In vivo three-dimensional motion analysis of the shoulder joint during internal and external rotation
The purpose of this study was to assess accurately the three-dimensional movements of the scapula and humerus relative to the thorax during internal/external rotation motion with abduction of the shoulder joint.
Ten right shoulders of ten healthy volunteers were examined using a wide-gantry open magnetic resonance imaging (MRI) system. MRI was performed every 30° from 90° external rotation to 90° internal rotation of the shoulder joint.
The contribution ratio of the scapulothoracic joint was 12.5% about the long axis of the humerus during internal/external rotation motion. With arm position changes from 90° external rotation to 60° internal rotation, most movement was performed by the glenohumeral joint. Conversely, at internal rotation of ≥60°, the scapula began to markedly tilt in the anterior direction. At 90° internal rotation, the scapula was significantly tilted anteriorly (p < 0.05) when compared with the other positions.
We clarified the existence of a specific scapulohumeral motion pattern, whereby the glenohumeral joint moves with internal rotation and the scapulothoracic joint moves with anterior tilt together with internal rotation motion of the shoulder joint.
KeywordsInternal Rotation External Rotation Neutral Position Shoulder Joint Contribution Ratio
We wish to thank Mr. Y. Sakaguchi, a radiological technologist, for performing MRI at Matsumoto medical clinic and Mr. R. Nakao, a programmer, for developing the software.
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