Muscle activities during shoulder internal rotation differ in arm position: a preliminary quantitative analysis using po
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SCIENTIFIC ARTICLE
Muscle activities during shoulder internal rotation differ in arm position: a preliminary quantitative analysis using positron emission tomography Gaku Matsuzawa 1 & Hirotaka Sano 2 & Nobuyuki Yamamoto 1 & Daisuke Kurokawa 1 & Shoichi Watanuki 3 & Manabu Tashiro 3 & Eiji Itoi 1 Received: 24 February 2020 / Revised: 24 May 2020 / Accepted: 25 May 2020 # ISS 2020
Abstract 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-[18F] 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 < 0.05). The SUV of the inferior 1/3 of the subscapularis was significantly higher at 90° of abduction than at 0° of abduction and was significantly higher than that of the superior 1/3 at 90° of abduction (P < 0.01). The SUV after exercise in the inferior infraspinatus and teres minor increased. Conclusions The middle and inferior parts of the subscapularis are the main shoulder internal rotators in 0° of abduction, whereas the inferior part of the subscapularis is the main internal rotator in 90° of abduction. Keywords Internal rotation . Subscapularis . Adduction . Abduction . Positron emission tomography
Introduction Shoulder internal rotation is an essential motion to achieve a number of activities of daily living. Since glenohumeral internal rotation deficit links to many musculoskeletal injuries [1, 2], it has been reported that stretch exercise of internal rotators might contribute to prevent shoulder injuries [3–6]. It is well known that the rotator cuff muscles, the scapulohumeral * Eiji Itoi [email protected] 1
Department of Orthopaedic Surgery, Tohoku University School of Medicine, 1-1 Seiryo-machi, Aobaku, Sendai 980-8574, Japan
2
Division of Orthopedic Surgery, Sendai City Hospital, Sendai, Japan
3
Division of Cyclotron Nuclear Medicine, Cyclotron and Radioisotope Center, Tohoku University, Sendai, Japan
muscles, and the thoracohumeral muscles work simultaneously during shoulder internal rotation. Especially, the subscapularis is believed to be the primary and strongest internal rotator among them [7–16]. Although many authors have tried to find the activities of each muscle during shoulder intern
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