Comparison of muscle activity in the empty-can and full-can testing positions using 18 F-FDG PET/CT

BACKGROUND There has been much controversy over specific tests for diagnosis of supraspinatus tendon tear. The aim of this study was to evaluate the metabolic activity of the deltoid and rotator cuff muscles while maintaining the full-can and empty-can testing positions using 2-deoxy-2-[18 F]fluoro-D-glucose (18 F-FDG) positron emission tomography (PET)/computed tomography (CT). METHODS Ten healthy volunteers without shoulder pain or diabetes mellitus participated in this study. Following FDG injection, both arms were maintained in either the empty-can or full-can position for 10 min. PET/CT was performed 40 min after injection. Maximum standardized uptake values (SUVs) were measured in the deltoid and rotator cuff muscles on axial PET images. RESULTS The middle deltoid exhibited the most significant increase in muscle activity at both testing positions. Additionally, a significant increase in muscle activity was observed in the middle deltoid compared with the supraspinatus (P < 0.05) in the empty-can testing position. SUVs of the middle deltoid, supraspinatus, and subscapularis showed a significant increase in the empty-can testing position compared with the full-can testing position (P < 0.05). CONCLUSIONS Significantly increased activity of the supraspinatus in conjunction with the middle deltoid and subscapularis after empty-can testing may result in decreased specificity of the empty-can test in detecting isolated supraspinatus activity. The full-can test, however, may be used to test the function of the supraspinatus with the least amount of surrounding middle deltoid and subscapularis activity.