes of elevation (r=0.4-0.6, p<0.05). External rotation decreased with arm elevation in forward flexion, in 30 degree anterior to the scapular plane, and in 60 degree posterior to the scapular plane (r=0.42, 0.46, 0.48, p<0.05), respectively. With humerus elevated at the 90 degree of arm elevation angle, range of internal rotation increased significantly as planes of elevation move backward, while the opposite trend was observed in the range of external rotation at the angles less than 90 degree of arm elevation angle.