Effects of scapular dyskinesis and scapular assistance test on subacromial space during static arm elevation

Background: Scapular dyskinesis is an abnormal scapular motion or position during active arm elevation. Dyskinesis is theorized to contribute to impingement syndrome by decreasing the subacromial space. A corrective maneuver of the scapular assistance test (SAT) proposes to increase scapular upward rotation and posterior tilt to increase the subacromial space. The purpose of this study is to determine the influence that 1) scapular dyskinesis and 2) passive manual correction with the SAT have on subacromial space and 3-dimensional (3-D) scapular kinematics. Materials and methods: Forty asymptomatic participants were classified with either obvious dyskinesis (n = 20) or normal motion (n = 20) using the scapular dyskinesis test. The anterior outlet of the subacromial space was measured via the acromiohumeral distance using ultrasound imaging and 3-D scapular orientation was assessed with electromagnetic motion analysis, with the arm at rest 45° and 90° of active elevation with and without the SAT, respectively. Results: There were no differences in acromiohumeral distance or scapular kinematics with static active arm elevation between groups. The SAT increased scapular upward rotation, posterior tilt, and acromiohumeral distance in both groups. Participants with dyskinesis demonstrated greater scapular mobility in upward rotation with the SAT, but no additional increase in acromiohumeral distance. Conclusion: Scapular dyskinesis identified during active motion did not result in different 3-D scapular orientation or acromiohumeral distance during active arm elevation in static positions; however, the SAT altered scapular kinematics and increased acromiohumeral distance. The SAT may be helpful to identify individuals where subacromial compression is producing symptoms, regardless of dyskinesis.