Three-dimensional in vivo scapular kinematics and scapulohumeral rhythm: a comparison between active and passive motion.

Background: The aim of this study was to compare the scapular kinematics and scapulohumeral rhythm of healthy participants during arm elevation and lowering and to find the difference between active motion and passive motion of the shoulder.
Methods: The study examined the shoulders of 10 healthy men (mean age, 23.5 years; age range, 22-28 years). The shoulders of participants were elevated and lowered while fluoroscopic images were taken, and 3-dimensional bone models were created from 2-dimensional to 3-dimensional images using model registration techniques. The Euler angle sequences of the models' scapular kinematics and scapulohumeral rhythm were compared during active and passive shoulder motion.
Results: There was a significant statistical difference of upward rotation during arm elevation between active and passive shoulder movements (P = .027). In particular, the upward rotation between 45° and 90° of elevation showed a statistically significant difference (P < .001). When the scapula was tilted posteriorly by active motion, it resulted in a statistically significant difference as there was more tilting in the high-degree range of motions than when it was tilted by passive motion (P < .001). There was no statistically significant difference between the 2 groups in scapular external rotation. However, during arm lowering, scapular kinematics did not show statistically significant difference between active and passive motion.
Conclusions: The scapular kinematics showed statistically significant differences between active and passive motion of upward rotation and posterior tilting of the scapula during arm elevation, but there were none during lowering. In terms of upward rotation, active shoulders rotated more upward during arm elevation.
(Copyright © 2019 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.)