Location of the instantaneous center of rotation for shoulder motion

Information regarding the instantaneous center of rotation for shoulder motion is important for the design of continuous passive motion (CPM) machines for the shoulders. In this study, we attempted to determine the locations of the instantaneous center of rotation for shoulder motion of the arm. Fourteen healthy adult subjects (age 18 to 30 years) participated in this study, five were females and the rest were males, The instantaneous center of rotation was computed for two different shoulder motions: (1) abduction motion in the sagittal plane and, (2) abduction motion in the coronal plane. The motion of the arm was monitored by a magnetic device (Polhemus). Our results showed that the location of the instantaneous center was much more proximal than the glenohumoral joint. It was located between 11 and 16 cm from the C/sub 7/ vertebra for the abduction in the coronal plane and this distance varied from 9 to 13 cm for the motion in sagittal plane.