The Scapular Assistance Test Results in Changes in Scapular Position and Subacromial Space but Not Rotator Cuff Strength in Subacromial Impingement

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Controlled laboratory study. To determine the effect of the modified scapular assistance test (SAT) on 3-dimensional shoulder kinematics, strength, and linear measures of subacromial space in patients with subacromial impingement syndrome (SAIS). Abnormal scapular kinematics have been identified in patients with SAIS. Increased scapular upward rotation and posterior tilt, as induced with manual assistance using the SAT, have been theorized to increase subacromial space and may alter shoulder strength. Forty-two subjects (21 with SAIS and 21 controls) participated in this study. The anterior outlet of the subacromial space, measured via the acromiohumeral distance on ultrasound images, and 3-dimensional scapular kinematics, measured using motion analysis, were determined with the arm at rest, and at 45° and 90° of active elevation with and without the SAT. A dynamometer was used to measure isometric shoulder strength. Full factorial mixed-model analyses of variance evaluated the effects of the SAT on variables between groups. There was an increase in scapular posterior tilt at all angles, upward rotation at rest and 45° of elevation, and acromiohumeral distance at 45° and at 90° with the SAT. The SAT did not alter normalized isometric strength. There were no differences in response to the SAT between the SAIS and control groups. Manual scapular assistance using the SAT influences factors associated with SAIS, such as subacromial space and potentially scapular orientation during static arm elevation, but not more so in individuals with SAIS than in healthy individuals. The SAT performed statically may be a way to identify potential subgroups of individuals with SAIS for whom subacromial space narrowing may be a contributing factor.