Comparison of 3-dimensional scapular position and orientation between subjects with and without shoulder impingement.

Abstract

Nonrandomized 2 group post-test only. To compare scapular position and orientation between subjects with and without impingement syndrome. Abnormal scapular motion is commonly believed to be a contributing factor to shoulder impingement syndrome. Twenty nonimpaired subjects with a mean age of 34.3 (+/- 7.5 years) and 17 patients with impingement syndrome with a mean age of 45.8 (+/- 11.0) participated. A 3-dimensional electromechanical digitizer was used to measure scapular position and orientation in 3 planes. Measurements were taken with the arm at the side, elevated in the scapular plane to horizontal, and at maximum elevation. One-way analysis of variance was used to compare nonimpaired subjects to the impingement group and the symptomatic and asymptomatic sides within the impingement group. Five scapular kinematic variables were assessed at each arm position. Orientation was described by posterior tilting angle, upward rotation angle, and internal rotation angle. Position was described by medial-lateral position and superior-inferior position and determined by the distance from the scapula centroid to the seventh cervical vertebra (C7). During scapular plane elevation of the arm, the scapula showed a general pattern of increasing posterior-tilt angle, increasing upward-rotation angle, and decreasing internal-rotation angle in both impingement and nonimpaired groups. Also, the scapula moved to a more superior position and a slightly more medial position with increasing arm elevation. Compared to nonimpaired subjects (34.6 degrees +/- 9.7), those with impingement demonstrated a significantly lower posterior tilting angle of the scapula in the sagittal plane (25.1 degrees +/- 9.1). Subjects with impingement also demonstrated higher superior-inferior scapular position with maximal arm elevation (5.2 cm +/- 1.6 below the first thoracic vertebrae) compared to nonimpaired subjects (7.5 cm +/- 1.5). These results suggest that altered scapular kinematics may be an important aspect of the impingement syndrome.