Correlation between the distance of scapular anterior tilting and the ratio of internal and external rotation angle of shoulder in supine position

[Purpose] This study investigated the relationship between the amount of scapular anterior tilting and the ratio of internal and external rotation of the shoulder in a supine position. [Participants and Methods] Twenty healthy participants (8 females, 12 males) were enrolled in this study. Internal rotation (IR) and external rotation (ER) of the glenohumeral joint were performed in a supine position, and the IR and ER angles were measured using a universal goniometer. The changing distance of scapular anterior tilting was measured by a three-dimensional motion analysis tracking system while participants performed IR and ER in a supine position. Pearson’s correlation coefficient was used to investigate the relationship between the distance of scapular anterior tilting and the ratio of internal and external rotation angle of the shoulder. [Results] The correlation of the degree of scapular anterior tilting with the IR/ER ratio, particularly the IR angle of the shoulder in a supine position, was good to excellent (r=−0.851). [Conclusion] The findings suggest that asymmetry of the IR and ER angles may cause increased scapular anterior tilting in a supine position.