Scapular kinematics during transfers in manual wheelchair users with and without shoulder impingement.

BACKGROUND: Scapular function during humeral elevation has been reported in groups with and without shoulder impingement pathology. To date, no one has assessed scapular kinematics during upper extremity loaded tasks that manual wheelchair users must perform on a daily basis. Therefore, the objective of this study was to compare scapular kinematics and muscle activation patterns during two different wheelchair transfers in groups of manual wheelchair users with and without shoulder impingement.
METHODS: A case controlled study of manual wheelchair users, with and without shoulder impingement was performed. Twenty-three male manual wheelchair users (13 without shoulder impingement, 10 with shoulder impingement) performed transfers toward the involved or dominant limb (lead limb transfer) and away from the instrumented limb (trail limb transfer). Position and orientation measures of the thorax, scapula and humerus were obtained using an electromagnetic tracking system. Muscle activity data were collected using telemetered electromyography. Each subject performed three trials of wheelchair transfers to each side.
FINDINGS: Manual wheelchair users with impingement performed transfers with reduced thoracic flexion, increased scapular internal rotation, and increased humeral internal rotation as compared to those without impingement. Differences were found between the tasks in the scapular motions and EMG amplitude. Trail limb transfer presented with reduced scapular upward rotation and posterior tip as compared to the lead limb transfer task. Increased muscle activity for the lower trapezius and serratus anterior muscles was demonstrated in the trail limb transfer.
INTERPRETATION: This study provides the first kinematic description of scapular kinematics during transfer tasks. Shoulder impingement and direction of transfer does affect transfer task performance in manual wheelchair users. Scapular kinematics and muscle patterns during transfers may predispose manual wheelchair users to the development of shoulder pathology.