Hypothesis: The scapulothoracic (ST) joint affects glenohumeral (GH) joint function. We observed 3-dimensional scapular motions during arm elevation and lowering to identify the scapulohumeral rhythm in healthy subjects and to compare it between the dominant and nondominant arms.
Materials and methods: Twenty-one healthy subjects participated in this study. Participants randomly elevated and lowered the arms in the scapular plane, and data were recorded by a computerized 3-dimensional motion analyzer at each 10 degrees increment.
Results: Of the 42 shoulders, 21 showed a greater ratio of GH motion relative to ST motion whereas the other 21 showed a smaller ratio of GH motion relative to ST motion. The angle of upward rotation of the scapula showed a statistically significant difference between both types. The mean maximum angles of upward rotation, posterior tilting, and internal rotation were 36.2 degrees +/- 7.0 degrees , 38.7 degrees +/- 5.7 degrees , and 36.8 degrees +/- 12.2 degrees , respectively. No significant difference was found in angles of 3 scapular rotations between the dominant and nondominant arms.
Discussion: These results indicate that there are 2 distinctly different scapulohumeral rhythms in healthy subjects but without a significant difference between dominant and nondominant arms. These findings should be referred to when one is interpreting kinematics in a variety of shoulder disorders.
Copyright 2010 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.