Muscle activities during shoulder internal rotation differ in arm position: a preliminary quantitative analysis using positron emission tomography

Objective To investigate the muscle activity patterns of the glenohumeral joint during internal rotation both with the arm at 0° and 90° of abduction using 2-deoxy-2-[ 18 F] fluoro- d -glucose (FDG) positron emission tomography (PET) and magnetic resonance imaging (MRI). Materials and methods Six healthy male volunteers underwent PET examination after performing active glenohumeral internal rotation exercise using an elastic band both with the arm at 0° and 90° of abduction. As a control, PET scan under resting condition was also performed. The exercise was performed before and after 18 fluorodeoxyglucose injection. Each PET image was fused to the corresponding MRI to identify each muscle. The standardized uptake value (SUV) of each muscle was compared between the two arm positions. Results With the arm at 0° of abduction, the SUV increased significantly after exercise both in the middle and inferior 1/3 of the subscapularis, which were significantly higher than that of the superior 1/3 of the subscapularis ( P