Abstract
Flexion movement of the shoulder joint was analyzed on the sagittal plane in 8 healthy men (mean age, 21 years), using MRI in the human body without the involvement. The task of the measurement included spontaneous flexion movement (at 0°, 90°, 120°, 150°, and the maximum flexion angle) of the right shoulder joint on the sagittal plane in a left lateral recumbent position. The position of the extremity at each angle was passively maintained during imaging. Actually, the maximum angle of flexion of the shoulder joint was approximately 170°. The ratio of glenohumeral to scapulothoracic motion (scapula-humeral rhythm) was about 2.1:1 after 170° of flexion of the shoulder joint. The head of humerus ultimately showed internal rotation of 36.4° at 170° of flexion of the shoulder joint, and a length of the supraspinatus was reduced by the internal rotation. Taking abduction/adduction and upward rotation of the scapula into account, however, the shoulder joint ultimately showed external rotation of 29.6°. Based on these results, we reconfirmed that it is important to consider motion of the humerus and scapula during movement for improvement in range of motion of the shoulder joint.
