The elderly population are at risk of having shoulder pain and dysfunction. One possible contributor to shoulder impairment is abnormal scapulothoracic and glenohumeral motion. Comparing the elderly and young age groups based on changes in kinematics and thoracic posture during completion of day-to-day functional tasks is not well understood. The purpose of this study was to compare three-dimensional shoulder kinematics, thoracic posture and shoulder strength between asymptomatic elderly and young individuals. Subjects included 50 asymptomatic right dominant, gender and BMI matched individuals equally divided into young (20 to 40 years) and elderly (above 65 years) groups. A 3D electromagnetic motion capture system was used to record scapulothoracic and glenohumeral angular positions during scapular plane abduction, forward reach, reaching the back, reaching the wallet and touching the head tasks. Kinematics were computed at 25%, 50%, 75% and 100% of the humeral angular motions. A 3D CT based reconstructed anatomical model was animated based on group mean motion data to compute the minimum linear distance from rotator cuff footprints to potential impinging structures. Thoracic posture in static and dynamic conditions was measured for flexion-extension. Isometric shoulder strength was measured in four directions with a portable dynamometer and strength ratios were computed. Significant kinematic differences between groups were present for humerothoracic elevation range of motion, scapular internal rotation during scapular plane abduction, scapular upward rotation during forward reach, glenohumeral external rotation during forward reach, scapular internal rotation during reaching the back, scapular posterior tilt during reaching the back and scapular internal rotation during reaching the wallet. The mean differences between groups were less than 8° with the exception of glenohumeral external rotation (<19°) during the forward reach task. Overall, relative to the number of comparisons, few group differences existed for the tested conditions and those that were different had small magnitude. It was believed that these differences represent natural consequences of aging even in the absence of shoulder pain or dysfunction. Minimum linear distance was reduced in the elderly for forward reach and reaching the wallet tasks. It was believed, however, that position was the issue during reaching the wallet task since both groups had submillimeter minimum distances for that task. Significant dynamic thoracic flexion-extension differences between groups existed for reaching the back and reaching the wallet tasks. However, the magnitudes of the differences between groups were less than 2°, so it was thought that these differences were not clinically meaningful. Significant reduction in shoulder strength for the elderly group was evident in flexion, abduction, external rotation and internal rotation directions, but strength ratios were similar for both the groups. Based on the findings it was assumed that forward reach and possibly reaching the wallet tasks may benefit from further investigation due to the possibility of higher potential for rotator cuff compression in the elderly group. Maintaining strength ratios may be protective for developing rotator cuff disease. Modification of the forward reaching and reaching the wallet tasks may be considered while planning shoulder intervention strategies for the elderly.
University of Minnesota Ph.D. dissertation. August 2014. Major: Rehabilitation Science. Advisor: Paula M. Ludewig, PhD. 1 computer file (PDF); xv, 247 pages, appendices 1-25.
Comparison of 3D shoulder kinematics, thoracic posture and shoulder strength between asymptomatic elderly and young population.
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