Three-dimensional clavicular and acromioclavicular rotations during arm abduction using vertically open MRI

Abstract

There have been several reports about the clavicular and acromioclavicular motion, but a precise motion has been unknown. The purpose of this study was to analyze the 3D kinematics of the clavicle and acromioclavicular joint during arm abduction, using 3D MR images obtained by a vertically open MRI. Seven subjects participated in this investigation, which included 14 shoulders. From a seated position, we obtained MR images of their shoulder in seven abducted positions of the arm in the coronal plane. We evaluated the 3D movements of each bone in the shoulder using the volume-based registration technique, and analyzed the clavicular positions relative to the lung and the scapular positions relative to the clavicle. During arm abduction, the clavicular motion relative to the lung showed 30.6° retraction, 7.3° elevation, and 33.2° posterior axial rotation. During arm abduction, the scapular motion relative to the clavicle showed 15.6° protraction, 21.5° upward rotation, and 22.2° posterior tilting. This study succeeded in describing the 3D clavicular and acromioclavicular motion including th axial rotation of the clavicle, and it revealed that both motions had large degrees of rotations. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.