Effect of loading and movement direction on scapulothoracic orientation

Richards, James G.In clinical settings, scapular orientation is routinely used as a factor to diagnose shoulder dyskinesis. Abnormal scapular function has been linked to shoulder pathologies including the inability to perform daily functions, rotator cuff injuries or chronic shoulder pain. The majority of upper extremity (UE) research evaluates scapular contributions to UE motion during unloaded conditions or while performing pure planar movements. However, activities of daily living frequently involve multi-planar UE motions under loaded conditions. Accurate measurement of scapular orientation is essential to predict, diagnose and treat scapular dyskinesis. ☐ The objective of this study was to compare scapular orientation between unloaded and loaded conditions during multi-planar UE motions. Twenty healthy, adult subjects placed their right arm into 11 multi-planar positions while wearing retroreflective markers on anatomical landmarks of the thorax, scapula, humerus, forearm and hand. Once markers were placed, one second of 3D motion capture data were recorded and tracked at 60 frames/sec. Subjects then repeated the positions while holding a 1kg weight. Kinematics were calculated for the scapulothoracic, glenohumeral and humerothoracic joints. ☐ This study utilized a novel, real-time matching feedback system to ensure the arm was in the same clinical position for the loaded condition relative to the unloaded condition. Data was not collected or recorded if the arm positions differed more than 20° between conditions. A secondary goal of the study was to determine how closely an acromion marker cluster (AMC) tracked scapular orientation relative to palpation. The AMC is a popular method utilized for upper extremity studies, yet it is known to exhibit large errors at humeral elevation angles greater than 90°. For comparison, palpated landmarks included the trigonum spinae (TS) and inferior angle (IA). The TS and IA markers were removed and repositioned after each of the eleven positions to mark the location of the scapula. ☐ No significant differences in scapular orientation were found for functional UE motions between unloaded and loaded conditions when supporting a load of ~1kg. Conversely, results confirm significant differences between the palpation and AMC methods. The AMC was accurate when measuring upward and downward rotation, but significantly overestimated internal rotation for three of the eleven positions while overestimating external rotation during the loaded external rotation position. The AMC had the greatest difficulty in measuring anterior and posterior tilt. The AMC significantly overestimated the amount of posterior tilt for five of the eleven positions and overestimated anterior tilt, for the hand to spine position, for both the unloaded and loaded conditions. These findings conclude that light, external loads do not impact scapular orientation and caution should be used when utilizing the AMC method at extreme humeral elevation angles. Further research to include children, athletes or those with shoulder pathologies could be conducted. Additionally, studies conducted on scapular orientation during loaded dynamic movements may prove to be beneficial for clinicians, surgeons and therapists.University of Delaware, Department of Kinesiology and Applied PhysiologyM.S